Important:
This is retired content. This content is outdated and is no longer being maintained. It is provided as a courtesy for individuals who are still using these technologies. This content may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist.
A version of this page is also available for
4/8/2010

This callback function is an application-defined function. ISAPI extensions call this function to read data from the body of the client's HTTP request. The ReadClientname for this function is a placeholder for the function name defined by the header.

Syntax 

BOOL (WINAPI* ReadClient)(
  HCONN 
ConnID,
  LPVOID 
lpvBuffer,
  LPDWORD 
lpdwSize 
);

Parameters

ConnID

[in] Connection handle.

lpvBuffer

[out] Pointer to the buffer to receive the requested information.

lpdwSize

[in, out] Pointer to the number of bytes available in the buffer specified by lpvBuffer. On completion, this parameter indicates the number of bytes actually transferred into the buffer.

Return Value

Returns TRUE if the function succeeds, and FALSE otherwise. To determine the cause of a failure, the extension should call GetLastError.

Remarks

This function reads information from the body of the Web client HTTP request into the buffer supplied by the extension. Therefore, the call can be used to read data from an HTML form that uses POST operations. The number of bytes that the Web Server reads when receiving POST data is specified in the HKEY_LOCAL_MACHINE\COMM\HTTPD\PostReadSizeregistry key. The Web Server will read in, at most, the number of bytes specified in this registry value before calling the ISAPI extension.

If the cbTotalBytesmember of the EXTENSION_CONTROL_BLOCKstructure is equal to the cbAvailablemember, then the Web Server has read all the data from the client. If cbTotalBytesis greater than cbAvailable, then the ISAPI extension is responsible for making the Web Server read more data by way of ReadClient.

The ISAPI extension might need to make multiple calls to ReadClientto retrieve all the data. If the buffer size is less than the number of bytes available, then ReadClientwill fill the available space.

The advantage of using multiple calls to ReadClientis related to Windows Embedded CE memory constraints. For example, you might want your extension to use the Web Server to upload a 10MB file to a flash card. You have only 2 MB of RAM available on your device, but you have sufficient storage space available on the card. If the entire buffer from the client is read at once, the device will run out of physical memory. However, if your extension uses a 4KB buffer while calling ReadClientand then calls WriteFileimmediately after each ReadClientcall, the extension can minimize the amount of RAM required.

Note:
ReadClientwill time out after 60 seconds, regardless of any Web Server timeout settings. Your extension can loop by initiating another synchronous ReadClientcall after the 60-second timeout period has elapsed.

If the socket on which the server is listening to the client is closed, ReadClientwill return TRUE, but with zero bytes read.

Requirements

Header httpext.h
Library Developer Implemented
Windows Embedded CE Windows CE 3.0 and later
Windows Mobile Pocket PC 2000 and later, Smartphone 2002 and later

See Also