VC中BASE64編碼和解碼使用詳解

來源：本站原創(chuàng)|時間：2020-01-10|欄目：C語言|點擊：次

BASE64可以用來將binary的字節(jié)序列數(shù)據(jù)編碼成ASCII字符序列構(gòu)成的文本。完整的BASE64定義可見 RFC1421和 RFC2045。編碼后的數(shù)據(jù)比原始數(shù)據(jù)略長，為原來的4/3。在電子郵件中，根據(jù)RFC822規(guī)定，每76個字符，還需要加上一個回車換行。

轉(zhuǎn)換的時候，將三個byte的數(shù)據(jù)，先后放入一個24bit的緩沖區(qū)中，先來的byte占高位。數(shù)據(jù)不足3byte的話，于緩沖區(qū)中剩下的Bit用0補足。然后，每次取出6個bit，按照其值選擇ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/中的字符作為編碼后的輸出。不斷進行，直到全部輸入數(shù)據(jù)轉(zhuǎn)換完成。如果最后剩下兩個輸入數(shù)據(jù)，在編碼結(jié)果后加1個“=”；如果最后剩下一個輸入數(shù)據(jù)，編碼結(jié)果后加2個“=”；如果沒有剩下任何數(shù)據(jù)，就什么都不要加，這樣才可以保證資料還原的正確性。

BASE64_API.h 文件內(nèi)容

/* ----------------------------------------------------------
文件名稱：BASE64_API.h

作者：秦建輝

MSN：splashcn@msn.com

當(dāng)前版本：V1.1

歷史版本：
  V1.1  2010年05月11日
      修正BASE64解碼的Bug。

  V1.0  2010年05月07日
      完成正式版本。

功能描述：
  BASE64編碼和解碼

接口函數(shù)：
  Base64_Encode
  Base64_Decode

說明：
  1.  參考o(jì)penssl-1.0.0。
  2.  改進接口，以使其適應(yīng)TCHAR字符串。
  3.  修正EVP_DecodeBlock函數(shù)解碼時未去掉填充字節(jié)的缺陷。
 ------------------------------------------------------------ */
#pragma once
#include "stdafx.h"

#include <windows.h>

#ifdef  __cplusplus
extern "C" {
#endif

/*
功能：將二進制數(shù)據(jù)轉(zhuǎn)換成BASE64編碼字符串
參數(shù)說明：
  inputBuffer：要編碼的二進制數(shù)據(jù)
  inputCount：數(shù)據(jù)長度
  outputBuffer：存儲轉(zhuǎn)換后的BASE64編碼字符串
返回值：
   -1：參數(shù)錯誤
  >=0：有效編碼長度（字符數(shù)）,不包括字符串結(jié)束符。
備注：
  等效于openssl中EVP_EncodeBlock函數(shù)
*/
INT BASE64_Encode( const BYTE* inputBuffer, INT inputCount, TCHAR* outputBuffer );

/*
功能：將BASE64編碼字符串轉(zhuǎn)換為二進制數(shù)據(jù)
參數(shù)說明：
  inputBuffer：BASE64編碼字符串
  inputCount：編碼長度（字符數(shù)）,應(yīng)該為4的倍數(shù)。
  outputBuffer：存儲轉(zhuǎn)換后的二進制數(shù)據(jù)
返回值：
   -1：參數(shù)錯誤
   -2：數(shù)據(jù)錯誤
  >=0：轉(zhuǎn)換后的字節(jié)數(shù)
備注：
  等效于openssl中EVP_DecodeBlock函數(shù)
*/
INT BASE64_Decode( const TCHAR* inputBuffer, INT inputCount, BYTE* outputBuffer );

#ifdef __cplusplus
}
#endif

BASE64_API.cpp 文件內(nèi)容

#pragma once

#include "stdafx.h"

#include "BASE64_API.h"

static const CHAR* DATA_BIN2ASCII = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

INT BASE64_Encode( const BYTE* inputBuffer, INT inputCount, TCHAR* outputBuffer )
{
  INT i;
  BYTE b0, b1, b2;

  if( (inputBuffer == NULL) || (inputCount < 0) )
  {
    return -1;  // 參數(shù)錯誤
  }

  if( outputBuffer != NULL )
  {
    for( i = inputCount; i > 0; i -= 3 )
    {
      if( i >= 3 )
      {  // 將3字節(jié)數(shù)據(jù)轉(zhuǎn)換成4個ASCII字符
        b0 = *inputBuffer++;
        b1 = *inputBuffer++;
        b2 = *inputBuffer++;

