[RFC,v2,2/2] utils: codegen: ipc: Simplify deserialization

24636 diff mbox series

First, introduce the `SeriReader` type, which is a collection
of bytes and file descriptors, with the appropriate methods to
consume the first couples bytes / file descriptors.

Then a new method is added to `IPCMessage` that returns an appropriately
constructed `SeriReader` for parsing the message contents.

Then three of the four `deserialize()` overloads are removed, the
remaining one is converted to have a single `SeriReader` and an
optional `ControlSerializer` as arguments.

The remaining `deserialize()` function is also changed to return an
`std::optional` to be able to report deserialization failure.

There is also a more fundamental change in the serialization: previously,
the number of bytes taken up by an item has been written before the serialized
bytes (and conditionally the number of file descriptors) when the item is
serialized as part of a struct, array, map, function parameter list. This
is changed: the number of bytes and file descriptors are *not* serialized
into the final buffer. This affords some simplification of the serialization
related code paths, but most importantly, it greatly simplifies and unifies
how an object is (de)serialized because the deserialization of every object
becomes completely self-contained.

As a consequence of that, strings now include their lengths as part of the
string serialization, and it is not left to an "upper" layer.

Another consequence is that an "out parameter" of a remote function call
must be deserialized if a later out parameter is needed, even if itself
is not. This does not appear to be a great limitation since in all
situations presently none of the out parameters are ignored.

Finally, the code generation templates are adapted to the above changes.
This allows the simplification of the deserialization templates as now
calling `IPADataSerializer<T>::deserialize(reader, &controlSerializer_)`
is appropriate for any type.

Bug: https://bugs.libcamera.org/show_bug.cgi?id=269
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
---
change in v2:
  * rebase
  * adjust comments

v1: https://patchwork.libcamera.org/patch/23373/
---
 .../libcamera/internal/ipa_data_serializer.h  | 234 +++---------
 include/libcamera/internal/ipc_pipe.h         |   3 +
 include/libcamera/internal/meson.build        |   1 +
 include/libcamera/internal/serialization.h    |  86 +++++
 src/libcamera/ipa_data_serializer.cpp         | 352 ++++--------------
 src/libcamera/ipc_pipe.cpp                    |   5 +
 src/libcamera/meson.build                     |   1 +
 src/libcamera/serialization.cpp               |  60 +++
 test/ipc/unixsocket_ipc.cpp                   |  18 +-
 .../generated_serializer_test.cpp             |  17 +-
 .../ipa_data_serializer_test.cpp              |  32 +-
 .../module_ipa_proxy.cpp.tmpl                 |  30 +-
 .../module_ipa_proxy.h.tmpl                   |   5 +-
 .../module_ipa_proxy_worker.cpp.tmpl          |   5 +-
 .../libcamera_templates/proxy_functions.tmpl  | 113 +-----
 .../libcamera_templates/serializer.tmpl       | 238 +-----------
 16 files changed, 372 insertions(+), 828 deletions(-)
 create mode 100644 include/libcamera/internal/serialization.h
 create mode 100644 src/libcamera/serialization.cpp

--
2.51.0

Hi Barnabás

On Tue, Oct 14, 2025 at 01:57:52PM +0200, Barnabás Pőcze wrote:
> First, introduce the `SeriReader` type, which is a collection
> of bytes and file descriptors, with the appropriate methods to
> consume the first couples bytes / file descriptors.
>
> Then a new method is added to `IPCMessage` that returns an appropriately
> constructed `SeriReader` for parsing the message contents.
>
> Then three of the four `deserialize()` overloads are removed, the
> remaining one is converted to have a single `SeriReader` and an
> optional `ControlSerializer` as arguments.
>
> The remaining `deserialize()` function is also changed to return an
> `std::optional` to be able to report deserialization failure.
>
> There is also a more fundamental change in the serialization: previously,
> the number of bytes taken up by an item has been written before the serialized
> bytes (and conditionally the number of file descriptors) when the item is
> serialized as part of a struct, array, map, function parameter list. This
> is changed: the number of bytes and file descriptors are *not* serialized
> into the final buffer. This affords some simplification of the serialization
> related code paths, but most importantly, it greatly simplifies and unifies
> how an object is (de)serialized because the deserialization of every object
> becomes completely self-contained.
>
> As a consequence of that, strings now include their lengths as part of the
> string serialization, and it is not left to an "upper" layer.
>
> Another consequence is that an "out parameter" of a remote function call
> must be deserialized if a later out parameter is needed, even if itself
> is not. This does not appear to be a great limitation since in all
> situations presently none of the out parameters are ignored.
>
> Finally, the code generation templates are adapted to the above changes.
> This allows the simplification of the deserialization templates as now
> calling `IPADataSerializer<T>::deserialize(reader, &controlSerializer_)`
> is appropriate for any type.
>
> Bug: https://bugs.libcamera.org/show_bug.cgi?id=269
> Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
> ---
> change in v2:
>   * rebase
>   * adjust comments
>
> v1: https://patchwork.libcamera.org/patch/23373/
> ---
>  .../libcamera/internal/ipa_data_serializer.h  | 234 +++---------
>  include/libcamera/internal/ipc_pipe.h         |   3 +
>  include/libcamera/internal/meson.build        |   1 +
>  include/libcamera/internal/serialization.h    |  86 +++++
>  src/libcamera/ipa_data_serializer.cpp         | 352 ++++--------------
>  src/libcamera/ipc_pipe.cpp                    |   5 +
>  src/libcamera/meson.build                     |   1 +
>  src/libcamera/serialization.cpp               |  60 +++
>  test/ipc/unixsocket_ipc.cpp                   |  18 +-
>  .../generated_serializer_test.cpp             |  17 +-
>  .../ipa_data_serializer_test.cpp              |  32 +-
>  .../module_ipa_proxy.cpp.tmpl                 |  30 +-
>  .../module_ipa_proxy.h.tmpl                   |   5 +-
>  .../module_ipa_proxy_worker.cpp.tmpl          |   5 +-
>  .../libcamera_templates/proxy_functions.tmpl  | 113 +-----
>  .../libcamera_templates/serializer.tmpl       | 238 +-----------
>  16 files changed, 372 insertions(+), 828 deletions(-)

That's quite dense.

Before getting into the details, I would like to better understand how
this could be unified with the control serialization effort you're
pushing for MetadataList.

I think that, if we want to get into redesigining the serialization of
at the IPC border, we should consider it in the larger re-design
of the libcamera API C requirement.

So let me digress a bit.

MetadataList addresses the first need to serialize controls at the API
level in order to avoid concurrent access to a storage that doesn't
support thread-safe access.

As we know the application thread could access the control list while
the libcamera thread populates it. The solution we designed is to
serialize controls into a binary buffer and implement an API on top of
it that guarantees safe read access to a portion of the buffer while
directing write access to a portion of the buffer that is not
available to readers.

The MetadataList class implements a control serialization protocol
while we have a different controls serialization protocol for IPC
implemented by the ControlSerializer class and used over IPC.

Do you envision re-implementing any of the two on top of the other ?
As MetadataList is "newer" I presume the IPC ControlSerializer should
be re-implemented on top the serialization format once broken-out from
MetadataList ?

If that's the plan, are there implications on the this patch or, as
I understand it, the IPADataSerializer still delegates the actual
control serialization format to the ControlSerializer implementation
and your patch only changes how the data around serialized ControlList
and ControlInfoMap are read ?

Now on the patch


>  create mode 100644 include/libcamera/internal/serialization.h
>  create mode 100644 src/libcamera/serialization.cpp
>
> diff --git a/include/libcamera/internal/ipa_data_serializer.h b/include/libcamera/internal/ipa_data_serializer.h
> index 927f5c4c7..3b2e0029b 100644
> --- a/include/libcamera/internal/ipa_data_serializer.h
> +++ b/include/libcamera/internal/ipa_data_serializer.h
> @@ -7,6 +7,7 @@
>
>  #pragma once
>
> +#include <optional>
>  #include <stdint.h>
>  #include <string.h>
>  #include <tuple>
> @@ -23,6 +24,7 @@
>  #include <libcamera/ipa/ipa_interface.h>
>
>  #include "libcamera/internal/control_serializer.h"
> +#include "libcamera/internal/serialization.h"
>
>  namespace libcamera {
>
> @@ -39,26 +41,6 @@ void appendPOD(std::vector<uint8_t> &vec, T val)
>  	memcpy(&*(vec.end() - byteWidth), &val, byteWidth);
>  }
>
> -template<typename T,
> -	 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
> -T readPOD(std::vector<uint8_t>::const_iterator it, size_t pos,
> -	  std::vector<uint8_t>::const_iterator end)
> -{
> -	ASSERT(pos + it < end);
> -
> -	T ret = 0;
> -	memcpy(&ret, &(*(it + pos)), sizeof(ret));
> -
> -	return ret;
> -}
> -
> -template<typename T,
> -	 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
> -T readPOD(std::vector<uint8_t> &vec, size_t pos)
> -{
> -	return readPOD<T>(vec.cbegin(), pos, vec.end());
> -}
> -
>  } /* namespace */
>
>  template<typename T, typename = void>
> @@ -68,20 +50,8 @@ public:
>  	static std::tuple<std::vector<uint8_t>, std::vector<SharedFD>>
>  	serialize(const T &data, ControlSerializer *cs = nullptr);
>
> -	static T deserialize(const std::vector<uint8_t> &data,
> -			     ControlSerializer *cs = nullptr);
> -	static T deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -			     std::vector<uint8_t>::const_iterator dataEnd,
> -			     ControlSerializer *cs = nullptr);
> -
> -	static T deserialize(const std::vector<uint8_t> &data,
> -			     const std::vector<SharedFD> &fds,
> -			     ControlSerializer *cs = nullptr);
> -	static T deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -			     std::vector<uint8_t>::const_iterator dataEnd,
> -			     std::vector<SharedFD>::const_iterator fdsBegin,
> -			     std::vector<SharedFD>::const_iterator fdsEnd,
> -			     ControlSerializer *cs = nullptr);
> +	[[nodiscard]] static std::optional<T>
> +	deserialize(SeriReader &reader, ControlSerializer *cs = nullptr);

nice!

>  };
>
>  #ifndef __DOXYGEN__
> @@ -93,8 +63,6 @@ public:
>   *
>   * For every element in the vector:
>   *
> - * 4 bytes - uint32_t Size of element, in bytes
> - * 4 bytes - uint32_t Number of fds for the element
>   * X bytes - Serialized element
>   *
>   * \todo Support elements that are references
> @@ -121,9 +89,6 @@ public:
>  			std::tie(dvec, fvec) =
>  				IPADataSerializer<V>::serialize(it, cs);
>
> -			appendPOD<uint32_t>(dataVec, dvec.size());
> -			appendPOD<uint32_t>(dataVec, fvec.size());
> -
>  			dataVec.insert(dataVec.end(), dvec.begin(), dvec.end());
>  			fdsVec.insert(fdsVec.end(), fvec.begin(), fvec.end());
>  		}
> @@ -131,49 +96,22 @@ public:
>  		return { dataVec, fdsVec };
>  	}
>
> -	static std::vector<V> deserialize(std::vector<uint8_t> &data, ControlSerializer *cs = nullptr)
> +	[[nodiscard]] static std::optional<std::vector<V>>
> +	deserialize(SeriReader &reader, ControlSerializer *cs = nullptr)
>  	{
> -		return deserialize(data.cbegin(), data.cend(), cs);
> -	}
> +		uint32_t vecLen;
> +		if (!reader.read(vecLen))
> +			return {};
>
> -	static std::vector<V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					  std::vector<uint8_t>::const_iterator dataEnd,
> -					  ControlSerializer *cs = nullptr)
> -	{
> -		std::vector<SharedFD> fds;
> -		return deserialize(dataBegin, dataEnd, fds.cbegin(), fds.cend(), cs);
> -	}
> +		std::vector<V> ret;
> +		ret.reserve(vecLen);
>
> -	static std::vector<V> deserialize(std::vector<uint8_t> &data, std::vector<SharedFD> &fds,
> -					  ControlSerializer *cs = nullptr)
> -	{
> -		return deserialize(data.cbegin(), data.cend(), fds.cbegin(), fds.cend(), cs);
> -	}
> -
> -	static std::vector<V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					  std::vector<uint8_t>::const_iterator dataEnd,
> -					  std::vector<SharedFD>::const_iterator fdsBegin,
> -					  [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -					  ControlSerializer *cs = nullptr)
> -	{
> -		uint32_t vecLen = readPOD<uint32_t>(dataBegin, 0, dataEnd);
> -		std::vector<V> ret(vecLen);
> -
> -		std::vector<uint8_t>::const_iterator dataIter = dataBegin + 4;
> -		std::vector<SharedFD>::const_iterator fdIter = fdsBegin;
>  		for (uint32_t i = 0; i < vecLen; i++) {
> -			uint32_t sizeofData = readPOD<uint32_t>(dataIter, 0, dataEnd);
> -			uint32_t sizeofFds = readPOD<uint32_t>(dataIter, 4, dataEnd);
> -			dataIter += 8;
> -
> -			ret[i] = IPADataSerializer<V>::deserialize(dataIter,
> -								   dataIter + sizeofData,
> -								   fdIter,
> -								   fdIter + sizeofFds,
> -								   cs);
> -
> -			dataIter += sizeofData;
> -			fdIter += sizeofFds;
Much nicer from a code point of view

Let me address this in pieces

> +			auto item = IPADataSerializer<V>::deserialize(reader, cs);

item (optionally) contains a variable of type V which has been copied
from the binary buffer

> +			if (!item)
> +				return {};
> +
> +			ret.emplace_back(std::move(*item));

Then we move item and call emplace_back which calls the move
constructor of type V.

