This function was sometimes used from a channel and sometimes from a buffer.
In both cases it requires knowledge of the size of the output data (to skip
them). Here the split ensures the channel can deal with this point, and that
other places not having output data can continue to work.
Where relevant, the channel version is used instead. The buffer version
was ported to be more generic and now takes a swap buffer and the output
byte count to know where to set the alignment point. The H2 mux still
uses buffer_slow_realign() with buf->o but it will change later.
Passing unsigned ints everywhere is painful, and will cause some headache
later when we'll want to integrate better with struct ist which already
uses size_t. Let's switch buffers to use size_t instead.
If a timeout strikes on the connection side with some active streams,
there is a corner case which can sometimes cause the following sequence
to happen :
- There are active streams but there are data in the mux buffer
(eg: a client suddenly disconnected during a download with pending
requests). The timeout is active.
- The timeout strikes, h2_timeout_task() is called, kills the task and
doesn't close the connection since there are streams left ; The
connection is marked in H2_CS_ERROR ;
- the streams are woken up and closed ;
- when the last stream closes, calling h2_detach(), it sees the
tree list is empty, but there is no condition allowing the
connection to be closed (mbuf->o > 0), thus it does nothing ;
- since the task is dead, there's no more hope to clear this
situation later
For now we can take care of this by adding a test for the presence of
H2_CS_ERROR and !task, implying the timeout task triggered already
and will not be able to handle this again.
Over the long term it seems like a more reliable test on should be
made, so that it is possible to know whether or not someone is still
able to close this connection.
A big thanks to Janusz Dziemidowicz and Milan Petruzelka for providing
many details helping in figuring this bug.
We currently don't process trailers on H2, but this has an impact : on
chunked HTTP/1 responses, we decide to emit the ES bit once we see the
0CRLF. From this point the stream switches to the CLOSED state, which
aborts processing of the remaining bytes. Thus the extra CRLF which ends
trailers is not processed and remains in the buffer. This prevents the
stream from being notified about end of transmission, which in turn keeps
the mux busy and prevents the connection from quitting.
The case of the trailers is not the root cause of this issue, though it
is what triggers it. The root cause is that upon error and/or close, once
we know we're not going to process any more data, we must absolutely flush
any remaining bytes from the output buffer, otherwise there is no way the
stream can quit. This is what this patch does.
It looks very likely related to the issues reported and debugged by
Janusz Dziemidowicz and Milan Petruzelka.
One way to reproduce it is to chain two proxies with the last one emitting
chunked data (typically using the stats page) :
global
stats socket /tmp/sock1 mode 666 level admin
stats timeout 1h
tune.ssl.default-dh-param 1024
tune.bufsize 16384
defaults
mode http
timeout connect 4s
timeout client 10s
timeout server 20s
listen px1
bind :4443 ssl crt rsa+dh2048.pem npn h2 alpn h2
server s1 127.0.0.1:4445
listen px2
bind :4444 ssl crt rsa+dh2048.pem npn h2 alpn h2
bind :4445
stats uri /
Then use curl to fetch the stats through px1 :
curl --http2 -k "https://127.0.0.1:4443/"
When curl is sent to the first one, "show sess" issued to the CLI will
show a remaining session during the client timeout. When curl is aimed at
port 4444 (px2), there is no such remaining session.
This fix needs to be backported to 1.8.
The streams bookkeeping made in H2 is used for protocol compliance only
but it doesn't consider the number of conn_streams still attached to the
mux. It causes an issue when http-request set-nice rules are applied on
H2 requests processed on a saturated machine. Indeed, in this case, the
requests are accepted and assigned a default nice value of zero. When
they are processed, their nice value changes to a higher one (say 1024).
The response is sent through the H2 mux, which detects the end of stream
and decrements the protocol-level stream count (h2c->nb_streams). The
client may then send a new request. But the conn_stream is still attached
and will require a new call to process_stream() to finish, which is made
through the scheduler. Given that the machine is saturated, it is assumed
that many tasks are present in the scheduler. Thus the closing tasks holding
a higher nice value will pass after the new stream creations. If the client
is fast enough with a low latency link, it may add a lot of new stream
creations before the stream terminations have a chance to disappear due
to their high nice value, resulting in a huge amount of memory being used.
The solution consists in letting a mux always monitor its conn_streams and
refrain from creating new ones when it is full. Here the H2 mux checks the
nb_cs counter and sets a new blocked flag (H2_CF_DEM_TOOMANY) if the limit
was reached, so that the frame parser requests a pause in the new stream
creation, leaving some time for the pending conn_streams to vanish.
Several experiments were made using varying thresholds to see if
overbooking would provide any benefit here but it turned out not to be
the case, so the conn_stream limit remains set to the exact streams
limit. Interestingly various performance measurements showed that the
code tends to be slightly faster now than without the limit, probably
due to the smoother memory usage.
This commit requires previous patch ("MINOR: h2: keep a count of the number
of conn_streams attached to the mux"). It needs to be backported to 1.8.
