HttpSendHttpResponse function (http.h)

The HttpSendHttpResponse function sends an HTTP response to the specified HTTP request.


  [in]           HANDLE             RequestQueueHandle,
  [in]           HTTP_REQUEST_ID    RequestId,
  [in]           ULONG              Flags,
  [in]           PHTTP_RESPONSE     HttpResponse,
  [in, optional] PHTTP_CACHE_POLICY CachePolicy,
  [out]          PULONG             BytesSent,
  [in]           PVOID              Reserved1,
  [in]           ULONG              Reserved2,
  [in]           LPOVERLAPPED       Overlapped,
  [in, optional] PHTTP_LOG_DATA     LogData


[in] RequestQueueHandle

A handle to the request queue from which the specified request was retrieved. A request queue is created and its handle returned by a call to the HttpCreateRequestQueue function.

Windows Server 2003 with SP1 and Windows XP with SP2:  The handle to the request queue is created by the HttpCreateHttpHandle function.

[in] RequestId

An identifier of the HTTP request to which this response corresponds. This value is returned in the RequestId member of the HTTP_REQUEST structure by a call to the HttpReceiveHttpRequest function. This value cannot be HTTP_NULL_ID.

[in] Flags

This parameter can be a combination of some of the following flag values. Those that are mutually exclusive are marked accordingly.

Flags Meaning
The network connection should be disconnected after sending this response, overriding any persistent connection features associated with the version of HTTP in use.
Caution  Combining HTTP_SEND_RESPONSE_FLAG_DISCONNECT and HTTP_SEND_RESPONSE_FLAG_MORE_DATA in a single call to the HttpSendHttpResponse function produces undefined results.
Additional entity body data for this response is sent by the application through one or more subsequent calls to HttpSendResponseEntityBody. The last call sending entity-body data then sets this flag to zero.
Caution  Combining HTTP_SEND_RESPONSE_FLAG_DISCONNECT and HTTP_SEND_RESPONSE_FLAG_MORE_DATA in a single call to the HttpSendHttpResponse function produces undefined results.
This flag enables buffering of data in the kernel on a per-response basis.

It should be used by an application doing synchronous I/O or by an application doing asynchronous I/O with no more than one outstanding send at a time.

Applications that use asynchronous I/O and that may have more than one send outstanding at a time should not use this flag.

When this flag is set, it should also be used consistently in calls to the HttpSendResponseEntityBody function.

Windows Server 2003:  This flag is not supported. This flag is new for Windows Server 2003 with SP1.

Enables the TCP nagling algorithm for this send only.

Windows Server 2003 with SP1 and Windows XP with SP2:  This flag is not supported.

Specifies that for a range request, the full response content is passed and the caller wants the HTTP API to process ranges appropriately.
Note  This flag is only supported for responses to HTTP GET requests and offers a limited subset of functionality. Applications that require full range processing should perform it in user mode and not rely on HTTP.sys. Its usage is discouraged.
Windows Server 2008 R2 and Windows 7 or later.

Note  This flag is supported.

Specifies that the request/response is not HTTP compliant and all subsequent bytes should be treated as entity-body. Applications specify this flag when it is accepting a Web Socket upgrade request and informing HTTP.sys to treat the connection data as opaque data.

This flag is only allowed when the StatusCode member of pHttpResponse is 101, switching protocols. HttpSendHttpResponse returns ERROR_INVALID_PARAMETER for all other HTTP response types if this flag is used.

Windows 8 and later:  This flag is supported.

[in] HttpResponse

A pointer to an HTTP_RESPONSE structure that defines the HTTP response.

[in, optional] CachePolicy

A pointer to the HTTP_CACHE_POLICY structure used to cache the response.

Windows Server 2003 with SP1 and Windows XP with SP2:  This parameter is reserved and must be NULL.

[out] BytesSent

Optional. A pointer to a variable that receives the number, in bytes, sent if the function operates synchronously.

When making an asynchronous call using pOverlapped, set pBytesSent to NULL. Otherwise, when pOverlapped is set to NULL, pBytesSent must contain a valid memory address and not be set to NULL.

[in] Reserved1

This parameter is reserved and must be NULL.

[in] Reserved2

This parameter is reserved and must be zero.

[in] Overlapped

For asynchronous calls, set pOverlapped to point to an OVERLAPPED structure; for synchronous calls, set to NULL.

A synchronous call blocks until all response data specified in the pHttpResponse parameter is sent, whereas an asynchronous call immediately returns ERROR_IO_PENDING and the calling application then uses GetOverlappedResult or I/O completion ports to determine when the operation is completed. For more information about using OVERLAPPED structures for synchronization, see Synchronization and Overlapped Input and Output.

[in, optional] LogData

A pointer to the HTTP_LOG_DATA structure used to log the response. Pass a pointer to the HTTP_LOG_FIELDS_DATA structure and cast it to PHTTP_LOG_DATA.

Be aware that even when logging is enabled on a URL Group, or server session, the response will not be logged unless the application supplies the log fields data structure.

Windows Server 2003 and Windows XP with SP2:  This parameter is reserved and must be NULL.

Windows Vista and Windows Server 2008:  This parameter is new for Windows Vista, and Windows Server 2008

Return value

If the function succeeds, the function returns NO_ERROR.

If the function is used asynchronously, a return value of ERROR_IO_PENDING indicates that the next request is not yet ready and is retrieved later through normal overlapped I/O completion mechanisms.

If the function fails, it returns one of the following error codes.

Value Meaning
One or more of the supplied parameters is in an unusable form.
A system error code defined in WinError.h.


The HttpSendHttpResponse function is used to create and send a response header, and the HttpSendResponseEntityBody function can be used to send entity-body data as required.

If neither a content-length header nor a transfer-encoding header is included with the response, the application must indicate the end of the response by explicitly closing the connection by using the HTTP_SEND_RESPONSE_DISCONNECT flag.

If an application specifies a "Server:" header in a response, using the HttpHeaderServer identifier in the HTTP_KNOWN_HEADER structure, that specified value is placed as the first part of the header, followed by a space and then "Microsoft-HTTPAPI/1.0". If no server header is specified, HttpSendHttpResponse supplies "Microsoft-HTTPAPI/1.0" as the server header.

Note  The HttpSendHttpResponse and HttpSendResponseEntityBody function must not be called simultaneously from different threads on the same RequestId.


Minimum supported client Windows Vista, Windows XP with SP2 [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Target Platform Windows
Header http.h
Library Httpapi.lib
DLL Httpapi.dll

See also

HTTP Server API Version 1.0 Functions