VC知识库文章 - URL编码

URL编码
作者： Chandrasekhar Vuppalapati
翻译：eastvc

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：

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)	Type	Values	Safe/Unsafe
0-31	ASCII Control Characters	These characters are not printable	Unsafe
32-47	Reserved Characters	'' ''!?#$%&''()*+,-./	Unsafe
48-57	ASCII Characters and Numbers	0-9	Safe
58-64	Reserved Characters	:;<=>?@	Unsafe
65-90	ASCII Characters	A-Z	Safe
91-96	Reserved Characters	[\]^_`	Unsafe
97-122	ASCII Characters	a-z	Safe
123-126	Reserved Characters	{|}~	Unsafe
127	Control Characters	'' ''	Unsafe
128-255	Non-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。

Character	Unsafe Reason	Character 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: .

RFC 1866: The HTML 2.0 规范 (纯文本). 附录包含了字符表: .

Web HTML 2.0 版本(RFC 1866) : .

The HTML 3.2 (Wilbur) 建议: .

The HTML 4.0 建议: .

W3C HTML 国际化区域: .

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