VC中BASE64編碼和解碼使用詳解
BASE64可以用來(lái)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(jiàn) RFC1421和 RFC2045。編碼后的數(shù)據(jù)比原始數(shù)據(jù)略長(zhǎng),為原來(lái)的4/3。在電子郵件中,根據(jù)RFC822規(guī)定,每76個(gè)字符,還需要加上一個(gè)回車換行。
轉(zhuǎn)換的時(shí)候,將三個(gè)byte的數(shù)據(jù),先后放入一個(gè)24bit的緩沖區(qū)中,先來(lái)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(bǔ)足。然后,每次取出6個(gè)bit,按照其值選擇ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/中的字符作為編碼后的輸出。不斷進(jìn)行,直到全部輸入數(shù)據(jù)轉(zhuǎn)換完成。如果最后剩下兩個(gè)輸入數(shù)據(jù),在編碼結(jié)果后加1個(gè)“=”;如果最后剩下一個(gè)輸入數(shù)據(jù),編碼結(jié)果后加2個(gè)“=”;如果沒(méi)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(shuō)明: 1. 參考o(jì)penssl-1.0.0。 2. 改進(jìn)接口,以使其適應(yīng)TCHAR字符串。 3. 修正EVP_DecodeBlock函數(shù)解碼時(shí)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(jìn)制數(shù)據(jù)轉(zhuǎn)換成BASE64編碼字符串 參數(shù)說(shuō)明: inputBuffer:要編碼的二進(jìn)制數(shù)據(jù) inputCount:數(shù)據(jù)長(zhǎng)度 outputBuffer:存儲(chǔ)轉(zhuǎn)換后的BASE64編碼字符串 返回值: -1:參數(shù)錯(cuò)誤 >=0:有效編碼長(zhǎng)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(jìn)制數(shù)據(jù) 參數(shù)說(shuō)明: inputBuffer:BASE64編碼字符串 inputCount:編碼長(zhǎng)度(字符數(shù)),應(yīng)該為4的倍數(shù)。 outputBuffer:存儲(chǔ)轉(zhuǎn)換后的二進(jìn)制數(shù)據(jù) 返回值: -1:參數(shù)錯(cuò)誤 -2:數(shù)據(jù)錯(cuò)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(cuò)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(gè)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(gè)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(cuò)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(cuò)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(cuò)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(cuò)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(zhǎng)度必須為4的倍數(shù) if( (inputCount % 4) != 0 ) { return -2; // 數(shù)據(jù)錯(cuò)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(cuò)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(cuò)誤,無(wú)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(gè)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(gè)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(cuò)誤,無(wú)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(jìn)制數(shù)據(jù)轉(zhuǎn)換成可見(jiàn)字符進(jìn)行傳遞就可以了.
那么如何使用呢?舉以下兩個(gè)例子
第一個(gè):將一個(gè)圖片轉(zhuǎn)換成 txt 文本 并保存起來(lái)
//選擇一個(gè)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(gè)例子,將一個(gè)文本文件還原為一個(gè)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(jìn)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(duì)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(lái)顯示保存顯示圖片的方法,就算是成功了!
我們?cè)賮?lái)看一個(gè)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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