The h2 mux only knows about the number of H2 streams which are not in a
CLOSED state. This is used for protocol compliance. But it doesn't hold
the number of really attached streams. It is a problem because depending
on scheduling, it is possible that more streams are attached to the mux
than the ones seen at the protocol level, due to some streams taking some
time to be detached. Let's add this count based on the conn_streams.
Note: this patch is part of a series of fixes which will have to be
backported to 1.8.
There's no real reason to have a specific scheduler for applets anymore, so
nuke it and just use tasks. This comes with some benefits, the first one
being that applets cannot induce high latencies anymore since they share
nice values with other tasks. Later it will be possible to configure the
applets' nice value. The second benefit is that the applet scheduler was
not very thread-friendly, having a big lock around it in prevision of this
change. Thus applet-intensive workloads should now scale much better with
threads.
Some more improvement is possible now : some applets also use a task to
handle timers and timeouts. These ones could now be simplified to use only
one task.
In preparation for thread-specific runqueues, change the task API so that
the callback takes 3 arguments, the task itself, the context, and the state,
those were retrieved from the task before. This will allow these elements to
change atomically in the scheduler while the application uses the copied
value, and even to have NULL tasks later.
Upload requests not carrying a content-length nor tunnelling data must
be sent chunked-encoded over HTTP/1. The code was planned but for some
reason forgotten during the implementation, leading to such payloads to
be sent as tunnelled data.
Browsers always emit a content length in uploads so this problem doesn't
happen for most sites. However some applications may send data frames
after a request without indicating it earlier.
The only way to detect that a client will need to send data is that the
HEADERS frame doesn't hold the ES bit. In this case it's wise to look
for the content-length header. If it's not there, either we're in tunnel
(CONNECT method) or chunked-encoding (other methods).
This patch implements this.
The following request is sent using content-length :
curl --http2 -sk https://127.0.0.1:4443/s2 -XPOST -T /large/file
and these ones using chunked-encoding :
curl --http2 -sk https://127.0.0.1:4443/s2 -XPUT -T /large/file
curl --http2 -sk https://127.0.0.1:4443/s2 -XPUT -T - < /dev/urandom
Thanks to Robert Samuel Newson for raising this issue with details.
This fix must be backported to 1.8.
We'll need this in order to support uploading chunks. The h2 to h1
converter checks for the presence of the content-length header field
as well as the CONNECT method and returns these information to the
caller. The caller indicates whether or not a body is detected for
the message (presence of END_STREAM or not). No transfer-encoding
header is emitted yet.
The incoming H2 frame length was checked against the max_frame_size
setting instead of being checked against the bufsize. The max_frame_size
only applies to outgoing traffic and not to incoming one, so if a large
enough frame size is advertised in the SETTINGS frame, a wrapped frame
will be defragmented into a temporary allocated buffer where the second
fragment my overflow the heap by up to 16 kB.
It is very unlikely that this can be exploited for code execution given
that buffers are very short lived and their address not realistically
predictable in production, but the likeliness of an immediate crash is
absolutely certain.
This fix must be backported to 1.8.
Many thanks to Jordan Zebor from F5 Networks for reporting this issue
in a responsible way.
When a stream blocks on a mux buffer full/unallocated or on connection
flow control, a flag among H2_SF_MUX_M* is set, but the stream is not
always added to the connection's list. It's properly done when the
operations are performed from the connection handler but not always when
done from the stream handler. For instance, a simple shutr or shutw may
fail by lack of room. If it's immediately followed by a call to h2_detach(),
the stream remains lying around in no list at all, and prevents the
connection from ending. This problem is actually quite difficult to
trigger and seems to require some large objects and low server-side
timeouts.
This patch covers all identified paths. Some are redundant but since the
code will change and will be simplified in 1.9, it's better to stay on
the safe side here for now. It must be backported to 1.8.
Commit e3f36cd ("MINOR: h2: implement a basic "show_fd" function")
accidently brought one surrounding debugging part that was in the same
context. No backport needed.
The purpose here is to dump some information regarding an H2 connection,
and a few statistics about its streams. The output looks like this :
35 : st=0x55(R:PrA W:PrA) ev=0x00(heopi) [lc] cache=0 owner=0x7ff49ee15e80 iocb=0x588a61(conn_fd_handler) tmask=0x1 umask=0x0 cflg=0x00201366 fe=decrypt mux=H2 mux_ctx=0x7ff49ee16f30 st0=2 flg=0x00000002 fctl_cnt=0 send_cnt=33 tree_cnt=33 orph_cnt=0
- st0 is the connection's state (FRAME_H here)
- flg is the connection's flags (MUX_MFULL here)
- fctl_cnt is the number of streams in the fctl_list
- send_cnt is the number of streams in the send_list
- tree_cnt is the number of streams in the streams_by_id tree
- orph_cnt is the number of orphaned streams (cs==0) in the tree
Interrupting an h2load test shows that some connections remain active till
the client timeout. This is due to the fact that h2_detach() immediately
returns if the h2s flags indicate that the h2s is still waiting for some
buffer room in the output mux (possibly to emit a response or to send some
window updates). If the connection is broken, these data will never leave
and must not prevent the stream from being terminated nor the connection
from being released.
