path: root/mp.c

/* SPDX-License-Identifier: GPL-2.0 */

/**
 * \file mp.c Mood parser helper functions.
 *
 * This file contains the public and the private API of the flex/bison based
 * mood parser.
 *
 * The public API (at the bottom of the file) allows parsing the same mood
 * definition many times in an efficient manner.
 *
 * The first function to call is \ref mp_init(), which analyzes the given mood
 * definition syntactically. It returns the abstract syntax tree of the mood
 * definition and pre-compiles all regular expression patterns to make later
 * pattern matching efficient.
 *
 * Semantic analysis is performed in \ref mp_eval_row(). This function is
 * called from \ref mood.c once for each file in the audio file table. It
 * utilizes the abstract syntax tree and the pre-compiled regular expressions
 * to determine the set of admissible audio files.
 *
 * If the mood is no longer needed, \ref mp_shutdown() should be called to free
 * the resources.
 *
 * The internal API is described in \ref mp.h.
 */

#include "para.h"

#include <fnmatch.h>
#include <osl.h>
#include <lopsub.h>

#include "string.h"
#include "error.h"
#include "afh.h"
#include "afs.h"
#include "mp.h"
#include "mp.bison.h"

struct mp_context {
	/* global context */
	char *errmsg;
	struct mp_ast_node *ast;
	/* per audio file context */
	const struct osl_row *aft_row;
	char *path;
	bool have_afsi;
	struct afs_info afsi;
	bool have_afhi;
	struct afh_info afhi;
};

/**
 * Parse a (generalized) string literal.
 *
 * \param src The string to parse.
 * \param quote_chars Opening and closing quote characters.
 * \param result The corresponding C string is returned here.
 *
 * This function turns a generalized C99 string literal like "xyz\n" into a C
 * string (containing the three characters 'x', 'y' and 'z', followed by a
 * newline character and the terminating zero byte). The function receives
 * quote characters as an argument so that, for example, regular expression
 * patterns enclosed in '/' can be parsed as well. To parse a proper string
 * literal, one has to pass two double quotes as the second argument.
 *
 * The function strips off the opening and leading quote characters, replaces
 * double backslashes by single backslashes and handles the usual escapes like
 * \n and \".
 *
 * The caller must make sure that the input is well-formed. The function simply
 * aborts if the input is not a valid C99 string literal (modulo the quote
 * characters).
 *
 * \return Offset of the first character after the closing quote. For proper
 * string literals this will be the terminating zero byte of the input string,
 * for regular expression patterns it is the beginning of the flags which
 * modify the matching behaviour.
 *
 * \sa \ref mp_parse_regex_pattern(), \ref mp_parse_wildcard_pattern().
 */
unsigned parse_quoted_string(const char *src, const char quote_chars[2],
		char **result)
{
	size_t n, len = strlen(src);
	char *dst, *p;
	bool backslash;

	assert(len >= 2);
	assert(src[0] == quote_chars[0]);
	p = dst = alloc(len - 1);
	backslash = false;
	for (n = 1;; n++) {
		char c;
		assert(n < len);
		c = src[n];
		if (!backslash) {
			if (c == '\\') {
				backslash = true;
				continue;
			}
			if (c == quote_chars[1])
				break;
			*p++ = c;
			continue;
		}
		if (c == quote_chars[1])
			*p++ = quote_chars[1];
		else switch (c) {
			case '\\': *p++ = '\\'; break;
			case 'a': *p++ = '\a'; break;
			case 'b': *p++ = '\b'; break;
			case 'f': *p++ = '\f'; break;
			case 'n': *p++ = '\n'; break;
			case 'r': *p++ = '\r'; break;
			case 't': *p++ = '\t'; break;
			case 'v': *p++ = '\v'; break;
			default: assert(false);
		}
		backslash = false;
	}
	assert(src[n] == quote_chars[1]);
	*p = '\0';
	*result = dst;
	return n + 1;
}

/**
 * Parse and compile an extended regular expression pattern, including flags.
 *
 * \param src The pattern to parse.
 * \param result C-string and flags are returned here.
 *
 * A regex pattern is identical to a C99 string literal except (a) it is
 * enclosed in '/' characters rather than double quotes, (b) double quote
 * characters which are part of the pattern do not need to be quoted with
 * backslashes, but slashes must be quoted in this way, and (c) the closing
 * slash may be followed by one or more flag characters which modify the
 * matching behaviour.
 *
 * The only flags which are currently supported are 'i' to ignore case in match
 * (REG_ICASE) and 'n' to change the handling of newline characters
 * (REG_NEWLINE).
 *
 * \return Standard. This function calls \ref parse_quoted_string(), hence it
 * aborts if the input string is malformed. However, errors from \ref
 * para_regcomp are returned without aborting the process. The rationale behind
 * this difference is that passing a malformed string must be considered an
 * implementation bug because malformed strings should be rejected earlier by
 * the lexer.
 *
 * \sa \ref mp_parse_wildcard_pattern(), \ref parse_quoted_string(),
 * \ref para_regcomp(), regex(3).
 */
int mp_parse_regex_pattern(const char *src, struct mp_re_pattern *result)
{
	int ret;
	char *pat;
	unsigned n = parse_quoted_string(src, "//", &pat);

