autolink.c

/*
 * Copyright (c) 2015, Vicent Marti
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "buffer.h"
#include "autolink.h"

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

#if defined(_WIN32)
#define strncasecmp	_strnicmp
#endif

int
sd_autolink_issafe(const uint8_t *link, size_t link_len)
{
	static const size_t valid_uris_count = 6;
	static const char *valid_uris[] = {
		"#", "/", "http://", "https://", "ftp://", "mailto:"
	};

	size_t i;

	for (i = 0; i < valid_uris_count; ++i) {
		size_t len = strlen(valid_uris[i]);

		if (link_len > len &&
			strncasecmp((char *)link, valid_uris[i], len) == 0 &&
			isalnum(link[len]))
			return 1;
	}

	return 0;
}

static size_t
autolink_delim(uint8_t *data, size_t link_end, size_t max_rewind, size_t size)
{
	uint8_t cclose, copen = 0;
	size_t i;

	for (i = 0; i < link_end; ++i)
		if (data[i] == '<') {
			link_end = i;
			break;
		}

	while (link_end > 0) {
		if (strchr("?!.,", data[link_end - 1]) != NULL)
			link_end--;

		else if (data[link_end - 1] == ';') {
			size_t new_end = link_end - 2;

			while (new_end > 0 && isalpha(data[new_end]))
				new_end--;

			if (new_end < link_end - 2 && data[new_end] == '&')
				link_end = new_end;
			else
				link_end--;
		}
		else break;
	}

	if (link_end == 0)
		return 0;

	cclose = data[link_end - 1];

	switch (cclose) {
	case '"':	copen = '"'; break;
	case '\'':	copen = '\''; break;
	case ')':	copen = '('; break;
	case ']':	copen = '['; break;
	case '}':	copen = '{'; break;
	}

	if (copen != 0) {
		size_t closing = 0;
		size_t opening = 0;
		size_t i = 0;

		/* Try to close the final punctuation sign in this same line;
		 * if we managed to close it outside of the URL, that means that it's
		 * not part of the URL. If it closes inside the URL, that means it
		 * is part of the URL.
		 *
		 * Examples:
		 *
		 *	foo http://www.pokemon.com/Pikachu_(Electric) bar
		 *		=> http://www.pokemon.com/Pikachu_(Electric)
		 *
		 *	foo (http://www.pokemon.com/Pikachu_(Electric)) bar
		 *		=> http://www.pokemon.com/Pikachu_(Electric)
		 *
		 *	foo http://www.pokemon.com/Pikachu_(Electric)) bar
		 *		=> http://www.pokemon.com/Pikachu_(Electric))
		 *
		 *	(foo http://www.pokemon.com/Pikachu_(Electric)) bar
		 *		=> foo http://www.pokemon.com/Pikachu_(Electric)
		 */

		while (i < link_end) {
			if (data[i] == copen)
				opening++;
			else if (data[i] == cclose)
				closing++;

			i++;
		}

		if (closing != opening)
			link_end--;
	}

	return link_end;
}

static size_t
check_domain(uint8_t *data, size_t size, int allow_short)
{
	size_t i, np = 0;

	if (!isalnum(data[0]))
		return 0;

	for (i = 1; i < size - 1; ++i) {
		if (strchr(".:", data[i]) != NULL) np++;
		else if (!isalnum(data[i]) && data[i] != '-') break;
	}

	if (allow_short) {
		/* We don't need a valid domain in the strict sense (with
		 * least one dot; so just make sure it's composed of valid
		 * domain characters and return the length of the the valid
		 * sequence. */
		return i;
	} else {
		/* a valid domain needs to have at least a dot.
		 * that's as far as we get */
		return np ? i : 0;
	}
}

size_t
sd_autolink__www(
	size_t *rewind_p,
	struct buf *link,
	uint8_t *data,
	size_t max_rewind,
	size_t size,
	unsigned int flags)
{
	size_t link_end;

	if (max_rewind > 0 && !ispunct(data[-1]) && !isspace(data[-1]))
		return 0;

	if (size < 4 || memcmp(data, "www.", strlen("www.")) != 0)
		return 0;

	link_end = check_domain(data, size, 0);

	if (link_end == 0)
		return 0;

	while (link_end < size && !isspace(data[link_end]))
		link_end++;

	link_end = autolink_delim(data, link_end, max_rewind, size);

	if (link_end == 0)
		return 0;

	bufput(link, data, link_end);
	*rewind_p = 0;

	return (int)link_end;
}

size_t
sd_autolink__email(
	size_t *rewind_p,
	struct buf *link,
	uint8_t *data,
	size_t max_rewind,
	size_t size,
	unsigned int flags)
{
	size_t link_end, rewind;
	int nb = 0, np = 0;

	for (rewind = 0; rewind < max_rewind; ++rewind) {
		uint8_t c = data[-rewind - 1];

		if (isalnum(c))
			continue;

		if (strchr(".+-_", c) != NULL)
			continue;

		break;
	}

	if (rewind == 0)
		return 0;

	for (link_end = 0; link_end < size; ++link_end) {
		uint8_t c = data[link_end];

		if (isalnum(c))
			continue;

		if (c == '@')
			nb++;
		else if (c == '.' && link_end < size - 1)
			np++;
		else if (c != '-' && c != '_')
			break;
	}

	if (link_end < 2 || nb != 1 || np == 0)
		return 0;

	link_end = autolink_delim(data, link_end, max_rewind, size);

	if (link_end == 0)
		return 0;

	bufput(link, data - rewind, link_end + rewind);
	*rewind_p = rewind;

	return link_end;
}

size_t
sd_autolink__url(
	size_t *rewind_p,
	struct buf *link,
	uint8_t *data,
	size_t max_rewind,
	size_t size,
	unsigned int flags)
{
	size_t link_end, rewind = 0, domain_len;

	if (size < 4 || data[1] != '/' || data[2] != '/')
		return 0;

	while (rewind < max_rewind && isalpha(data[-rewind - 1]))
		rewind++;

	if (!sd_autolink_issafe(data - rewind, size + rewind))
		return 0;

	link_end = strlen("://");

	domain_len = check_domain(
		data + link_end,
		size - link_end,
		flags & SD_AUTOLINK_SHORT_DOMAINS);

	if (domain_len == 0)
		return 0;

	link_end += domain_len;
	while (link_end < size && !isspace(data[link_end]))
		link_end++;

	link_end = autolink_delim(data, link_end, max_rewind, size);

	if (link_end == 0)
		return 0;

	bufput(link, data - rewind, link_end + rewind);
	*rewind_p = rewind;

	return link_end;
}