URL Encoder / Decoder in C, (C) Geek Hideout

urlencoder.c

/**
 * @file urlencode.c
 * @brief URL Encoder and Decoder
 * @author Geek Hideout
 * @date 2011
 */

/* Copyright 2011 Geek Hideout. http://geekhideout.com
 * Retrieved May 11th, 2012
 */

#include "urlencode.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(char *str) {
  char *pstr = str, *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++;
  }
  *pbuf = '\0';
  return buf;
}

/* Returns a url-decoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
char *url_decode(char *str) {
  char *pstr = str, *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;
}

urlencoder.h

/*
 * @file urlencode.h
 * @breif URL Encoder and Decoder Interface
 * @author Alex Hart
 * @date May 11th, 2012
 */

/**
 * @brief Converts an integer value into hex char
 * @param code The character to encode
 * @return The encoded character
 */
char from_hex(char code);

/**
 * @brief Returns a url-encoded version of str
 * @warning Returned string is dynamically allocated, and must be released with free()
 * @param str A pointer to the string to be encoded
 * @return The encoded string
 */
char *url_encode(char *str);

/**
 * @brief Decodes a string
 * @warning Returned string is dynamically allocated, and must be released with free()
 * @param str The string to decode
 * @return The URL decoded string
 */
char *url_decode(char *str);