The transient flag CO_RFL_BUF_NOT_STUCK should now be set when the mux's
rcv_buf() function is called, in si_cs_recv(), to be sure the mux is able to
perform some optimisation during data copy. This flag is set when we are
sure the channel buffer is not stuck. Concretely, it happens when there are
data scheduled to be sent.
It is not a fix and this flag is not used for now. But it makes sense to have
this info to be sure to be able to do some optimisations if necessary.
This patch is related to the issue #1362. It may be backported to 2.4 to
ease future backports.
In mux_pt_io_cb(), if a connection error or a shutdown is detected, the mux
is destroyed. Thus we must be careful to not use it in a trace message once
destroyed.
No backport needed. This patch should fix the issue #1220.
As for the other muxes, traces are now supported in the pt mux. All parts of
the multiplexer is covered by these traces. Events are splitted by
categories (connection, stream, rx and tx).
In traces, the first argument is always a connection. So it is easy to get
the mux context (conn->ctx). The second argument is always a conn-stream and
mau be NUUL. The third one is a buffer and it may also be NULL. Depending on
the context it is the request or the response. In all cases it is owned by a
channel. Finally, the fourth argument is an integer value. Its meaning
depends on the calling context.
Add "none" in the list of supported mux protocols. It relies on the
passthrough multiplexer and use almost the same mux_ops structure. Only the
flags differ because this "new" mux does not support the upgrades. "none"
was chosen to explicitly stated there is not processing at the mux level.
Thus it is now possible to set "proto none" or "check-proto none" on
bind/server lines, depending on the context. However, when set, no upgrade
to HTTP is performed. It may be a way to disable HTTP upgrades per bind
line.
When tasklets were derived from tasks, there was no immediate need for
the scheduler to know their status after execution, and in a spirit of
simplicity they just started to always return NULL. The problem is that
it simply prevents the scheduler from 1) accounting their execution time,
and 2) keeping track of their current execution status. Indeed, a remote
wake-up could very well end up manipulating a tasklet that's currently
being executed. And this is the reason why those handlers have to take
the idle lock before checking their context.
In 2.5 we'll take care of making tasklets and tasks work more similarly,
but trouble is to be expected if we continue to propagate the trend of
returning NULL everywhere, especially if some fixes relying on a stricter
model later need to be backported. For this reason this patch updates all
known tasklet handlers to make them return NULL only when the tasklet was
freed. It has no effect for now and isn't even guaranteed to always be
100% safe but it puts the code into the right direction for this.
It's been too short for quite a while now and is now full. It's still
time to extend it to 32-bits since we have room for this without
wasting any space, so we now gained 16 new bits for future flags.
The values were not reassigned just in case there would be a few
hidden u16 or short somewhere in which these flags are placed (as
it used to be the case with stream->pending_events).
The patch is tagged MEDIUM because this required to update the task's
process() prototype to use an int instead of a short, that's quite a
bunch of places.
In FD dumps it's often very important to figure what upper layer function
is going to be called. Let's export the few I/O callbacks that appear as
tasklet functions so that "show fd" can resolve them instead of printing
a pointer relative to main. For example:
1028 : st=0x21(R:rA W:Ra) ev=0x01(heopI) [lc] tmask=0x2 umask=0x2 owner=0x7f00b889b200 iocb=0x65b638(sock_conn_iocb) back=0 cflg=0x00001300 fe=recv mux=H2 ctx=0x7f00c8824de0 h2c.st0=FRH .err=0 .maxid=795 .lastid=-1 .flg=0x0000 .nbst=0 .nbcs=0 .fctl_cnt=0 .send_cnt=0 .tree_cnt=0 .orph_cnt=0 .sub=1 .dsi=795 .dbuf=0@(nil)+0/0 .msi=-1 .mbuf=[1..1|32],h=[0@(nil)+0/0],t=[0@(nil)+0/0] xprt=SSL xprt_ctx=0x7f00c86d0750 xctx.st=0 .xprt=RAW .wait.ev=1 .subs=0x7f00c88252e0(ev=1 tl=0x7f00a07d1aa0 tl.calls=1047 tl.ctx=0x7f00c8824de0 tl.fct=h2_io_cb) .sent_early=0 .early_in=0
Now we don't touch the fd anymore there, instead we rely on the ->drain()
provided by the control layer. As such the function was renamed to
conn_ctrl_drain().
