base64.cpp

一个在redhat下面做的邮件收发程序

#include "base64.h"


int Base64::Encode(char *buf, char*text,int size)
{
    static char* base64_encoding = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    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)];
        *buf++ = base64_encoding[((text[1] & 0xF) << 2) | (text[2] >> 6)];
        *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)];
            *buf++ = base64_encoding[((text[1] & 0x0F) << 2) | (text[2] >> 6)];
            *buf++ = '=';
            break;
    }
    }

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

    *buf = 0;
    return buflen;
}

//base64解码的实现

char Base64::GetIndex(char ch)
{
    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 0;
        default:
            return 0;
    }
}

//进行base64解码输入应该是4的倍数(根据mime标准)
//如果不是4倍数返回错误
//注意 如果是最后一个字符 那么长度不准备 可能会多1
//返回buf长度
int Base64::Decode(char *buf,char*text,int size)
{
    if(size%4)
        return -1;
    unsigned char chunk[4];
    int parsenum=0;

    while(size>0)
    {
        chunk[0] = GetIndex(text[0]);
        chunk[1] = GetIndex(text[1]);
        chunk[2] = GetIndex(text[2]);
        chunk[3] = GetIndex(text[3]);

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

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

    return parsenum;
}