File: base64.c

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/*

	This code is public domain software.

*/

#include "base64.h"

#include <stdlib.h>
#include <string.h>

//  base64 encoding
//
//  buf:     binary input data
//  size:    size of input (bytes)
//  return:  base64-encoded string (null-terminated)
//           memory for output will be allocated here, free it later
//
char* base64_encode(const void* buf, size_t size)
{
	static const char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

	char* str = (char*) malloc((size+3)*4/3 + 1);

	char* p = str;
	const unsigned char* q = (const unsigned char*) buf;
	size_t i = 0;

	if (str == NULL) {
		return NULL;
	}

	while (i < size) {
		int c = q[i++];
		c *= 256;
		if (i < size)
            c += q[i];
		i++;

		c *= 256;
		if (i < size)
            c += q[i];
		i++;

		*p++ = base64[(c & 0x00fc0000) >> 18];
		*p++ = base64[(c & 0x0003f000) >> 12];

		if (i > size + 1)
			*p++ = '=';
		else
			*p++ = base64[(c & 0x00000fc0) >> 6];

		if (i > size)
			*p++ = '=';
		else
			*p++ = base64[c & 0x0000003f];
	}

	*p = 0;

	return str;
}


//  single base64 character conversion
//
static int POS(char c)
{
	if (c>='A' && c<='Z') return c - 'A';
	if (c>='a' && c<='z') return c - 'a' + 26;
	if (c>='0' && c<='9') return c - '0' + 52;
	if (c == '+') return 62;
	if (c == '/') return 63;
	if (c == '=') return -1;
    return -2;
}

//  base64 decoding
//
//  s:       base64 string, must be null-terminated
//  data:    output buffer for decoded data
//  data_len size of decoded data
//  return:  allocated data buffer
//
void* base64_decode(const char* s, size_t *data_len)
{
    const char *p;
    unsigned char *q, *data;
    int n[4] = { 0, 0, 0, 0 };

	size_t len = strlen(s);
	if (len % 4)
		return NULL;
	data = (unsigned char*) malloc(len/4*3);
	q = (unsigned char*) data;

	for (p = s; *p; ) {
	    n[0] = POS(*p++);
	    n[1] = POS(*p++);
	    n[2] = POS(*p++);
	    n[3] = POS(*p++);

            if (n[0] == -2 || n[1] == -2 || n[2] == -2 || n[3] == -2)
                return NULL;

	    if (n[0] == -1 || n[1] == -1)
		return NULL;

	    if (n[2] == -1 && n[3] != -1)
		return NULL;

            q[0] = (n[0] << 2) + (n[1] >> 4);
	    if (n[2] != -1)
                q[1] = ((n[1] & 15) << 4) + (n[2] >> 2);
	    if (n[3] != -1)
                q[2] = ((n[2] & 3) << 6) + n[3];
	    q += 3;
	}

	*data_len = q-data - (n[2]==-1) - (n[3]==-1);

	return data;
}