	result->flags = 0;
	for (; src[n]; n++) {
		switch (src[n]) {
		case 'i': result->flags |= REG_ICASE; break;
		case 'n': result->flags |= REG_NEWLINE; break;
		default: assert(false);
		}
	}
	ret = para_regcomp(&result->preg, pat, result->flags);
	free(pat);
	return ret;
}

/**
 * Parse a wildcard pattern, including flags.
 *
 * \param src The pattern to parse.
 * \param result C-string and flags are returned here.
 *
 * This function parses a shell wildcard pattern. It is similar to \ref
 * mp_parse_regex_pattern(), so the remarks mentioned there apply to this
 * function as well.
 *
 * Wildcard patterns differ from regular expression patterns in that (a) they
 * must be enclosed in '|' characters, (b) they support different flags for
 * modifying matching behaviour, and (c) there is no cache for them.
 *
 * The following flags, whose meaning is explained in fnmatch(3), are currently
 * supported: 'n' (FNM_NOESCAPE), 'p' (FNM_PATHNAME), 'P' (FNM_PERIOD), 'l'
 * (FNM_LEADING_DIR), 'i' (FNM_CASEFOLD), 'e' (FNM_EXTMATCH). The last flag is
 * a GNU extension. It is silently ignored on non GNU systems.
 *
 * \sa \ref parse_quoted_string(), \ref mp_parse_regex_pattern(), fnmatch(3).
 */
void mp_parse_wildcard_pattern(const char *src, struct mp_wc_pattern *result)
{
	unsigned n = parse_quoted_string(src, "||", &result->pat);

	result->flags = 0;
	for (; src[n]; n++) {
		switch (src[n]) {
		case 'n': result->flags |= FNM_NOESCAPE; break;
		case 'p': result->flags |= FNM_PATHNAME; break;
		case 'P': result->flags |= FNM_PERIOD; break;
		/* not POSIX, but both FreeBSD and NetBSD have it */
		case 'l': result->flags |= FNM_LEADING_DIR; break;
		case 'i': result->flags |= FNM_CASEFOLD; break;
		/* GNU only */
#ifdef HAVE_FNM_EXTMATCH
		case 'e': result->flags |= FNM_EXTMATCH; break;
#else /* silently ignore extglob flag */
		case 'e': break;
#endif
		default: assert(false);
		}
	}
}

/**
 * Set the error bit in the parser context and log a message.
 *
 * \param line The number of the input line which caused the error.
 * \param ctx Contains the error bit.
 * \param fmt Usual format string.
 *
 * This is called if the lexer or the parser detect an error in the mood
 * definition. Only the first error is logged (with a severity of "warn").
 */
__printf_3_4 void mp_parse_error(int line, struct mp_context *ctx,
		const char *fmt, ...)
{
	va_list ap;
	char *tmp;

	if (ctx->errmsg) /* we already printed an error message */
		return;
	va_start(ap, fmt);
	xvasprintf(&tmp, fmt, ap);
	va_end(ap);
	xasprintf(&ctx->errmsg, "line %d: %s", line, tmp);
	free(tmp);
	PARA_NOTICE_LOG("%s\n", ctx->errmsg);
}

static int get_afsi(struct mp_context *ctx)
{
	int ret;

	if (ctx->have_afsi)
		return 0;
	ret = get_afsi_of_row(ctx->aft_row, &ctx->afsi);
	if (ret < 0)
		return ret;
	ctx->have_afsi = true;
	return 1;
}

static int get_afhi(struct mp_context *ctx)
{
	int ret;

	if (ctx->have_afhi)
		return 0;
	ret = get_afhi_of_row(ctx->aft_row, &ctx->afhi);
	if (ret < 0)
		return ret;
	ctx->have_afhi = true;
	return 1;
}

/**
 * Return the full path to the audio file.
 *
 * \param ctx Contains a reference to the row of the audio file table which
 * corresponds to the current audio file. The path of the audio file, the
 * afs_info and the afh_info structures (which contain the tag information) can
 * be retrieved through this reference.
 *
 * \return A reference to the path. Must not be freed by the caller.
 *
 * \sa \ref get_audio_file_path_of_row().
 */
char *mp_path(struct mp_context *ctx)
{
	if (!ctx->path)
		get_audio_file_path_of_row(ctx->aft_row, &ctx->path);
	return ctx->path;
}