However, since the data from the serialized buffer have already been
copied to 'item' do move() and emplace_back() actually help ? Won't we
end up doing a copy inside ret anyway ?

>  		}
>
>  		return ret;
> @@ -187,11 +125,7 @@ public:
>   *
>   * For every pair in the map:
>   *
> - * 4 bytes - uint32_t Size of key, in bytes
> - * 4 bytes - uint32_t Number of fds for the key
>   * X bytes - Serialized key
> - * 4 bytes - uint32_t Size of value, in bytes
> - * 4 bytes - uint32_t Number of fds for the value
>   * X bytes - Serialized value
>   *
>   * \todo Support keys or values that are references
> @@ -218,18 +152,12 @@ public:
>  			std::tie(dvec, fvec) =
>  				IPADataSerializer<K>::serialize(it.first, cs);
>
> -			appendPOD<uint32_t>(dataVec, dvec.size());
> -			appendPOD<uint32_t>(dataVec, fvec.size());
> -
>  			dataVec.insert(dataVec.end(), dvec.begin(), dvec.end());
>  			fdsVec.insert(fdsVec.end(), fvec.begin(), fvec.end());
>
>  			std::tie(dvec, fvec) =
>  				IPADataSerializer<V>::serialize(it.second, cs);
>
> -			appendPOD<uint32_t>(dataVec, dvec.size());
> -			appendPOD<uint32_t>(dataVec, fvec.size());
> -
>  			dataVec.insert(dataVec.end(), dvec.begin(), dvec.end());
>  			fdsVec.insert(fdsVec.end(), fvec.begin(), fvec.end());
>  		}
> @@ -237,63 +165,27 @@ public:
>  		return { dataVec, fdsVec };
>  	}
>
> -	static std::map<K, V> deserialize(std::vector<uint8_t> &data, ControlSerializer *cs = nullptr)
> +	[[nodiscard]] static std::optional<std::map<K, V>>
> +	deserialize(SeriReader &reader, ControlSerializer *cs = nullptr)
>  	{
> -		return deserialize(data.cbegin(), data.cend(), cs);
> -	}
> +		uint32_t mapLen;
> +		if (!reader.read(mapLen))
> +			return {};
>
> -	static std::map<K, V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					  std::vector<uint8_t>::const_iterator dataEnd,
> -					  ControlSerializer *cs = nullptr)
> -	{
> -		std::vector<SharedFD> fds;
> -		return deserialize(dataBegin, dataEnd, fds.cbegin(), fds.cend(), cs);
> -	}
> -
> -	static std::map<K, V> deserialize(std::vector<uint8_t> &data, std::vector<SharedFD> &fds,
> -					  ControlSerializer *cs = nullptr)
> -	{
> -		return deserialize(data.cbegin(), data.cend(), fds.cbegin(), fds.cend(), cs);
> -	}
> -
> -	static std::map<K, V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					  std::vector<uint8_t>::const_iterator dataEnd,
> -					  std::vector<SharedFD>::const_iterator fdsBegin,
> -					  [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -					  ControlSerializer *cs = nullptr)
> -	{
>  		std::map<K, V> ret;
>
> -		uint32_t mapLen = readPOD<uint32_t>(dataBegin, 0, dataEnd);
> -
> -		std::vector<uint8_t>::const_iterator dataIter = dataBegin + 4;
> -		std::vector<SharedFD>::const_iterator fdIter = fdsBegin;
>  		for (uint32_t i = 0; i < mapLen; i++) {
> -			uint32_t sizeofData = readPOD<uint32_t>(dataIter, 0, dataEnd);
> -			uint32_t sizeofFds = readPOD<uint32_t>(dataIter, 4, dataEnd);
> -			dataIter += 8;
> -
> -			K key = IPADataSerializer<K>::deserialize(dataIter,
> -								  dataIter + sizeofData,
> -								  fdIter,
> -								  fdIter + sizeofFds,
> -								  cs);
> -
> -			dataIter += sizeofData;
> -			fdIter += sizeofFds;
> -			sizeofData = readPOD<uint32_t>(dataIter, 0, dataEnd);
> -			sizeofFds = readPOD<uint32_t>(dataIter, 4, dataEnd);
> -			dataIter += 8;
> -
> -			const V value = IPADataSerializer<V>::deserialize(dataIter,
> -									  dataIter + sizeofData,
> -									  fdIter,
> -									  fdIter + sizeofFds,
> -									  cs);
> -			ret.insert({ key, value });
> -
> -			dataIter += sizeofData;
> -			fdIter += sizeofFds;
> +			auto key = IPADataSerializer<K>::deserialize(reader, cs);
> +			if (!key)
> +				return {};
> +
> +			auto value = IPADataSerializer<V>::deserialize(reader, cs);
> +			if (!value)
> +				return {};
> +
> +			auto [it, inserted] = ret.try_emplace(std::move(*key), std::move(*value));
> +			if (!inserted)
> +				return {};
>  		}
>
>  		return ret;
> @@ -314,33 +206,14 @@ public:
>  		return { dataVec, {} };
>  	}
>
> -	static Flags<E> deserialize(std::vector<uint8_t> &data,
> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
> +	[[nodiscard]] static std::optional<Flags<E>>
> +	deserialize(SeriReader &reader, [[maybe_unused]] ControlSerializer *cs = nullptr)
>  	{
> -		return deserialize(data.cbegin(), data.cend());
> -	}
> +		uint32_t value;
> +		if (!reader.read(value))
> +			return {};
>
> -	static Flags<E> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -				    std::vector<uint8_t>::const_iterator dataEnd,
> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
> -	{
> -		return Flags<E>{ static_cast<E>(readPOD<uint32_t>(dataBegin, 0, dataEnd)) };
> -	}
> -
> -	static Flags<E> deserialize(std::vector<uint8_t> &data,
> -				    [[maybe_unused]] std::vector<SharedFD> &fds,
> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
> -	{
> -		return deserialize(data.cbegin(), data.cend());
> -	}
> -
> -	static Flags<E> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -				    std::vector<uint8_t>::const_iterator dataEnd,
> -				    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
> -				    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
> -	{
> -		return deserialize(dataBegin, dataEnd);
> +		return Flags<E>{ static_cast<E>(value) };
>  	}
>  };
>
> @@ -360,33 +233,14 @@ public:
>  		return { dataVec, {} };
>  	}
>
> -	static E deserialize(std::vector<uint8_t> &data,
> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
> -	{
> -		return deserialize(data.cbegin(), data.cend());
> -	}
> -
> -	static E deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -			     std::vector<uint8_t>::const_iterator dataEnd,
> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
> -	{
> -		return static_cast<E>(readPOD<U>(dataBegin, 0, dataEnd));
> -	}
> -
> -	static E deserialize(std::vector<uint8_t> &data,
> -			     [[maybe_unused]] std::vector<SharedFD> &fds,
> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
> +	[[nodiscard]] static std::optional<E>
> +	deserialize(SeriReader &reader, [[maybe_unused]] ControlSerializer *cs = nullptr)
>  	{
> -		return deserialize(data.cbegin(), data.cend());
> -	}
> +		U value;
> +		if (!reader.read(value))
> +			return {};
>
> -	static E deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -			     std::vector<uint8_t>::const_iterator dataEnd,
> -			     [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
> -			     [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
> -	{
> -		return deserialize(dataBegin, dataEnd);
> +		return static_cast<E>(value);
>  	}
>  };
>
> diff --git a/include/libcamera/internal/ipc_pipe.h b/include/libcamera/internal/ipc_pipe.h
> index 418c4622f..2b6cde042 100644
> --- a/include/libcamera/internal/ipc_pipe.h
> +++ b/include/libcamera/internal/ipc_pipe.h
> @@ -14,6 +14,7 @@
>  #include <libcamera/base/signal.h>
>
>  #include "libcamera/internal/ipc_unixsocket.h"
> +#include "libcamera/internal/serialization.h"
>
>  namespace libcamera {
>
> @@ -40,6 +41,8 @@ public:
>  	const std::vector<uint8_t> &data() const { return data_; }
>  	const std::vector<SharedFD> &fds() const { return fds_; }
>
> +	SeriReader reader() const { return { data(), fds() }; }
> +
>  private:
>  	Header header_;
>
> diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build
> index 45c299f6a..a11a52a01 100644
> --- a/include/libcamera/internal/meson.build
> +++ b/include/libcamera/internal/meson.build
> @@ -39,6 +39,7 @@ libcamera_internal_headers = files([
>      'process.h',
>      'pub_key.h',
>      'request.h',
> +    'serialization.h',
>      'shared_mem_object.h',
>      'source_paths.h',
>      'sysfs.h',
> diff --git a/include/libcamera/internal/serialization.h b/include/libcamera/internal/serialization.h
> new file mode 100644
> index 000000000..f20fd8ca7
> --- /dev/null
> +++ b/include/libcamera/internal/serialization.h
> @@ -0,0 +1,86 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2025, Ideas On Board Oy
> + *
> + * Data (de)serialization helper structures
> + */
> +#pragma once
> +
> +#include <cstddef>
> +#include <optional>
> +#include <stdint.h>
> +#include <string.h>
> +#include <tuple>
> +#include <type_traits>
> +
> +#include <libcamera/base/shared_fd.h>
> +#include <libcamera/base/span.h>
> +
> +namespace libcamera {
> +
> +class SeriReader
> +{
> +public:
> +	SeriReader(Span<const uint8_t> data, Span<const SharedFD> fds = {})
> +		: data_(reinterpret_cast<const std::byte *>(data.data()),
> +			reinterpret_cast<const std::byte *>(data.data() + data.size())),
> +		  fds_(fds)
> +	{
> +	}
> +
> +	[[nodiscard]] bool empty() const { return data_.empty() && fds_.empty(); }
> +
> +	[[nodiscard]] const std::byte *consume(std::size_t s)
> +	{
> +		if (data_.size() < s)
> +			return nullptr;
> +
> +		const auto *p = data_.data();
> +		data_ = data_.subspan(s);
> +
> +		return p;
> +	}

I'm missing why this need to be public, shouldn't the callers use the
read() functions to access data instead of accessing the raw buffer ?

I see 4 occurrences, and it seems the reason is to support handling of
strings, ControlInfoMap and ControlList. Is this because they're just
a bit special ?

> +
> +	template<typename... Ts>

Now, not that I'm against template packs, but I see this being only
used to do things like

	if (!reader.read(offset, length))

isn't it equivalent to do

	if (!reader.read(offset))
	if (!reader.read(length))

Do you envision other usage for supporting multiple template arguments ?


> +	[[nodiscard]] bool read(Ts &...xs)
> +	{
> +		static_assert((std::is_trivially_copyable_v<Ts> && ...));
> +
> +		const auto *p = consume((sizeof(xs) + ...));
> +		if (p)
> +			((memcpy(&xs, p, sizeof(xs)), p += sizeof(xs)), ...);
> +
> +		return p;
> +	}
> +
> +	template<typename... Ts>
> +	[[nodiscard]] auto read()
> +	{
> +		std::tuple<Ts...> xs;
> +		bool ok = std::apply([&](auto &...vs) {
> +			return read(vs...);
> +		}, xs);

if I

                if (!ok)
                        return std::nullopt;

here and remove the "ok ? : " below

../include/libcamera/internal/serialization.h:67:37: error: inconsistent deduction for auto return type: ‘std::nullopt_t’ and then ‘std::optional<double>’
   67 |                         return std::optional(std::get<0>(xs));



> +
> +		if constexpr (sizeof...(Ts) == 1)
> +			return ok ? std::optional(std::get<0>(xs)) : std::nullopt;
> +		else
> +			return ok ? std::optional(xs) : std::nullopt;

While it works this way....

Not complaining about it, just wondering why the compiler can deduce
in one case and not in the other

> +	}
> +
> +	[[nodiscard]] const SharedFD *popFd()
> +	{
> +		if (fds_.empty())
> +			return nullptr;
> +
> +		const auto *p = fds_.data();
> +		fds_ = fds_.subspan(1);
> +
> +		return p;
> +	}
> +
> +private:
> +	Span<const std::byte> data_;
> +	Span<const SharedFD> fds_;
> +};
> +
> +} /* namespace libcamera */

Do you plan a SeriWriter ? :)

The rest looks good (I didn't look at the mojo part) and there's no
doubt this is better.

However, I would like to see it tested with an IPC running isolated.
Did you have chance to give it a spin ?

