ftu/base64.c

/*
This is derived from the libb64 project, which has been placed in the public domain.
For details, see http://sourceforge.net/projects/libb64
*/

#include <string.h>
#include "base64.h"

int base64_decode_value(char value_in)
{
	static const char decoding[] = {62,-1,-1,-1,63,52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-2,-1,-1,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51};
	static const char decoding_size = sizeof(decoding);
	value_in -= 43;
	if (value_in < 0 || value_in >= decoding_size) return -1;
	return decoding[(int)value_in];
}

void base64_init_decodestate(base64_decodestate* state_in)
{
	state_in->step = step_a;
	state_in->plainchar = 0;
}

int base64_decode_block(const char* code_in, const int length_in, char* plaintext_out, base64_decodestate* state_in)
{
	const char* codechar = code_in;
	char* plainchar = plaintext_out;
	char fragment;
	
	*plainchar = state_in->plainchar;
	
	switch (state_in->step)
	{
		while (1)
		{
	case step_a:
			do {
				if (codechar == code_in+length_in)
				{
					state_in->step = step_a;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = (char)base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar    = (fragment & 0x03f) << 2;
			// fall through
	case step_b:
			do {
				if (codechar == code_in+length_in)
				{
					state_in->step = step_b;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = (char)base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar++ |= (fragment & 0x030) >> 4;
			*plainchar    = (fragment & 0x00f) << 4;
			// fall through
	case step_c:
			do {
				if (codechar == code_in+length_in)
				{
					state_in->step = step_c;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = (char)base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar++ |= (fragment & 0x03c) >> 2;
			*plainchar    = (fragment & 0x003) << 6;
			// fall through
	case step_d:
			do {
				if (codechar == code_in+length_in)
				{
					state_in->step = step_d;
					state_in->plainchar = *plainchar;
					return plainchar - plaintext_out;
				}
				fragment = (char)base64_decode_value(*codechar++);
			} while (fragment < 0);
			*plainchar++   |= (fragment & 0x03f);
		}
	}
	/* control should not reach here */
	return plainchar - plaintext_out;
}

void base64_init_encodestate(base64_encodestate* state_in)
{
	state_in->step = step_A;
	state_in->result = 0;
	state_in->stepcount = 0;
}

char base64_encode_value(char value_in)
{
	static const char* encoding = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	if (value_in > 63) return '=';
	return encoding[(int)value_in];
}

int base64_encode_block(const char* plaintext_in, int length_in, char* code_out, base64_encodestate* state_in)
{
	const char* plainchar = plaintext_in;
	const char* const plaintextend = plaintext_in + length_in;
	char* codechar = code_out;
	char result;
	char fragment;
	
	result = state_in->result;
	
	switch (state_in->step)
	{
		while (1)
		{
	case step_A:
			if (plainchar == plaintextend)
			{
				state_in->result = result;
				state_in->step = step_A;
				return codechar - code_out;
			}
			fragment = *plainchar++;
			result = (fragment & 0x0fc) >> 2;
			*codechar++ = base64_encode_value(result);
			result = (fragment & 0x003) << 4;
			// fall through
	case step_B:
			if (plainchar == plaintextend)
			{
				state_in->result = result;
				state_in->step = step_B;
				return codechar - code_out;
			}
			fragment = *plainchar++;
			result |= (fragment & 0x0f0) >> 4;
			*codechar++ = base64_encode_value(result);
			result = (fragment & 0x00f) << 2;
			// fall through
	case step_C:
			if (plainchar == plaintextend)
			{
				state_in->result = result;
				state_in->step = step_C;
				return codechar - code_out;
			}
			fragment = *plainchar++;
			result |= (fragment & 0x0c0) >> 6;
			*codechar++ = base64_encode_value(result);
			result  = (fragment & 0x03f) >> 0;
			*codechar++ = base64_encode_value(result);
			
			++(state_in->stepcount);

			#ifdef BASE64_USE_NEWLINES
			if (state_in->stepcount == BASE64_CHARS_PER_LINE/4)
			{
				*codechar++ = '\n';
				state_in->stepcount = 0;
			}
			#endif
		}
	}
	/* control should not reach here */
	return codechar - code_out;
}

int base64_encode_blockend(char* code_out, base64_encodestate* state_in)
{
	char* codechar = code_out;
	
	switch (state_in->step)
	{
	case step_B:
		*codechar++ = base64_encode_value(state_in->result);
		*codechar++ = '=';
		*codechar++ = '=';
		break;
	case step_C:
		*codechar++ = base64_encode_value(state_in->result);
		*codechar++ = '=';
		break;
	case step_A:
		break;
	}
	#ifdef BASE64_USE_NEWLINES
	*codechar++ = '\n';
	#endif
	
	return codechar - code_out;
}

// These "one-shot" functions were not in the original project, I have added them and still need to be sure they work

// note - output MUST be large enough to accomodate the base64'd input (i.e. must be 1/3 bigger than input_len plus the null terminator - 65 bytes for 48-byte input)
void base64_encode_oneshot(char* input, int input_len, char* output){
	base64_encodestate s;
	char* c = output;

	base64_init_encodestate(&s);
	c += base64_encode_block(input, input_len, output, &s);
	c += base64_encode_blockend(c, &s);
	*c = '\0';
}

// note - output MUST be large enough to accomodate the decoded input (i.e. must be at least 3/4 the size of the input - 48 bytes for 64-byte input)
void base64_decode_oneshot(char* input, int input_len, char* output){
	base64_decodestate s;

	base64_init_decodestate(&s);
	base64_decode_block(input, input_len, output, &s);
}

// Provides the length of the binary you would get if you decoded base64 string b64, accounting for padding
int base64_binlength(char* b64){
	int length, padding;
	length = strlen(b64);

	if(length % 4 != 0) return -1; // return -1 if length is not divisible by four (i.e. if invalid base64)

	// somewhat messy way to determine how many bytes of padding are at the end of a base64 string
	if(b64[length - 1] == '=' && b64[length - 2] == '=' && b64[length - 3] == '='){padding = 3;}
	else if(b64[length - 1] == '=' && b64[length - 2] == '='){padding = 2;}
	else if(b64[length - 1] == '='){padding = 1;}
	else{padding = 0;}

	return(((length / 4) * 3) - padding);
}

// Provides the base64 length of a binary of length binlength bytes
int base64_base64length(int binlength){
	return(((binlength + 2) / 3) * 4);
}