URL编码

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原文链接：http://www.vckbase.com/index.php/wv/1436

本文的目的是设计一个完成URL编码的C++类。在我曾经的项目中，我需要从VC++ 6.0应用程序中POST数据，而这些数据需要进行URL编码。我在MSDN中查找能根据提供的字符串生成URL编码的相关类或API，但我没有找到，因此我必须设计一个自己的URLEncode C++类。

URLEncoder.exe是一个使用URLEncode类的MFC对话框程序。

如何处理

一些特殊字符在Internet上传送是件棘手的事情, 经URL编码特殊处理，可以使所有字符安全地从Internet传送。

例如，回车的ASCII值是13，在发送FORM数据时候这就认为是一行数据的结束。

通常，所有应用程序采用HTTP或HTTPS协议在客户端和服务器端传送数据。服务器端从客户端接收数据有两种基本方法：

1、数据可以从HTTP头传送（COOKIES或作为FORM数据发送）

2、可以包含在URL中的查询部分

当数据包含在URL，它必须遵循URL语法进行编码。在WEB服务器端，数据自动解码。考虑一下下面的URL，哪个数据是作为查询参数。

例如：http://WebSite/ResourceName?Data=Data

WebSite是URL名称

ResourceName可以是ASP或Servlet名称

Data是需要发送的数据。如果MIME类型是Content-Type: application/x-www-form-urlencoded，则要求进行编码。

RFC 1738

RFC 1738指明了统一资源定位(URLs)中的字符应该是US-ASCII字符集的子集。这是受HTML的限制，另一方面，允许在文档中使用所有ISO-8859-1(ISO-Latin)字符集。这将意味着在HTML FORM里POST的数据（或作为查询字串的一部分），所有HTML编码必须被编码。

ISO-8859-1 (ISO-Latin)字符集

在下表中，包含了完整的ISO-8859-1 (ISO-Latin)字符集，表格提供了每个字符范围（10进制），描述，实际值，十六进制值，HTML结果。某个范围中的字符是否安全。
Character range(decimal)TypeValuesSafe/Unsafe0-31ASCII Control CharactersThese characters are not printableUnsafe32-47Reserved Characters'' ''!?#$%&''()*+,-./Unsafe48-57ASCII Characters and Numbers0-9Safe58-64Reserved Characters:;<=>?@Unsafe65-90ASCII CharactersA-ZSafe91-96Reserved Characters[\]^_`Unsafe97-122ASCII Charactersa-zSafe123-126Reserved Characters{|}~Unsafe127Control Characters'' ''Unsafe128-255Non-ASCII Characters'' ''Unsafe

所有不安全的ASCII字符都需要编码，例如，范围(32-47, 58-64, 91-96, 123-126)。
下表描述了这些字符为什么不安全。CharacterUnsafe ReasonCharacter Encode"<"Delimiters around URLs in free text%3C>Delimiters around URLs in free text%3E.Delimits URLs in some systems%22#It is used in the World Wide Web and in other systems to delimit a URL from a fragment/anchor identifier that might follow it.%23{Gateways and other transport agents are known to sometimes modify such characters%7B}Gateways and other transport agents are known to sometimes modify such characters%7D|Gateways and other transport agents are known to sometimes modify such characters%7C\Gateways and other transport agents are known to sometimes modify such characters%5C^Gateways and other transport agents are known to sometimes modify such characters%5E~Gateways and other transport agents are known to sometimes modify such characters%7E[Gateways and other transport agents are known to sometimes modify such characters%5B]Gateways and other transport agents are known to sometimes modify such characters%5D`Gateways and other transport agents are known to sometimes modify such characters%60+Indicates a space (spaces cannot be used in a URL)%20/Separates directories and subdirectories%2F?Separates the actual URL and the parameters%3F&Separator between parameters specified in the URL%26

如何实现

字符的URL编码是将字符转换到8位16进制并在前面加上''%''前缀。例如，US-ASCII字符集中空格是10进制的32或16进制的20，因此，URL编码是%20。

URLEncode: URLEncode是一个C++类，来实现字符串的URL编码。CURLEncode类包含如下函数：

isUnsafeString

decToHex

convert

URLEncode

URLEncode()函数完成编码过程，URLEncode检查每个字符，看是否安全。如果不安全将用%16进制值进行转换并添加
到原始字符串中。

代码片断:

class CURLEncode
{
private:
static CString csUnsafeString;
CString (char num, int radix);
bool isUnsafe(char compareChar);
CString convert(char val);
 
public:
CURLEncode() { };
virtual ~CURLEncode() { };
CString (CString vData);
};
 
bool CURLEncode::isUnsafe(char compareChar)
{
bool bcharfound = false;
char tmpsafeChar;
int m_strLen = 0;
 
m_strLen = csUnsafeString.GetLength();
for(int ichar_pos = 0; ichar_pos < m_strLen ;ichar_pos++)
{
tmpsafeChar = csUnsafeString.GetAt(ichar_pos);
if(tmpsafeChar == compareChar)
{
bcharfound = true;
break;
}
}
int char_ascii_value = 0;
//char_ascii_value = __toascii(compareChar);
char_ascii_value = (int) compareChar;
 
if(bcharfound == false &&  char_ascii_value > 32 &&
char_ascii_value < 123)
{
return false;
}
// found no unsafe chars, return false
else
{
return true;
}
 
return true;
}
 
CString CURLEncode::decToHex(char num, int radix)
{
int temp=0;
CString csTmp;
int num_char;
 
num_char = (int) num;
if (num_char < 0)
num_char = 256 + num_char;
 
while (num_char >= radix)
{
temp = num_char % radix;
num_char = (int)floor(num_char / radix);
csTmp = hexVals[temp];
}
 
csTmp += hexVals[num_char];
 
if(csTmp.GetLength() < 2)
{
csTmp += ''0'';
} 
CString strdecToHex(csTmp);
// Reverse the String
strdecToHex.MakeReverse();
 
return strdecToHex;
}
 
CString CURLEncode::convert(char val)
{
CString csRet;
csRet += "%";
csRet += decToHex(val, 16);
return  csRet;
}

参考：

URL编码: http://www.blooberry.com/indexdot/html/topics/urlencoding.htm.

RFC 1866: The HTML 2.0 规范 (纯文本). 附录包含了字符表: http://www.rfc-editor.org/rfc/rfc1866.txt.

Web HTML 2.0 版本(RFC 1866) : http://www.w3.org/MarkUp/html-spec/html-spec_13.html.

The HTML 3.2 (Wilbur) 建议: http://www.w3.org/MarkUp/Wilbur/.

The HTML 4.0 建议: http://www.w3.org/TR/REC-html40/.

W3C HTML 国际化区域: http://www.w3.org/International/O-HTML.html.

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