Pipelining

Advanced HTTPClient Info

Pipelining

If the connection is kept open across requests then the requests may
be pipelined. Pipelining here means that a new request is sent before
the response to a previous request is received. Since this can
obviously enhance performance by reducing the overall round-trip time
for a series of requests to the same server, the HTTPClient has been
written to support pipelining (at the expense of some extra code to
keep track of the outstanding requests).

The programming model is always the same: for every request you send
you get a response back which contains the headers and data of the
servers response. Now, to support pipelining, the fields in the
response aren't necessarily filled in yet when the HTTPResponse object
is returned to the caller (i.e. the actual response headers and data
haven't been read off the net), but the first call to any method in the
response (e.g. a getStatusCode()) will wait till the
response has actually been read and parsed. Also any previous requests
will be forced to read their responses if they have not already done so
(so e.g. if you send two consecutive requests and receive responses
r1 and r2, calling
r2.getHeader("Content-type") will first force the complete
response r1 to be read before reading the response
r2). All this should be completely transparent, except for
the fact that invoking a method on one response may sometimes take a
few seconds to complete, while the same method on a different response
will return immediately with the desired info.