/**
 * Check whether the given attribute is set for the current audio file.
 *
 * \param attr The string to look up in the attribute table.
 * \param ctx See \ref mp_path().
 *
 * First, determine the bit number which corresponds to the attribute, then
 * check if this bit is set in the ->attributes field of the afs_info structure
 * of the audio file.
 *
 * \return True if the attribute is set, false if it is not. On errors, for
 * example if the given string is no attribute, the function returns false.
 *
 * \sa \ref attr_name_to_bitnum().
 */
bool mp_is_set(const char *attr, struct mp_context *ctx)
{
	int ret;
	uint8_t bitnum;
	const uint64_t one = 1;

	ret = attr_name_to_bitnum(attr);
	if (ret < 0) /* treat invalid attributes as not set */
		return false;
	bitnum = ret;
	ret = get_afsi(ctx);
	if (ret < 0)
		return false;
	return (one << bitnum) & ctx->afsi.attributes;
}

/**
 * Count the number of attributes set.
 *
 * \param ctx See \ref mp_path().
 *
 * \return The number of bits which are set in the ->attributes field of the
 * afs_info structure of the current audio file.
 */
int64_t mp_num_attributes_set(struct mp_context *ctx)
{
	const uint64_t m = ~(uint64_t)0;
	int ret;
	uint64_t v;

	ret = get_afsi(ctx);
	if (ret < 0)
		return 0;

	v = ctx->afsi.attributes;
	/* taken from https://graphics.stanford.edu/~seander/bithacks.html */
	v = v - ((v >> 1) & m / 3);
	v = (v & m / 15 * 3) + ((v >> 2) & m / 15 * 3);
	v = (v + (v >> 4)) & m / 255 * 15;
	v = (v * (m / 255)) >> 56;
	assert(v <= 64);
	return v;
}

/**
 * Define a function which returns a field of the afs_info structure.
 *
 * \param _name The name of the field.
 *
 * The defined function casts the value to int64_t. On errors, zero is returned.
 */
#define MP_AFSI(_name) \
	int64_t mp_ ## _name(struct mp_context *ctx) \
	{ \
		int ret = get_afsi(ctx); \
		if (ret < 0) \
			return 0; \
		return ctx->afsi._name; \
	}
/** \cond MP_AFSI */
MP_AFSI(num_played)
MP_AFSI(image_id)
MP_AFSI(lyrics_id)
/** \endcond */

/**
 * Define a function which returns a field of the afh_info structure.
 *
 * \param _name The name of the field.
 *
 * The defined function casts the value to int64_t. On errors, zero is returned.
 */
#define MP_AFHI(_name) \
	int64_t mp_ ## _name(struct mp_context *ctx) \
	{ \
		int ret = get_afhi(ctx); \
		if (ret < 0) \
			return 0; \
		return ctx->afhi._name; \
	}
/** \cond MP_AFHI */
MP_AFHI(bitrate)
MP_AFHI(frequency)
MP_AFHI(channels)
/** \endcond */

/**
 * Return the duration of the audio file from the afh info structure.
 *
 * \param ctx See \ref mp_path().
 *
 * The duration is computed by multiplying the number of chunks and the
 * duration of one chunk.
 *
 * \return The approximate number of milliseconds.
 */
int64_t mp_duration(struct mp_context *ctx)
{
	struct timeval tmp;
	int ret = get_afhi(ctx);

	if (ret < 0)
		return 0;
	tv_scale(ctx->afhi.chunks_total, &ctx->afhi.chunk_tv, &tmp);
	return tv2ms(&tmp);
}

/**
 * Define a function which extracts and returns the value of a meta tag.
 *
 * \param _name The name of the tag (artist, title, ...).
 *
 * The function will return a pointer to memory owned by the audio file
 * selector. On errors, or if the current audio file has no tag of the given
 * name, the function returns the empty string. The caller must not attempt to
 * free the returned string.
 */
#define MP_TAG(_name) \
	char *mp_ ## _name (struct mp_context *ctx) \
	{ \
		int ret = get_afhi(ctx); \
		if (ret < 0) \
			return ""; \
		return ctx->afhi.tags._name; \
	}
/** \cond MP_TAG */
MP_TAG(artist)
MP_TAG(title)
MP_TAG(album)
MP_TAG(comment)
/** \endcond */

