HTTPClient
Interface HTTPClientModule

All Known Implementing Classes:

CookieModule

public interface HTTPClientModule

extends HTTPClientModuleConstants

This is the interface that a module must implement. There are two parts during a request: the construction of the request, and the handling of the response. A request may cycle through these parts multiple times when a module generates additional subrequests (such as a redirection status handling module might do).

In the first step the request handler is invoked; here the headers, the request-uri, etc. can be modified, or a complete response can be generated. Then, if no response was generated, the request is sent over the wire. In the second step the response handlers are invoked. These may modify the response or, in phase 2, may generate a new request; the returned status from the phase 2 handler specifies how the processing of the request or response should further proceed.

The response handling is split into three phases. In the first phase the response handling cannot be modified; this is so that all modules get a chance to see the returned response. Modules will typically make notes of responses and do certain header processing here (for example the cookie module does it's work in this phase). In the second phase modules may generate new subrequests or otherwise control the further handling of the response. This is typically used for response status handling (such as for redirections and authentication). Finally, if no new subrequest was generated, the phase 3 response handlers are invoked so that modules can perform any necessary cleanups and final processing (no additional subrequests can be made anymore). It is recommended that any response processing which needn't be done if the request is not returned to the user is deferred until this phase. For example, the Content-MD5, Content-Encoding and Transfer-Encoding modules do their work in this phase as the response body is usually discarded if a new subrequest is generated.

When the user invokes any request method (such as Get(...)) a list of of modules to be used is built. Then, for each module in the list, an instance is created using the Class.newInstance() method. This means that each module must have a constructor which takes no arguments. This instance is then used to handle the request, its response, and any additional subrequests and their responses. In this way a module can easily keep state between related subrequests. For example, a redirection module might want to keep track of the number of redirections made to detect redirect loops; it could do this by defining an instance variable and incrementing it each time the request handler is invoked.

Since:

V0.3

Version:

0.3-3 06/05/2001

Author:

Ronald Tschalär

Fields inherited from interface HTTPClient.HTTPClientModuleConstants

REQ_CONTINUE, REQ_NEWCON_RST, REQ_NEWCON_SND, REQ_RESPONSE, REQ_RESTART, REQ_RETURN, REQ_SHORTCIRC, RSP_CONTINUE, RSP_NEWCON_REQ, RSP_NEWCON_SND, RSP_REQUEST, RSP_RESTART, RSP_SEND, RSP_SHORTCIRC

Method Summary

int	requestHandler(Request request, Response[] response) This is invoked before the request is sent.
void	responsePhase1Handler(Response response, RoRequest request) The phase 1 response handler.
int	responsePhase2Handler(Response response, Request request) The phase 2 response handler.
void	responsePhase3Handler(Response response, RoRequest request) The phase 3 response handler.
void	trailerHandler(Response response, RoRequest request) The chunked transfer-encoding (and in future maybe others) can contain trailer fields at the end of the body.

Method Detail

requestHandler

public int requestHandler(Request request,
                          Response[] response)
                   throws IOException,
                          ModuleException

This is invoked before the request is sent. A module will typically use this to make a note of headers, to modify headers and/or data, or even generate and return a response (e.g. for a cache module). If a response is generated the module must return the appropriate return code (REQ_RESPONSE or REQ_RETURN).

Return codes for phase 1 (defined in HTTPClientModuleConstants.java)

REQ_CONTINUE continue processing

REQ_RESTART restart processing with first module

REQ_SHORTCIRC stop processing and send

REQ_RESPONSE go to phase 2

REQ_RETURN return response immediately (no processing)

REQ_NEWCON_RST use a new HTTPConnection, restart processing

REQ_NEWCON_SND use a new HTTPConnection, send immediately

Parameters:

request - the request - may be modified as needed

response - the response if the status is REQ_RESPONSE or REQ_RETURN

Returns:

status code REQ_XXX specifying further action

Throws:

IOException - if an IOException occurs on the socket

ModuleException - if an exception occurs during the handling of the request

responsePhase1Handler

public void responsePhase1Handler(Response response,
                                  RoRequest request)
                           throws IOException,
                                  ModuleException

The phase 1 response handler. This will be invoked for every response. Modules will typically make notes of the response and do any header processing which must always be performed.

Parameters:

response - the response - may be modified

request - the original request

Throws:

IOException - if an IOException occurs on the socket

ModuleException - if an exception occurs during the handling of the response

responsePhase2Handler

public int responsePhase2Handler(Response response,
                                 Request request)
                          throws IOException,
                                 ModuleException

The phase 2 response handler. A module may modify the response or generate a new request (e.g. for redirection). This handler will only be invoked for a given module if all previous modules returned RSP_CONTINUE. If the request is modified the handler must return an appropriate return code (RSP_REQUEST, RSP_SEND, RSP_NEWCON_REQ or RSP_NEWCON_SND). If any other code is return the request must not be modified.

Return codes for phase 2 (defined in HTTPClientModuleConstants.java)

RSP_CONTINUE continue processing

RSP_RESTART restart processing with first module (phase 1)

RSP_SHORTCIRC stop processing and return

RSP_REQUEST go to phase 1

RSP_SEND send request immediately (no processing)

RSP_NEWCON_REQ go to phase 1 using a new HTTPConnection

RSP_NEWCON_SND send request using a new HTTPConnection

Parameters:

response - the response - may be modified

request - the request; if the status is RSP_REQUEST then this must contain the new request; however do not modify this if you don't return a RSP_REQUEST status.

Returns:

status code RSP_XXX specifying further action

Throws:

IOException - if an IOException occurs on the socket

ModuleException - if an exception occurs during the handling of the response

responsePhase3Handler

public void responsePhase3Handler(Response response,
                                  RoRequest request)
                           throws IOException,
                                  ModuleException

The phase 3 response handler. This will only be invoked if no new subrequest was generated in phase 2. Modules should defer any repsonse handling which need only be done if the response is returned to the user to this phase.

Parameters:

response - the response - may be modified

request - the original request

Throws:

IOException - if an IOException occurs on the socket

ModuleException - if an exception occurs during the handling of the response

trailerHandler

public void trailerHandler(Response response,
                           RoRequest request)
                    throws IOException,
                           ModuleException

The chunked transfer-encoding (and in future maybe others) can contain trailer fields at the end of the body. Since the responsePhaseXHandler()'s are invoked before the body is read and therefore do not have access to the trailers (unless they force the complete body to be read) this method will be invoked when the trailers have been read and parsed (sort of a post-response handling).

Note: This method must not modify any part of the response other than the trailers.

Parameters:

response - the response

request - the request

Throws:

IOException - if an IOException occurs on the socket

ModuleException - if an exception occurs during the handling of the trailers