base64.c

一个base64编码解码的源程序

#include <stdio.h>
#include <string.h>

main(int argc,char* argv[])
{
 if (argc<2) return;
 FILE *fp;
 fp=fopen(argv[1],"rb");
 if (fp==NULL) return;
 fseek(fp,0,2);
 int ll=ftell(fp);
    fseek(fp,0,0);

char s1[65536];
fread(s1,1,ll,fp);
int a=65536;
char* s="http://digwtx.51.net";
//char* q="diflwkfsdl";
char d[65536];
char db[65536];
int len = base64_enc(d,s,strlen(s));
d[len]=0;
printf("%s\n",d);
len = base64_dec(db,s1,&ll);
db[len]=0;
printf("%s\n",db);
printf("%d",ll);
return 0;
}


static char base64_encoding[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

 


// encode to BASE 64
// return buflen
int base64_enc(char *buf,char*text,int size)
{
int buflen = 0 ;

while(size>0){
*buf++ = base64_encoding[ (text[0] >> 2 ) & 0x3f];
if(size>2){
*buf++ = base64_encoding[((text[0] & 3) << 4) | ((text[1] >> 4) & 0x0f)];
*buf++ = base64_encoding[((text[1] & 0xF) << 2) | ((text[2] >> 6) &3)];
*buf++ = base64_encoding[text[2] & 0x3F];
}else{
switch(size){
case 1:
*buf++ = base64_encoding[(text[0] & 3) << 4 ];
*buf++ = '=';
*buf++ = '=';
break;
case 2:
*buf++ = base64_encoding[((text[0] & 3) << 4) | ((text[1] >> 4) & 0x0f)];
*buf++ = base64_encoding[((text[1] & 0xF) << 2) | ((text[2] >> 6) &3)];
*buf++ = '=';
break;
}
}

text +=3;
size -=3;
buflen +=4;
}

*buf = 0;
return buflen;
}

static char get_base64_value(char ch,char default_value)
{
if ((ch >= 'A') && (ch <= 'Z'))
return ch - 'A';
if ((ch >= 'a') && (ch <= 'z'))
return ch - 'a' + 26;
if ((ch >= '0') && (ch <= '9'))
return ch - '0' + 52;
switch (ch) {
case '+':
return 62;
case '/':
return 63;
case '=': /* base64 padding */
return default_value;
default:
return default_value;
}
}

//进行base64解码 返回buf中内容长度
//注意 如果是最后一个字符 那么长度不准备 可能会多1
int base64_dec(char *buf,char*text,int *size)
{
char chunk[4];
int parsenum=0;

int linelen=*size;
*size =0;

while(linelen>*size){
if(get_base64_value(*text,-1)==-1){
text++;
size++;
continue;
}

if(linelen-*size<3)
return parsenum;

chunk[0] = get_base64_value(text[0],0);
chunk[1] = get_base64_value(text[1],0);
chunk[2] = get_base64_value(text[2],0);
chunk[3] = get_base64_value(text[3],0);

*buf++ = (chunk[0] << 2) | (chunk[1] >> 4);
*buf++ = (chunk[1] << 4) | (chunk[2] >> 2);
*buf++ = (chunk[2] << 6) | (chunk[3]);

if(text[1]=='='){
*size+=1;
return parsenum+1;
}
else if(text[2]=='='){
*size+=2;
return parsenum+2;
}
else if(text[3]=='='){
*size+=3;
return parsenum+3;
}

text+=4;
*size+=4;
parsenum+=3;
}

return parsenum;
}


//解码Quoted-Printable,返回解码的长度
int QPrintable_dec(char *buf,char*text,int size)
{
int buflen=0; // 输出的字符计数
int i=0;

while (size>0)
{
if (strncmp(text, "=\r\n", 3) == 0) // 软回车，跳过
{
text += 3;
size -= 3;
}
else
{
if (*text == '=') // 是编码字节
{
sscanf(text, "=%02X", buf);
buf++;
text += 3;
size -= 3;
}
else // 非编码字节
{
*buf++ = (unsigned char)*text++;
size--;
}

buflen++;
}
}

return buflen;
}