/*
You're in luck, here is some ANSI C code that I happened to be working on
before lunch.  I happen to be using MSVC 5.0, but I don't see anything in
there that shouldn't compile anywhere.  Have fun with it.

Ryan Alyn Porter, President
Endymion Corporation
http://www.endymion.com

*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

void CGIEncode(char* strString, int maxlen);
void RFC1630Encode(char* strString, int maxlen, int loose);
int  bWordChar(char cChar, int loose);
int  bWhitespaceChar(char cChar);

/* Helper to determine if a character is a whitespace
   character.  Returns 1 for true, 0 for false. */
int bWhitespaceChar(char cChar)
{
    if((cChar == 0x0A) || /* Newline. */
       (cChar == 0x0D) || /* Carriage Return. */
       (cChar == 0x20) || /* Space. */
       (cChar == 0x0B) ||
       (cChar == 0x0C))
       return 1;
    else
       return 0;
}

/* Performs encoding on a string in accordance with
   commonly accepted standards set forth in cgi-lib.pl
   and CGI.pm. */
void CGIEncode(char* strString, int maxlen)
{
    unsigned int uiStrLen,
                 uiIndex = 0;
    char cCurrentChar = 0;

    /* Find the initial length of the string. */
    uiStrLen = strlen(strString);
    
    /* Loop through the string, replacing 
       whitespace characters one-for-one. */
    for(uiIndex=0;uiIndex<uiStrLen;uiIndex++)
    {
        cCurrentChar = strString[uiIndex];

        /* If this is whitespace, replace it
           with '+', otherwise pass it through. */
        if(bWhitespaceChar(cCurrentChar))
            strString[uiIndex] = '+';
    }

    /* Encode non-word characters according to 
       RFC 1630. */
    RFC1630Encode(strString, maxlen, 0);
}

/* Helper to determine if a character is a non-word
   character.  Returns 1 for true, 0 for false. */
int bWordChar(char cChar, int loose)
{
    if((cChar >= 'a' && cChar <= 'z') ||
       (cChar >= 'A' && cChar <= 'Z') ||
       (cChar >= '0' && cChar <= '9') ||
       (loose && (cChar == '.'))
 )
/*
        ||
       (cChar == '+'))
*/
       return 1;
    else
       return 0;
}
/* %-encode a string according to RFC 1630.  This 
  function assumes that there are not already %-encoded
  characters present in the string to be encoded. */
void RFC1630Encode(char* strString, int maxlen, int loose)
{
    unsigned int uiStrLen,
                 uiStrLenEncoded,
                 uiIndex,
                 uiCurrentPosition = 0;
    char cCurrentChar = 0;
    char *strStringTemp;
    char strEncodedChar[4];

    /* Find the initial length of the string. */
    uiStrLen = strlen(strString);
    uiStrLenEncoded = uiStrLen;


    /* Find out how big the %-encoded string will be. */
    for(uiIndex=0;uiIndex<uiStrLen;uiIndex++)
    {
        cCurrentChar = strString[uiIndex];

        /* If this character must be encoded, it will
           take up an additional two characters in the
           encoded string. */
        if(!bWordChar(cCurrentChar, loose))
            uiStrLenEncoded += 2;
    }

    if (uiStrLenEncoded >= maxlen) {
       return;  // Can't encode, too long
    } 
    /* Allocate space for a temporary copy of the string. */
    strStringTemp = (char *)malloc(uiStrLenEncoded);

    /* Copy the un-encoded string to the temp string. */
    strcpy(strStringTemp,strString);

    /* Empty the original string. */
    strString[0] = 0;

    /* Encode the string into the new buffer. */
    for(uiIndex=0;uiIndex<uiStrLen;uiIndex++)
    {
        cCurrentChar = strStringTemp[uiIndex];
        
        /* If the character doesn't have to be encoded, */
        if(bWordChar(cCurrentChar, loose))
        {
            /* ...then simply copy it into the output. */
            strString[uiCurrentPosition++] = 
                strStringTemp[uiIndex];
            strString[uiCurrentPosition] = 0;
        }
        else
            /* ...otherwise encode it into the output. */
        {
            sprintf(strEncodedChar,"%%%X",
                strStringTemp[uiIndex]);
            strcat(strString,strEncodedChar);
            uiCurrentPosition += 3;
        }
    }
    free(strStringTemp);

    return;
}

/* encode a string for html.  */
void HtmlEncode(char* strString, int maxlen)
{
    unsigned int uiStrLen,
                 uiStrLenEncoded,
                 uiIndex,
                 uiCurrentPosition = 0;
    char cCurrentChar = 0;
    char *strStringTemp;
    char strEncodedChar[4];
    char *sp_char = "&<>";
    char *rep_char[] = {"&amp;", "&lt;", &gt;");
    char *c;

    /* Find the initial length of the string. */
    uiStrLen = strlen(strString);
    uiStrLenEncoded = uiStrLen;


    /* Find out how big the %-encoded string will be. */
    for(uiIndex=0;uiIndex<uiStrLen;uiIndex++)
    {
        cCurrentChar = strString[uiIndex];

        /* If this character must be encoded, it will
           take up an additional two characters in the
           encoded string. */
        if((c = strchr(cCurrentChar, sp_char)) != NULL)
            uiStrLenEncoded += strlen(rep_char[c - sp_char]);
    }

    if (uiStrLenEncoded >= maxlen) {
       return;  // Can't encode, too long
    } 
    /* Allocate space for a temporary copy of the string. */
    strStringTemp = (char *)malloc(uiStrLenEncoded);

    /* Copy the un-encoded string to the temp string. */
    strcpy(strStringTemp,strString);

    /* Empty the original string. */
    strString[0] = 0;

    /* Encode the string into the new buffer. */
    for(uiIndex=0;uiIndex<uiStrLen;uiIndex++)
    {
        cCurrentChar = strStringTemp[uiIndex];
        
        /* If the character doesn't have to be encoded, */
        if((c = strchr(cCurrentChar, sp_char)) != NULL)
        {
            /* ...then simply copy it into the output. */
            strString[uiCurrentPosition++] = 
                strStringTemp[uiIndex];
            strString[uiCurrentPosition] = 0;
        }
        else
            /* ...otherwise encode it into the output. */
        {
            strcat(strString, rep_char[c - sp_char]);
            uiCurrentPosition += strlen(rep_char[c - sp_char]);
        }
    }
    free(strStringTemp);

    return;
}