Thanks
  j


> diff --git a/src/libcamera/ipa_data_serializer.cpp b/src/libcamera/ipa_data_serializer.cpp
> index 0537f785b..ecb68c94e 100644
> --- a/src/libcamera/ipa_data_serializer.cpp
> +++ b/src/libcamera/ipa_data_serializer.cpp
> @@ -50,42 +50,6 @@ namespace {
>   * generated IPA proxies.
>   */
>
> -/**
> - * \fn template<typename T> T readPOD(std::vector<uint8_t>::iterator it, size_t pos,
> - * 				      std::vector<uint8_t>::iterator end)
> - * \brief Read POD from byte vector, in little-endian order
> - * \tparam T Type of POD to read
> - * \param[in] it Iterator of byte vector to read from
> - * \param[in] pos Index in byte vector to read from
> - * \param[in] end Iterator marking end of byte vector
> - *
> - * This function is meant to be used by the IPA data serializer, and the
> - * generated IPA proxies.
> - *
> - * If the \a pos plus the byte-width of the desired POD is past \a end, it is
> - * a fata error will occur, as it means there is insufficient data for
> - * deserialization, which should never happen.
> - *
> - * \return The POD read from \a it at index \a pos
> - */
> -
> -/**
> - * \fn template<typename T> T readPOD(std::vector<uint8_t> &vec, size_t pos)
> - * \brief Read POD from byte vector, in little-endian order
> - * \tparam T Type of POD to read
> - * \param[in] vec Byte vector to read from
> - * \param[in] pos Index in vec to start reading from
> - *
> - * This function is meant to be used by the IPA data serializer, and the
> - * generated IPA proxies.
> - *
> - * If the \a pos plus the byte-width of the desired POD is past the end of
> - * \a vec, a fatal error will occur, as it means there is insufficient data
> - * for deserialization, which should never happen.
> - *
> - * \return The POD read from \a vec at index \a pos
> - */
> -
>  } /* namespace */
>
>  /**
> @@ -106,80 +70,13 @@ namespace {
>
>  /**
>   * \fn template<typename T> IPADataSerializer<T>::deserialize(
> - * 	const std::vector<uint8_t> &data,
> + * 	SeriReader &reader,
>   * 	ControlSerializer *cs = nullptr)
> - * \brief Deserialize byte vector into an object
> + * \brief Deserialize bytes and file descriptors vector into an object
>   * \tparam T Type of object to deserialize to
> - * \param[in] data Byte vector to deserialize from
> + * \param[in] reader Source of bytes and file descriptors
>   * \param[in] cs ControlSerializer
>   *
> - * This version of deserialize() can be used if the object type \a T and its
> - * members don't have any SharedFD.
> - *
> - * \a cs is only necessary if the object type \a T or its members contain
> - * ControlList or ControlInfoMap.
> - *
> - * \return The deserialized object
> - */
> -
> -/**
> - * \fn template<typename T> IPADataSerializer<T>::deserialize(
> - * 	std::vector<uint8_t>::const_iterator dataBegin,
> - * 	std::vector<uint8_t>::const_iterator dataEnd,
> - * 	ControlSerializer *cs = nullptr)
> - * \brief Deserialize byte vector into an object
> - * \tparam T Type of object to deserialize to
> - * \param[in] dataBegin Begin iterator of byte vector to deserialize from
> - * \param[in] dataEnd End iterator of byte vector to deserialize from
> - * \param[in] cs ControlSerializer
> - *
> - * This version of deserialize() can be used if the object type \a T and its
> - * members don't have any SharedFD.
> - *
> - * \a cs is only necessary if the object type \a T or its members contain
> - * ControlList or ControlInfoMap.
> - *
> - * \return The deserialized object
> - */
> -
> -/**
> - * \fn template<typename T> IPADataSerializer<T>::deserialize(
> - * 	const std::vector<uint8_t> &data,
> - * 	const std::vector<SharedFD> &fds,
> - * 	ControlSerializer *cs = nullptr)
> - * \brief Deserialize byte vector and fd vector into an object
> - * \tparam T Type of object to deserialize to
> - * \param[in] data Byte vector to deserialize from
> - * \param[in] fds Fd vector to deserialize from
> - * \param[in] cs ControlSerializer
> - *
> - * This version of deserialize() (or the iterator version) must be used if
> - * the object type \a T or its members contain SharedFD.
> - *
> - * \a cs is only necessary if the object type \a T or its members contain
> - * ControlList or ControlInfoMap.
> - *
> - * \return The deserialized object
> - */
> -
> -/**
> - * \fn template<typename T> IPADataSerializer::deserialize(
> - * 	std::vector<uint8_t>::const_iterator dataBegin,
> - * 	std::vector<uint8_t>::const_iterator dataEnd,
> - * 	std::vector<SharedFD>::const_iterator fdsBegin,
> - * 	std::vector<SharedFD>::const_iterator fdsEnd,
> - * 	ControlSerializer *cs = nullptr)
> - * \brief Deserialize byte vector and fd vector into an object
> - * \tparam T Type of object to deserialize to
> - * \param[in] dataBegin Begin iterator of byte vector to deserialize from
> - * \param[in] dataEnd End iterator of byte vector to deserialize from
> - * \param[in] fdsBegin Begin iterator of fd vector to deserialize from
> - * \param[in] fdsEnd End iterator of fd vector to deserialize from
> - * \param[in] cs ControlSerializer
> - *
> - * This version of deserialize() (or the vector version) must be used if
> - * the object type \a T or its members contain SharedFD.
> - *
>   * \a cs is only necessary if the object type \a T or its members contain
>   * ControlList or ControlInfoMap.
>   *
> @@ -202,37 +99,11 @@ IPADataSerializer<type>::serialize(const type &data,			\
>  }									\
>  									\
>  template<>								\
> -type IPADataSerializer<type>::deserialize(std::vector<uint8_t>::const_iterator dataBegin, \
> -					  std::vector<uint8_t>::const_iterator dataEnd, \
> -					  [[maybe_unused]] ControlSerializer *cs) \
> +std::optional<type> IPADataSerializer<type>::deserialize(SeriReader &reader, \
> +							 [[maybe_unused]] ControlSerializer *cs) \
>  {									\
> -	return readPOD<type>(dataBegin, 0, dataEnd);			\
> +	return reader.read<type>();					\
>  }									\
> -									\
> -template<>								\
> -type IPADataSerializer<type>::deserialize(const std::vector<uint8_t> &data, \
> -					  ControlSerializer *cs)	\
> -{									\
> -	return deserialize(data.cbegin(), data.end(), cs);		\
> -}									\
> -									\
> -template<>								\
> -type IPADataSerializer<type>::deserialize(const std::vector<uint8_t> &data, \
> -					  [[maybe_unused]] const std::vector<SharedFD> &fds, \
> -					  ControlSerializer *cs)	\
> -{									\
> -	return deserialize(data.cbegin(), data.end(), cs);		\
> -}									\
> -									\
> -template<>								\
> -type IPADataSerializer<type>::deserialize(std::vector<uint8_t>::const_iterator dataBegin, \
> -					  std::vector<uint8_t>::const_iterator dataEnd, \
> -					  [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin, \
> -					  [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd, \
> -					  ControlSerializer *cs)	\
> -{									\
> -	return deserialize(dataBegin, dataEnd, cs);			\
> -}
>
>  DEFINE_POD_SERIALIZER(bool)
>  DEFINE_POD_SERIALIZER(uint8_t)
> @@ -256,44 +127,29 @@ std::tuple<std::vector<uint8_t>, std::vector<SharedFD>>
>  IPADataSerializer<std::string>::serialize(const std::string &data,
>  					  [[maybe_unused]] ControlSerializer *cs)
>  {
> -	return { { data.cbegin(), data.end() }, {} };
> -}
> +	std::vector<uint8_t> dataVec;
>
> -template<>
> -std::string
> -IPADataSerializer<std::string>::deserialize(const std::vector<uint8_t> &data,
> -					    [[maybe_unused]] ControlSerializer *cs)
> -{
> -	return { data.cbegin(), data.cend() };
> -}
> +	ASSERT(data.size() <= std::numeric_limits<uint32_t>::max());
> +	appendPOD<uint32_t>(dataVec, data.size());
> +	dataVec.insert(dataVec.end(), data.c_str(), data.c_str() + data.size());
>
> -template<>
> -std::string
> -IPADataSerializer<std::string>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					    std::vector<uint8_t>::const_iterator dataEnd,
> -					    [[maybe_unused]] ControlSerializer *cs)
> -{
> -	return { dataBegin, dataEnd };
> +	return { dataVec, {} };
>  }
>
>  template<>
> -std::string
> -IPADataSerializer<std::string>::deserialize(const std::vector<uint8_t> &data,
> -					    [[maybe_unused]] const std::vector<SharedFD> &fds,
> +std::optional<std::string>
> +IPADataSerializer<std::string>::deserialize(SeriReader &reader,
>  					    [[maybe_unused]] ControlSerializer *cs)
>  {
> -	return { data.cbegin(), data.cend() };
> -}
> +	uint32_t length;
> +	if (!reader.read(length))
> +		return {};
>
> -template<>
> -std::string
> -IPADataSerializer<std::string>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					    std::vector<uint8_t>::const_iterator dataEnd,
> -					    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
> -					    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -					    [[maybe_unused]] ControlSerializer *cs)
> -{
> -	return { dataBegin, dataEnd };
> +	const auto *p = reader.consume(length);
> +	if (!p)
> +		return {};
> +
> +	return { { reinterpret_cast<const char *>(p), std::size_t(length) } };
>  }
>
>  /*
> @@ -356,75 +212,45 @@ IPADataSerializer<ControlList>::serialize(const ControlList &data, ControlSerial
>  }
>
>  template<>
> -ControlList
> -IPADataSerializer<ControlList>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					    std::vector<uint8_t>::const_iterator dataEnd,
> +std::optional<ControlList>
> +IPADataSerializer<ControlList>::deserialize(SeriReader &reader,
>  					    ControlSerializer *cs)
>  {
>  	if (!cs)
>  		LOG(IPADataSerializer, Fatal)
>  			<< "ControlSerializer not provided for deserialization of ControlList";
>
> -	if (std::distance(dataBegin, dataEnd) < 8)
> -		return {};
> -
> -	uint32_t infoDataSize = readPOD<uint32_t>(dataBegin, 0, dataEnd);
> -	uint32_t listDataSize = readPOD<uint32_t>(dataBegin, 4, dataEnd);
> -
> -	std::vector<uint8_t>::const_iterator it = dataBegin + 8;
> -
> -	if (infoDataSize + listDataSize < infoDataSize ||
> -	    static_cast<uint32_t>(std::distance(it, dataEnd)) < infoDataSize + listDataSize)
> +	uint32_t infoDataSize, listDataSize;
> +	if (!reader.read(infoDataSize, listDataSize))
>  		return {};
>
>  	if (infoDataSize > 0) {
> -		ByteStreamBuffer buffer(&*it, infoDataSize);
> +		const auto *p = reader.consume(infoDataSize);
> +		if (!p)
> +			return {};
> +
> +		ByteStreamBuffer buffer(reinterpret_cast<const uint8_t *>(p), infoDataSize);
>  		ControlInfoMap map = cs->deserialize<ControlInfoMap>(buffer);
>  		/* It's fine if map is empty. */
>  		if (buffer.overflow()) {
>  			LOG(IPADataSerializer, Error)
>  				<< "Failed to deserialize ControlLists's ControlInfoMap: buffer overflow";
> -			return ControlList();
> +			return {};
>  		}
>  	}
>
> -	it += infoDataSize;
> -	ByteStreamBuffer buffer(&*it, listDataSize);
> +	const auto *p = reader.consume(listDataSize);
> +
> +	ByteStreamBuffer buffer(reinterpret_cast<const uint8_t *>(p), listDataSize);
>  	ControlList list = cs->deserialize<ControlList>(buffer);
> -	if (buffer.overflow())
> +	if (buffer.overflow()) {
>  		LOG(IPADataSerializer, Error) << "Failed to deserialize ControlList: buffer overflow";
> +		return {};
> +	}
>
>  	return list;
>  }
>
> -template<>
> -ControlList
> -IPADataSerializer<ControlList>::deserialize(const std::vector<uint8_t> &data,
> -					    ControlSerializer *cs)
> -{
> -	return deserialize(data.cbegin(), data.end(), cs);
> -}
> -
> -template<>
> -ControlList
> -IPADataSerializer<ControlList>::deserialize(const std::vector<uint8_t> &data,
> -					    [[maybe_unused]] const std::vector<SharedFD> &fds,
> -					    ControlSerializer *cs)
> -{
> -	return deserialize(data.cbegin(), data.end(), cs);
> -}
> -
> -template<>
> -ControlList
> -IPADataSerializer<ControlList>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					    std::vector<uint8_t>::const_iterator dataEnd,
