Add iterator-style API

[argpar.git] / argpar / argpar.h

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright (c) 2019-2021 Philippe Proulx <pproulx@efficios.com>
 * Copyright (c) 2020-2021 Simon Marchi <simon.marchi@efficios.com>
 */

#ifndef BABELTRACE_ARGPAR_H
#define BABELTRACE_ARGPAR_H

#include <stdbool.h>

/*
 * argpar is a library which provides facilities for command-line
 * argument parsing.
 *
 * Two APIs are available:
 *
 * Iterator API:
 *     Create a parsing iterator with argpar_iter_create(), then
 *     repeatedly call argpar_iter_parse_next() to access the parsing
 *     results, until one of:
 *
 *     * There are no more arguments.
 *
 *     * The argument parser encounters an error (for example, an
 *       unknown option).
 *
 *     * You need to stop.
 *
 *     This API provides more parsing control than the next one.
 *
 * Single call API:
 *     Call argpar_parse(), which parses the arguments until one of:
 *
 *     * There are no more arguments.
 *
 *     * It encounters an argument parsing error.
 *
 *     argpar_parse() returns a single array of parsing results.
 *
 * Both methods parse the arguments `argv` of which the count is `argc`
 * using the sentinel-terminated (use `ARGPAR_OPT_DESCR_SENTINEL`)
 * option descriptor array `descrs`.
 *
 * argpar considers ALL the elements of `argv`, including the first one,
 * so that you would typically pass `argc - 1` and `&argv[1]` from what
 * main() receives.
 *
 * The argpar parsers support:
 *
 * * Short options without an argument, possibly tied together:
 *
 *       -f -auf -n
 *
 * * Short options with argument:
 *
 *       -b 45 -f/mein/file -xyzhello
 *
 * * Long options without an argument:
 *
 *       --five-guys --burger-king --pizza-hut --subway
 *
 * * Long options with arguments:
 *
 *       --security enable --time=18.56
 *
 * * Non-option arguments (anything else).
 *
 * The argpar parsers don't accept `-` or `--` as arguments. The latter
 * means "end of options" for many command-line tools, but this library
 * is all about keeping the order of the arguments, so it doesn't mean
 * much to put them at the end. This has the side effect that a
 * non-option argument cannot have the form of an option, for example if
 * you need to pass the exact relative path `--component`. In that case,
 * you would need to pass `./--component`. There's no generic way to
 * escape `-` as of this version.
 *
 * Both argpar_iter_create() and argpar_parse() accept duplicate options
 * (they produce one item for each instance).
 *
 * A returned parsing item has the type `struct argpar_item *`. Each
 * item is to be casted to the appropriate type
 * (`struct argpar_item_opt *` or `struct argpar_item_non_opt *`)
 * depending on its `type` member.
 *
 * Both argpar_iter_create() and argpar_parse() produce the items in
 * the same order that the arguments were parsed, including non-option
 * arguments. This means, for example, that for:
 *
 *     --hello --count=23 /path/to/file -ab --type file magie
 *
 * The produced items are, in this order:
 *
 * 1. Option item (`--hello`).
 * 2. Option item (`--count` with argument `23`).
 * 3. Non-option item (`/path/to/file`).
 * 4. Option item (`-a`).
 * 5. Option item (`-b`).
 * 6. Option item (`--type` with argument `file`).
 * 7. Non-option item (`magie`).
 */

/* Sentinel for an option descriptor array */
#define ARGPAR_OPT_DESCR_SENTINEL	{ -1, '\0', NULL, false }

/*
 * ARGPAR_HIDDEN: if argpar is used in some shared library, we don't
 * want them to be exported by that library, so mark them as "hidden".
 *
 * On Windows, symbols are local unless explicitly exported; see
 * <https://gcc.gnu.org/wiki/Visibility>.
 */
#if defined(_WIN32) || defined(__CYGWIN__)
#define ARGPAR_HIDDEN
#else
#define ARGPAR_HIDDEN __attribute__((visibility("hidden")))
#endif

/* Forward-declaration for the opaque type */
struct argpar_iter;

/* Option descriptor */
struct argpar_opt_descr {
	/* Numeric ID for this option */
	const int id;

	/* Short option character, or `\0` */
	const char short_name;

	/* Long option name (without `--`), or `NULL` */
	const char * const long_name;

	/* True if this option has an argument */
	const bool with_arg;
};

/* Item type */
enum argpar_item_type {
	/* Option */
	ARGPAR_ITEM_TYPE_OPT,

	/* Non-option */
	ARGPAR_ITEM_TYPE_NON_OPT,
};

/* Base item */
struct argpar_item {
	enum argpar_item_type type;
};

/* Option item */
struct argpar_item_opt {
	struct argpar_item base;

	/* Corresponding descriptor */
	const struct argpar_opt_descr *descr;

	/* Argument, or `NULL` if none */
	const char *arg;
};

/* Non-option item */
struct argpar_item_non_opt {
	struct argpar_item base;

	/*
	 * Complete argument, pointing to one of the entries of the
	 * original arguments (`argv`).
	 */
	const char *arg;

	/* Index of this argument amongst all original arguments (`argv`) */
	unsigned int orig_index;

	/* Index of this argument amongst other non-option arguments */
	unsigned int non_opt_index;
};

struct argpar_item_array {
	/* Array of `struct argpar_item *`, or `NULL` on error */
	struct argpar_item **items;

	/* Number of used slots in `items`. */
	unsigned int n_items;

	/* Number of allocated slots in `items`. */
	unsigned int n_alloc;
};