/**
 * Parse and return the value of the year tag.
 *
 * \param ctx See \ref mp_path().
 *
 * \return If the year tag is not present, can not be parsed, or its value is
 * less than zero, the function returns 0. If the value is less than 100, we
 * add 1900.
 */
int64_t mp_year(struct mp_context *ctx)
{
	int64_t year;
	int ret = get_afhi(ctx);

	if (ret < 0)
		return 0;
	assert(ctx->afhi.tags.year);
	ret = para_atoi64(ctx->afhi.tags.year, &year);
	if (ret < 0)
		return 0;
	if (year < 0)
		return 0;
	if (year < 100)
		year += 1900;
	return year;
}

/*
 * Ideally, these functions should be declared in a header file which is
 * created by flex with the --header-file option. However, for flex-2.6.x
 * (2017) this option is borken: if --reentrant is also given, the generated
 * header file contains syntax errors. As a workaround we declare the functions
 * here.
 */
/** \cond flex_workaround */
int mp_yylex_init(mp_yyscan_t *yyscanner);
struct yy_buffer_state *mp_yy_scan_bytes(const char *buf, int len,
	mp_yyscan_t yyscanner);
void mp_yy_delete_buffer(struct yy_buffer_state *bs, mp_yyscan_t yyscanner);
int mp_yylex_destroy(mp_yyscan_t yyscanner);
void mp_yyset_lineno(int lineno, mp_yyscan_t scanner);
/** \endcond */

/* Public API */

/**
 * Initialize the mood parser.
 *
 * This allocates and sets up the internal structures of the mood parser
 * and creates an abstract syntax tree from the given mood definition.
 * It must be called before \ref mp_eval_row() can be called.
 *
 * The context pointer returned by this function may be passed to \ref
 * mp_eval_row() to determine whether an audio file is admissible.
 *
 * \param definition A reference to the mood definition.
 * \param nbytes The size of the mood definition.
 * \param result Opaque context pointer is returned here.
 * \param errmsg Optional error message is returned here.
 *
 * It's OK to pass a NULL pointer or a zero sized buffer as the mood
 * definition. This corresponds to the "dummy" mood for which all audio files
 * are admissible.
 *
 * The error message pointer may also be NULL in which case no error message
 * is returned. Otherwise, the caller must free the returned string.
 *
 * \return Standard. On success *errmsg is set to NULL.
 */
int mp_init(const char *definition, int nbytes, struct mp_context **result,
		 char **errmsg)
{
	mp_yyscan_t scanner;
	struct mp_context *ctx;
	struct yy_buffer_state *buffer_state;

	*result = NULL;
	if (!definition || nbytes == 0) { /* dummy mood */
		if (errmsg)
			*errmsg = NULL;
		return 0;
	}
	ctx = zalloc(sizeof(*ctx));
	ctx->errmsg = NULL;
	ctx->ast = NULL;

	assert(mp_yylex_init(&scanner) == 0);
	buffer_state = mp_yy_scan_bytes(definition, nbytes, scanner);
	mp_yyset_lineno(1, scanner);
	PARA_NOTICE_LOG("creating abstract syntax tree\n");
	mp_yyparse(ctx, &ctx->ast, scanner);
	mp_yy_delete_buffer(buffer_state, scanner);
	mp_yylex_destroy(scanner);
	if (ctx->errmsg) { /* parse error */
		PARA_NOTICE_LOG("%s\n", ctx->errmsg);
		mp_free_ast(ctx->ast);
		if (errmsg)
			*errmsg = make_message("%s\n", ctx->errmsg);
		free(ctx->errmsg);
		free(ctx);
		return -E_MOOD_PARSE;
	}
	if (errmsg)
		*errmsg = NULL;
	*result = ctx;
	return 1;
}

/**
 * Determine whether the given audio file is admissible.
 *
 * \param aft_row The audio file to check for admissibility.
 * \param ctx As returned from \ref mp_init().
 *
 * \return Whether the audio file is admissible.
 *
 * If the mood parser was set up without an input buffer (dummy mood), this
 * function returns true (without looking at the audio file metadata) to
 * indicate that the given audio file should be considered admissible.
 *
 * \sa \ref mp_eval_ast().
 */
bool mp_eval_row(const struct osl_row *aft_row, struct mp_context *ctx)
{
	if (!ctx) /* dummy mood */
		return true;
	if (!ctx->ast) /* empty mood */
		return true;
	assert(aft_row);
	ctx->aft_row = aft_row;
	ctx->have_afsi = false;
	ctx->have_afhi = false;
	ctx->path = NULL;
	return mp_eval_ast(ctx->ast, ctx);
}

/**
 * Deallocate the resources of a mood parser.
 *
 * This function frees the abstract syntax tree which was created by \ref
 * mp_init().
 *
 * \param ctx As returned from \ref mp_init().
 *
 * It's OK to pass a NULL pointer, in which case the function does nothing.
 */
void mp_shutdown(struct mp_context *ctx)
{
	if (!ctx)
		return;
	mp_free_ast(ctx->ast);
	free(ctx);
}