        *outputBuffer++ = DATA_BIN2ASCII[b0 >> 2];
        *outputBuffer++ = DATA_BIN2ASCII[((b0 << 4) | (b1 >> 4)) & 0x3F];
        *outputBuffer++ = DATA_BIN2ASCII[((b1 << 2) | (b2 >> 6)) & 0x3F];
        *outputBuffer++ = DATA_BIN2ASCII[b2 & 0x3F];
      }
      else
      {
        b0 = *inputBuffer++;
        if( i == 2 )b1 = *inputBuffer++; else b1 = 0;

        *outputBuffer++ = DATA_BIN2ASCII[b0 >> 2];
        *outputBuffer++ = DATA_BIN2ASCII[((b0 << 4) | (b1 >> 4)) & 0x3F];
        *outputBuffer++ = (i == 1) ? TEXT('=') : DATA_BIN2ASCII[(b1 << 2) & 0x3F];
        *outputBuffer++ = TEXT('=');
      }
    } // End for i

    *outputBuffer++ = TEXT('/0');  // 添加字符串結(jié)束標(biāo)記
  }

  return ((inputCount + 2) / 3) * 4;  // 返回有效字符個數(shù)
}

#define B64_EOLN      0xF0  // 換行/n
#define B64_CR        0xF1  // 回車/r
#define B64_EOF        0xF2  // 連字符-
#define B64_WS        0xE0  // 跳格或者空格（/t、space）
#define B64_ERROR   0xFF  // 錯誤字符
#define B64_NOT_BASE64(a)  (((a)|0x13) == 0xF3)

static const BYTE DATA_ASCII2BIN[128] = {
  0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xE0,0xF0,0xFF,0xFF,0xF1,0xFF,0xFF,
  0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
  0xE0,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x3E,0xFF,0xF2,0xFF,0x3F,
  0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B,0x3C,0x3D,0xFF,0xFF,0xFF,0x00,0xFF,0xFF,
  0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
  0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF,
  0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,
  0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31,0x32,0x33,0xFF,0xFF,0xFF,0xFF,0xFF
};

INT BASE64_Decode( const TCHAR* inputBuffer, INT inputCount, BYTE* outputBuffer )
{
  INT i, j;
  BYTE b[4];
  TCHAR ch;

  if( (inputBuffer == NULL) || (inputCount < 0) )
  {
    return -1;  // 參數(shù)錯誤
  }

  // 去除頭部空白字符
  while( inputCount > 0 )
  {
    ch = *inputBuffer;
    if( (ch < 0) || (ch >= 0x80) )
    {
      return -2;  // 數(shù)據(jù)錯誤，不在ASCII字符編碼范圍內(nèi)
    }
    else
    {
      if( DATA_ASCII2BIN[ch] == B64_WS )
      {
        inputBuffer++;
        inputCount--;
      }
      else
      {
        break;
      }
    }
  }

  // 去除尾部的空白字符、回車換行字符、連字符
  while( inputCount >= 4 )
  {
    ch = inputBuffer[inputCount - 1];
    if( (ch < 0) || (ch >= 0x80) )
    {
      return -2;  // 數(shù)據(jù)錯誤，不在ASCII字符編碼范圍內(nèi)
    }
    else
    {
      if( B64_NOT_BASE64(DATA_ASCII2BIN[ch]) )
      {
        inputCount--;
      }
      else
      {
        break;
      }
    }
  }

  // 字符串長度必須為4的倍數(shù)
  if( (inputCount % 4) != 0 )
  {
    return -2;  // 數(shù)據(jù)錯誤
  }

  if( outputBuffer != NULL )
  {
    for( i = 0; i < inputCount; i += 4 )
    {
      for( j = 0; j < 4; j++ )
      {
        ch = *inputBuffer++;
        if( (ch < 0) || (ch >= 0x80) )
        {
          return -2;  // 數(shù)據(jù)錯誤，不在ASCII字符編碼范圍內(nèi)
        }
        else
        {
          if( ch == '=' )  // 發(fā)現(xiàn)BASE64編碼中的填充字符
          {
            break;
          }
          else
          {
            b[j] = DATA_ASCII2BIN[ch];
            if( b[j] & 0x80 )
            {
              return -2;  // 數(shù)據(jù)錯誤，無效的Base64編碼字符
            }
          }          
        }
      } // End for j

