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nessa video aula eu ensino a codificar e decodificar base64 com o b64.c
[Tens de ter uma conta e sessão iniciada para poderes visualizar este link]
- Código:
#include <stdio.h>
#include <stdlib.h>
/*
** 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
*/
void encodeblock( unsigned char in[3], unsigned char out[4], int len )
{
out[0] = cb64[ in[0] >> 2 ];
out[1] = cb64[ ((in[0] & 0x03) << 4) | ((in[1] & 0xf0) >> 4) ];
out[2] = (unsigned char) (len > 1 ? cb64[ ((in[1] & 0x0f) << 2) | ((in[2] & 0xc0) >> 6) ] : '=');
out[3] = (unsigned char) (len > 2 ? cb64[ in[2] & 0x3f ] : '=');
}
/*
** encode
**
** base64 encode a stream adding padding and line breaks as per spec.
*/
void encode( FILE *infile, FILE *outfile, int linesize )
{
unsigned char in[3], out[4];
int i, len, blocksout = 0;
while( !feof( infile ) ) {
len = 0;
for( i = 0; i < 3; i++ ) {
in[i] = (unsigned char) getc( infile );
if( !feof( infile ) ) {
len++;
}
else {
in[i] = 0;
}
}
if( len ) {
encodeblock( in, out, len );
for( i = 0; i < 4; i++ ) {
putc( out[i], outfile );
}
blocksout++;
}
if( blocksout >= (linesize/4) || feof( infile ) ) {
if( blocksout ) {
fprintf( outfile, "\r\n" );
}
blocksout = 0;
}
}
}
/*
** decodeblock
**
** decode 4 '6-bit' characters into 3 8-bit binary bytes
*/
void decodeblock( unsigned char in[4], unsigned char out[3] )
{
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
*/
void decode( FILE *infile, FILE *outfile )
{
unsigned char in[4], out[3], v;
int i, len;
while( !feof( infile ) ) {
for( len = 0, i = 0; i < 4 && !feof( infile ); i++ ) {
v = 0;
while( !feof( infile ) && v == 0 ) {
v = (unsigned char) getc( infile );
v = (unsigned char) ((v < 43 || v > 122) ? 0 : cd64[ v - 43 ]);
if( v ) {
v = (unsigned char) ((v == '$') ? 0 : v - 61);
}
}
if( !feof( infile ) ) {
len++;
if( v ) {
in[ i ] = (unsigned char) (v - 1);
}
}
else {
in[i] = 0;
}
}
if( len ) {
decodeblock( in, out );
for( i = 0; i < len - 1; i++ ) {
putc( out[i], outfile );
}
}
}
}
/*
** returnable errors
**
** Error codes returned to the operating system.
**
*/
#define B64_SYNTAX_ERROR 1
#define B64_FILE_ERROR 2
#define B64_FILE_IO_ERROR 3
#define B64_ERROR_OUT_CLOSE 4
#define B64_LINE_SIZE_TO_MIN 5
/*
** b64_message
**
** Gather text messages in one place.
**
*/
char *b64_message( int errcode )
{
#define B64_MAX_MESSAGES 6
char *msgs[ B64_MAX_MESSAGES ] = {
"b64:000:Invalid Message Code.",
"b64:001:Syntax Error -- check help for usage.",
"b64:002:File Error Opening/Creating Files.",
"b64:003:File I/O Error -- Note: output file not removed.",
"b64:004:Error on output file close.",
"b64:004:linesize set to minimum."
