src/houdini_href_e.c

#include <assert.h>
#include <stdio.h>
#include <string.h>

#include "houdini.h"

/*
 * The following characters will not be escaped:
 *
 *		-_.+!*'(),%#@?=;:/,+&$ alphanum
 *
 * Note that this character set is the addition of:
 *
 *	- The characters which are safe to be in an URL
 *	- The characters which are *not* safe to be in
 *	an URL because they are RESERVED characters.
 *
 * We asume (lazily) that any RESERVED char that
 * appears inside an URL is actually meant to
 * have its native function (i.e. as an URL
 * component/separator) and hence needs no escaping.
 *
 * There are two exceptions: the chacters & (amp)
 * and ' (single quote) do not appear in the table.
 * They are meant to appear in the URL as components,
 * yet they require special HTML-entity escaping
 * to generate valid HTML markup.
 *
 * All other characters will be escaped to %XX.
 *
 */
static const char HREF_SAFE[] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,
    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
};

int houdini_escape_href(cmark_strbuf *ob, const uint8_t *src, bufsize_t size) {
  static const uint8_t hex_chars[] = "0123456789ABCDEF";
  bufsize_t i = 0, org;
  uint8_t hex_str[3];

  hex_str[0] = '%';

  while (i < size) {
    org = i;
    while (i < size && HREF_SAFE[src[i]] != 0)
      i++;

    if (likely(i > org))
      cmark_strbuf_put(ob, src + org, i - org);

    /* escaping */
    if (i >= size)
      break;

    switch (src[i]) {
    /* amp appears all the time in URLs, but needs
     * HTML-entity escaping to be inside an href */
    case '&':
      cmark_strbuf_puts(ob, "&amp;");
      break;

    /* the single quote is a valid URL character
     * according to the standard; it needs HTML
     * entity escaping too */
    case '\'':
      cmark_strbuf_puts(ob, "&#x27;");
      break;

/* the space can be escaped to %20 or a plus
 * sign. we're going with the generic escape
 * for now. the plus thing is more commonly seen
 * when building GET strings */
#if 0
		case ' ':
			cmark_strbuf_putc(ob, '+');
			break;
#endif

    /* every other character goes with a %XX escaping */
    default:
      hex_str[1] = hex_chars[(src[i] >> 4) & 0xF];
      hex_str[2] = hex_chars[src[i] & 0xF];
      cmark_strbuf_put(ob, hex_str, 3);
    }

    i++;
  }

  return 1;
}