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CHttpFile::QueryInfo 

Call this member function to return response or request headers from an HTTP request.


BOOL QueryInfo(
   DWORD dwInfoLevel,
   LPVOID lpvBuffer,
   LPDWORD lpdwBufferLength,
   LPDWORD lpdwIndex = NULL 
) const;
BOOL QueryInfo(
   DWORD dwInfoLevel,
   CString& str,
   LPDWORD dwIndex = NULL 
) const;
BOOL QueryInfo(
   DWORD dwInfoLevel,
   SYSTEMTIME* pSysTime,
   LPDWORD dwIndex = NULL 
) const;

Parameters

dwInfoLevel

A combination of the attribute to query and the following flags that specify the type of information requested:

  • HTTP_QUERY_CUSTOM   Finds the header name and returns this value in lpvBuffer on output. HTTP_QUERY_CUSTOM throws an assertion if the header isn't found.

  • HTTP_QUERY_FLAG_REQUEST_HEADERS   Typically, the application queries the response headers, but an application can also query request headers by using this flag.

  • HTTP_QUERY_FLAG_SYSTEMTIME   For those headers whose value is a date/time string, such as "Last-Modified-Time," this flag returns the header value as a standard Win32 SYSTEMTIME structure that does not require the application to parse the data. If you use this flag, you may want to use the SYSTEMTIME override of the function.

  • HTTP_QUERY_FLAG_NUMBER   For those headers whose value is a number, such as the status code, this flag returns the data as a 32-bit number.

See the Remarks section for a list of the possible values.

lpvBuffer

A pointer to the buffer that receives the information.

lpdwBufferLength

On entry, this points to a value containing the length of the data buffer, in number of characters or bytes. See the Remarks section for more detailed information about this parameter.

lpdwIndex

A pointer to a zero-based header index. Can be NULL. Use this flag to enumerate multiple headers with the same name. On input, lpdwIndex indicates the index of the specified header to return. On output, lpdwIndex indicates the index of the next header. If the next index cannot be found, ERROR_HTTP_HEADER_NOT_FOUND is returned.

str

A reference to the CString object receiving the returned information.

dwIndex

An index value. See lpdwIndex.

pSysTime

A pointer to a Win32 SYSTEMTIME structure.

Nonzero if successful; otherwise 0. If the call fails, the Win32 function GetLastError may be called to determine the cause of the error.

Use this member function only after a successful call to SendRequest or on a CHttpFile object successfully created by OpenURL.

You can retrieve the following types of data from QueryInfo:

  • strings (default)

  • SYSTEMTIME (for "Data:" "Expires:" etc, headers)

  • DWORD (for STATUS_CODE, CONTENT_LENGTH, etc.)

When a string is written to the buffer, and the member function succeeds, lpdwBufferLength contains the length of the string in characters minus 1 for the terminating NULL character.

The possible dwInfoLevel values include:

  • HTTP_QUERY_MIME_VERSION

  • HTTP_QUERY_CONTENT_TYPE

  • HTTP_QUERY_CONTENT_TRANSFER_ENCODING

  • HTTP_QUERY_CONTENT_ID

  • HTTP_QUERY_CONTENT_DESCRIPTION

  • HTTP_QUERY_CONTENT_LENGTH

  • HTTP_QUERY_ALLOWED_METHODS

  • HTTP_QUERY_PUBLIC_METHODS

  • HTTP_QUERY_DATE

  • HTTP_QUERY_EXPIRES

  • HTTP_QUERY_LAST_MODIFIED

  • HTTP_QUERY_MESSAGE_ID

  • HTTP_QUERY_URI

  • HTTP_QUERY_DERIVED_FROM

  • HTTP_QUERY_LANGUAGE

  • HTTP_QUERY_COST

  • HTTP_QUERY_WWW_LINK

  • HTTP_QUERY_PRAGMA

  • HTTP_QUERY_VERSION

  • HTTP_QUERY_STATUS_CODE

  • HTTP_QUERY_STATUS_TEXT

  • HTTP_QUERY_RAW_HEADERS

  • HTTP_QUERY_RAW_HEADERS_CRLF

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