When the shutr() requests CS_SHR_DRAIN and there's no particular shutr
implemented on the underlying transport layer, we must drain pending data.
This is what happens when cs_drain_and_close() is called. It is important
for TCP checks to drain large responses and close cleanly.
The ctl param MUX_EXIT_STATUS can be request to get the exit status of a
multiplexer. For instance, it may be an HTTP status code or an H2 error. For
now, 0 is always returned. When the mux h1 will be able to return HTTP
errors itself, this ctl param will be used to get the HTTP status code from
the logs.
the mux_exit_status enum has been created to map internal mux exist status
to generic one. Thus there is 5 possible status for now: success, invalid
error, timeout error, internal error and unknown.
It is now possible to set the buffer used by the channel request buffer when
a stream is created. It may be useful if input data are already received,
instead of waiting the first call to the mux rcv_buf() callback. This change
is mandatory to support H1 connection with no stream attached.
For now, the multiplexers don't pass any buffer. BUF_NULL is thus used to
call stream_create_from_cs().
When a TCP connection is upgraded to HTTP, the passthrough multiplexer owning
the client connection is detroyed and replaced by an HTTP multiplexer. When it
happens, the connection context is changed (it is in fact the mux itself). Thus,
when the mux-pt is destroyed, the connection is not released. But, only the
connection must be kept. Everything else concerning the mux must be
released. Especially, the tasklet used for I/O subscriptions. In this part,
there was a bug and the tasklet was never released.
This patch should fix the issue #935. It must be backported as far as 2.0.
When a new connection is created, its target is always set just after. So the
connection target may set when it is created instead, during its initialisation
to be precise. It is the purpose of this patch. Now, conn_new() function is
called with the connection target as parameter. The target is then passed to
conn_init(). It means the target must be passed when cs_new() is called. In this
case, the target is only used when the conn-stream is created with no
connection. This only happens for tcpchecks for now.
This one was not easy because it was embarking many includes with it,
which other files would automatically find. At least global.h, arg.h
and tools.h were identified. 93 total locations were identified, 8
additional includes had to be added.
In the rare files where it was possible to finalize the sorting of
includes by adjusting only one or two extra lines, it was done. But
all files would need to be rechecked and cleaned up now.
It was the last set of files in types/ and proto/ and these directories
must not be reused anymore.
The type file is becoming a mess, half of it is for the proxy protocol,
another good part describes conn_streams and mux ops, it would deserve
being split again. At least it was reordered so that elements are easier
to find, with the PP-stuff left at the end. The MAX_SEND_FD macro was moved
to compat.h as it's said to be the value for Linux.
The TASK_IS_TASKLET() macro was moved to the proto file instead of the
type one. The proto part was a bit reordered to remove a number of ugly
forward declaration of static inline functions. About a tens of C and H
files had their dependency dropped since they were not using anything
from task.h.
Most of the file was a large set of HTX elements manipulation functions
and few types, so splitting them allowed to further reduce dependencies
and shrink the build time. Doing so revealed that a few files (h2.c,
mux_pt.c) needed haproxy/buf.h and were previously getting it through
htx.h. They were fixed.
All files that were including one of the following include files have
been updated to only include haproxy/api.h or haproxy/api-t.h once instead:
- common/config.h
- common/compat.h
- common/compiler.h
- common/defaults.h
- common/initcall.h
- common/tools.h
The choice is simple: if the file only requires type definitions, it includes
api-t.h, otherwise it includes the full api.h.
In addition, in these files, explicit includes for inttypes.h and limits.h
were dropped since these are now covered by api.h and api-t.h.
No other change was performed, given that this patch is large and
affects 201 files. At least one (tools.h) was already freestanding and
didn't get the new one added.
Don't bother trying to remove the connection from the idle list, as the
only connections the mux_pt handles are now the TCP-mode connections, and
those are never added to the idle list.
There are still leftovers from the pre-xprt_handshake era with lots
of places where I/O callbacks refrain from receiving/sending if they
see that a handshake is present. This needlessly duplicates the
subscribe calls as it will automatically be done by the underlying
xprt_handshake code when attempting the operation.
The only reason for still checking CO_FL_HANDSHAKE is when we decide
to instantiate xprt_handshake. This patch removes all other ones.
