How it works ?  (unfinished and inexact)

For TCP and HTTP :

- listeners create listening sockets with a READ callback pointing to the
  protocol-specific accept() function. 

- the protocol-specific accept() function then accept()'s the connection and
  instantiates a "server TCP socket" (which is dedicated to the client side),
  and configures it (non_block, get_original_dst, ...).

For TCP :
- in case of pure TCP, a request buffer is created, as well as a "client TCP
  socket", which tries to connect to the server.

- once the connection is established, the response buffer is allocated and
  connected to both ends.

- both sockets are set to "autonomous mode" so that they only wake up their
  supervising session when they encounter a special condition (error or close).


For HTTP :
- in case of HTTP, a request buffer is created with the "HOLD" flag set and
  a read limit to support header rewriting (may be this one will be removed
  eventually because it's better to limit only to the buffer size and report
  an error when rewritten data overflows)

- a "flow analyzer" is attached to the buffer (or possibly multiple flow
  analyzers). For the request, the flow analyzer is "http_lb_req". The flow
  analyzer is a function which gets called when new data is present and
  blocked. It has a timeout (request timeout). It can also be bypassed on
  demand.

- when the "http_lb_req" has received the whole request, it creates a client
  socket with all the parameters needed to try to connect to the server. When
  the connection establishes, the response buffer is allocated on the fly,
  put to HOLD mode, and a an "http_lb_resp" flow analyzer is attached to the
  buffer.


For client-side HTTPS :

- the accept() function must completely instantiate a TCP socket + an SSL
  reader. It is when the SSL session is complete that we call the
  protocol-specific accept(), and create its buffer.


Conclusions
-----------

- we need a generic TCP accept() function with a lot of flags set by the
  listener, to tell it what info we need to get at the accept() time, and
  what flags will have to be set on the socket.

- once the TCP accept() function ends, it wakes up the protocol supervisor
  which is in charge of creating the buffers, etc, switch states, etc...