root/urlcode.c

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

/* Converts a hex character to its integer value */
char from_hex(char ch) {
  return isdigit(ch) ? ch - '0' : tolower(ch) - 'a' + 10;
}

/* Converts an integer value to its hex character*/
char to_hex(char code) {
  static char hex[] = "0123456789abcdef";
  return hex[code & 15];
}

/* Returns a url-encoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
char *url_encode(const char *str) {
  const char *pstr = str;
  char *buf = malloc(strlen(str) * 3 + 1), *pbuf = buf;
  while (*pstr) {
    if (isalnum(*pstr) || *pstr == '-' || *pstr == '_' || *pstr == '.' || *pstr == '~')
      *pbuf++ = *pstr;
    /* else if (*pstr == ' ') */
    /*   *pbuf++ = '+'; */
    else
      *pbuf++ = '%', *pbuf++ = to_hex(*pstr >> 4), *pbuf++ = to_hex(*pstr & 15);
    pstr++;
  }
  if (buf) { *pbuf = '\0'; }
  return buf;
}

/* Returns a url-decoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
char *url_decode(const char *str) {
  const char *pstr = str;
  char *buf = malloc(strlen(str) + 1), *pbuf = buf;
  while (*pstr) {
    if (*pstr == '%') {
      if (pstr[1] && pstr[2]) {
        *pbuf++ = from_hex(pstr[1]) << 4 | from_hex(pstr[2]);
        pstr += 2;
      }
    /* } else if (*pstr == '+') { */
    /*   *pbuf++ = ' '; */
    } else {
      *pbuf++ = *pstr;
    }
    pstr++;
  }
  *pbuf = '\0';
  return buf;
}