[libcamera-devel] [RFC PATCH 6/8] libcamera: Add configuration interface

[Kieran Bingham]

Hi Kieran,


On 23/11/2020 16:43, Kieran Bingham wrote:
> Provide an interface to support reading configuration files.
> 
> Initial support is included for JSON formatted files, but extending this
> with other configuration file formats is not excluded.
> 

Ahem, that was an earlier design intention, which now that this class
directly exposes a json object - does not currently hold true.

Of course all of this is internal, so things can be refactored later -
but right now - Configuration() supports only JSON.

--
Kieran


> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> ---
>  README.rst                                 |  2 +-
>  include/libcamera/internal/configuration.h | 37 +++++++++
>  src/libcamera/configuration.cpp            | 91 ++++++++++++++++++++++
>  src/libcamera/meson.build                  |  1 +
>  4 files changed, 130 insertions(+), 1 deletion(-)
>  create mode 100644 include/libcamera/internal/configuration.h
>  create mode 100644 src/libcamera/configuration.cpp
> 
> diff --git a/README.rst b/README.rst
> index 251291b77c62..c09e262fcc43 100644
> --- a/README.rst
> +++ b/README.rst
> @@ -58,7 +58,7 @@ Meson Build system: [required]
>              pip3 install --user --upgrade meson
>  
>  for the libcamera core: [required]
> -        python3-yaml python3-ply python3-jinja2
> +        python3-yaml python3-ply python3-jinja2 nlohmann-json3-dev
>  
>  for IPA module signing: [required]
>          libgnutls28-dev openssl
> diff --git a/include/libcamera/internal/configuration.h b/include/libcamera/internal/configuration.h
> new file mode 100644
> index 000000000000..a89732f0210f
> --- /dev/null
> +++ b/include/libcamera/internal/configuration.h
> @@ -0,0 +1,37 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2020, Google Inc.
> + *
> + * configuration.h - Parsing configuration files
> + */
> +#ifndef __LIBCAMERA_INTERNAL_CONFIGURATION_H__
> +#define __LIBCAMERA_INTERNAL_CONFIGURATION_H__
> +
> +#include <fstream>
> +#include <string>
> +
> +/* https://nlohmann.github.io/json/home/exceptions/#switch-off-exceptions */
> +#define JSON_NOEXCEPTION 1
> +#include <nlohmann/json.hpp>
> +
> +using json = nlohmann::json;
> +
> +namespace libcamera {
> +
> +class Configuration
> +{
> +public:
> +	int open(std::string filename);
> +
> +	json &data() { return json_; }
> +
> +private:
> +	std::string findFile(std::string filename);
> +
> +	json json_;
> +};
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_INTERNAL_CONFIGURATION_H__ */
> +
> diff --git a/src/libcamera/configuration.cpp b/src/libcamera/configuration.cpp
> new file mode 100644
> index 000000000000..f849088bbc45
> --- /dev/null
> +++ b/src/libcamera/configuration.cpp
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2020, Google Inc.
> + *
> + * configuration.cpp - Parsing configuration files
> + */
> +#include "libcamera/internal/configuration.h"
> +
> +#include "libcamera/internal/file.h"
> +#include "libcamera/internal/log.h"
> +#include "libcamera/internal/utils.h"
> +
> +#include <iostream>
> +#include <stdlib.h>
> +
> +/**
> + * \file configuration.h
> + * \brief Read interface for configuration files
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(Configuration)
> +
> +/*
> + * Configuration files can be stored in system paths, which are identified
> + * through the build configuration.
> + *
> + * However, when running uninstalled - the source location takes precedence.
> + */
> +std::string Configuration::findFile(std::string filename)
> +{
> +	static std::array<std::string, 2> searchPaths = {
> +		LIBCAMERA_SYSCONF_DIR,
> +		LIBCAMERA_DATA_DIR,
> +	};
> +
> +	std::string root = utils::libcameraSourcePath();
> +	if (!root.empty()) {
> +		std::string configurationPath = root + "data/" + filename;
> +
> +		if (File::exists(configurationPath))
> +			return configurationPath;
> +	}
> +
> +	for (std::string &path : searchPaths) {
> +		std::string configurationPath = path + "/" + filename;
> +		if (File::exists(configurationPath))
> +			return configurationPath;
> +	}
> +
> +	return "";
> +}
> +
> +/**
> + * \brief Open and parse a configuration file.
> + *
> + * The filename will be searched for on the libcamera configuration and paths,
> + * and then parsed.
> + *
> + * Successfully parsed files will present the data contained therein through the
> + * json object exposed from data();
> + */
> +int Configuration::open(std::string filename)
> +{
> +	std::string data = findFile(filename);
> +	if (data.empty()) {
> +		LOG(Configuration, Warning)
> +			<< "file: \"" << filename
> +			<< "\" was not found.";
> +		return -ENOENT;
> +	}
> +
> +	LOG(Configuration, Debug) << "Reading configuration from " << data;
> +
> +	/* Parse with no error callbacks and exceptions disabled. */
> +	std::ifstream input(data);
> +	json j = json::parse(input, nullptr, false);
> +	if (j.is_discarded()) {
> +		LOG(Configuration, Error)
> +			<< "file: \"" << data
> +			<< "\" was not parsable.";
> +		return -EINVAL;
> +	}
> +
> +	json_ = std::move(j);
> +
> +	return 0;
> +}
> +
> +} /* namespace libcamera */
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index 387d5d88ecae..5d655c87a7a0 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -9,6 +9,7 @@ libcamera_sources = files([
>      'camera_controls.cpp',
>      'camera_manager.cpp',
>      'camera_sensor.cpp',
> +    'configuration.cpp',
>      'controls.cpp',
>      'control_serializer.cpp',
>      'control_validator.cpp',
> 

-- 
Regards
--
Kieran