WINHTTP_STATUS

The WINHTTP_STATUS_CALLBACK callback function is a prototype for an application-defined status callback function.

SUB CALLBACK WINHTTP_STATUS_CALLBACK ( _

BYVAL hInternet AS DWORD _

BYVAL dwContext AS DWORD _

BYVAL dwInternetStatus AS DWORD _

BYVAL lpvStatusInformation AS DWORD _

BYVAL dwStatusInformationLength AS DWORD _

)

[in] A pointer to a value of type unsigned long integer that specifies the application-defined context value associated with the handle in the hInternet parameter.

A context value can be assigned to a Session, Connect, or Request handle by calling WinHttpSetOption with the WINHTTP_OPTION_CONTEXT_VALUE option. Alternatively, WinHttpSendRequest can be used to associate a context value with a Request handle.

[in] Value of type unsigned long integer that specifies the status code that indicates why the callback function is called. This can be one of the following values:

Closing the connection to the server. The lpvStatusInformation parameter is NULL. This flag has been deprecated.

Successfully connected to the server. The lpvStatusInformation parameter contains a pointer to a null-terminated Unicode string that indicates the IP address of the server in dotted notation. This flag has been deprecated.

Connecting to the server. The lpvStatusInformation parameter contains a pointer to a null-terminated Unicode string that indicates the IP address of the server in dotted notation. This flag has been deprecated.

Successfully closed the connection to the server. The lpvStatusInformation parameter is NULL. This flag has been deprecated.

Data is available to be retrieved with WinHttpReadData. The lpvStatusInformation parameter points to a DWORD that contains the number of bytes of data available. The dwStatusInformationLength parameter itself is 4 (the size of a DWORD).

An HINTERNET handle has been created. The lpvStatusInformation parameter contains a pointer to the HINTERNET handle. This flag has been deprecated.

This handle value has been terminated. The lpvStatusInformation parameter contains a pointer to the HINTERNET handle.

The response header has been received and is available with WinHttpQueryHeaders. The lpvStatusInformation parameter is NULL.

Received an intermediate (100 level) status code message from the server. The lpvStatusInformation parameter contains a pointer to a DWORD that indicates the status code.

Successfully found the IP address of the server. The lpvStatusInformation parameter contains a pointer to a null-terminated Unicode string that indicates the name that was resolved. This flag has been deprecated.

Data was successfully read from the server. The lpvStatusInformation parameter contains a pointer to the buffer specified in the call to WinHttpReadData. The dwStatusInformationLength parameter contains the number of bytes read.

Waiting for the server to respond to a request. The lpvStatusInformation parameter is NULL. This flag has been deprecated.

An HTTP request is about to automatically redirect the request. The lpvStatusInformation parameter contains a pointer to a null-terminated Unicode string indicating the new URL. At this point, the application can read any data returned by the server with the redirect response and can query the response headers. It can also cancel the operation by closing the handle.

An error occurred while sending an HTTP request. The lpvStatusInformation parameter contains a pointer to a WINHTTP_ASYNC_RESULT structure, of which the dwResult member indicates the return value of the function and any error codes that apply.

Successfully sent the information request to the server. The lpvStatusInformation parameter contains a pointer to a DWORD indicating the number of bytes sent. This flag has been deprecated.

Looking up the IP address of a server name. The lpvStatusInformation parameter contains a pointer to the server name being resolved. This flag has been deprecated.

Successfully received a response from the server. The lpvStatusInformation parameter contains a pointer to a DWORD indicating the number of bytes received. This flag has been deprecated.

One or more errors were encountered while retrieving a Secure Sockets Layer (SSL) certificate from the server. The lpvStatusInformation parameter contains a flag. For more information, see the description for lpvStatusInformation.

Sending the information request to the server. The lpvStatusInformation parameter is NULL. This flag has been deprecated.

Data was successfully written to the server. The lpvStatusInformation parameter contains a pointer to a DWORD that indicates the number of bytes written.

[in] A pointer to a buffer that specifies information pertinent to this call to the callback function. The format of this data depends on the value of the dwInternetStatus parameter. For more information, see dwInternetStatus.

If the dwInternetStatus parameter is WINHTTP_CALLBACK_STATUS_SECURE_FAILURE, this parameter can be one of the following values.

Certification revocation checking has been enabled, but the revocation check failed to verify whether a certificate has been revoked. The server used to check for revocation might be unreachable.

The function is unfamiliar with the Certificate Authority that generated the server's certificate.

SSL certificate common name (host name field) is incorrect, for example, if you entered www.microsoft.com and the common name on the certificate says www.msn.com.

SSL certificate date that was received from the server is bad. The certificate is expired.

[in] A value of type unsigned long integer that specifies the size, in bytes, of the lpvStatusInformation buffer.

This callback function must be threadsafe and should be able to handle reentered for the same request while it is processing. A value of WINHTTP_CALLBACK_STATUS_HANDLE_CLOSING in the dwInternetStatus parameter indicates that this is the last callback the application receives, and that no other messages for this request are processed.

The callback function must be threadsafe and reentrant because it can be called on another thread for a separate request, and reentered on the same thread for the current request. It must therefore be coded to handle reentrance safely while processing. When the dwInternetStatus parameter is equal to WINHTTP_CALLBACK_STATUS_HANDLE_CLOSING, the callback does not need to be able to handle reentrance for the same request, because this callback is guaranteed to be the last, and does not occur when other messages for this request are handled.

The status callback function receives updates on the status of asynchronous operations through notification flags. Notifications that indicate a particular operation is complete are called completion notifications, or just completions. The following table lists the six completion flags and the corresponding function that is complete when this flag is received.

Completion flag	Function
WINHTTP_CALLBACK_STATUS_DATA_AVAILABLE	WinHttpQueryDataAvailable
WINHTTP_CALLBACK_STATUS_HEADERS_AVAILABLE	WinHttpReceiveResponse
WINHTTP_CALLBACK_STATUS_READ_COMPLETE	WinHttpReadData
WINHTTP_CALLBACK_STATUS_SENDREQUEST_COMPLETE	WinHttpSendRequest
WINHTTP_CALLBACK_STATUS_WRITE_COMPLETE	WinHttpWriteData
WINHTTP_CALLBACK_STATUS_REQUEST_ERROR	Any of the above functions when an error occurs.

Because callbacks are made during the processing of the request, the application should spend as little time as possible in the callback function to avoid degrading data throughput on the network. For example, displaying a dialog box in a callback function can be such a lengthy operation that the server terminates the request.

The callback function can be called in a thread context different from the thread that initiated the request.