urldecode.c

#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include "urldecode.h"

/* Function: urlDecode */
char *urlDecode(const char *str) {
  int d = 0; /* whether or not the string is decoded */

  char *dStr = malloc(strlen(str) + 1);
  char eStr[] = "00"; /* for a hex code */

  strcpy(dStr, str);

  while(!d) {
    d = 1;
    int i; /* the counter for the string */

    for(i=0;i<strlen(dStr);++i) {

      if(dStr[i] == '%') {
        if(dStr[i+1] == 0)
          return dStr;

        if(isxdigit(dStr[i+1]) && isxdigit(dStr[i+2])) {

          d = 0;

          /* combine the next to numbers into one */
          eStr[0] = dStr[i+1];
          eStr[1] = dStr[i+2];

          /* convert it to decimal */
          long int x = strtol(eStr, NULL, 16);

          /* remove the hex */
          memmove(&dStr[i+1], &dStr[i+3], strlen(&dStr[i+3])+1);

          dStr[i] = x;
        }
      }
    }
  }

  return dStr;
}