format.c

/*
 * music player command (mpc)
 * Copyright 2003-2018 The Music Player Daemon Project
 * http://www.musicpd.org
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "format.h"

#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

/**
 * Reallocate the given string and append the source string.
 */
gcc_malloc
static char *
string_append(char *dest, const char *src, size_t len)
{
	size_t destlen = dest != NULL
		? strlen(dest)
		: 0;

	dest = realloc(dest, destlen + len + 1);
	memcpy(dest + destlen, src, len);
	dest[destlen + len] = '\0';

	return dest;
}

/**
 * Skip the format string until the current group is closed by either
 * '&', '|' or ']' (supports nesting).
 */
gcc_pure
static const char *
skip_format(const char *p)
{
	unsigned stack = 0;

	while (*p != '\0') {
		if (*p == '[')
			stack++;
		else if (*p == '#' && p[1] != '\0')
			/* skip escaped stuff */
			++p;
		else if (stack > 0) {
			if (*p == ']')
				--stack;
		} else if (*p == '&' || *p == '|' || *p == ']')
			break;

		++p;
	}

	return p;
}

static bool
is_name_char(char ch)
{
	return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') ||
		(ch >= '0' && ch <= '9') || ch == '_';
}

static char *
format_object2(const char *format, const char **last, const void *object,
	       const char *(*getter)(const void *object, const char *name))
{
	char *ret = NULL;
	const char *p;
	bool found = false;

	for (p = format; *p != '\0';) {
		switch (p[0]) {
		case '|':
			++p;
			if (!found) {
				/* nothing found yet: try the next
				   section */
				free(ret);
				ret = NULL;
			} else
				/* already found a value: skip the
				   next section */
				p = skip_format(p);
			break;

		case '&':
			++p;
			if (!found)
				/* nothing found yet, so skip this
				   section */
				p = skip_format(p);
			else
				/* we found something yet, but it will
				   only be used if the next section
				   also found something, so reset the
				   flag */
				found = false;
			break;

		case '[': {
			char *t = format_object2(p + 1, &p, object, getter);
			if (t != NULL) {
				ret = string_append(ret, t, strlen(t));
				free(t);
				found = true;
			}
		}
			break;

		case ']':
			if (last != NULL)
				*last = p + 1;
			if (!found) {
				free(ret);
				ret = NULL;
			}
			return ret;

		case '\\': {
			/* take care of escape sequences */
			char ltemp;
			switch (p[1]) {
			case 'a':
				ltemp = '\a';
				break;

			case 'b':
				ltemp = '\b';
				break;

			case 't':
				ltemp = '\t';
				break;

			case 'n':
				ltemp = '\n';
				break;

			case 'v':
				ltemp = '\v';
				break;

			case 'f':
				ltemp = '\f';
				break;

			case 'r':
				ltemp = '\r';
				break;

			case '[':
			case ']':
				ltemp = p[1];
				break;

			default:
				/* unknown escape: copy the
				   backslash */
				ltemp = p[0];
				--p;
				break;
			}

			ret = string_append(ret, &ltemp, 1);
			p += 2;
		}
			break;

		case '%': {
			/* find the extent of this format specifier
			   (stop at \0, ' ', or esc) */
			const char *end = p + 1;
			while (is_name_char(*end))
				++end;

			const size_t length = end - p + 1;

			if (*end != '%') {
				ret = string_append(ret, p, length - 1);
				p = end;
				continue;
			}

			char name[32];
			if (length > (int)sizeof(name)) {
				ret = string_append(ret, p, length);
				p = end + 1;
				continue;
			}

			memcpy(name, p + 1, length - 2);
			name[length - 2] = 0;

			const char *value = getter(object, name);
			size_t value_length;
			if (value != NULL) {
				if (*value != 0)
					found = true;
				value_length = strlen(value);
			} else {
				/* unknown variable: copy verbatim
				   from format string */
				value = p;
				value_length = length;
			}

			ret = string_append(ret, value, value_length);

			/* advance past the specifier */
			p = end + 1;
		}
			break;

		case '#':
			/* let the escape character escape itself */
			if (p[1] != '\0') {
				ret = string_append(ret, p + 1, 1);
				p += 2;
				break;
			}

			/* fall through */

		default:
			/* pass-through non-escaped portions of the format string */
			ret = string_append(ret, p, 1);
			++p;
		}
	}

	if (last != NULL)
		*last = p;
	return ret;
}

char *
format_object(const char *format, const void *object,
	      const char *(*getter)(const void *object, const char *name))
{
	return format_object2(format, NULL, object, getter);
}