base64.c

/*
 / _____)             _              | |
( (____  _____ ____ _| |_ _____  ____| |__
 \____ \| ___ |    (_   _) ___ |/ ___)  _ \
 _____) ) ____| | | || |_| ____( (___| | | |
(______/|_____)_|_|_| \__)_____)\____)_| |_|
  (C)2013 Semtech-Cycleo

Description:
	Base64 encoding & decoding library

License: Revised BSD License, see LICENSE.TXT file include in the project
Maintainer: Sylvain Miermont
*/


/* -------------------------------------------------------------------------- */
/* --- DEPENDANCIES --------------------------------------------------------- */

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#include "base64.h"

/* -------------------------------------------------------------------------- */
/* --- PRIVATE MACROS ------------------------------------------------------- */

#define ARRAY_SIZE(a)	(sizeof(a) / sizeof((a)[0]))
#define CRIT(a)			fprintf(stderr, "\nCRITICAL file:%s line:%u msg:%s\n", __FILE__, __LINE__,a);exit(EXIT_FAILURE)

//#define DEBUG(args...)	fprintf(stderr,"debug: " args) /* diagnostic message that is destined to the user */
#define DEBUG(args...)

/* -------------------------------------------------------------------------- */
/* --- PRIVATE CONSTANTS ---------------------------------------------------- */

/* -------------------------------------------------------------------------- */
/* --- PRIVATE MODULE-WIDE VARIABLES ---------------------------------------- */

static char code_62 = '+';	/* RFC 1421 standard character for code 62 */
static char code_63 = '/';	/* RFC 1421 standard character for code 63 */
static char code_pad = '=';	/* RFC 1421 padding character if padding */

/* -------------------------------------------------------------------------- */
/* --- PRIVATE FUNCTIONS DECLARATION ---------------------------------------- */

/**
@brief Convert a code in the range 0-63 to an ASCII character
*/
char code_to_char(uint8_t x);

/**
@brief Convert an ASCII character to a code in the range 0-63
*/
uint8_t char_to_code(char x);

/* -------------------------------------------------------------------------- */
/* --- PRIVATE FUNCTIONS DEFINITION ----------------------------------------- */

char code_to_char(uint8_t x) {
	if (x <= 25) {
		return 'A' + x;
	} else if ((x >= 26) && (x <= 51)) {
		return 'a' + (x-26);
	} else if ((x >= 52) && (x <= 61)) {
		return '0' + (x-52);
	} else if (x == 62) {
		return code_62;
	} else if (x == 63) {
		return code_63;
	} else {
		DEBUG("ERROR: %i IS OUT OF RANGE 0-63 FOR BASE64 ENCODING\n", x);
		exit(EXIT_FAILURE);
	} //TODO: improve error management
}

uint8_t char_to_code(char x) {
	if ((x >= 'A') && (x <= 'Z')) {
		return (uint8_t)x - (uint8_t)'A';
	} else if ((x >= 'a') && (x <= 'z')) {
		return (uint8_t)x - (uint8_t)'a' + 26;
	} else if ((x >= '0') && (x <= '9')) {
		return (uint8_t)x - (uint8_t)'0' + 52;
	} else if (x == code_62) {
		return 62;
	} else if (x == code_63) {
		return 63;
	} else {
		DEBUG("ERROR: %c (0x%x) IS INVALID CHARACTER FOR BASE64 DECODING\n", x, x);
		exit(EXIT_FAILURE);
	} //TODO: improve error management
}

/* -------------------------------------------------------------------------- */
/* --- PUBLIC FUNCTIONS DEFINITION ------------------------------------------ */

int bin_to_b64_nopad(const uint8_t * in, int size, char * out, int max_len) {
	int i;
	int result_len; /* size of the result */
	int full_blocks; /* number of 3 unsigned chars / 4 characters blocks */
	int last_bytes; /* number of unsigned chars <3 in the last block */
	int last_chars; /* number of characters <4 in the last block */
	uint32_t b;
	
