b64_cencode.c

/*
  This is cencode.c from libb64. It is written by

      Chris Venter chris.venter@gmail.com http://rocketpod.blogspot.com

  who placed it in the public domain. The full text of the license and the
  source is below. I'm copying this source instead of linking to the library
  because

  1. the library hard-codes the line length (CHARS_PER_LINE), and I need the
     whole string to appear in a single line

  2. I want to make sure that I don't overrun my buffer, so
     base64_encode_block() takes in the buffer length

 */



/*
Copyright-Only Dedication (based on United States law)
or Public Domain Certification

The person or persons who have associated work with this document (the
"Dedicator" or "Certifier") hereby either (a) certifies that, to the best of
his knowledge, the work of authorship identified is in the public domain of the
country from which the work is published, or (b) hereby dedicates whatever
copyright the dedicators holds in the work of authorship identified below (the
"Work") to the public domain. A certifier, moreover, dedicates any copyright
interest he may have in the associated work, and for these purposes, is
described as a "dedicator" below.

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work. Certifier recognizes that his good faith efforts may not shield him from
liability if in fact the work certified is not in the public domain.

Dedicator makes this dedication for the benefit of the public at large and to
the detriment of the Dedicator's heirs and successors. Dedicator intends this
dedication to be an overt act of relinquishment in perpetuity of all present
and future rights under copyright law, whether vested or contingent, in the
Work. Dedicator understands that such relinquishment of all rights includes
the relinquishment of all rights to enforce (by lawsuit or otherwise) those
copyrights in the Work.

Dedicator recognizes that, once placed in the public domain, the Work may be
freely reproduced, distributed, transmitted, used, modified, built upon, or
otherwise exploited by anyone for any purpose, commercial or non-commercial,
and in any way, including by methods that have not yet been invented or
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*/

/*
cencoder.c - c source to a base64 encoding algorithm implementation

This is part of the libb64 project, and has been placed in the public domain.
For details, see http://sourceforge.net/projects/libb64
*/


#include "vnlog-base64.h"

typedef enum
{
	step_A, step_B, step_C
} base64_encodestep;

typedef struct
{
	base64_encodestep step;
	char result;
} base64_encodestate;


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

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

static 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;
	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;
	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);
		}
	}
	/* control should not reach here */
	return codechar - code_out;
}

static 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;
	}

	return codechar - code_out;
}

int vnlog_base64_encode(       char* dst, int dstlen,
                         const char* src, int srclen )
{
    if(srclen <= 0)
    {
        if(dstlen > 0)
            *dst = '\0';
        return 0;
    }

    base64_encodestate s;
    base64_init_encodestate(&s);

    const int dstlen_needed = vnlog_base64_dstlen_to_encode(srclen);

    if(dstlen < dstlen_needed)
        return -1;

    int len = base64_encode_block(src, srclen, dst, &s);
    len += base64_encode_blockend(&dst[len], &s);
    dst[len] = '\0';

    // The number of bytes in the output (not including the trailing '\0') is
    // returned
    return len;
}