> -					    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
> -					    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -					    ControlSerializer *cs)
> -{
> -	return deserialize(dataBegin, dataEnd, cs);
> -}
> -
>  /*
>   * const ControlInfoMap is serialized as:
>   *
> @@ -458,59 +284,30 @@ IPADataSerializer<ControlInfoMap>::serialize(const ControlInfoMap &map,
>  }
>
>  template<>
> -ControlInfoMap
> -IPADataSerializer<ControlInfoMap>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					       std::vector<uint8_t>::const_iterator dataEnd,
> +std::optional<ControlInfoMap>
> +IPADataSerializer<ControlInfoMap>::deserialize(SeriReader &reader,
>  					       ControlSerializer *cs)
>  {
>  	if (!cs)
>  		LOG(IPADataSerializer, Fatal)
>  			<< "ControlSerializer not provided for deserialization of ControlInfoMap";
>
> -	if (std::distance(dataBegin, dataEnd) < 4)
> +	uint32_t infoDataSize;
> +	if (!reader.read(infoDataSize))
>  		return {};
>
> -	uint32_t infoDataSize = readPOD<uint32_t>(dataBegin, 0, dataEnd);
> -
> -	std::vector<uint8_t>::const_iterator it = dataBegin + 4;
> -
> -	if (static_cast<uint32_t>(std::distance(it, dataEnd)) < infoDataSize)
> +	const auto *p = reader.consume(infoDataSize);
> +	if (!p)
>  		return {};
>
> -	ByteStreamBuffer buffer(&*it, infoDataSize);
> +	ByteStreamBuffer buffer(reinterpret_cast<const uint8_t *>(p), infoDataSize);
>  	ControlInfoMap map = cs->deserialize<ControlInfoMap>(buffer);
> +	if (buffer.overflow())
> +		return {};
>
>  	return map;
>  }
>
> -template<>
> -ControlInfoMap
> -IPADataSerializer<ControlInfoMap>::deserialize(const std::vector<uint8_t> &data,
> -					       ControlSerializer *cs)
> -{
> -	return deserialize(data.cbegin(), data.end(), cs);
> -}
> -
> -template<>
> -ControlInfoMap
> -IPADataSerializer<ControlInfoMap>::deserialize(const std::vector<uint8_t> &data,
> -					       [[maybe_unused]] const std::vector<SharedFD> &fds,
> -					       ControlSerializer *cs)
> -{
> -	return deserialize(data.cbegin(), data.end(), cs);
> -}
> -
> -template<>
> -ControlInfoMap
> -IPADataSerializer<ControlInfoMap>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -					       std::vector<uint8_t>::const_iterator dataEnd,
> -					       [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
> -					       [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -					       ControlSerializer *cs)
> -{
> -	return deserialize(dataBegin, dataEnd, cs);
> -}
> -
>  /*
>   * SharedFD instances are serialized into four bytes that tells if the SharedFD
>   * is valid or not. If it is valid, then for serialization the fd will be
> @@ -542,27 +339,23 @@ IPADataSerializer<SharedFD>::serialize(const SharedFD &data,
>  }
>
>  template<>
> -SharedFD IPADataSerializer<SharedFD>::deserialize([[maybe_unused]] std::vector<uint8_t>::const_iterator dataBegin,
> -						  [[maybe_unused]] std::vector<uint8_t>::const_iterator dataEnd,
> -						  std::vector<SharedFD>::const_iterator fdsBegin,
> -						  std::vector<SharedFD>::const_iterator fdsEnd,
> -						  [[maybe_unused]] ControlSerializer *cs)
> +std::optional<SharedFD>
> +IPADataSerializer<SharedFD>::deserialize(SeriReader &reader,
> +					 [[maybe_unused]] ControlSerializer *cs)
>  {
> -	ASSERT(std::distance(dataBegin, dataEnd) >= 4);
> +	uint32_t valid;
>
> -	uint32_t valid = readPOD<uint32_t>(dataBegin, 0, dataEnd);
> +	if (!reader.read(valid))
> +		return {};
>
> -	ASSERT(!(valid && std::distance(fdsBegin, fdsEnd) < 1));
> +	if (!valid)
> +		return SharedFD{};
>
> -	return valid ? *fdsBegin : SharedFD();
> -}
> +	const auto *fd = reader.popFd();
> +	if (!fd)
> +		return {};
>
> -template<>
> -SharedFD IPADataSerializer<SharedFD>::deserialize(const std::vector<uint8_t> &data,
> -						  const std::vector<SharedFD> &fds,
> -						  [[maybe_unused]] ControlSerializer *cs)
> -{
> -	return deserialize(data.cbegin(), data.end(), fds.cbegin(), fds.end());
> +	return *fd;
>  }
>
>  /*
> @@ -594,30 +387,19 @@ IPADataSerializer<FrameBuffer::Plane>::serialize(const FrameBuffer::Plane &data,
>  }
>
>  template<>
> -FrameBuffer::Plane
> -IPADataSerializer<FrameBuffer::Plane>::deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -						   std::vector<uint8_t>::const_iterator dataEnd,
> -						   std::vector<SharedFD>::const_iterator fdsBegin,
> -						   [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> +std::optional<FrameBuffer::Plane>
> +IPADataSerializer<FrameBuffer::Plane>::deserialize(SeriReader &reader,
>  						   [[maybe_unused]] ControlSerializer *cs)
>  {
> -	FrameBuffer::Plane ret;
> -
> -	ret.fd = IPADataSerializer<SharedFD>::deserialize(dataBegin, dataBegin + 4,
> -							  fdsBegin, fdsBegin + 1);
> -	ret.offset = readPOD<uint32_t>(dataBegin, 4, dataEnd);
> -	ret.length = readPOD<uint32_t>(dataBegin, 8, dataEnd);
> +	auto fd = IPADataSerializer<SharedFD>::deserialize(reader);
> +	if (!fd)
> +		return {};
>
> -	return ret;
> -}
> +	uint32_t offset, length;
> +	if (!reader.read(offset, length))
> +		return {};
>
> -template<>
> -FrameBuffer::Plane
> -IPADataSerializer<FrameBuffer::Plane>::deserialize(const std::vector<uint8_t> &data,
> -						   const std::vector<SharedFD> &fds,
> -						   ControlSerializer *cs)
> -{
> -	return deserialize(data.cbegin(), data.end(), fds.cbegin(), fds.end(), cs);
> +	return { { std::move(*fd), offset, length } };
>  }
>
>  #endif /* __DOXYGEN__ */
> diff --git a/src/libcamera/ipc_pipe.cpp b/src/libcamera/ipc_pipe.cpp
> index 548299d05..71d0c2cb4 100644
> --- a/src/libcamera/ipc_pipe.cpp
> +++ b/src/libcamera/ipc_pipe.cpp
> @@ -148,6 +148,11 @@ IPCUnixSocket::Payload IPCMessage::payload() const
>   * \brief Returns a const reference to the vector containing file descriptors
>   */
>
> +/**
> + * \fn IPCMessage::reader() const
> + * \brief Returns a `SeriReader` instance for parsing the message
> + */
> +
>  /**
>   * \class IPCPipe
>   * \brief IPC message pipe for IPA isolation
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index 5b9b86f21..1834ff9b1 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -49,6 +49,7 @@ libcamera_internal_sources = files([
>      'pipeline_handler.cpp',
>      'process.cpp',
>      'pub_key.cpp',
> +    'serialization.cpp',
>      'shared_mem_object.cpp',
>      'source_paths.cpp',
>      'sysfs.cpp',
> diff --git a/src/libcamera/serialization.cpp b/src/libcamera/serialization.cpp
> new file mode 100644
> index 000000000..1b1d3d38e
> --- /dev/null
> +++ b/src/libcamera/serialization.cpp
> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2025, Ideas On Board Oy
> + *
> + * Data (de)serialization helper structures
> + */
> +
> +#include "libcamera/internal/serialization.h"
> +
> +namespace libcamera {
> +
> +/**
> + * \class SeriReader
> + * \brief Class to consume a byte and file descriptor buffer
> + */
> +
> +/**
> + * \fn SeriReader::SeriReader(Span<const uint8_t> data, Span<const SharedFD> fds)
> + * \brief Constructor
> + */
> +
> +/**
> + * \fn SeriReader::empty() const
> + * \brief Check if there is at least one byte or file descriptor to read
> + */
> +
> +/**
> + * \fn SeriReader::consume(std::size_t s)
> + * \brief Consume \a s bytes
> + * \return A pointer to the start of the data, or \a nullptr if there are not
> + *         enough bytes left.
> + */
> +
> +/**
> + * \fn template<typename... Ts> SeriReader::read(Ts &...xs)
> + * \brief Read bytes into \a xs
> + * \return \a true on success, or \a false if there are not enough bytes left
> + *
> + * This function reads \a sizeof(xs) bytes into \a xs, for each parameter
> + * in the argument pack, in order.
> + */
> +
> +/**
> + * \fn template<typename... Ts> SeriReader::read()
> + * \brief Extract \a Ts objects
> + * \return \a std::nullopt if there are not enough bytes left
> + *
> + * This function creates an \a std::tuple with types \a Ts, and then tries to read
> + * enough bytes into each element, in order. If that succeeds, the \a std::tuple
> + * (or just the value if \a Ts has a single element) is returned in an \a std::optional.
> + */
> +
> +/**
> + * \fn SeriReader::popFd()
> + * \brief Try to consume a single file descriptor
> + * \return A pointer to the file descriptor, or \a nullptr if there are not
> + *         enough file descriptors left.
> + */
> +
> +} /* namespace libcamera */
> diff --git a/test/ipc/unixsocket_ipc.cpp b/test/ipc/unixsocket_ipc.cpp
> index f3e3c09ef..c314e4514 100644
> --- a/test/ipc/unixsocket_ipc.cpp
> +++ b/test/ipc/unixsocket_ipc.cpp
> @@ -102,7 +102,14 @@ private:
>  		}
>
>  		case CmdSetAsync: {
> -			value_ = IPADataSerializer<int32_t>::deserialize(ipcMessage.data());
> +			SeriReader reader = ipcMessage.reader();
> +			auto value = IPADataSerializer<int32_t>::deserialize(reader);
> +			if (!value) {
> +				cerr << "Failed to deserialize value" << endl;
> +				stop(-ENODATA);
> +			} else {
> +				value_ = *value;
> +			}
>  			break;
>  		}
>  		}
> @@ -155,7 +162,14 @@ protected:
>  			return ret;
>  		}
>
> -		return IPADataSerializer<int32_t>::deserialize(buf.data());
> +		SeriReader reader = buf.reader();
> +		auto value = IPADataSerializer<int32_t>::deserialize(reader);
> +		if (!value) {
> +			cerr << "Failed to deserialize value" << endl;
> +			return -ENODATA;
> +		}
> +
> +		return *value;
>  	}
>
>  	int exit()
> diff --git a/test/serialization/generated_serializer/generated_serializer_test.cpp b/test/serialization/generated_serializer/generated_serializer_test.cpp
> index dd6968850..0640e741d 100644
> --- a/test/serialization/generated_serializer/generated_serializer_test.cpp
> +++ b/test/serialization/generated_serializer/generated_serializer_test.cpp
> @@ -43,7 +43,7 @@ if (struct1.field != struct2.field) {				\
>  }
>
>
> -		ipa::test::TestStruct t, u;
> +		ipa::test::TestStruct t;
>
>  		t.m = {
>  			{ "a", "z" },
> @@ -71,8 +71,13 @@ if (struct1.field != struct2.field) {				\
>
>  		std::tie(serialized, ignore) =
>  			IPADataSerializer<ipa::test::TestStruct>::serialize(t);
> +		SeriReader reader(serialized);
>
> -		u = IPADataSerializer<ipa::test::TestStruct>::deserialize(serialized);
> +		auto optu = IPADataSerializer<ipa::test::TestStruct>::deserialize(reader);
> +		if (!optu)
> +			return TestFail;
> +
> +		auto &u = *optu;
>
>  		if (!equals(t.m, u.m))
>  			return TestFail;
> @@ -91,12 +96,16 @@ if (struct1.field != struct2.field) {				\
>
>  		/* Test vector of generated structs */
>  		std::vector<ipa::test::TestStruct> v = { t, u };
> -		std::vector<ipa::test::TestStruct> w;
>
>  		std::tie(serialized, ignore) =
>  			IPADataSerializer<vector<ipa::test::TestStruct>>::serialize(v);
> +		reader = SeriReader(serialized);
> +
> +		auto optw = IPADataSerializer<vector<ipa::test::TestStruct>>::deserialize(reader);
> +		if (!optw)
> +			return TestFail;
>
> -		w = IPADataSerializer<vector<ipa::test::TestStruct>>::deserialize(serialized);
> +		auto &w = *optw;
>
>  		if (!equals(v[0].m, w[0].m) ||
>  		    !equals(v[1].m, w[1].m))
> diff --git a/test/serialization/ipa_data_serializer_test.cpp b/test/serialization/ipa_data_serializer_test.cpp
> index afea93a6c..3873808a6 100644
> --- a/test/serialization/ipa_data_serializer_test.cpp
> +++ b/test/serialization/ipa_data_serializer_test.cpp
> @@ -52,7 +52,9 @@ int testPodSerdes(T in)
>  	std::vector<SharedFD> fds;
>
>  	std::tie(buf, fds) = IPADataSerializer<T>::serialize(in);
> -	T out = IPADataSerializer<T>::deserialize(buf, fds);
> +	SeriReader reader(buf, fds);
> +
> +	auto out = IPADataSerializer<T>::deserialize(reader);
>  	if (in == out)
>  		return TestPass;
>
> @@ -71,7 +73,9 @@ int testVectorSerdes(const std::vector<T> &in,
>  	std::vector<SharedFD> fds;
>
>  	std::tie(buf, fds) = IPADataSerializer<std::vector<T>>::serialize(in, cs);
