cutil-base64.c

Linux环境下常用功能的实现

#include "cutil.h"

static char b64EncTable[64] = 
{
    'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',   
    'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f',   
    'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v',   
    'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/'
};

/**
 * cutil_base64_from_string
 * @pszInputString:	要求转换的字符串
 * @nInputLen: 要求转换的长度
 * @pszOutputString: 保存转换的结果
 * 
 * 将字符串编码转变为BASE64的编码
 * 
 * Returns: 成功操作返回转换后长度 失败操作返回-1
 */
int cutil_base64_from_string(unsigned char * pszInputString, int nInputLen, 
		unsigned char * pszOutputString)
{
    int nInputStrPos;
    int nOutputStrPos;
    unsigned char cInputByte[3];
    unsigned char outBytes[4];
    int nOutputLen;
    int nLineLen = 0;

    if(!pszInputString || (nInputLen == 0)) 
    	return -1;

    nOutputLen = ((nInputLen + 2) / 3) * 4;
    nOutputLen += (nOutputLen / 76);

    for(nInputStrPos = 0, nOutputStrPos = 0; nInputStrPos < nInputLen; 
    	nInputStrPos += 3, nOutputStrPos += 4)
	{
		cInputByte[0] = pszInputString[nInputStrPos];
		cInputByte[1] = cInputByte[2] = 0;
        if((nInputStrPos + 1) < nInputLen)
		{
			cInputByte[1] = pszInputString[nInputStrPos + 1];
            if((nInputStrPos + 2) < nInputLen)
				cInputByte[2] = pszInputString[nInputStrPos + 2];
        }
            
        outBytes[0] = cInputByte[0] >> 2;
        outBytes[1] = ((cInputByte[0] & 0x03) << 4) | (cInputByte[1] >> 4);
        outBytes[2] = ((cInputByte[1] & 0x0F) << 2) | (cInputByte[2] >> 6);
        outBytes[3] = cInputByte[2] & 0x3F;
            
        pszOutputString[nOutputStrPos] = b64EncTable[outBytes[0]];
        pszOutputString[nOutputStrPos + 1] = b64EncTable[outBytes[1]];
            
        if((nInputStrPos + 1) < nInputLen) 
			pszOutputString[nOutputStrPos + 2] = b64EncTable[outBytes[2]];
        else
            pszOutputString[nOutputStrPos + 2] = '=';
        
        if((nInputStrPos + 2) < nInputLen) 
			pszOutputString[nOutputStrPos + 3] = b64EncTable[outBytes[3]];
        else
            pszOutputString[nOutputStrPos + 3] = '=';
         
        nLineLen ++;
        if(nLineLen == 19)
		{
			pszOutputString[nOutputStrPos + 4] = '\n';
			nOutputStrPos ++;
			nLineLen = 0;
        }
    }
    return nOutputStrPos;
}

/*
 * 校验是否为BASE64编码格式
 */
static int ValidBase64(char cInputChar)
{
    if(((cInputChar >= 'A') && (cInputChar <= 'Z')) ||
       ((cInputChar >= 'a') && (cInputChar <= 'z')) ||
       ((cInputChar >= '0') && (cInputChar <= '9')) ||
       (cInputChar == '+') || 
       (cInputChar == '/') || 
       (cInputChar == '='))
	{
        return 1;
    }
    return 0;
}

static unsigned char DecodeBase64Char(unsigned char cInputChar)
{
    if((cInputChar >= 'A') && (cInputChar <= 'Z')) 
    {
        return (cInputChar - 'A');
    } 
    else if((cInputChar >= 'a') && (cInputChar <= 'z')) 
    {
        return((cInputChar - 'a') + 26);
    } 
    else if((cInputChar >= '0') && (cInputChar <= '9')) 
    {
        return((cInputChar - '0') + 52);
    } 
    else if(cInputChar == '+') 
    {
        return 62;
    }
    return 63;
}
    
/**
 * cutil_base64_to_string
 * @pszInputString:	要求转换的字符串
 * @nInputLen:	要求转换的长度
 * @pszOutputString: 保存转换的结果
 * 
 * @函数说明: 将BASE64编码转变为字符串编码
 
 * Returns: 成功返回转换的长度 失败返回 -1
 */
int cutil_base64_to_string(unsigned char * pszInputString, 
			unsigned int nInputLen, unsigned char * pszOutputString)
{
    unsigned int nRealLen;
    unsigned int nInputStrPos;
    unsigned int nOutputStrPos;
    char cInputByte[4];

    if(!pszInputString || (nInputLen == 0)) 
    	return 0;

    nOutputStrPos = 0;
    for(nInputStrPos = 0; nInputStrPos < nInputLen; nInputStrPos ++) 
    {
		if(ValidBase64(pszInputString[nInputStrPos])) 
		{
            if(nInputStrPos > nOutputStrPos) 
            	pszInputString[nOutputStrPos] = pszInputString[nInputStrPos];
            nOutputStrPos ++;
        }
    }
    pszInputString[nOutputStrPos] = '\0';
    nRealLen = (nOutputStrPos / 4) * 3;
 
    if(pszInputString[nOutputStrPos - 1] == '=') 
    	nRealLen --;
    if(pszInputString[nOutputStrPos - 2] == '=') 
    	nRealLen --;

    for(nInputStrPos = 0, nOutputStrPos = 0; nOutputStrPos < nRealLen;
    	nInputStrPos += 4, nOutputStrPos += 3)
	{
		cInputByte[0] = DecodeBase64Char(pszInputString[nInputStrPos]);
        cInputByte[1] = cInputByte[2] = cInputByte[3] = 0;
        if((nInputStrPos + 1) < nInputLen) 
			cInputByte[1] = DecodeBase64Char(pszInputString[nInputStrPos + 1]);             
        if((nInputStrPos + 2) < nInputLen)
			cInputByte[2] = DecodeBase64Char(pszInputString[nInputStrPos + 2]);
        if((nInputStrPos + 3) < nInputLen)
			cInputByte[3] = DecodeBase64Char(pszInputString[nInputStrPos + 3]); 

        pszOutputString[nOutputStrPos] 
        	= ((cInputByte[0] << 2) | (cInputByte[1] >> 4));
        	
        if(pszInputString[nInputStrPos + 2] != '=')
        {
			pszOutputString[nOutputStrPos + 1] 
				= (((cInputByte[1] & 0xF) << 4) | (cInputByte[2] >> 2));
		}
		
        if(pszInputString[nInputStrPos + 3] != '=') 
       	{
			pszOutputString[nOutputStrPos + 2] 
				= (((cInputByte[2] & 0x3) << 6) | cInputByte[3]);
		}
    }
	return nRealLen;
}