VC中BASE64編碼和解碼使用詳解

2020-01-26 14:49:48

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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  __cplusplusextern "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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