As mentioned in commit c192b0ab95 ("MEDIUM: connection: remove
CO_FL_CONNECTED and only rely on CO_FL_WAIT_*"), there is a lack of
consistency on which flags are checked among L4/L6/HANDSHAKE depending
on the code areas. A number of sample fetch functions only check for
L4L6 to report MAY_CHANGE, some places only check for HANDSHAKE and
many check both L4L6 and HANDSHAKE.
This patch starts to make all of this more consistent by introducing a
new mask CO_FL_WAIT_XPRT which is the union of L4/L6/HANDSHAKE and
reports whether the transport layer is ready or not.
All inconsistent call places were updated to rely on this one each time
the goal was to check for the readiness of the transport layer.
Commit 477902bd2e ("MEDIUM: connections: Get ride of the xprt_done
callback.") broke the master CLI for a very obscure reason. It happens
that short requests immediately terminated by a shutdown are properly
received, CS_FL_EOS is correctly set, but in si_cs_recv(), we refrain
from setting CF_SHUTR on the channel because CO_FL_CONNECTED was not
yet set on the connection since we've not passed again through
conn_fd_handler() and it was not done in conn_complete_session(). While
commit a8a415d31a ("BUG/MEDIUM: connections: Set CO_FL_CONNECTED in
conn_complete_session()") fixed the issue, such accident may happen
again as the root cause is deeper and actually comes down to the fact
that CO_FL_CONNECTED is lazily set at various check points in the code
but not every time we drop one wait bit. It is not the first time we
face this situation.
Originally this flag was used to detect the transition between WAIT_*
and CONNECTED in order to call ->wake() from the FD handler. But since
at least 1.8-dev1 with commit 7bf3fa3c23 ("BUG/MAJOR: connection: update
CO_FL_CONNECTED before calling the data layer"), CO_FL_CONNECTED is
always synchronized against the two others before being checked. Moreover,
with the I/Os moved to tasklets, the decision to call the ->wake() function
is performed after the I/Os in si_cs_process() and equivalent, which don't
care about this transition either.
So in essence, checking for CO_FL_CONNECTED has become a lazy wait to
check for (CO_FL_WAIT_L4_CONN | CO_FL_WAIT_L6_CONN), but that always
relies on someone else having synchronized it.
This patch addresses it once for all by killing this flag and only checking
the two others (for which a composite mask CO_FL_WAIT_L4L6 was added). This
revealed a number of inconsistencies that were purposely not addressed here
for the sake of bisectability:
- while most places do check both L4+L6 and HANDSHAKE at the same time,
some places like assign_server() or back_handle_st_con() and a few
sample fetches looking for proxy protocol do check for L4+L6 but
don't care about HANDSHAKE ; these ones will probably fail on TCP
request session rules if the handshake is not complete.
- some handshake handlers do validate that a connection is established
at L4 but didn't clear CO_FL_WAIT_L4_CONN
- the ->ctl method of mux_fcgi, mux_pt and mux_h1 only checks for L4+L6
before declaring the mux ready while the snd_buf function also checks
for the handshake's completion. Likely the former should validate the
handshake as well and we should get rid of these extra tests in snd_buf.
- raw_sock_from_buf() would directly set CO_FL_CONNECTED and would only
later clear CO_FL_WAIT_L4_CONN.
- xprt_handshake would set CO_FL_CONNECTED itself without actually
clearing CO_FL_WAIT_L4_CONN, which could apparently happen only if
waiting for a pure Rx handshake.
- most places in ssl_sock that were checking CO_FL_CONNECTED don't need
to include the L4 check as an L6 check is enough to decide whether to
wait for more info or not.
It also becomes obvious when reading the test in si_cs_recv() that caused
the failure mentioned above that once converted it doesn't make any sense
anymore: having CS_FL_EOS set while still waiting for L4 and L6 to complete
cannot happen since for CS_FL_EOS to be set, the other ones must have been
validated.
Some of these parts will still deserve further cleanup, and some of the
observations above may induce some backports of potential bug fixes once
totally analyzed in their context. The risk of breaking existing stuff
is too high to blindly backport everything.
The subscriber used to be passed as a "void *param" that was systematically
cast to a struct wait_event*. By now it appears clear that the subscribe()
call at every layer is well defined and always takes a pointer to an event
subscriber of type wait_event, so let's enforce this in the functions'
prototypes, remove the intermediary variables used to cast it and clean up
the comments to clarify what all these functions do in their context.
