urlencode.c

#include <stdlib.h>
#include <string.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( 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;
}