> -	std::vector<T> out = IPADataSerializer<std::vector<T>>::deserialize(buf, fds, cs);
> +	SeriReader reader(buf, fds);
> +
> +	auto out = IPADataSerializer<std::vector<T>>::deserialize(reader, cs);
>  	if (in == out)
>  		return TestPass;
>
> @@ -91,7 +95,9 @@ int testMapSerdes(const std::map<K, V> &in,
>  	std::vector<SharedFD> fds;
>
>  	std::tie(buf, fds) = IPADataSerializer<std::map<K, V>>::serialize(in, cs);
> -	std::map<K, V> out = IPADataSerializer<std::map<K, V>>::deserialize(buf, fds, cs);
> +	SeriReader reader(buf, fds);
> +
> +	auto out = IPADataSerializer<std::map<K, V>>::deserialize(reader, cs);
>  	if (in == out)
>  		return TestPass;
>
> @@ -171,17 +177,27 @@ private:
>  		std::tie(listBuf, std::ignore) =
>  			IPADataSerializer<ControlList>::serialize(list, &cs);
>
> -		const ControlInfoMap infoMapOut =
> -			IPADataSerializer<ControlInfoMap>::deserialize(infoMapBuf, &cs);
> +		SeriReader listReader(listBuf);
> +		SeriReader infoMapReader(infoMapBuf);
> +
> +		auto infoMapOut = IPADataSerializer<ControlInfoMap>::deserialize(infoMapReader, &cs);
> +		if (!infoMapOut) {
> +			cerr << "`ControlInfoMap` cannot be deserialized" << endl;
> +			return TestFail;
> +		}
>
> -		ControlList listOut = IPADataSerializer<ControlList>::deserialize(listBuf, &cs);
> +		auto listOut = IPADataSerializer<ControlList>::deserialize(listReader, &cs);
> +		if (!listOut) {
> +			cerr << "`ControlList` cannot be deserialized" << endl;
> +			return TestFail;
> +		}
>
> -		if (!SerializationTest::equals(infoMap, infoMapOut)) {
> +		if (!SerializationTest::equals(infoMap, *infoMapOut)) {
>  			cerr << "Deserialized map doesn't match original" << endl;
>  			return TestFail;
>  		}
>
> -		if (!SerializationTest::equals(list, listOut)) {
> +		if (!SerializationTest::equals(list, *listOut)) {
>  			cerr << "Deserialized list doesn't match original" << endl;
>  			return TestFail;
>  		}
> diff --git a/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.cpp.tmpl b/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.cpp.tmpl
> index 0d03c1df0..6146b7932 100644
> --- a/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.cpp.tmpl
> +++ b/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.cpp.tmpl
> @@ -195,29 +195,34 @@ namespace {{ns}} {
>  		return;
>  {%- endif %}
>  	}
> +{% if has_output %}
> +	SeriReader _outputReader = _ipcOutputBuf.reader();
> +{% endif -%}
>  {% if method|method_return_value != "void" %}
> -	{{method|method_return_value}} _retValue = IPADataSerializer<{{method|method_return_value}}>::deserialize(_ipcOutputBuf.data(), 0);
> -
> -{{proxy_funcs.deserialize_call(method|method_param_outputs, '_ipcOutputBuf.data()', '_ipcOutputBuf.fds()', init_offset = method|method_return_value|byte_width|int)}}
> +	auto _retValue = IPADataSerializer<{{method|method_return_value}}>::deserialize(_outputReader);
> +	ASSERT(_retValue);
> +{% endif -%}
>
> -	return _retValue;
> +{% if has_output %}
> +	{{proxy_funcs.deserialize_call(method|method_param_outputs, '_outputReader')}}
> +	ASSERT(_outputReader.empty());
> +{% endif -%}
>
> -{% elif method|method_param_outputs|length > 0 %}
> -{{proxy_funcs.deserialize_call(method|method_param_outputs, '_ipcOutputBuf.data()', '_ipcOutputBuf.fds()')}}
> +{% if method|method_return_value != "void" %}
> +	return std::move(*_retValue);
>  {% endif -%}
>  }
> -
>  {% endfor %}
>
>  void {{proxy_name}}Isolated::recvMessage(const IPCMessage &data)
>  {
> -	size_t dataSize = data.data().size();
> +	SeriReader reader = data.reader();
>  	{{cmd_event_enum_name}} _cmd = static_cast<{{cmd_event_enum_name}}>(data.header().cmd);
>
>  	switch (_cmd) {
>  {%- for method in interface_event.methods %}
>  	case {{cmd_event_enum_name}}::{{method.mojom_name|cap}}: {
> -		{{method.mojom_name}}Handler(data.data().cbegin(), dataSize, data.fds());
> +		{{method.mojom_name}}Handler(reader);
>  		break;
>  	}
>  {%- endfor %}
> @@ -227,12 +232,9 @@ void {{proxy_name}}Isolated::recvMessage(const IPCMessage &data)
>  }
>
>  {% for method in interface_event.methods %}
> -void {{proxy_name}}Isolated::{{method.mojom_name}}Handler(
> -	[[maybe_unused]] std::vector<uint8_t>::const_iterator data,
> -	[[maybe_unused]] size_t dataSize,
> -	[[maybe_unused]] const std::vector<SharedFD> &fds)
> +void {{proxy_name}}Isolated::{{method.mojom_name}}Handler([[maybe_unused]] SeriReader &reader)
>  {
> -{{proxy_funcs.deserialize_call(method.parameters, 'data', 'fds', false, true, true, 'dataSize')}}
> +	{{proxy_funcs.deserialize_call(method.parameters, 'reader', false, true)}}
>  	{{method.mojom_name}}.emit({{method.parameters|params_comma_sep}});
>  }
>  {% endfor %}
> diff --git a/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.h.tmpl b/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.h.tmpl
> index ef280ca42..f33529f71 100644
> --- a/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.h.tmpl
> +++ b/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy.h.tmpl
> @@ -123,10 +123,7 @@ private:
>  	void recvMessage(const IPCMessage &data);
>
>  {% for method in interface_event.methods %}
> -	void {{method.mojom_name}}Handler(
> -		std::vector<uint8_t>::const_iterator data,
> -		size_t dataSize,
> -		const std::vector<SharedFD> &fds);
> +	void {{method.mojom_name}}Handler(SeriReader &reader);
>  {% endfor %}
>
>  	std::unique_ptr<IPCPipeUnixSocket> ipc_;
> diff --git a/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy_worker.cpp.tmpl b/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy_worker.cpp.tmpl
> index 1f990d3f9..de6378be0 100644
> --- a/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy_worker.cpp.tmpl
> +++ b/utils/codegen/ipc/generators/libcamera_templates/module_ipa_proxy_worker.cpp.tmpl
> @@ -71,6 +71,7 @@ public:
>  		}
>
>  		IPCMessage _ipcMessage(_message);
> +		SeriReader _reader = _ipcMessage.reader();
>
>  		{{cmd_enum_name}} _cmd = static_cast<{{cmd_enum_name}}>(_ipcMessage.header().cmd);
>
> @@ -85,7 +86,9 @@ public:
>  {%- if method.mojom_name == "configure" %}
>  			controlSerializer_.reset();
>  {%- endif %}
> -		{{proxy_funcs.deserialize_call(method|method_param_inputs, '_ipcMessage.data()', '_ipcMessage.fds()', false, true)|indent(16, true)}}
> +			{{proxy_funcs.deserialize_call(method|method_param_inputs, '_reader', false, true)|indent(16, true)}}
> +			ASSERT(_reader.empty());
> +
>  {% for param in method|method_param_outputs %}
>  			{{param|name}} {{param.mojom_name}};
>  {% endfor %}
> diff --git a/utils/codegen/ipc/generators/libcamera_templates/proxy_functions.tmpl b/utils/codegen/ipc/generators/libcamera_templates/proxy_functions.tmpl
> index 01e2567ca..b6835ca35 100644
> --- a/utils/codegen/ipc/generators/libcamera_templates/proxy_functions.tmpl
> +++ b/utils/codegen/ipc/generators/libcamera_templates/proxy_functions.tmpl
> @@ -64,15 +64,6 @@
>  );
>  {%- endfor %}
>
> -{%- if params|length > 1 %}
> -{%- for param in params %}
> -	appendPOD<uint32_t>({{buf}}, {{param.mojom_name}}Buf.size());
> -{%- if param|has_fd %}
> -	appendPOD<uint32_t>({{buf}}, {{param.mojom_name}}Fds.size());
> -{%- endif %}
> -{%- endfor %}
> -{%- endif %}
> -
>  {%- for param in params %}
>  	{{buf}}.insert({{buf}}.end(), {{param.mojom_name}}Buf.begin(), {{param.mojom_name}}Buf.end());
>  {%- endfor %}
> @@ -84,104 +75,28 @@
>  {%- endfor %}
>  {%- endmacro -%}
>
> -
> -{#
> - # \brief Deserialize a single object from data buffer and fd vector
> - #
> - # \param pointer If true, deserialize the object into a dereferenced pointer
> - # \param iter If true, treat \a buf as an iterator instead of a vector
> - # \param data_size Variable that holds the size of the vector referenced by \a buf
> - #
> - # Generate code to deserialize a single object, as specified in \a param,
> - # from \a buf data buffer and \a fds fd vector.
> - # This code is meant to be used by macro deserialize_call.
> - #}
> -{%- macro deserialize_param(param, pointer, loop, buf, fds, iter, data_size) -%}
> -{{"*" if pointer}}{{param.mojom_name}} =
> -IPADataSerializer<{{param|name_full}}>::deserialize(
> -	{{buf}}{{- ".cbegin()" if not iter}} + {{param.mojom_name}}Start,
> -{%- if loop.last and not iter %}
> -	{{buf}}.cend()
> -{%- elif not iter %}
> -	{{buf}}.cbegin() + {{param.mojom_name}}Start + {{param.mojom_name}}BufSize
> -{%- elif iter and loop.length == 1 %}
> -	{{buf}} + {{data_size}}
> -{%- else %}
> -	{{buf}} + {{param.mojom_name}}Start + {{param.mojom_name}}BufSize
> -{%- endif -%}
> -{{- "," if param|has_fd}}
> -{%- if param|has_fd %}
> -	{{fds}}.cbegin() + {{param.mojom_name}}FdStart,
> -{%- if loop.last %}
> -	{{fds}}.cend()
> -{%- else %}
> -	{{fds}}.cbegin() + {{param.mojom_name}}FdStart + {{param.mojom_name}}FdsSize
> -{%- endif -%}
> -{%- endif -%}
> -{{- "," if param|needs_control_serializer}}
> -{%- if param|needs_control_serializer %}
> -	&controlSerializer_
> -{%- endif -%}
> -);
> -{%- endmacro -%}
> -
> -
>  {#
> - # \brief Deserialize multiple objects from data buffer and fd vector
> + # \brief Deserialize multiple objects
>   #
>   # \param pointer If true, deserialize objects into pointers, and adds a null check.
>   # \param declare If true, declare the objects in addition to deserialization.
> - # \param iter if true, treat \a buf as an iterator instead of a vector
> - # \param data_size Variable that holds the size of the vector referenced by \a buf
> - #
> - # Generate code to deserialize multiple objects, as specified in \a params
> - # (which are the parameters to some function), from \a buf data buffer and
> - # \a fds fd vector.
> - # This code is meant to be used by the proxy, for deserializing after IPC calls.
>   #
> - # \todo Avoid intermediate vectors
> + # Generate code to deserialize multiple objects, as specified in \a params,
> + # from \a reader. This code is meant to be used by the proxy, for deserializing
> + # after IPC calls.
>   #}
> -{%- macro deserialize_call(params, buf, fds, pointer = true, declare = false, iter = false, data_size = '', init_offset = 0) -%}
> -{% set ns = namespace(size_offset = init_offset) %}
> -{%- if params|length > 1 %}
> +{%- macro deserialize_call(params, reader, pointer = true, declare = false) -%}
>  {%- for param in params %}
> -	[[maybe_unused]] const size_t {{param.mojom_name}}BufSize = readPOD<uint32_t>({{buf}}, {{ns.size_offset}}
> -{%- if iter -%}
> -, {{buf}} + {{data_size}}
> -{%- endif -%}
> -);
> -	{%- set ns.size_offset = ns.size_offset + 4 %}
> -{%- if param|has_fd %}
> -	[[maybe_unused]] const size_t {{param.mojom_name}}FdsSize = readPOD<uint32_t>({{buf}}, {{ns.size_offset}}
> -{%- if iter -%}
> -, {{buf}} + {{data_size}}
> -{%- endif -%}
> -);
> -	{%- set ns.size_offset = ns.size_offset + 4 %}
> -{%- endif %}
> -{%- endfor %}
> -{%- endif %}
> -{% for param in params %}
> -{%- if loop.first %}
> -	const size_t {{param.mojom_name}}Start = {{ns.size_offset}};
> -{%- else %}
> -	const size_t {{param.mojom_name}}Start = {{loop.previtem.mojom_name}}Start + {{loop.previtem.mojom_name}}BufSize;
> -{%- endif %}
> -{%- endfor %}
> -{% for param in params|with_fds %}
> -{%- if loop.first %}
> -	const size_t {{param.mojom_name}}FdStart = 0;
> +	auto param_{{param.mojom_name}} = IPADataSerializer<{{param|name_full}}>::deserialize({{reader}}, &controlSerializer_);
> +	ASSERT(param_{{param.mojom_name}});
> +
> +{%- if pointer %}
> +	if ({{param.mojom_name}})
> +		*{{param.mojom_name}} = std::move(*param_{{param.mojom_name}});
> +{%- elif declare %}
> +	{{param|name}} &{{param.mojom_name}} = *param_{{param.mojom_name}};
>  {%- else %}
> -	const size_t {{param.mojom_name}}FdStart = {{loop.previtem.mojom_name}}FdStart + {{loop.previtem.mojom_name}}FdsSize;
> +	{{param.mojom_name}} = std::move(*param_{{param.mojom_name}});
>  {%- endif %}
> -{%- endfor %}