In practice all callers use the same wait_event notification for any I/O
so instead of keeping specific code to handle them separately, let's merge
them and it will allow us to create new events later.
Commit c640ef1a7d ("BUG/MINOR: stream-int: avoid calling rcv_buf() when
splicing is still possible") fixed splicing in TCP and legacy mode but
broke it badly in HTX mode.
What happens in HTX mode is that the channel's to_forward value remains
set to CHN_INFINITE_FORWARD during the whole transfer, and as such it is
not a reliable signal anymore to indicate whether more data are expected
or not. Thus, when data are spliced out of the mux using rcv_pipe(), even
when the end is reached (that only the mux knows about), the call to
rcv_buf() to get the final HTX blocks completing the message were skipped
and there was often no new event to wake this up, resulting in transfer
timeouts at the end of large objects.
All this goes down to the fact that the channel has no more information
about whether it can splice or not despite being the one having to take
the decision to call rcv_pipe() or not. And we cannot afford to call
rcv_buf() inconditionally because, as the commit above showed, this
reduces the forwarding performance by 2 to 3 in TCP and legacy modes
due to data lying in the buffer preventing splicing from being used
later.
The approach taken by this patch consists in offering the muxes the ability
to report a bit more information to the upper layers via the conn_stream.
This information could simply be to indicate that more data are awaited
but the real need being to distinguish splicing and receiving, here
instead we clearly report the mux's willingness to be called for splicing
or not. Hence the flag's name, CS_FL_MAY_SPLICE.
The mux sets this flag when it knows that its buffer is empty and that
data waiting past what is currently known may be spliced, and clears it
when it knows there's no more data or that the caller must fall back to
rcv_buf() instead.
The stream-int code now uses this to determine if splicing may be used
or not instead of looking at the rcv_pipe() callbacks through the whole
chain. And after the rcv_pipe() call, it checks the flag again to decide
whether it may safely skip rcv_buf() or not.
All this bitfield dance remains a bit complex and it starts to appear
obvious that splicing vs reading should be a decision of the mux based
on permission granted by the data layer. This would however increase
the API's complexity but definitely need to be thought about, and should
even significantly simplify the data processing layer.
The way it was integrated in mux-h1 will also result in no more calls
to rcv_pipe() on chunked encoded data, since these ones are currently
disabled at the mux level. However once the issue with chunks+splice
is fixed, it will be important to explicitly check for curr_len|CHNK
to set MAY_SPLICE, so that we don't call rcv_buf() after each chunk.
This fix must be backported to 2.1 and 2.0.
Add a new method, ctl(), to muxes. It uses a "enum mux_ctl_type" to
let it know which information we're asking for, and can output it either
directly by returning the expected value, or by using an optional argument.
"output" argument.
Right now, the only known mux_ctl_type is MUX_STATUS, that will return 0 if
the mux is not ready, or MUX_STATUS_READY if the mux is ready.
We probably want to backport this to 1.9 and 2.0.
In mux_pt_io_cb(), instead of always calling the wake method, only do so
if nobody subscribed for receive. If we have a subscription, just wake the
associated tasklet up.
This should be backported to 1.9 and 2.0.
There's a small window where the mux_pt tasklet may be woken up, and thus
mux_pt_io_cb() get scheduled, and then the connection is attached to a new
stream. If this happen, don't do anything, and just let the stream know
by calling its wake method. If the connection had an error, the stream should
take care of destroying it by calling the detach method.
This should be backported to 2.0 and 1.9.
This reverts commit "BUG/MEDIUM: mux_pt: Make sure we don't have a
conn_stream before freeing.".
mux_pt_io_cb() is only used if we have no associated stream, so we will
never have a cs, so there's no need to check that, and we of course have to
destroy the mux in mux_pt_detach() if we have no associated session, or if
there's an error on the connection.
This should be backported to 2.0 and 1.9.
On error, make sure we don't have a conn_stream before freeing the connection
and the associated mux context. Otherwise a stream will still reference
the connection, and attempt to use it.
If we still have a conn_stream, it will properly be free'd when the detach
method is called, anyway.
This should be backported to 2.0 and 1.9.
In mux_pt_attach(), don't inconditionally call unsubscribe, and only do so
if we were subscribed. The idea was that at this point we would always be
subscribed, as for the mux_pt attach would only be called after at least one
request, after which the mux_pt would have subscribed, but this is wrong.
