c_cpp Base64编码和解码

Posted 2021-05-14

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

/*
**   modified by wention 11.22.2013
**   
**   more information about original please visite http://base64.sourceforge.net/
**
*/

/*
** Translation Table as described in RFC1113
*/
static const char cb64[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/*
** Translation Table to decode (created by author)
*/
static const char cd64[]="|$$$}rstuvwxyz{$$$$$$$>?@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[\\]^_`abcdefghijklmnopq";

/*
** encodeblock
**
** encode 3 8-bit binary bytes as 4 '6-bit' characters
*/
static void encodeblock( unsigned char *in, unsigned char *out, int len )
{
    out[0] = (unsigned char) cb64[ (int)(in[0] >> 2) ];
    out[1] = (unsigned char) cb64[ (int)(((in[0] & 0x03) << 4) | ((in[1] & 0xf0) >> 4)) ];
    out[2] = (unsigned char) (len > 1 ? cb64[ (int)(((in[1] & 0x0f) << 2) | ((in[2] & 0xc0) >> 6)) ] : '=');
    out[3] = (unsigned char) (len > 2 ? cb64[ (int)(in[2] & 0x3f) ] : '=');
}

/*
** encode
**
** base64 encode a stream adding padding and line breaks as per spec.
*/
int base64_encode( unsigned char *infile,unsigned long insize, unsigned char *outfile, int linesize )
{
	unsigned char in[3]={0};
	unsigned char out[4]={0};
    int i,len, cin = 0,cout = 0,blocksout = 0;

	*in = (unsigned char) 0;
	*out = (unsigned char) 0;
    while( cin < insize ) {
        len = 0;
        for( i = 0; i < 3; i++ ) {
            in[i] = (unsigned char)  infile[cin++];

            if( cin <= insize ) {
                len++;
            }
            else {
                in[i] = (unsigned char) 0;
            }
        }
        if( len > 0 ) {
            encodeblock( in, out, len );
	        memmove(&outfile[cout],out,4);
            cout+=4;
            blocksout++;
        }
        if( blocksout >= (linesize/4) || cin >= insize ) {
            if( blocksout > 0 ) {
                memmove( &outfile[cout], "\r\n", 2 );
                cout+=2;
            }
            blocksout = 0;
        }
    }
    return true;
}

/*
** decodeblock
**
** decode 4 '6-bit' characters into 3 8-bit binary bytes
*/
static void decodeblock( unsigned char *in, unsigned char *out )
{   
    out[ 0 ] = (unsigned char ) (in[0] << 2 | in[1] >> 4);
    out[ 1 ] = (unsigned char ) (in[1] << 4 | in[2] >> 2);
    out[ 2 ] = (unsigned char ) (((in[2] << 6) & 0xc0) | in[3]);
}

/*
** decode
**
** decode a base64 encoded stream discarding padding, line breaks and noise
*/
int base64_decode( unsigned char *infile,unsigned long insize, unsigned char *outfile )
{
	unsigned char in[4]={0};
	unsigned char out[3]={0};
    int v;
    int i, len, cin =0, cout =0;

    while( cin < insize ) {
        for( len = 0, i = 0; i < 4 && cin < insize; i++ ) {
            v = 0;
            while( cin < insize && v == 0 ) {
                v = infile[cin++];
                if( v != 0 ) {
	                v = ((v < 43 || v > 122) ? 0 : (int) cd64[ v - 43 ]);
					if( v != 0 ) {
						v = ((v == (int)'$') ? 0 : v - 61);
					}
                }
            }
            if( cin < insize ) {
                len++;
                if( v != 0 ) {
                    in[ i ] = (unsigned char) (v - 1);
                }
            }
            else {
                in[i] = (unsigned char) 0;
            }
        }
        if( len > 0 ) {
            decodeblock( in, out );
            memmove(&outfile[cout],out,3);
            cout+=3;
        }
    }
       return true;
}