> -{% for param in params %}
> -	{%- if pointer %}
> -	if ({{param.mojom_name}}) {
> -{{deserialize_param(param, pointer, loop, buf, fds, iter, data_size)|indent(16, True)}}
> -	}
> -	{%- else %}
> -	{{param|name + " " if declare}}{{deserialize_param(param, pointer, loop, buf, fds, iter, data_size)|indent(8)}}
> -	{%- endif %}
>  {% endfor %}
>  {%- endmacro -%}
> diff --git a/utils/codegen/ipc/generators/libcamera_templates/serializer.tmpl b/utils/codegen/ipc/generators/libcamera_templates/serializer.tmpl
> index e316dd88a..9e9dd0ca6 100644
> --- a/utils/codegen/ipc/generators/libcamera_templates/serializer.tmpl
> +++ b/utils/codegen/ipc/generators/libcamera_templates/serializer.tmpl
> @@ -2,22 +2,6 @@
>   # SPDX-License-Identifier: LGPL-2.1-or-later
>   # Copyright (C) 2020, Google Inc.
>  -#}
> -{#
> - # \brief Verify that there is enough bytes to deserialize
> - #
> - # Generate code that verifies that \a size is not greater than \a dataSize.
> - # Otherwise log an error with \a name and \a typename.
> - #}
> -{%- macro check_data_size(size, dataSize, name, typename) %}
> -		if ({{dataSize}} < {{size}}) {
> -			LOG(IPADataSerializer, Error)
> -				<< "Failed to deserialize " << "{{name}}"
> -				<< ": not enough {{typename}}, expected "
> -				<< ({{size}}) << ", got " << ({{dataSize}});
> -			return ret;
> -		}
> -{%- endmacro %}
> -
>
>  {#
>   # \brief Serialize a field into return vector
> @@ -42,15 +26,10 @@
>  		retData.insert(retData.end(), {{field.mojom_name}}.begin(), {{field.mojom_name}}.end());
>  		retFds.insert(retFds.end(), {{field.mojom_name}}Fds.begin(), {{field.mojom_name}}Fds.end());
>  {%- elif field|is_controls %}
> -		if (data.{{field.mojom_name}}.size() > 0) {
> -			std::vector<uint8_t> {{field.mojom_name}};
> -			std::tie({{field.mojom_name}}, std::ignore) =
> -				IPADataSerializer<{{field|name}}>::serialize(data.{{field.mojom_name}}, cs);
> -			appendPOD<uint32_t>(retData, {{field.mojom_name}}.size());
> -			retData.insert(retData.end(), {{field.mojom_name}}.begin(), {{field.mojom_name}}.end());
> -		} else {
> -			appendPOD<uint32_t>(retData, 0);
> -		}
> +		std::vector<uint8_t> {{field.mojom_name}};
> +		std::tie({{field.mojom_name}}, std::ignore) =
> +			IPADataSerializer<{{field|name}}>::serialize(data.{{field.mojom_name}}, cs);
> +		retData.insert(retData.end(), {{field.mojom_name}}.begin(), {{field.mojom_name}}.end());
>  {%- elif field|is_plain_struct or field|is_array or field|is_map or field|is_str %}
>  		std::vector<uint8_t> {{field.mojom_name}};
>  	{%- if field|has_fd %}
> @@ -65,10 +44,6 @@
>  			IPADataSerializer<{{field|name}}>::serialize(data.{{field.mojom_name}});
>  	{%- else %}
>  			IPADataSerializer<{{field|name_full}}>::serialize(data.{{field.mojom_name}}, cs);
> -	{%- endif %}
> -		appendPOD<uint32_t>(retData, {{field.mojom_name}}.size());
> -	{%- if field|has_fd %}
> -		appendPOD<uint32_t>(retData, {{field.mojom_name}}Fds.size());
>  	{%- endif %}
>  		retData.insert(retData.end(), {{field.mojom_name}}.begin(), {{field.mojom_name}}.end());
>  	{%- if field|has_fd %}
> @@ -79,89 +54,6 @@
>  {%- endif %}
>  {%- endmacro %}
>
> -
> -{#
> - # \brief Deserialize a field into return struct
> - #
> - # Generate code to deserialize \a field into object ret.
> - # This code is meant to be used by the IPADataSerializer specialization.
> - #}
> -{%- macro deserializer_field(field, loop) %}
> -{% if field|is_pod or field|is_enum %}
> -	{%- set field_size = (field|bit_width|int / 8)|int %}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name, 'data')}}
> -		ret.{{field.mojom_name}} = IPADataSerializer<{{field|name_full}}>::deserialize(m, m + {{field_size}});
> -	{%- if not loop.last %}
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -	{%- endif %}
> -{% elif field|is_fd %}
> -	{%- set field_size = 4 %}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name, 'data')}}
> -		ret.{{field.mojom_name}} = IPADataSerializer<{{field|name}}>::deserialize(m, m + {{field_size}}, n, n + 1, cs);
> -	{%- if not loop.last %}
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -		n += ret.{{field.mojom_name}}.isValid() ? 1 : 0;
> -		fdsSize -= ret.{{field.mojom_name}}.isValid() ? 1 : 0;
> -	{%- endif %}
> -{% elif field|is_controls %}
> -	{%- set field_size = 4 %}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name + 'Size', 'data')}}
> -		const size_t {{field.mojom_name}}Size = readPOD<uint32_t>(m, 0, dataEnd);
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -	{%- set field_size = field.mojom_name + 'Size' -%}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name, 'data')}}
> -		if ({{field.mojom_name}}Size > 0)
> -			ret.{{field.mojom_name}} =
> -				IPADataSerializer<{{field|name}}>::deserialize(m, m + {{field.mojom_name}}Size, cs);
> -	{%- if not loop.last %}
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -	{%- endif %}
> -{% elif field|is_plain_struct or field|is_array or field|is_map or field|is_str %}
> -	{%- set field_size = 4 %}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name + 'Size', 'data')}}
> -		const size_t {{field.mojom_name}}Size = readPOD<uint32_t>(m, 0, dataEnd);
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -	{%- if field|has_fd %}
> -	{%- set field_size = 4 %}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name + 'FdsSize', 'data')}}
> -		const size_t {{field.mojom_name}}FdsSize = readPOD<uint32_t>(m, 0, dataEnd);
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -		{{- check_data_size(field.mojom_name + 'FdsSize', 'fdsSize', field.mojom_name, 'fds')}}
> -	{%- endif %}
> -	{%- set field_size = field.mojom_name + 'Size' -%}
> -		{{- check_data_size(field_size, 'dataSize', field.mojom_name, 'data')}}
> -		ret.{{field.mojom_name}} =
> -	{%- if field|is_str %}
> -			IPADataSerializer<{{field|name}}>::deserialize(m, m + {{field.mojom_name}}Size);
> -	{%- elif field|has_fd and (field|is_array or field|is_map) %}
> -			IPADataSerializer<{{field|name}}>::deserialize(m, m + {{field.mojom_name}}Size, n, n + {{field.mojom_name}}FdsSize, cs);
> -	{%- elif field|has_fd and (not (field|is_array or field|is_map)) %}
> -			IPADataSerializer<{{field|name_full}}>::deserialize(m, m + {{field.mojom_name}}Size, n, n + {{field.mojom_name}}FdsSize, cs);
> -	{%- elif (not field|has_fd) and (field|is_array or field|is_map) %}
> -			IPADataSerializer<{{field|name}}>::deserialize(m, m + {{field.mojom_name}}Size, cs);
> -	{%- else %}
> -			IPADataSerializer<{{field|name_full}}>::deserialize(m, m + {{field.mojom_name}}Size, cs);
> -	{%- endif %}
> -	{%- if not loop.last %}
> -		m += {{field_size}};
> -		dataSize -= {{field_size}};
> -	{%- if field|has_fd %}
> -		n += {{field.mojom_name}}FdsSize;
> -		fdsSize -= {{field.mojom_name}}FdsSize;
> -	{%- endif %}
> -	{%- endif %}
> -{% else %}
> -		/* Unknown deserialization for {{field.mojom_name}}. */
> -{%- endif %}
> -{%- endmacro %}
> -
> -
>  {#
>   # \brief Serialize a struct
>   #
> @@ -194,126 +86,30 @@
>
>
>  {#
> - # \brief Deserialize a struct that has fds
> + # \brief Deserialize a struct
>   #
> - # Generate code for IPADataSerializer specialization, for deserializing
> - # \a struct, in the case that \a struct has file descriptors.
> + # Generate code for IPADataSerializer specialization, for deserializing \a struct.
>   #}
> -{%- macro deserializer_fd(struct) %}
> -	static {{struct|name_full}}
> -	deserialize(std::vector<uint8_t> &data,
> -		    std::vector<SharedFD> &fds,
> -{%- if struct|needs_control_serializer %}
> -		    ControlSerializer *cs)
> -{%- else %}
> -		    ControlSerializer *cs = nullptr)
> -{%- endif %}
> -	{
> -		return IPADataSerializer<{{struct|name_full}}>::deserialize(data.cbegin(), data.cend(), fds.cbegin(), fds.cend(), cs);
> -	}
> -
> +{%- macro deserializer(struct) %}
>  {# \todo Don't inline this function #}
> -	static {{struct|name_full}}
> -	deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -		    std::vector<uint8_t>::const_iterator dataEnd,
> -		    std::vector<SharedFD>::const_iterator fdsBegin,
> -		    std::vector<SharedFD>::const_iterator fdsEnd,
> +	[[nodiscard]] static std::optional<{{struct|name_full}}>
> +	deserialize(SeriReader &reader,
>  {%- if struct|needs_control_serializer %}
>  		    ControlSerializer *cs)
>  {%- else %}
>  		    [[maybe_unused]] ControlSerializer *cs = nullptr)
>  {%- endif %}
>  	{
> -		{{struct|name_full}} ret;
> -		std::vector<uint8_t>::const_iterator m = dataBegin;
> -		std::vector<SharedFD>::const_iterator n = fdsBegin;
> -
> -		size_t dataSize = std::distance(dataBegin, dataEnd);
> -		[[maybe_unused]] size_t fdsSize = std::distance(fdsBegin, fdsEnd);
> -{%- for field in struct.fields -%}
> -{{deserializer_field(field, loop)}}
> +{%- for field in struct.fields %}
> +		auto {{field.mojom_name}} = IPADataSerializer<{{field|name_full}}>::deserialize(reader, cs);
> +		if (!{{field.mojom_name}})
> +			return {};
>  {%- endfor %}
> -		return ret;
> -	}
> -{%- endmacro %}
> -
> -{#
> - # \brief Deserialize a struct that has fds, using non-fd
> - #
> - # Generate code for IPADataSerializer specialization, for deserializing
> - # \a struct, in the case that \a struct has no file descriptors but requires
> - # deserializers with file descriptors.
> - #}
> -{%- macro deserializer_fd_simple(struct) %}
> -	static {{struct|name_full}}
> -	deserialize(std::vector<uint8_t> &data,
> -		    [[maybe_unused]] std::vector<SharedFD> &fds,
> -		    ControlSerializer *cs = nullptr)
> -	{
> -		return IPADataSerializer<{{struct|name_full}}>::deserialize(data.cbegin(), data.cend(), cs);
> -	}
> -
> -	static {{struct|name_full}}
> -	deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -		    std::vector<uint8_t>::const_iterator dataEnd,
> -		    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
> -		    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
> -		    ControlSerializer *cs = nullptr)
> -	{
> -		return IPADataSerializer<{{struct|name_full}}>::deserialize(dataBegin, dataEnd, cs);
> -	}
> -{%- endmacro %}
> -
> -
> -{#
> - # \brief Deserialize a struct that has no fds
> - #
> - # Generate code for IPADataSerializer specialization, for deserializing
> - # \a struct, in the case that \a struct does not have file descriptors.
> - #}
> -{%- macro deserializer_no_fd(struct) %}
> -	static {{struct|name_full}}
> -	deserialize(std::vector<uint8_t> &data,
> -{%- if struct|needs_control_serializer %}
> -		    ControlSerializer *cs)
> -{%- else %}
> -		    ControlSerializer *cs = nullptr)
> -{%- endif %}
> -	{
> -		return IPADataSerializer<{{struct|name_full}}>::deserialize(data.cbegin(), data.cend(), cs);
> -	}
>
> -{# \todo Don't inline this function #}
> -	static {{struct|name_full}}
> -	deserialize(std::vector<uint8_t>::const_iterator dataBegin,
> -		    std::vector<uint8_t>::const_iterator dataEnd,
> -{%- if struct|needs_control_serializer %}
> -		    ControlSerializer *cs)
> -{%- else %}
> -		    [[maybe_unused]] ControlSerializer *cs = nullptr)
> -{%- endif %}
> -	{
> -		{{struct|name_full}} ret;
> -		std::vector<uint8_t>::const_iterator m = dataBegin;
> -
> -		size_t dataSize = std::distance(dataBegin, dataEnd);
> -{%- for field in struct.fields -%}
> -{{deserializer_field(field, loop)}}
> +		return { {
> +{%- for field in struct.fields %}
> +			std::move(*{{field.mojom_name}}),
>  {%- endfor %}
> -		return ret;
> +		} };
>  	}
>  {%- endmacro %}
> -
> -{#
> - # \brief Deserialize a struct
> - #
> - # Generate code for IPADataSerializer specialization, for deserializing \a struct.
> - #}
> -{%- macro deserializer(struct) %}
> -{%- if struct|has_fd %}
> -{{deserializer_fd(struct)}}
> -{%- else %}
> -{{deserializer_no_fd(struct)}}
> -{{deserializer_fd_simple(struct)}}
> -{%- endif %}
> -{%- endmacro %}
> --
> 2.51.0