We can also be called if for some reason the connection failed before the
xprt was created. And with no xprt, attempting to call unsubscribe will
probably lead to a crash.
This should be backported to 2.0.
From this commit, the legacy HTTP mode is now definitely disabled. It is the
first commit of a long series to remove the legacy HTTP code. Now, all HTTP
processing is done using the HTX internal representation. Since the version 2.0,
It is the default mode. So now, it is no more possible to disable the HTX to
fallback on the legacy HTTP mode. If you still use "[no] option http-use-htx", a
warning will be emitted during HAProxy startup. Note the passthough multiplexer
is now only usable for TCP proxies.
Commit 8706c8131 ("BUG/MEDIUM: mux_pt: Always set CS_FL_RCV_MORE.")
was a bit excessive in setting this flag, it refrained from removing
it after read0 unless it was on an empty call. The problem it causes
is that read0 is thus ignored on the first call :
$ strace -tts200 -e trace=recvfrom,epoll_wait,sendto ./haproxy -db -f tcp.cfg
06:34:23.956897 recvfrom(9, "blah\n", 15360, 0, NULL, NULL) = 5
06:34:23.956938 recvfrom(9, "", 15355, 0, NULL, NULL) = 0
06:34:23.956958 recvfrom(9, "", 15355, 0, NULL, NULL) = 0
06:34:23.957033 sendto(8, "blah\n", 5, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 5
06:34:23.957229 epoll_wait(3, [{EPOLLIN|EPOLLHUP|EPOLLRDHUP, {u32=8, u64=8}}], 200, 0) = 1
06:34:23.957297 recvfrom(8, "", 15360, 0, NULL, NULL) = 0
If CO_FL_SOCK_RD_SH is reported by the transport layer, it indicates the
read0 was already seen thus we must not try again and we must immedaitely
report it. The simple fix consists in removing the test on ret==0 :
$ strace -tts200 -e trace=recvfrom,epoll_wait,sendto ./haproxy -db -f tcp.cfg
06:44:21.634835 recvfrom(9, "blah\n", 15360, 0, NULL, NULL) = 5
06:44:21.635020 recvfrom(9, "", 15355, 0, NULL, NULL) = 0
06:44:21.635056 sendto(8, "blah\n", 5, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 5
06:44:21.635269 epoll_wait(3, [{EPOLLIN|EPOLLHUP|EPOLLRDHUP, {u32=8, u64=8}}], 200, 0) = 1
06:44:21.635330 recvfrom(8, "", 15360, 0, NULL, NULL) = 0
The issue is minor, it only results in extra syscalls and CPU usage.
This fix should be backported to 2.0 and 1.9.
It's really confusing to call it a task because it's a tasklet and used
in places where tasks and tasklets are used together. Let's rename it
to tasklet to remove this confusion.
We still have quite a number of build macros which are mapped 1:1 to a
USE_something setting in the makefile but which have a different name.
This patch cleans this up by renaming them to use the USE_something
one, allowing to clean up the makefile and make it more obvious when
reading the code what build option needs to be added.
The following renames were done :
ENABLE_POLL -> USE_POLL
ENABLE_EPOLL -> USE_EPOLL
ENABLE_KQUEUE -> USE_KQUEUE
ENABLE_EVPORTS -> USE_EVPORTS
TPROXY -> USE_TPROXY
NETFILTER -> USE_NETFILTER
NEED_CRYPT_H -> USE_CRYPT_H
CONFIG_HAP_CRYPT -> USE_LIBCRYPT
CONFIG_HAP_NS -> DUSE_NS
CONFIG_HAP_LINUX_SPLICE -> USE_LINUX_SPLICE
CONFIG_HAP_LINUX_TPROXY -> USE_LINUX_TPROXY
CONFIG_HAP_LINUX_VSYSCALL -> USE_LINUX_VSYSCALL
For most of the xprt methods, provide a xprt_ctx. This will be useful later
when we'll want to be able to stack xprts.
The init() method now has to create and provide the said xprt_ctx if needed.
When a mux context is released, we must be sure it exists before dereferencing
it. The bug was introduced in the commit 39a96ee16 ("MEDIUM: muxes: Be prepared
to don't own connection during the release").
No need to backport this patch, expect if the commit 39a96ee16 is backported
too.
This happens during mux upgrades. In such case, when the destroy() callback is
called, the connection points to a different mux's context than the one passed
to the callback. It means the connection is owned by another mux. The old mux is
then released but the connection is not closed.