	/* check input values */
	if ((out == NULL) || (in == NULL)) {
		DEBUG("ERROR: NULL POINTER AS OUTPUT IN BIN_TO_B64\n");
		return -1;
	}
	if (size == 0) {
		*out = 0; /* null string */
		return 0;
	}
	
	/* calculate the number of base64 'blocks' */
	full_blocks = size / 3;
	last_bytes = size % 3;
	switch (last_bytes) {
		case 0: /* no byte left to encode */
			last_chars = 0;
			break;
		case 1: /* 1 byte left to encode -> +2 chars */
			last_chars = 2;
			break;
		case 2: /* 2 bytes left to encode -> +3 chars */
			last_chars = 3;
			break;
		default:
			CRIT("switch default that should not be possible");
	}
	
	/* check if output buffer is big enough */
	result_len = (4*full_blocks) + last_chars;
	if (max_len < (result_len + 1)) { /* 1 char added for string terminator */
		DEBUG("ERROR: OUTPUT BUFFER TOO SMALL IN BIN_TO_B64\n");
		return -1;
	}
	
	/* process all the full blocks */
	for (i=0; i < full_blocks; ++i) {
		b  = (0xFF & in[3*i]    ) << 16;
		b |= (0xFF & in[3*i + 1]) << 8;
		b |=  0xFF & in[3*i + 2];
		out[4*i + 0] = code_to_char((b >> 18) & 0x3F);
		out[4*i + 1] = code_to_char((b >> 12) & 0x3F);
		out[4*i + 2] = code_to_char((b >> 6 ) & 0x3F);
		out[4*i + 3] = code_to_char( b        & 0x3F);
	}
	
	/* process the last 'partial' block and terminate string */
	i = full_blocks;
	if (last_chars == 0) {
		out[4*i] =  0; /* null character to terminate string */
	} else if (last_chars == 2) {
		b  = (0xFF & in[3*i]    ) << 16;
		out[4*i + 0] = code_to_char((b >> 18) & 0x3F);
		out[4*i + 1] = code_to_char((b >> 12) & 0x3F);
		out[4*i + 2] =  0; /* null character to terminate string */
	} else if (last_chars == 3) {
		b  = (0xFF & in[3*i]    ) << 16;
		b |= (0xFF & in[3*i + 1]) << 8;
		out[4*i + 0] = code_to_char((b >> 18) & 0x3F);
		out[4*i + 1] = code_to_char((b >> 12) & 0x3F);
		out[4*i + 2] = code_to_char((b >> 6 ) & 0x3F);
		out[4*i + 3] = 0; /* null character to terminate string */
	}
	
	return result_len;
}

int b64_to_bin_nopad(const char * in, int size, uint8_t * out, int max_len) {
	int i;
	int result_len; /* size of the result */
	int full_blocks; /* number of 3 unsigned chars / 4 characters blocks */
	int last_chars; /* number of characters <4 in the last block */
	int last_bytes; /* number of unsigned chars <3 in the last block */
	uint32_t b;
	;
	
	/* check input values */
	if ((out == NULL) || (in == NULL)) {
		DEBUG("ERROR: NULL POINTER AS OUTPUT OR INPUT IN B64_TO_BIN\n");
		return -1;
	}
	if (size == 0) {
		return 0;
	}
	
	/* calculate the number of base64 'blocks' */
	full_blocks = size / 4;
	last_chars = size % 4;
	switch (last_chars) {
		case 0: /* no char left to decode */
			last_bytes = 0;
			break;
		case 1: /* only 1 char left is an error */
			DEBUG("ERROR: ONLY ONE CHAR LEFT IN B64_TO_BIN\n");
			return -1;
		case 2: /* 2 chars left to decode -> +1 byte */
			last_bytes = 1;
			break;
		case 3: /* 3 chars left to decode -> +2 bytes */
			last_bytes = 2;
			break;
		default:
			CRIT("switch default that should not be possible");
	}
	