      if( j == 4 )
      {
        *outputBuffer++ = (b[0] << 2) | (b[1] >> 4);
        *outputBuffer++ = (b[1] << 4) | (b[2] >> 2 );
        *outputBuffer++ = (b[2] << 6) | b[3];
      }
      else if( j == 3 )
      {  // 有1個填充字節(jié)
        *outputBuffer++ = (b[0] << 2) | (b[1] >> 4);
        *outputBuffer++ = (b[1] << 4) | (b[2] >> 2 );

        return (i >> 2) * 3 + 2;
      }
      else if( j == 2 )
      {  // 有2個填充字節(jié)
        *outputBuffer++ = (b[0] << 2) | (b[1] >> 4);

        return (i >> 2) * 3 + 1;
      }
      else
      {
        return -2;  // 數(shù)據(jù)錯誤，無效的Base64編碼字符
      }      
    }  // End for i
  }

  return (inputCount >> 2) * 3;
}

采用以上方法就可以將二進制數(shù)據(jù)轉(zhuǎn)換成可見字符進行傳遞就可以了.

那么如何使用呢?舉以下兩個例子

第一個:將一個圖片轉(zhuǎn)換成 txt 文本并保存起來

//選擇一個圖像文件,將它轉(zhuǎn)為 文本保存至 _T("D:\\2.txt"
void CTextPicDlg::OnBnClickedButton2()
{
  // TODO: 在此添加控件通知處理程序代碼
  CFileDialog file(TRUE,".jpg","");
  if (file.DoModal() == IDOK)
  {
    CFile data(file.GetPathName(), CFile::modeReadWrite);
    int len = data.GetLength();
    BYTE *dv;
    dv = (BYTE *)malloc(len*sizeof(BYTE));
    data.Read(dv, len);
    data.Close();
    int slen = (len / 3) * 4;
    slen += 10;
    TCHAR * tc;
    tc = (TCHAR *)malloc(slen);
    slen = BASE64_Encode(dv, len, tc);
    CFile save(_T("D:\\2.txt"), CFile::modeCreate | CFile::modeWrite);
    save.Write(tc, slen);
    save.Close();
    free(tc);
    free(dv);
  }
}

第二個例子,將一個文本文件還原為一個圖像

void CTextPicDlg::OnBnClickedButton3()
{
  // TODO: 在此添加控件通知處理程序代碼
  CFileDialog file(TRUE, ".txt", "");
  if (file.DoModal() == IDOK)
  {
    CFile data(file.GetPathName(), CFile::modeReadWrite);
    int len = data.GetLength();
    TCHAR *dv;
    dv = (TCHAR *)malloc(len*sizeof(TCHAR));
    data.Read(dv, len);
    data.Close();
    int slen = (len / 4) * 3;
    slen += 10;
    BYTE * tc;
    tc = (BYTE *)malloc(slen);
    BASE64_Decode(dv, len, tc);
    //直接在內(nèi)存里面構(gòu)建CIMAGE,需要使用IStream接口,如何使用
    //構(gòu)建內(nèi)存環(huán)境    
    HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, slen);
    void * pData = GlobalLock(hGlobal);
    memcpy(pData, tc, slen); // 拷貝位圖數(shù)據(jù)進去
    GlobalUnlock(hGlobal);
    // 創(chuàng)建IStream
    IStream * pStream = NULL;
    if (CreateStreamOnHGlobal(hGlobal, TRUE, &pStream) != S_OK)
      return ;
    //  使用CImage加載位圖內(nèi)存
    CImage img;
    if (SUCCEEDED(img.Load(pStream)) )
    {
      CClientDC dc(this);
       //使用內(nèi)在中構(gòu)造的圖像 直接在對話框上繪圖
       img.Draw(dc.m_hDC, 0, 0, 500, 300);
    }
     //釋放內(nèi)存
    pStream->Release();
    GlobalFree(hGlobal);
    //如果要保存圖像文件的話,那就使用下面的代碼
    //CFileDialog savefile(FALSE, ".jpg", "");
    //if (savefile.DoModal()==IDOK)
    //{
    //  CFile save(savefile.GetPathName(), CFile::modeCreate | CFile::modeWrite);
    //  save.Write(tc, slen);
    //  save.Close();
    //}
    free(tc);
    free(dv);
  }
}

至此,利用Base64轉(zhuǎn)碼的方式,來顯示保存顯示圖片的方法,就算是成功了!

