Q172551: PRB: CInternetSession::OpenURL() Fails with File Protocol

Article: Q172551
Product(s): Microsoft C Compiler
Version(s): winnt:5.0,6.0
Operating System(s): 
Keyword(s): kbInternet kbMFC kbVC kbVC500 kbVC600 kbVS97 kbVS600 kbGrpDSMFCATL
Last Modified: 03-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

CInternetSession::OpenURL() fails if you use a URL that specifies a file that
contains spaces or other unsafe characters. For example, the following will
fail:

     CMyInternetSession s("");
     CStdioFile* p = s.OpenURL("file://c:/temp/Text Document.txt");

As a result, a File Exception is thrown and the following message appears:

  c:\temp\Text%20Document.txt was not found.

CAUSE
=====

The specifications for a URL designate certain characters that must be escaped
when they are present in a URL. The space character is one of the characters
that must be escaped.

The function CInternetSession::OpenURL() calls a function that converts unsafe
characters in the URL to their escape sequences before processing the URL
further. If the URL is using the file protocol it creates a CStdioFile and
returns a pointer to this object. However, CStdioFile does not understand the
escaped path and, as a result, an exception is thrown.

RESOLUTION
==========

When you use the file protocol, you must not convert unsafe characters to their
escape sequences. The following code demonstrates how to do this by writing a
CInternetSession derived class to override OpenURL().

     // class definition
     class CMyInternetSession : CInternetSession
     {
     public:
        CMyInternetSession::CMyInternetSession(LPCTSTR pstrAgent = NULL,
           DWORD dwContext = 1, DWORD dwAccessType =
           PRE_CONFIG_INTERNET_ACCESS, LPCTSTR pstrProxyName = NULL,
           LPCTSTR pstrProxyBypass = NULL, DWORD dwFlags = 0);

        CStdioFile* CMyInternetSession::OpenURL(LPCTSTR pstrURL,
           DWORD dwContext = 1, DWORD dwFlags =
           INTERNET_FLAG_TRANSFER_ASCII, LPCTSTR pstrHeaders = NULL,
           DWORD dwHeadersLength = 0);
     };

     // CMyInternetSession constructor
     CMyInternetSession::CMyInternetSession(LPCTSTR pstrAgent,
        DWORD dwContext, DWORD dwAccessType, LPCTSTR pstrProxyName,
        LPCTSTR pstrProxyBypass, DWORD dwFlags)
     {
        CInternetSession(pstrAgent, dwContext, dwAccessType, pstrProxyName,
           pstrProxyBypass, dwFlags);
     }

     CStdioFile* CMyInternetSession::OpenURL(LPCTSTR pstrURL,
        DWORD dwContext, DWORD dwFlags, LPCTSTR pstrHeaders,
        DWORD dwHeadersLength)
     {
        ASSERT(pstrURL != NULL);
        ASSERT(dwHeadersLength == 0 || pstrHeaders != NULL);

        // must have TRANSFER_BINARY or TRANSFER_ASCII but not both
        #define _AFX_TRANSFER_MASK (INTERNET_FLAG_TRANSFER_BINARY \ 
           | INTERNET_FLAG_TRANSFER_ASCII)

        ASSERT((dwFlags & _AFX_TRANSFER_MASK) != 0);
        ASSERT((dwFlags & _AFX_TRANSFER_MASK) != _AFX_TRANSFER_MASK);

        DWORD dwServiceType;
        CString strServer;
        CString strObject;
        INTERNET_PORT nPort;

        BOOL bParsed = AfxParseURL(pstrURL, dwServiceType,
           strServer, strObject, nPort);

        // if it turns out to be a file...
        if (bParsed && dwServiceType == AFX_INET_SERVICE_FILE)
        {
           CString userName;
           CString password;

           // Get the normalized file name with out converting
           // unsafe characters to escape sequence.

           AfxParseURLEx(pstrURL, dwServiceType, strServer,
              strObject, nPort, userName, password, ICU_NO_ENCODE);

           int nMode = CFile::modeRead | CFile::shareCompat;
           if (dwFlags & INTERNET_FLAG_TRANSFER_BINARY)
              nMode |= CFile::typeBinary;
           else
              nMode |= CFile::typeText;

           return new CStdioFile(strObject, nMode);
        }

        return CInternetSession::OpenURL(pstrURL,   dwContext, dwFlags,
           pstrHeaders, dwHeadersLength);
     }

REFERENCES
==========

The specification for URL's are published by The World Wide Web Consortium
(W3C). The specifications define the escape sequences and unsafe characters. Its
URL is:

  http://www.w3.org/

NOTE: Web links may change without notice.

Additional query words: 4.20b space file OpenURL filename

======================================================================
Keywords          : kbInternet kbMFC kbVC kbVC500 kbVC600 kbVS97 kbVS600 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:5.0,6.0
Issue type        : kbprb

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