Hi

2025. 11. 01. 12:19 keltezéssel, Jacopo Mondi írta:
> Hi Barnabás
> 
> On Tue, Oct 14, 2025 at 01:57:52PM +0200, Barnabás Pőcze wrote:
>> First, introduce the `SeriReader` type, which is a collection
>> of bytes and file descriptors, with the appropriate methods to
>> consume the first couples bytes / file descriptors.
>>
>> Then a new method is added to `IPCMessage` that returns an appropriately
>> constructed `SeriReader` for parsing the message contents.
>>
>> Then three of the four `deserialize()` overloads are removed, the
>> remaining one is converted to have a single `SeriReader` and an
>> optional `ControlSerializer` as arguments.
>>
>> The remaining `deserialize()` function is also changed to return an
>> `std::optional` to be able to report deserialization failure.
>>
>> There is also a more fundamental change in the serialization: previously,
>> the number of bytes taken up by an item has been written before the serialized
>> bytes (and conditionally the number of file descriptors) when the item is
>> serialized as part of a struct, array, map, function parameter list. This
>> is changed: the number of bytes and file descriptors are *not* serialized
>> into the final buffer. This affords some simplification of the serialization
>> related code paths, but most importantly, it greatly simplifies and unifies
>> how an object is (de)serialized because the deserialization of every object
>> becomes completely self-contained.
>>
>> As a consequence of that, strings now include their lengths as part of the
>> string serialization, and it is not left to an "upper" layer.
>>
>> Another consequence is that an "out parameter" of a remote function call
>> must be deserialized if a later out parameter is needed, even if itself
>> is not. This does not appear to be a great limitation since in all
>> situations presently none of the out parameters are ignored.
>>
>> Finally, the code generation templates are adapted to the above changes.
>> This allows the simplification of the deserialization templates as now
>> calling `IPADataSerializer<T>::deserialize(reader, &controlSerializer_)`
>> is appropriate for any type.
>>
>> Bug: https://bugs.libcamera.org/show_bug.cgi?id=269
>> Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
>> ---
>> change in v2:
>>    * rebase
>>    * adjust comments
>>
>> v1: https://patchwork.libcamera.org/patch/23373/
>> ---
>>   .../libcamera/internal/ipa_data_serializer.h  | 234 +++---------
>>   include/libcamera/internal/ipc_pipe.h         |   3 +
>>   include/libcamera/internal/meson.build        |   1 +
>>   include/libcamera/internal/serialization.h    |  86 +++++
>>   src/libcamera/ipa_data_serializer.cpp         | 352 ++++--------------
>>   src/libcamera/ipc_pipe.cpp                    |   5 +
>>   src/libcamera/meson.build                     |   1 +
>>   src/libcamera/serialization.cpp               |  60 +++
>>   test/ipc/unixsocket_ipc.cpp                   |  18 +-
>>   .../generated_serializer_test.cpp             |  17 +-
>>   .../ipa_data_serializer_test.cpp              |  32 +-
>>   .../module_ipa_proxy.cpp.tmpl                 |  30 +-
>>   .../module_ipa_proxy.h.tmpl                   |   5 +-
>>   .../module_ipa_proxy_worker.cpp.tmpl          |   5 +-
>>   .../libcamera_templates/proxy_functions.tmpl  | 113 +-----
>>   .../libcamera_templates/serializer.tmpl       | 238 +-----------
>>   16 files changed, 372 insertions(+), 828 deletions(-)
> 
> That's quite dense.
> 
> Before getting into the details, I would like to better understand how
> this could be unified with the control serialization effort you're
> pushing for MetadataList.
> 
> I think that, if we want to get into redesigining the serialization of
> at the IPC border, we should consider it in the larger re-design
> of the libcamera API C requirement.
> 
> So let me digress a bit.
> 
> MetadataList addresses the first need to serialize controls at the API
> level in order to avoid concurrent access to a storage that doesn't
> support thread-safe access.
> 
> As we know the application thread could access the control list while
> the libcamera thread populates it. The solution we designed is to
> serialize controls into a binary buffer and implement an API on top of
> it that guarantees safe read access to a portion of the buffer while
> directing write access to a portion of the buffer that is not
> available to readers.
> 
> The MetadataList class implements a control serialization protocol
> while we have a different controls serialization protocol for IPC
> implemented by the ControlSerializer class and used over IPC.
> 
> Do you envision re-implementing any of the two on top of the other ?
> As MetadataList is "newer" I presume the IPC ControlSerializer should
> be re-implemented on top the serialization format once broken-out from
> MetadataList ?

Sorry, I don't have a good answer here. This will depend on how/if/when
`MetadataList` is merged, and whether or not there is a will to unify the two.
I am unsure what the best course of action is at the moment.


> 
> If that's the plan, are there implications on the this patch or, as
> I understand it, the IPADataSerializer still delegates the actual
> control serialization format to the ControlSerializer implementation
> and your patch only changes how the data around serialized ControlList
> and ControlInfoMap are read ?

That is correct, the serialization of control values, lists, info maps, etc.
is not changed.


> 
> Now on the patch
> 
> 
>>   create mode 100644 include/libcamera/internal/serialization.h
>>   create mode 100644 src/libcamera/serialization.cpp
>>
>> diff --git a/include/libcamera/internal/ipa_data_serializer.h b/include/libcamera/internal/ipa_data_serializer.h
>> index 927f5c4c7..3b2e0029b 100644
>> --- a/include/libcamera/internal/ipa_data_serializer.h
>> +++ b/include/libcamera/internal/ipa_data_serializer.h
>> @@ -7,6 +7,7 @@
>>
>>   #pragma once
>>
>> +#include <optional>
>>   #include <stdint.h>
>>   #include <string.h>
>>   #include <tuple>
>> @@ -23,6 +24,7 @@
>>   #include <libcamera/ipa/ipa_interface.h>
>>
>>   #include "libcamera/internal/control_serializer.h"
>> +#include "libcamera/internal/serialization.h"
>>
>>   namespace libcamera {
>>
>> @@ -39,26 +41,6 @@ void appendPOD(std::vector<uint8_t> &vec, T val)
>>   	memcpy(&*(vec.end() - byteWidth), &val, byteWidth);
>>   }
>>
>> -template<typename T,
>> -	 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
>> -T readPOD(std::vector<uint8_t>::const_iterator it, size_t pos,
>> -	  std::vector<uint8_t>::const_iterator end)
>> -{
>> -	ASSERT(pos + it < end);
>> -
>> -	T ret = 0;
>> -	memcpy(&ret, &(*(it + pos)), sizeof(ret));
>> -
>> -	return ret;
>> -}
>> -
>> -template<typename T,
>> -	 std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
>> -T readPOD(std::vector<uint8_t> &vec, size_t pos)
>> -{
>> -	return readPOD<T>(vec.cbegin(), pos, vec.end());
>> -}
>> -
>>   } /* namespace */
>>
>>   template<typename T, typename = void>
>> @@ -68,20 +50,8 @@ public:
>>   	static std::tuple<std::vector<uint8_t>, std::vector<SharedFD>>
>>   	serialize(const T &data, ControlSerializer *cs = nullptr);
>>
>> -	static T deserialize(const std::vector<uint8_t> &data,
>> -			     ControlSerializer *cs = nullptr);
>> -	static T deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -			     std::vector<uint8_t>::const_iterator dataEnd,
>> -			     ControlSerializer *cs = nullptr);
>> -
>> -	static T deserialize(const std::vector<uint8_t> &data,
>> -			     const std::vector<SharedFD> &fds,
>> -			     ControlSerializer *cs = nullptr);
>> -	static T deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -			     std::vector<uint8_t>::const_iterator dataEnd,
>> -			     std::vector<SharedFD>::const_iterator fdsBegin,
>> -			     std::vector<SharedFD>::const_iterator fdsEnd,
>> -			     ControlSerializer *cs = nullptr);
>> +	[[nodiscard]] static std::optional<T>
>> +	deserialize(SeriReader &reader, ControlSerializer *cs = nullptr);
> 
> nice!
> 
>>   };
>>
>>   #ifndef __DOXYGEN__
>> @@ -93,8 +63,6 @@ public:
>>    *
>>    * For every element in the vector:
>>    *
>> - * 4 bytes - uint32_t Size of element, in bytes
>> - * 4 bytes - uint32_t Number of fds for the element
>>    * X bytes - Serialized element
>>    *
>>    * \todo Support elements that are references
>> @@ -121,9 +89,6 @@ public:
>>   			std::tie(dvec, fvec) =
>>   				IPADataSerializer<V>::serialize(it, cs);
>>
>> -			appendPOD<uint32_t>(dataVec, dvec.size());
>> -			appendPOD<uint32_t>(dataVec, fvec.size());
>> -
>>   			dataVec.insert(dataVec.end(), dvec.begin(), dvec.end());
>>   			fdsVec.insert(fdsVec.end(), fvec.begin(), fvec.end());
>>   		}
>> @@ -131,49 +96,22 @@ public:
>>   		return { dataVec, fdsVec };
>>   	}
>>
>> -	static std::vector<V> deserialize(std::vector<uint8_t> &data, ControlSerializer *cs = nullptr)
>> +	[[nodiscard]] static std::optional<std::vector<V>>
>> +	deserialize(SeriReader &reader, ControlSerializer *cs = nullptr)
>>   	{
>> -		return deserialize(data.cbegin(), data.cend(), cs);
>> -	}
>> +		uint32_t vecLen;
>> +		if (!reader.read(vecLen))
>> +			return {};
>>
>> -	static std::vector<V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -					  std::vector<uint8_t>::const_iterator dataEnd,
>> -					  ControlSerializer *cs = nullptr)
>> -	{
>> -		std::vector<SharedFD> fds;
>> -		return deserialize(dataBegin, dataEnd, fds.cbegin(), fds.cend(), cs);
>> -	}
>> +		std::vector<V> ret;
>> +		ret.reserve(vecLen);
>>
>> -	static std::vector<V> deserialize(std::vector<uint8_t> &data, std::vector<SharedFD> &fds,
>> -					  ControlSerializer *cs = nullptr)
>> -	{
>> -		return deserialize(data.cbegin(), data.cend(), fds.cbegin(), fds.cend(), cs);
>> -	}
>> -
>> -	static std::vector<V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -					  std::vector<uint8_t>::const_iterator dataEnd,
>> -					  std::vector<SharedFD>::const_iterator fdsBegin,
>> -					  [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
>> -					  ControlSerializer *cs = nullptr)
>> -	{
>> -		uint32_t vecLen = readPOD<uint32_t>(dataBegin, 0, dataEnd);
>> -		std::vector<V> ret(vecLen);
>> -
>> -		std::vector<uint8_t>::const_iterator dataIter = dataBegin + 4;
>> -		std::vector<SharedFD>::const_iterator fdIter = fdsBegin;
>>   		for (uint32_t i = 0; i < vecLen; i++) {
>> -			uint32_t sizeofData = readPOD<uint32_t>(dataIter, 0, dataEnd);
>> -			uint32_t sizeofFds = readPOD<uint32_t>(dataIter, 4, dataEnd);
>> -			dataIter += 8;
>> -
>> -			ret[i] = IPADataSerializer<V>::deserialize(dataIter,
>> -								   dataIter + sizeofData,
>> -								   fdIter,
>> -								   fdIter + sizeofFds,
>> -								   cs);
>> -
>> -			dataIter += sizeofData;
>> -			fdIter += sizeofFds;
> Much nicer from a code point of view
> 
> Let me address this in pieces
> 
>> +			auto item = IPADataSerializer<V>::deserialize(reader, cs);
> 
> item (optionally) contains a variable of type V which has been copied
> from the binary buffer
> 
>> +			if (!item)
>> +				return {};
>> +
>> +			ret.emplace_back(std::move(*item));
> 
> Then we move item and call emplace_back which calls the move
> constructor of type V.
> 
> However, since the data from the serialized buffer have already been
> copied to 'item' do move() and emplace_back() actually help ? Won't we
> end up doing a copy inside ret anyway ?

The move constructor of `V` might be more efficient that the copy constructor.
This is especially relevant if `V` contains e.g. `SharedFD` or `std::string`
or other "non trivial" types. For trivially copyable things (e.g. just integers
here and there), there is no difference.


