HTTP/2 demux must be handled with care for active reverse connection.
Until accept has been completed, it should be forbidden to handle
HEADERS frame as session is not yet ready to handle streams.
To implement this, use the flag H2_CF_DEM_TOOMANY which blocks demux
process. This flag is automatically set just after conn_reverse()
invocation. The flag is removed on rev_accept_conn() callback via a new
H2 ctl enum. H2 tasklet is woken up to restart demux process.
As a side-effect, reporting in H2 mux may be blocked as demux functions
are used to convert error status at the connection level with
CO_FL_ERROR. To ensure error is reported for a reverse connection, check
h2c_is_dead() specifically for this case in h2_wake(). This change also
has its own side-effect : h2c_is_dead() conditions have been adjusted to
always exclude !h2c->conn->owner condition which is always true for
reverse connection or else H2 mux may kill them unexpectedly.
An error can occured on a reverse connection before accept is completed.
In this case, no parent session can be notified. Instead, wake up the
receiver task on conn_create_mux().
As a counterpart to this, receiver task is extended to match CO_FL_ERROR
flag on pending connection. In this case, the onnection is freed. The
task is then requeued with a 1 second delay to start a new reverse
connection attempt.
Implement active reverse connection initialization. This is done through
a new task stored in the receiver structure. This task is instantiated
via bind callback and first woken up via enable callback.
Task handler is separated into two halves. On the first step, a new
connection is allocated and stored in <pend_conn> member of the
receiver. This new client connection will proceed to connect using the
server instance referenced in the bind_conf.
When connect has successfully been executed and HTTP/2 connection is
ready for exchange after SETTINGS, reverse_connect task is woken up. As
<pend_conn> is still set, the second halve is executed which only
execute listener_accept(). This will in turn execute accept_conn
callback which is defined to return the pending connection.
The task is automatically requeued inside accept_conn callback if bind
maxconn is not yet reached. This allows to specify how many connection
should be opened. Each connection is instantiated and reversed serially
one by one until maxconn is reached.
conn_free() has been modified to handle failure if a reverse connection
fails before being accepted. In this case, no session exists to notify
about the failure. Instead, reverse_connect task is requeud with a 1
second delay, giving time to fix a possible network issue. This will
allow to attempt a new connection reverse.
Note that for the moment connection rebinding after accept is disabled
for simplicity. Extra operations are required to migrate an existing
connection and its stack to a new thread which will be implemented
later.
Implement parsing for "rev@" addresses on bind line. On config parsing,
server name is stored on the bind_conf.
Several new callbacks are defined on reverse_connect protocol to
complete parsing. listen callback is used to retrieve the server
instance from the bind_conf server name. If found, the server instance
is stored on the receiver. Checks are implemented to ensure HTTP/2
protocol only is used by the server.
A new protocol named "reverse_connect" is created. This will be used to
instantiate connections that are opened by a reverse bind.
For the moment, only a minimal set of callbacks are defined with no real
work. This will be extended along the next patches.
