docuconf for C++

cmake -S . -B build && cmake --build build

include(FetchContent)
# Until the first release: the main branch (pin a commit SHA for reproducible builds).
FetchContent_Declare(docuconf
  GIT_REPOSITORY https://github.com/Docuconf/docuconf-cpp.git
  GIT_TAG main)
FetchContent_MakeAvailable(docuconf)

add_executable(app main.cpp)
target_link_libraries(app PRIVATE docuconf::docuconf)

CLI::App app{"orders: a small HTTP service configured with docuconf"};
// The service name becomes the contract's metadata.name.
docuconf::Declaration config{app, "orders"};

// Each variable is read from its environment variable and checked at
// boot; --help lists them all. PORT is also a command-line flag (--port)
// for local runs; the platform only ever sets the environment.
int port = 0;
config.add_var("PORT", port, "HTTP listen port").range(1, 65535).default_val(8080).flag();

std::string log_level;
config.add_var("LOG_LEVEL", log_level, "Minimum log level emitted")
    .values({"debug", "info", "warn", "error"})
    .default_val("info");

// A secret: never printed, never given a default, supplied by the
// platform from a Kubernetes Secret.
std::string database_url;
config.add_var("DATABASE_URL", database_url, "Primary Postgres connection string")
    .secret()
    .required()
    .schemes({"postgres"})
    .max_length(2048);

std::vector<std::string> allowed_origins;
config.add_var("ALLOWED_ORIGINS", allowed_origins, "Origins allowed to call the API (CORS)")
    .min_items(1)
    .default_val({"http://localhost:3000"});

std::chrono::milliseconds request_timeout{};
config.add_var("REQUEST_TIMEOUT", request_timeout, "Time allowed to read a request")
    .range("1s", "5m")
    .default_val("30s");

int worker_count = 0;
config.add_var("WORKER_COUNT", worker_count)
    .doc(R"(
        /// Number of request worker threads.
        ///
        /// Each worker answers one connection at a time, so this is also the
        /// number of requests served at once. Raise it when requests queue up.
        ///
        /// Keep it at or below the database pool size:
        /// @li one connection per worker;
        /// @li plus one for migrations.
    )")
    .range(1, 64)
    .default_val(4);

// Parses, validates every input and binds the values, or exits:
// 0 after --help or --docuconf-export, 1 with every violation listed,
// 2 for a mistake in the declaration.
DOCUCONF_PARSE(config, argc, argv);

cmake -S . -B build -G Ninja && cmake --build build --target orders && DATABASE_URL=postgres://orders:pw@localhost:5432/orders ./build/examples/orders/orders

$ PORT=0 ./build/examples/orders/orders
docuconf: 2 configuration problems:
  PORT: 0 is below min 1 (out_of_range)
  DATABASE_URL: is required but not set (missing_required)

#include <gtest/gtest.h>

#include <string>
#include <vector>

#include <docuconf/docuconf.hpp>

struct Config {
    int port = 0;
    std::string database_url;
};

// The declaration, in a function that main and the tests both call.
void declare(docuconf::Declaration& d, Config& c) {
    d.add_var("PORT", c.port, "HTTP listen port").range(1, 65535).default_val(8080);
    d.add_var("DATABASE_URL", c.database_url, "Primary Postgres connection string").secret().required().schemes({"postgres"});
}

TEST(Config, UsesDefaults) {
    CLI::App app;
    docuconf::Declaration d{app, "orders"};
    Config c;
    declare(d, c);
    // load(env) reads only this map, never the process environment.
    d.load({{"DATABASE_URL", "postgres://orders@db/orders"}});
    EXPECT_EQ(c.port, 8080);
}

TEST(Config, ReportsEveryProblem) {
    CLI::App app;
    docuconf::Declaration d{app, "orders"};
    Config c;
    declare(d, c);
    try {
        d.load({{"PORT", "70000"}});
        FAIL() << "expected a ValidationError";
    } catch (const docuconf::ValidationError& e) {
        EXPECT_EQ(e.codes_for("PORT"), std::vector<docuconf::Code>{docuconf::Code::OutOfRange});
        EXPECT_TRUE(e.has(docuconf::Code::MissingRequired));
    }
}

cmake --build build --target config_test && ./build/config_test

./build/examples/orders/orders --docuconf-export examples/orders/contract.cue

// Code generated by docuconf. DO NOT EDIT.
package orders

import "docuconf.dev/contract"

contract.#Contract & {
	apiVersion: "docuconf.dev/v1alpha1"
	kind: "ConfigContract"
	metadata: {
		name: "orders"
		generator: {
			language: "cpp"
			sdk: "docuconf-cpp"
			version: "0.1.0"
		}
	}
	vars: {
		ALLOWED_ORIGINS: {
			type: "list"
			description: "Origins allowed to call the API (CORS)"
			default: ["http://localhost:3000"]
			items: "string"
			encoding: "csv"
			separator: ","
			minItems: 1
		}
		DATABASE_URL: {
			type: "url"
			description: "Primary Postgres connection string"
			required: true
			secret: true
			maxLength: 2048
			schemes: ["postgres"]
		}
		LOG_LEVEL: {
			type: "enum"
			description: "Minimum log level emitted"
			default: "info"
			values: ["debug", "info", "warn", "error"]
		}
		PORT: {
			type: "int"
			description: "HTTP listen port"
			default: 8080
			min: 1
			max: 65535
		}
		REQUEST_TIMEOUT: {
			type: "duration"
			description: "Time allowed to read a request"
			default: "30s"
			min: "1s"
			max: "5m"
			encoding: "go"
		}
		WORKER_COUNT: {
			type: "int"
			description: "Number of request worker threads"
			details: "Each worker answers one connection at a time, so this is also the\nnumber of requests served at once. Raise it when requests queue up.\n\nKeep it at or below the database pool size:\n- one connection per worker;\n- plus one for migrations."
			default: 4
			min: 1
			max: 64
		}
	}
}

$ ./build/examples/orders/orders --help
orders: a small HTTP service configured with docuconf
Usage: ./build/examples/orders/orders [OPTIONS]

Options:
  -h,--help                   Print this help message and exit
  --port INT [8080]           HTTP listen port


docuconf:
  --docuconf-export PATH      Write the configuration contract (contract.cue) to this path, or - for standard output, and exit without reading the environment

Environment variables:
  PORT             HTTP listen port [int, default "8080", or --port]
  LOG_LEVEL        Minimum log level emitted [one of debug|info|warn|error, default "info"]
  DATABASE_URL     Primary Postgres connection string [url, REQUIRED, secret]
  ALLOWED_ORIGINS  Origins allowed to call the API (CORS) [list of string, separated by ",", default "http://localhost:3000"]
  REQUEST_TIMEOUT  Time allowed to read a request [duration, default "30s"]
  WORKER_COUNT     Number of request worker threads [int, default "4"]