> 
>>   		}
>>
>>   		return ret;
>> @@ -187,11 +125,7 @@ public:
>>    *
>>    * For every pair in the map:
>>    *
>> - * 4 bytes - uint32_t Size of key, in bytes
>> - * 4 bytes - uint32_t Number of fds for the key
>>    * X bytes - Serialized key
>> - * 4 bytes - uint32_t Size of value, in bytes
>> - * 4 bytes - uint32_t Number of fds for the value
>>    * X bytes - Serialized value
>>    *
>>    * \todo Support keys or values that are references
>> @@ -218,18 +152,12 @@ public:
>>   			std::tie(dvec, fvec) =
>>   				IPADataSerializer<K>::serialize(it.first, cs);
>>
>> -			appendPOD<uint32_t>(dataVec, dvec.size());
>> -			appendPOD<uint32_t>(dataVec, fvec.size());
>> -
>>   			dataVec.insert(dataVec.end(), dvec.begin(), dvec.end());
>>   			fdsVec.insert(fdsVec.end(), fvec.begin(), fvec.end());
>>
>>   			std::tie(dvec, fvec) =
>>   				IPADataSerializer<V>::serialize(it.second, cs);
>>
>> -			appendPOD<uint32_t>(dataVec, dvec.size());
>> -			appendPOD<uint32_t>(dataVec, fvec.size());
>> -
>>   			dataVec.insert(dataVec.end(), dvec.begin(), dvec.end());
>>   			fdsVec.insert(fdsVec.end(), fvec.begin(), fvec.end());
>>   		}
>> @@ -237,63 +165,27 @@ public:
>>   		return { dataVec, fdsVec };
>>   	}
>>
>> -	static std::map<K, V> deserialize(std::vector<uint8_t> &data, ControlSerializer *cs = nullptr)
>> +	[[nodiscard]] static std::optional<std::map<K, V>>
>> +	deserialize(SeriReader &reader, ControlSerializer *cs = nullptr)
>>   	{
>> -		return deserialize(data.cbegin(), data.cend(), cs);
>> -	}
>> +		uint32_t mapLen;
>> +		if (!reader.read(mapLen))
>> +			return {};
>>
>> -	static std::map<K, V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -					  std::vector<uint8_t>::const_iterator dataEnd,
>> -					  ControlSerializer *cs = nullptr)
>> -	{
>> -		std::vector<SharedFD> fds;
>> -		return deserialize(dataBegin, dataEnd, fds.cbegin(), fds.cend(), cs);
>> -	}
>> -
>> -	static std::map<K, V> deserialize(std::vector<uint8_t> &data, std::vector<SharedFD> &fds,
>> -					  ControlSerializer *cs = nullptr)
>> -	{
>> -		return deserialize(data.cbegin(), data.cend(), fds.cbegin(), fds.cend(), cs);
>> -	}
>> -
>> -	static std::map<K, V> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -					  std::vector<uint8_t>::const_iterator dataEnd,
>> -					  std::vector<SharedFD>::const_iterator fdsBegin,
>> -					  [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
>> -					  ControlSerializer *cs = nullptr)
>> -	{
>>   		std::map<K, V> ret;
>>
>> -		uint32_t mapLen = readPOD<uint32_t>(dataBegin, 0, dataEnd);
>> -
>> -		std::vector<uint8_t>::const_iterator dataIter = dataBegin + 4;
>> -		std::vector<SharedFD>::const_iterator fdIter = fdsBegin;
>>   		for (uint32_t i = 0; i < mapLen; i++) {
>> -			uint32_t sizeofData = readPOD<uint32_t>(dataIter, 0, dataEnd);
>> -			uint32_t sizeofFds = readPOD<uint32_t>(dataIter, 4, dataEnd);
>> -			dataIter += 8;
>> -
>> -			K key = IPADataSerializer<K>::deserialize(dataIter,
>> -								  dataIter + sizeofData,
>> -								  fdIter,
>> -								  fdIter + sizeofFds,
>> -								  cs);
>> -
>> -			dataIter += sizeofData;
>> -			fdIter += sizeofFds;
>> -			sizeofData = readPOD<uint32_t>(dataIter, 0, dataEnd);
>> -			sizeofFds = readPOD<uint32_t>(dataIter, 4, dataEnd);
>> -			dataIter += 8;
>> -
>> -			const V value = IPADataSerializer<V>::deserialize(dataIter,
>> -									  dataIter + sizeofData,
>> -									  fdIter,
>> -									  fdIter + sizeofFds,
>> -									  cs);
>> -			ret.insert({ key, value });
>> -
>> -			dataIter += sizeofData;
>> -			fdIter += sizeofFds;
>> +			auto key = IPADataSerializer<K>::deserialize(reader, cs);
>> +			if (!key)
>> +				return {};
>> +
>> +			auto value = IPADataSerializer<V>::deserialize(reader, cs);
>> +			if (!value)
>> +				return {};
>> +
>> +			auto [it, inserted] = ret.try_emplace(std::move(*key), std::move(*value));
>> +			if (!inserted)
>> +				return {};
>>   		}
>>
>>   		return ret;
>> @@ -314,33 +206,14 @@ public:
>>   		return { dataVec, {} };
>>   	}
>>
>> -	static Flags<E> deserialize(std::vector<uint8_t> &data,
>> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
>> +	[[nodiscard]] static std::optional<Flags<E>>
>> +	deserialize(SeriReader &reader, [[maybe_unused]] ControlSerializer *cs = nullptr)
>>   	{
>> -		return deserialize(data.cbegin(), data.cend());
>> -	}
>> +		uint32_t value;
>> +		if (!reader.read(value))
>> +			return {};
>>
>> -	static Flags<E> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -				    std::vector<uint8_t>::const_iterator dataEnd,
>> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
>> -	{
>> -		return Flags<E>{ static_cast<E>(readPOD<uint32_t>(dataBegin, 0, dataEnd)) };
>> -	}
>> -
>> -	static Flags<E> deserialize(std::vector<uint8_t> &data,
>> -				    [[maybe_unused]] std::vector<SharedFD> &fds,
>> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
>> -	{
>> -		return deserialize(data.cbegin(), data.cend());
>> -	}
>> -
>> -	static Flags<E> deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -				    std::vector<uint8_t>::const_iterator dataEnd,
>> -				    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
>> -				    [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
>> -				    [[maybe_unused]] ControlSerializer *cs = nullptr)
>> -	{
>> -		return deserialize(dataBegin, dataEnd);
>> +		return Flags<E>{ static_cast<E>(value) };
>>   	}
>>   };
>>
>> @@ -360,33 +233,14 @@ public:
>>   		return { dataVec, {} };
>>   	}
>>
>> -	static E deserialize(std::vector<uint8_t> &data,
>> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
>> -	{
>> -		return deserialize(data.cbegin(), data.cend());
>> -	}
>> -
>> -	static E deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -			     std::vector<uint8_t>::const_iterator dataEnd,
>> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
>> -	{
>> -		return static_cast<E>(readPOD<U>(dataBegin, 0, dataEnd));
>> -	}
>> -
>> -	static E deserialize(std::vector<uint8_t> &data,
>> -			     [[maybe_unused]] std::vector<SharedFD> &fds,
>> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
>> +	[[nodiscard]] static std::optional<E>
>> +	deserialize(SeriReader &reader, [[maybe_unused]] ControlSerializer *cs = nullptr)
>>   	{
>> -		return deserialize(data.cbegin(), data.cend());
>> -	}
>> +		U value;
>> +		if (!reader.read(value))
>> +			return {};
>>
>> -	static E deserialize(std::vector<uint8_t>::const_iterator dataBegin,
>> -			     std::vector<uint8_t>::const_iterator dataEnd,
>> -			     [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsBegin,
>> -			     [[maybe_unused]] std::vector<SharedFD>::const_iterator fdsEnd,
>> -			     [[maybe_unused]] ControlSerializer *cs = nullptr)
>> -	{
>> -		return deserialize(dataBegin, dataEnd);
>> +		return static_cast<E>(value);
>>   	}
>>   };
>>
>> diff --git a/include/libcamera/internal/ipc_pipe.h b/include/libcamera/internal/ipc_pipe.h
>> index 418c4622f..2b6cde042 100644
>> --- a/include/libcamera/internal/ipc_pipe.h
>> +++ b/include/libcamera/internal/ipc_pipe.h
>> @@ -14,6 +14,7 @@
>>   #include <libcamera/base/signal.h>
>>
>>   #include "libcamera/internal/ipc_unixsocket.h"
>> +#include "libcamera/internal/serialization.h"
>>
>>   namespace libcamera {
>>
>> @@ -40,6 +41,8 @@ public:
>>   	const std::vector<uint8_t> &data() const { return data_; }
>>   	const std::vector<SharedFD> &fds() const { return fds_; }
>>
>> +	SeriReader reader() const { return { data(), fds() }; }
>> +
>>   private:
>>   	Header header_;
>>
>> diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build
>> index 45c299f6a..a11a52a01 100644
>> --- a/include/libcamera/internal/meson.build
>> +++ b/include/libcamera/internal/meson.build
>> @@ -39,6 +39,7 @@ libcamera_internal_headers = files([
>>       'process.h',
>>       'pub_key.h',
>>       'request.h',
>> +    'serialization.h',
>>       'shared_mem_object.h',
>>       'source_paths.h',
>>       'sysfs.h',
>> diff --git a/include/libcamera/internal/serialization.h b/include/libcamera/internal/serialization.h
>> new file mode 100644
>> index 000000000..f20fd8ca7
>> --- /dev/null
>> +++ b/include/libcamera/internal/serialization.h
>> @@ -0,0 +1,86 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2025, Ideas On Board Oy
>> + *
>> + * Data (de)serialization helper structures
>> + */
>> +#pragma once
>> +
>> +#include <cstddef>
>> +#include <optional>
>> +#include <stdint.h>
>> +#include <string.h>
>> +#include <tuple>
>> +#include <type_traits>
>> +
>> +#include <libcamera/base/shared_fd.h>
>> +#include <libcamera/base/span.h>
>> +
>> +namespace libcamera {
>> +
>> +class SeriReader
>> +{
>> +public:
>> +	SeriReader(Span<const uint8_t> data, Span<const SharedFD> fds = {})
>> +		: data_(reinterpret_cast<const std::byte *>(data.data()),
>> +			reinterpret_cast<const std::byte *>(data.data() + data.size())),
>> +		  fds_(fds)
>> +	{
>> +	}
>> +
>> +	[[nodiscard]] bool empty() const { return data_.empty() && fds_.empty(); }
>> +
>> +	[[nodiscard]] const std::byte *consume(std::size_t s)
>> +	{
>> +		if (data_.size() < s)
>> +			return nullptr;
>> +
>> +		const auto *p = data_.data();
>> +		data_ = data_.subspan(s);
>> +
>> +		return p;
>> +	}
> 
> I'm missing why this need to be public, shouldn't the callers use the
> read() functions to access data instead of accessing the raw buffer ?
> 
> I see 4 occurrences, and it seems the reason is to support handling of
> strings, ControlInfoMap and ControlList. Is this because they're just
> a bit special ?

I think it's fine to have it as public. The idea is that `consume()` is for
simply consuming a number of bytes for arbitrary processing. This is especially
relevant for e.g. strings as you have noted, where one wants to get the bytes
of the string, and the use that to construct the `std::string` instance. Or if
a different mechanism is needed to make sense of the bytes, e.g. ControlSerializer.

While `read()` is mostly from extracting data into objects of concrete (mostly integral)
types. I see the `read()` overloads as convenience functions on top of `consume()`.


> 
>> +
>> +	template<typename... Ts>
> 
> Now, not that I'm against template packs, but I see this being only
> used to do things like
> 
> 	if (!reader.read(offset, length))
> 
> isn't it equivalent to do
> 
> 	if (!reader.read(offset))
> 	if (!reader.read(length))
> 
> Do you envision other usage for supporting multiple template arguments ?

Yes it is equivalent, but the advantage of the single call is that it
calculates the necessary amount of bytes once and only does a single check.

I also believe it is more convenient than a longer `if` chain.


> 
> 
>> +	[[nodiscard]] bool read(Ts &...xs)
>> +	{
>> +		static_assert((std::is_trivially_copyable_v<Ts> && ...));
>> +
>> +		const auto *p = consume((sizeof(xs) + ...));
>> +		if (p)
>> +			((memcpy(&xs, p, sizeof(xs)), p += sizeof(xs)), ...);
>> +
>> +		return p;
>> +	}
>> +
>> +	template<typename... Ts>
>> +	[[nodiscard]] auto read()
>> +	{
>> +		std::tuple<Ts...> xs;
>> +		bool ok = std::apply([&](auto &...vs) {
>> +			return read(vs...);
>> +		}, xs);
> 
> if I
> 
>                  if (!ok)
>                          return std::nullopt;
> 
> here and remove the "ok ? : " below
> 
> ../include/libcamera/internal/serialization.h:67:37: error: inconsistent deduction for auto return type: ‘std::nullopt_t’ and then ‘std::optional<double>’
>     67 |                         return std::optional(std::get<0>(xs));
> 
> 
> 
>> +
>> +		if constexpr (sizeof...(Ts) == 1)
>> +			return ok ? std::optional(std::get<0>(xs)) : std::nullopt;
>> +		else
>> +			return ok ? std::optional(xs) : std::nullopt;
> 
> While it works this way....
> 
> Not complaining about it, just wondering why the compiler can deduce
> in one case and not in the other

Well, the rules for determining the type of `(x ? y : z)` are different
from the rules of return type deduction. The ternary operator is more
"permissive" in a sense.


> 
>> +	}
>> +
>> +	[[nodiscard]] const SharedFD *popFd()
>> +	{
>> +		if (fds_.empty())
>> +			return nullptr;
>> +
>> +		const auto *p = fds_.data();
>> +		fds_ = fds_.subspan(1);
>> +
>> +		return p;
>> +	}
>> +
>> +private:
>> +	Span<const std::byte> data_;
>> +	Span<const SharedFD> fds_;
>> +};
>> +
>> +} /* namespace libcamera */
> 
> Do you plan a SeriWriter ? :)

Well, I would like to. Currently serialization creates a lot of temporary
`std::vector`s. It would be nice to eliminate them.


> 
> The rest looks good (I didn't look at the mojo part) and there's no
> doubt this is better.
> 
> However, I would like to see it tested with an IPC running isolated.
> Did you have chance to give it a spin ?

I have been using this since the first submission, so I have tested it
many times on rpi and rkisp1.


Regards,
Barnabás Pőcze

> 
> Thanks
>    j
> 
> [...]