It is mandatory to handle mux upgrades, because during a mux upgrade, the
connection will be reassigned to another multiplexer. So when the old one is
destroyed, it does not own the connection anymore. Or in other words, conn->ctx
does not point to the old mux's context when its destroy() callback is
called. So we now rely on the multiplexer context do destroy it instead of the
connection.
In addition, h1_release() and h2_release() have also been updated in the same
way.
The mux's callback init() now take a pointer to a buffer as extra argument. It
must be used by the multiplexer as its input buffer. This buffer is always NULL
when a multiplexer is initialized with a fresh connection. But if a mux upgrade
is performed, it may be filled with existing data. Note that, for now, mux
upgrades are not supported. But this commit is mandatory to do so.
For conveniance, in HTTP muxes (h1 and h2), the end of the stream and the end of
the message are reported the same way to the stream, by setting the flag
CS_FL_EOS. In the stream-interface, when CS_FL_EOS is detected, a shutdown for
read is reported on the channel side. This is historical. With the legacy HTTP
layer, because the parsing is done by the stream in HTTP analyzers, the EOS
really means a shutdown for read.
Most of time, for muxes h1 and h2, it works pretty well, especially because the
keep-alive is handled by the muxes. The stream is only used for one
transaction. So mixing EOS and EOM is good enough. But not everytime. For now,
client aborts are only reported if it happens before the end of the request. It
is an error and it is properly handled. But because the EOS was already
reported, client aborts after the end of the request are silently
ignored. Eventually an error can be reported when the response is sent to the
client, if the sending fails. Otherwise, if the server does not reply fast
enough, an error is reported when the server timeout is reached. It is the
expected behaviour, excpect when the option abortonclose is set. In this case,
we must report an error when the client aborts. But as said before, this event
can be ignored. So to be short, for now, the abortonclose is broken.
In fact, it is a design problem and we have to rethink all channel's flags and
probably the conn-stream ones too. It is important to split EOS and EOM to not
loose information anymore. But it is not a small job and the refactoring will be
far from straightforward.
So for now, temporary flags are introduced. When the last read is received, the
flag CS_FL_READ_NULL is set on the conn-stream. This way, we can set the flag
SI_FL_READ_NULL on the stream interface. Both flags are persistant. And to be
sure to wake the stream, the event CF_READ_NULL is reported. So the stream will
always have the chance to handle the last read.
This patch must be backported to 1.9 because it will be used by another patch to
fix the option abortonclose.
With variable connection limits, it's not possible to accurately determine
whether the mux is still in use by comparing usage and max to be equal due
to the fact that one determines the capacity and the other one takes care
of the context. This can cause some connections to be dropped before they
reach their stream ID limit.
It seems it could also cause some connections to be terminated with
streams still alive if the limit was reduced to match the newly computed
avail_streams() value, though this cannot yet happen with existing muxes.
Instead let's switch to usage reports and simply check whether connections
are both unused and available before adding them to the idle list.
This should be backported to 1.9.
We most often store the mux context there but it can also be something
else while setting up the connection. Better call it "ctx" and know
that it's the owner's context than misleadingly call it mux_ctx and
get caught doing suspicious tricks.
The SUB_CAN_SEND/SUB_CAN_RECV enum values have been confusing a few
times, especially when checking them on reading. After some discussion,
it appears that calling them SUB_RETRY_SEND/SUB_RETRY_RECV more
accurately reflects their purpose since these events may only appear
after a first attempt to perform the I/O operation has failed or was
not completed.
In addition the wait_reason field in struct wait_event which carries
them makes one think that a single reason may happen at once while
it is in fact a set of events. Since the struct is called wait_event
it makes sense that this field is called "events" to indicate it's the
list of events we're subscribed to.
Last, the values for SUB_RETRY_RECV/SEND were swapped so that value
1 corresponds to recv and 2 to send, as is done almost everywhere else
in the code an in the shutdown() call.
When count is zero in the function mux_pt_rcv_buf(), it means the channel's
buffer is full. So we need to set the CS_FL_WANT_ROOM on the
conn_stream. Otherwise, while the channel is full, we will try to receive in
loop more data.
Instead of trying to get the session from the connection, which is not
always there, and of course there could be multiple sessions per connection,
provide it with the init() and attach() methods, so that we know the
session for each outgoing stream.