	/* check if output buffer is big enough */
	result_len = (3*full_blocks) + last_bytes;
	if (max_len < result_len) {
		DEBUG("ERROR: OUTPUT BUFFER TOO SMALL IN B64_TO_BIN\n");
		return -1;
	}
	
	/* process all the full blocks */
	for (i=0; i < full_blocks; ++i) {
		b  = (0x3F & char_to_code(in[4*i]    )) << 18;
		b |= (0x3F & char_to_code(in[4*i + 1])) << 12;
		b |= (0x3F & char_to_code(in[4*i + 2])) << 6;
		b |=  0x3F & char_to_code(in[4*i + 3]);
		out[3*i + 0] = (b >> 16) & 0xFF;
		out[3*i + 1] = (b >> 8 ) & 0xFF;
		out[3*i + 2] =  b        & 0xFF;
	}
	
	/* process the last 'partial' block */
	i = full_blocks;
	if (last_bytes == 1) {
		b  = (0x3F & char_to_code(in[4*i]    )) << 18;
		b |= (0x3F & char_to_code(in[4*i + 1])) << 12;
		out[3*i + 0] = (b >> 16) & 0xFF;
		if (((b >> 12) & 0x0F) != 0) {
			DEBUG("WARNING: last character contains unusable bits\n");
		}
	} else if (last_bytes == 2) {
		b  = (0x3F & char_to_code(in[4*i]    )) << 18;
		b |= (0x3F & char_to_code(in[4*i + 1])) << 12;
		b |= (0x3F & char_to_code(in[4*i + 2])) << 6;
		out[3*i + 0] = (b >> 16) & 0xFF;
		out[3*i + 1] = (b >> 8 ) & 0xFF;
		if (((b >> 6) & 0x03) != 0) {
			DEBUG("WARNING: last character contains unusable bits\n");
		}
	}
	
	return result_len;
}

int bin_to_b64(const uint8_t * in, int size, char * out, int max_len) {
	int ret;
	
	ret = bin_to_b64_nopad(in, size, out, max_len);
	
	if (ret == -1) {
		return -1;
	}	
	switch (ret%4) {
		case 0: /* nothing to do */
			return ret;
		case 1:
			DEBUG("ERROR: INVALID UNPADDED BASE64 STRING\n");
			return -1;
		case 2: /* 2 chars in last block, must add 2 padding char */
			if (max_len > (ret + 2 + 1)) {
				out[ret] = code_pad;
				out[ret+1] = code_pad;
				out[ret+2] = 0;
				return ret+2;
			} else {
				DEBUG("ERROR: not enough room to add padding in bin_to_b64\n");
				return -1;
			}
		case 3: /* 3 chars in last block, must add 1 padding char */
			if (max_len > (ret + 1 + 1)) {
				out[ret] = code_pad;
				out[ret+1] = 0;
				return ret+1;
			} else {
				DEBUG("ERROR: not enough room to add padding in bin_to_b64\n");
				return -1;
			}
		default:
			CRIT("switch default that should not be possible");
	}
}

int b64_to_bin(const char * in, int size, uint8_t * out, int max_len) {
	if (in == NULL) {
		DEBUG("ERROR: NULL POINTER AS OUTPUT OR INPUT IN B64_TO_BIN\n");
		return -1;
	}
	if ((size%4 == 0) && (size >= 4)) { /* potentially padded Base64 */
		if (in[size-2] == code_pad) { /* 2 padding char to ignore */
			return b64_to_bin_nopad(in, size-2, out, max_len);
		} else if (in[size-1] == code_pad) { /* 1 padding char to ignore */
			return b64_to_bin_nopad(in, size-1, out, max_len);
		} else { /* no padding to ignore */
			return b64_to_bin_nopad(in, size, out, max_len);
		}
	} else { /* treat as unpadded Base64 */
		return b64_to_bin_nopad(in, size, out, max_len);
	}
}


/* --- EOF ------------------------------------------------------------------ */