};
char *msg = msgs[ 0 ];
if( errcode > 0 && errcode < B64_MAX_MESSAGES ) {
msg = msgs[ errcode ];
}
return( msg );
}
/*
** b64
**
** 'engine' that opens streams and calls encode/decode
*/
int b64( int opt, char *infilename, char *outfilename, int linesize )
{
FILE *infile;
int retcode = B64_FILE_ERROR;
if( !infilename ) {
infile = stdin;
}
else {
infile = fopen( infilename, "rb" );
}
if( !infile ) {
perror( infilename );
}
else {
FILE *outfile;
if( !outfilename ) {
outfile = stdout;
}
else {
outfile = fopen( outfilename, "wb" );
}
if( !outfile ) {
perror( outfilename );
}
else {
if( opt == 'e' ) {
encode( infile, outfile, linesize );
}
else {
decode( infile, outfile );
}
if (ferror( infile ) || ferror( outfile )) {
retcode = B64_FILE_IO_ERROR;
}
else {
retcode = 0;
}
if( outfile != stdout ) {
if( fclose( outfile ) != 0 ) {
perror( b64_message( B64_ERROR_OUT_CLOSE ) );
retcode = B64_FILE_IO_ERROR;
}
}
}
if( infile != stdin ) {
fclose( infile );
}
}
return( retcode );
}
/*
** showuse
**
** display usage information, help, version info
*/
void showuse( int morehelp )
{
{
printf( "\n" );
printf( " b64 (Base64 Encode/Decode) Bob Trower 08/03/01 \n" );
printf( " (C) Copr Bob Trower 1986-01. Version 0.00B \n" );
printf( " Usage: b64 -option [ -l num ] [<FileIn> [<FileOut>]] \n" );
printf( " Purpose: This program is a simple utility that implements\n" );
printf( " Base64 Content-Transfer-Encoding (RFC1113). \n" );
}
if( !morehelp ) {
printf( " Use -h option for additional help. \n" );
}
else {
printf( " Options: -e encode to Base64 -h This help text. \n" );
printf( " -d decode from Base64 -? This help text. \n" );
printf( " Note: -l use to change line size (from 72 characters)\n" );
printf( " Returns: 0 = success. Non-zero is an error code. \n" );
printf( " ErrCode: 1 = Bad Syntax, 2 = File Open, 3 = File I/O \n" );
printf( " Example: b64 -e binfile b64file <- Encode to b64 \n" );
printf( " b64 -d b64file binfile <- Decode from b64 \n" );
printf( " b64 -e -l40 infile outfile <- Line Length of 40 \n" );
printf( " Note: Will act as a filter, but this should only be \n" );
printf( " used on text files due to translations made by \n" );
printf( " operating systems. \n" );
printf( " Release: 0.00.00, Tue Aug 7 2:00:00 2001, ANSI-SOURCE C\n" );
}
}
#define B64_DEF_LINE_SIZE 72
#define B64_MIN_LINE_SIZE 4
#define THIS_OPT(ac, av) (ac > 1 ? av[1][0] == '-' ? av[1][1] : 0 : 0)
/*
** main
**
** parse and validate arguments and call b64 engine or help
*/
int main( int argc, char **argv )
{
int opt = 0;
int retcode = 0;
int linesize = B64_DEF_LINE_SIZE;
char *infilename = NULL, *outfilename = NULL;
while( THIS_OPT( argc, argv ) ) {
switch( THIS_OPT(argc, argv) ) {
case 'l':
linesize = atoi( &(argv[1][2]) );
if( linesize < B64_MIN_LINE_SIZE ) {
linesize = B64_MIN_LINE_SIZE;
printf( "%s\n", b64_message( B64_LINE_SIZE_TO_MIN ) );
}
break;
case '?':
case 'h':
opt = 'h';
break;
case 'e':
case 'd':
opt = THIS_OPT(argc, argv);
break;
default:
opt = 0;
break;
}
argv++;
argc--;
}
switch( opt ) {
case 'e':
case 'd':
infilename = argc > 1 ? argv[1] : NULL;
outfilename = argc > 2 ? argv[2] : NULL;
retcode = b64( opt, infilename, outfilename, linesize );
break;
case 0:
retcode = B64_SYNTAX_ERROR;
case 'h':
showuse( opt );
break;
}
if( retcode ) {
printf( "%s\n", b64_message( retcode ) );
}
return( retcode );
}
