SpdyProxyClientSocket uses read_callback_ for both Connect() and
Read(), and its OnIOComplete() calls read_callback_, thus its fast
connect code checks read_callback_. The code was ported to
QuicProxyClientSocket without much change.
But QuicProxyClientSocket uses a separate connect_callback_ apart from
read_callback_, and its OnIOComplete() calls connect_callback_, thus
when headers are received after Connect() it doesn't need to check
read_callback_ and should always avoid calling connect_callback_.
SpdyProxyClientSocket waits for 200 OK before returning OK for Connect.
Change that behavior to returning OK immediately after CONNECT header.
This feature is enabled by default. It should probably be turned on
through an interface but that implies passing a flag through deep
interface chains right now requiring intrusive changes to multiple
places.
Design notes:
The current approach is better than the obvious TCP Fast Open style fake
Connect().
Fast Open should not be used for preconnects as preconnects need actual
connections set up. The Naive client does not use preconnects per se
(using "...RawConnect") but the user agent will use preconnects and the
Naive client has to infer that. Hence there is a need to check the
incoming socket for available bytes right before Connect() and configure
whether a socket should be connected with Fast Open. But fake Connect()
make it difficult to check the incoming socket because it immediately
returns and there is not enough time for the first read of the incoming
socket to arrive.
To check for preconnects it is best to push the first read of the
incoming socket to as late as possible. The other (wrong) way of doing
that is to pass in an early read callback and call it immediately after
sending HEADERS and then send the available bytes right there. This way
is wrong because it does not work with late binding, which assumes
Connect() is idempotent and causes sockets opened in this way to be
potentially bound to the wrong socket requests.
The current approach is to return OK in Connect() right after sending
HEADERS before getting the reply, which is to be received later. If the
reply is received during a subsequent Read() and the reply indicates an
error, the error is returned to the callback of the Read(); otherwise
the error is ignored with the connection disconnected and subsequent
Read() and Write() should discover the disconnection.
