[轉]URL編碼

URL編碼
作者： Chandrasekhar Vuppalapati
翻譯：eastvc

下載源代碼

本文的目的是設計一個完成URL編碼的C++類。在我曾經的項目中，我需要從VC++ 6.0應用程序中POST數據，而這些數據需要進行URL編碼。我在MSDN中查找能根據提供的字符串生成URL編碼的相關類或API，但我沒有找到，因此我必須設計一個自己的URLEncode C++類。

URLEncoder.exe是一個使用URLEncode類的MFC對話框程序。

如何處理

一些特殊字符在Internet上傳送是件棘手的事情, 經URL編碼特殊處理，可以使所有字符安全地從Internet傳送。

例如，回車的ASCII值是13，在發送FORM數據時候這就認為是一行數據的結束。

通常，所有應用程序采用HTTP或HTTPS協議在客戶端和服務器端傳送數據。服務器端從客戶端接收數據有兩種基本方法：

1、數據可以從HTTP頭傳送（COOKIES或作為FORM數據發送）
2、可以包含在URL中的查詢部分

當數據包含在URL，它必須遵循URL語法進行編碼。在WEB服務器端，數據自動解碼。考慮一下下面的URL，哪個數據是作為查詢參數。

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

WebSite是URL名稱
ResourceName可以是ASP或Servlet名稱
Data是需要發送的數據。如果MIME類型是Content-Type: application/x-www-form-urlencoded，則要求進行編碼。

RFC 1738

RFC 1738指明了統一資源定位(URLs)中的字符應該是US-ASCII字符集的子集。這是受HTML的限制，另一方面，允許在文檔中使用所有ISO- 8859-1(ISO-Latin)字符集。這將意味著在HTML FORM里POST的數據（或作為查詢字串的一部分），所有HTML編碼必須被編碼。

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，表格提供了每個字符范圍（10進制），描述，實際值，十六進制值，HTML結果。某個范圍中的字符是否安全。

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字符都需要編碼，例如，范圍(32-47, 58-64, 91-96, 123-126)。
下表描述了這些字符為什么不安全。

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

如何實現

字符的URL編碼是將字符轉換到8位16進制并在前面加上''%''前綴。例如，US-ASCII字符集中空格是10進制
的32或16進制的20，因此，URL編碼是%20。

URLEncode: URLEncode是一個C++類，來實現字符串的URL編碼。CURLEncode類包含如下函數：
isUnsafeString
decToHex
convert
URLEncode

URLEncode()函數完成編碼過程，URLEncode檢查每個字符，看是否安全。如果不安全將用%16進制值進行轉換并添加
到原始字符串中。

代碼片斷 :

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;
}

參考：

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

RFC 1866: The HTML 2.0 規范 (純文本). 附錄包含了字符表: 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) 建議: http://www.w3.org/MarkUp/Wilbur/.

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

W3C HTML 國際化區域: http://www.w3.org/International/O-HTML.html.

posted on 2007-01-04 13:46 永遇樂 閱讀(2633) 評論(3)  編輯 收藏 引用 所屬分類: 網絡