[v10,04/13] config: Add configuration retrieval helpers

23567 diff mbox series

Let's add some helpers to make accessing simple configuration values
simpler.

GlobalConfiguration::option must check for the key presence before
retrieving the value using operator[] because if the key is not present
then YamlObject::empty may be returned as a regular value.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
---
 .../libcamera/internal/global_configuration.h |  5 ++
 src/libcamera/base/global_configuration.cpp   | 52 +++++++++++++++++++
 2 files changed, 57 insertions(+)

Hi Milan,

Thank you for the patch.

On Mon, Jun 16, 2025 at 10:47:22AM +0200, Milan Zamazal wrote:
> Let's add some helpers to make accessing simple configuration values
> simpler.
> 
> GlobalConfiguration::option must check for the key presence before
> retrieving the value using operator[] because if the key is not present
> then YamlObject::empty may be returned as a regular value.
> 
> Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
> ---
>  .../libcamera/internal/global_configuration.h |  5 ++
>  src/libcamera/base/global_configuration.cpp   | 52 +++++++++++++++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/include/libcamera/internal/global_configuration.h b/include/libcamera/internal/global_configuration.h
> index 8d0410ac2..5d9531158 100644
> --- a/include/libcamera/internal/global_configuration.h
> +++ b/include/libcamera/internal/global_configuration.h
> @@ -8,6 +8,8 @@
>  #pragma once
>  
>  #include <filesystem>
> +#include <optional>
> +#include <string>
>  
>  #include "libcamera/internal/yaml_parser.h"
>  
> @@ -22,6 +24,9 @@ public:
>  
>  	unsigned int version() const;
>  	Configuration configuration() const;
> +	std::optional<std::string> option(const std::string &confPath) const;
> +	std::optional<std::string> envOption(const char *const envVariable,
> +					     const std::string &confPath) const;
>  
>  private:
>  	bool loadFile(const std::filesystem::path &fileName);
> diff --git a/src/libcamera/base/global_configuration.cpp b/src/libcamera/base/global_configuration.cpp
> index 1ddf5bc33..1ef63750c 100644
> --- a/src/libcamera/base/global_configuration.cpp
> +++ b/src/libcamera/base/global_configuration.cpp
> @@ -8,6 +8,8 @@
>  #include "libcamera/internal/global_configuration.h"
>  
>  #include <filesystem>
> +#include <memory>
> +#include <string>
>  #include <string_view>
>  #include <sys/types.h>
>  
> @@ -40,6 +42,11 @@ LOG_DEFINE_CATEGORY(Configuration)
>   * is not found then in system-wide configuration directories. If multiple
>   * configuration files exist then only the first one found is used and no
>   * configuration merging is performed.
> + *
> + * The configuration can be accessed using the provided helpers. Namely
> + * GlobalConfiguration::option() or GlobalConfiguration::envOption() to access
> + * individual options or GlobalConfiguration::configuration() to access the
> + * whole configuration.
>   */
>  
>  bool GlobalConfiguration::loadFile(const std::filesystem::path &fileName)
> @@ -112,6 +119,51 @@ GlobalConfiguration::GlobalConfiguration()
>   * the underlying type.
>   */
>  
> +/**
> + * \brief Return value of the configuration option identified by \a confPath
> + * \param[in] confPath Sequence of the YAML section names (excluding
> + * `configuration') leading to the requested option separated by dots

Periods are allowed in key names, but I suppose we can forbid them in
libcamera. Is there a specific reason you picked the period as a
separator over, for instance, '/' ? I suppose somehow matching the
jquery syntax is a good idea.

> + * \return A value if an item corresponding to \a confPath exists in the
> + * configuration file, no value otherwise
> + */
> +std::optional<std::string> GlobalConfiguration::option(const std::string &confPath) const

This seems possibly useful for YamlObject, not just GlobalConfiguration.
Would it make sense to implement it there ?

I'll comment more on this patch after reviewing the callers.

> +{
> +	const YamlObject *c = &configuration();
> +	for (auto part : utils::split(confPath, ".")) {
> +		c = &(*c)[part];
> +		if (!*c)
> +			return {};
> +	}
> +	return c->get<std::string>();
> +}
> +
> +/**
> + * \brief Return value of the configuration option from a file or environment
> + * \param[in] envVariable Environment variable to get the value from
> + * \param[in] confPath The same as in GlobalConfiguration::option
> + *
> + * This helper looks first at the given environment variable and if it is
> + * defined then it returns its value (even if it is empty). Otherwise it looks
> + * for \a confPath the same way as in GlobalConfiguration::option. Only string
> + * values are supported.
> + *
> + * \note Support for using environment variables to configure libcamera behavior
> + * is provided here mostly for backward compatibility reasons. Introducing new
> + * configuration environment variables is discouraged.
> + *
> + * \return A value retrieved from the given environment option or configuration
> + * file or no value if not found
> + */
> +std::optional<std::string> GlobalConfiguration::envOption(
> +	const char *const envVariable,
> +	const std::string &confPath) const
> +{
> +	const char *envValue = utils::secure_getenv(envVariable);
> +	if (envValue)
> +		return std::optional{ std::string{ envValue } };
> +	return option(confPath);
> +}
> +
>  /**
>   * \brief Return configuration version
>   *