我們再來看一個base64編碼解碼的例子

首先是編碼

const BYTE Base64ValTab[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

#define AVal(x) Base64ValTab[x]
int CSeeBase64Dlg::EncodeBase64(char * pInput, char * pOutput)
{
    int i = 0;
    int loop = 0;
    int remain = 0;
    int iDstLen = 0;
    int iSrcLen = (int)strlen(pInput);

    loop = iSrcLen/3;
    remain = iSrcLen%3;

    // also can encode native char one by one as decode method
    // but because all of char in native string is to be encoded so encode 3-chars one time is easier.

    for (i=0; i < loop; i++)
    {
        BYTE a1 = (pInput[i*3] >> 2);
        BYTE a2 = ( ((pInput[i*3] & 0x03) << 4) | (pInput[i*3+1] >> 4) );
        BYTE a3 = ( ((pInput[i*3+1] & 0x0F) << 2) | ((pInput[i*3+2] & 0xC0) >> 6) );
        BYTE a4 = (pInput[i*3+2] & 0x3F);

        pOutput[i*4] = AVal(a1);
        pOutput[i*4+1] = AVal(a2);
        pOutput[i*4+2] = AVal(a3);
        pOutput[i*4+3] = AVal(a4);
    }

    iDstLen = i*4;

    if (remain == 1)
    {
        // should pad two equal sign
        i = iSrcLen-1;
        BYTE a1 = (pInput[i] >> 2);
        BYTE a2 = ((pInput[i] & 0x03) << 4);
        
        pOutput[iDstLen++] = AVal(a1);
        pOutput[iDstLen++] = AVal(a2);
        pOutput[iDstLen++] = '=';
        pOutput[iDstLen++] = '=';
        pOutput[iDstLen] = 0x00;
    }
    else if (remain == 2)
    {
        // should pad one equal sign
        i = iSrcLen-2;
        BYTE a1 = (pInput[i] >> 2);
        BYTE a2 = ( ((pInput[i] & 0x03) << 4) | (pInput[i+1] >> 4));
        BYTE a3 = ( (pInput[i+1] & 0x0F) << 2);

        pOutput[iDstLen++] = AVal(a1);
        pOutput[iDstLen++] = AVal(a2);
        pOutput[iDstLen++] = AVal(a3);
        pOutput[iDstLen++] = '=';
        pOutput[iDstLen] = 0x00;
    }
    else
    {
        // just division by 3
        pOutput[iDstLen] = 0x00;
    }

    return iDstLen;
}

下面是解碼

const BYTE Base64IdxTab[128] =
{
255,255,255,255, 255,255,255,255, 255,255,255,255, 255,255,255,255,
255,255,255,255, 255,255,255,255, 255,255,255,255, 255,255,255,255,
255,255,255,255, 255,255,255,255, 255,255,255,62,  255,255,255,63,
52,53,54,55,   56,57,58,59,   60,61,255,255,  255,255,255,255,
255,0,1,2,    3,4,5,6,     7,8,9,10,     11,12,13,14,
15,16,17,18,   19,20,21,22,   23,24,25,255,   255,255,255,255,
255,26,27,28,   29,30,31,32,   33,34,35,36,   37,38,39,40,
41,42,43,44,   45,46,47,48,   49,50,51,255,   255,255,255,255
};

#define BVal(x) Base64IdxTab[x]

int CSeeBase64Dlg::DecodeBase64(char * pInput, char * pOutput)
{
    int i = 0;
    int iCnt = 0;
    int iSrcLen = (int)strlen(pInput);

    char * p = pOutput;

    for (i=0; i < iSrcLen; i++)
    {
        if (pInput[i] > 127) continue;
        if (pInput[i] == '=') return p-pOutput+1;

        BYTE a = BVal(pInput[i]);
        if (a == 255) continue;
        
        switch (iCnt)
        {
        case 0:
            {
                *p = a << 2;
                iCnt++;
            }
            break;

        case 1:
            {
                *p++ |= a >> 4;
                *p = a << 4;
                iCnt++;
            }
            break;

        case 2:
            {
                *p++ |= a >> 2;
                *p = a << 6;
                iCnt++;
            }
            break;
        case 3:
            {
                *p++ |= a;
                iCnt = 0;
            }
            break;
        } 
    }

    *p = 0x00;
    return p-pOutput;
}

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