/* What is returned by argpar_parse() */
struct argpar_parse_ret {
	/*
	 * Array of `struct argpar_item *`, or `NULL` on error.
	 *
	 * Do NOT destroy those items manually with
	 * argpar_iter_destroy(): call argpar_parse_ret_fini() to
	 * finalize the whole structure.
	 */
	struct argpar_item_array *items;

	/* Error string, or `NULL` if none */
	char *error;

	/* Number of original arguments (`argv`) ingested */
	unsigned int ingested_orig_args;
};

/*
 * Parses arguments in `argv` until the end is reached or an error is
 * encountered.
 *
 * On success, this function returns an array of items (field `items` of
 * `struct argpar_parse_ret`).
 *
 * In the returned structure, `ingested_orig_args` is the number of
 * ingested arguments within `argv` to produce the resulting array of
 * items.
 *
 * If `fail_on_unknown_opt` is true, then on success
 * `ingested_orig_args` is equal to `argc`. Otherwise,
 * `ingested_orig_args` contains the number of original arguments until
 * an unknown _option_ occurs. For example, with
 *
 *     --great --white contact nuance --shark nuclear
 *
 * if `--shark` is not described within `descrs` and
 * `fail_on_unknown_opt` is false, then `ingested_orig_args` is 4 (two
 * options, two non-options), whereas `argc` is 6.
 *
 * This makes it possible to know where a command name is, for example.
 * With those arguments:
 *
 *     --verbose --stuff=23 do-something --specific-opt -f -b
 *
 * and the descriptors for `--verbose` and `--stuff` only, the function
 * returns the `--verbose` and `--stuff` option items, the
 * `do-something` non-option item, and that three original arguments
 * were ingested. This means you can start the next argument parsing
 * stage, with option descriptors depending on the command name, at
 * `&argv[3]`.
 *
 * Note that `ingested_orig_args` is not always equal to the number of
 * returned items, as
 *
 *     --hello -fdw
 *
 * for example contains two ingested original arguments, but four
 * resulting items.
 *
 * On failure, the `items` member of the returned structure is `NULL`,
 * and the `error` string member contains details about the error.
 *
 * Finalize the returned structure with argpar_parse_ret_fini().
 */
ARGPAR_HIDDEN
struct argpar_parse_ret argpar_parse(unsigned int argc,
		const char * const *argv,
		const struct argpar_opt_descr *descrs,
		bool fail_on_unknown_opt);

/*
 * Finalizes what argpar_parse() returns.
 *
 * You may call argpar_parse() multiple times with the same structure.
 */
ARGPAR_HIDDEN
void argpar_parse_ret_fini(struct argpar_parse_ret *ret);

/*
 * Creates an argument parsing iterator.
 *
 * This function initializes the returned structure, but doesn't
 * actually start parsing the arguments.
 *
 * `*argv` and `*descrs` must NOT change for the lifetime of the
 * returned iterator (until you call argpar_iter_destroy()).
 *
 * Call argpar_iter_parse_next() with the returned iterator to obtain
 * the next parsing result (item).
 */
ARGPAR_HIDDEN
struct argpar_iter *argpar_iter_create(unsigned int argc,
		const char * const *argv,
		const struct argpar_opt_descr *descrs);

/*
 * Destroys `iter`, as returned by argpar_iter_create().
 */
ARGPAR_HIDDEN
void argpar_iter_destroy(struct argpar_iter *iter);

/*
 * Return type of argpar_iter_parse_next().
 */
enum argpar_iter_parse_next_status {
	ARGPAR_ITER_PARSE_NEXT_STATUS_OK,
	ARGPAR_ITER_PARSE_NEXT_STATUS_END,
	ARGPAR_ITER_PARSE_NEXT_STATUS_ERROR_UNKNOWN_OPT,
	ARGPAR_ITER_PARSE_NEXT_STATUS_ERROR,
};

/*
 * Parses and returns the next item from `iter`.
 *
 * On success, this function sets `*item` to an item which describes the
 * next option or non-option argument and returns
 * `ARGPAR_ITER_PARSE_NEXT_STATUS_OK`. Destroy `*item` with
 * argpar_item_destroy().
 *
 * If there are no more items to return, this function returns
 * `ARGPAR_ITER_PARSE_NEXT_STATUS_END`.
 *
 * On failure (status codes
 * `ARGPAR_ITER_PARSE_NEXT_STATUS_ERROR_UNKNOWN_OPT` and
 * `ARGPAR_ITER_PARSE_NEXT_STATUS_ERROR`), this function sets `*error`
 * to a descriptive error string. Free `*error` with free().
 *
 * Create an argument parsing iterator with argpar_iter_create().
 */
enum argpar_iter_parse_next_status argpar_iter_parse_next(
		struct argpar_iter *iter, const struct argpar_item **item,
		char **error);

/*
 * Returns the number of ingested elements from `argv`, as passed to
 * argpar_iter_create() to create `*iter`, that were required to produce
 * the previously returned items.
 */
ARGPAR_HIDDEN
unsigned int argpar_iter_get_ingested_orig_args(const struct argpar_iter *iter);

/*
 * Destroys `item`, as created by argpar_iter_parse_next().
 */
ARGPAR_HIDDEN
void argpar_item_destroy(const struct argpar_item *item);

/*
 * Destroys `_item` (`const struct argpar_item *`) and sets it to
 * `NULL`.
 */
#define ARGPAR_ITEM_DESTROY_AND_RESET(_item)	\
	{					\
		argpar_item_destroy(_item);	\
		_item = NULL;			\
	}

#endif /* BABELTRACE_ARGPAR_H */