This fix must be backported to 1.8.
Currently, h2_release() will release all resources assigned to the h2
connection, including the timeout task if any. But since the multi-threaded
scheduler, the timeout task could very well be queued in the thread-local
list of running tasks without any way to remove it, so task_delete() will
have no effect and task_free() will cause this undefined object to be
dereferenced.
In order to prevent this from happening, we never release the task in
h2_release(), instead we wake it up after marking its context NULL so that
the task handler can release the task.
Future improvements could consist in modifying the scheduler so that a
task_wakeup() has to be done on any task having to be killed, letting
the scheduler take care of it.
This fix must be backported to 1.8. This bug was apparently not reported
so far.
Since these two functions are always used together, let's simplify
the code by having a single one for both operations. It also ensures
we don't leave wandering elements that risk to leak later.
The code is safer and more robust this way, it avoids multiple paths.
This is possible due to the idempotence of LIST_DEL() and eb32_delete()
that are called in h2s_detach().
Several people reported very strange occasional crashes when using H2.
Every time it appeared that either an h2s or a task was corrupted. The
outcome is that a missing LIST_DEL() when removing an orphaned stream
from the list in h2_wake_some_streams() can cause this stream to
remain present in the send list after it was freed. This may happen
when receiving a GOAWAY frame for example. In the mean time the send
list may be processed due to pending streams, and the just released
stream is still found. If due to a buffer full condition we left the
h2_process_demux() loop before being able to process the pending
stream, the pool entry may be reassigned somewhere else. Either another
h2 connection will get it, or a task, since they are the same size and
are shared. Then upon next pass in h2_process_mux(), the stream is
processed again. Either it crashes here due to modifications, or the
contents are harmless to it and its last changes affect the other object
reasigned to this area (typically a struct task). In the case of a
collision with struct task, the LIST_DEL operation performed on h2s
corrupts the task's wait queue's leaf_p pointer, thus all the wait
queue's structure.
The fix consists in always performing the LIST_DEL in h2s_detach().
It will also make h2s_stream_new() more robust against a possible
future situation where stream_create_from_cs() could have sent data
before failing.
Many thanks to all the reporters who provided extremely valuable
information, traces and/or cores, namely Thierry Fournier, Yves Lafon,
Holger Amann, Peter Lindegaard Hansen, and discourse user "slawekc".
This fix must be backported to 1.8. It is probably better to also
backport the following code cleanups with it as well to limit the
divergence between master and 1.8-stable :
00dd078 CLEANUP: h2: rename misleading h2c_stream_close() to h2s_close()
0a10de6 MINOR: h2: provide and use h2s_detach() and h2s_free()
There are some corner cases where this could happen by accident. Since
the spec explicitly forbids this (RFC7540#5.4.2), let's add a test in
the two only functions which make the RST to avoid this. Thanks to user
klzgrad for reporting this problem. Usually it is expected to be harmless
but may result in browsers issuing a warning.
This fix must be backported to 1.8.
Recent fixes made to process partial frames broke the flow control on
DATA frames, as the padding is not considered anymore, only the actual
data is. Let's simply take account of the padding once the transfer
ends. The probability to meet this bug is low because, when used, padding
is small and it can require a large number of padded transfers before the
window is completely depleted.
Thanks to user klzgrad for reporting this bug and confirming the fix.
This fix must be backported to 1.8.
Right now the h2 idle timeout is only set when there is no stream. If we
fail to send because the socket buffers are full (generally indicating
the client has left), we also need to arm it so that we can properly
expire such connections, otherwise some failed transfers might leave
H2 connections pending forever.
Thanks to Thierry Fournier for the diag and the traces.
This patch needs to be backported to 1.8.
We used to have one buffer allocator per direction while we can never
block on two buffers at once. Let's have a single one and rely on the
connection's flags to know which one we're waitinf for.
This function takes an h2c and an h2s but it never uses the h2c, which
is a bit confusing at some places in the code. Let's make it clear that
it only operates on the h2s instead by renaming it and removing the
unused h2c argument.
In case a stream tries to emit more data than advertised by the chunks
or content-length headers, the extra data remains in the channel's output
buffer until the channel's timeout expires. It can easily happen when
sending malformed error files making use of a wrong content-length or
having extra CRLFs after the empty chunk. It may also be possible to
forge such a bad response using Lua.
The H1 to H2 encoder must protect itself against this by marking the data
presented to it as consumed if it decides to discard them, so that the
sending stream doesn't wait for the timeout to trigger.
The visible effect of this problem is a huge memory usage and a high
concurrent connection count during benchmarks when using such bad data
(a typical place where this easily happens).
This fix must be backported to 1.8.
In h2_get_dbuf, when the buffer allocation was failing, dbuf_wait.target was
errornously set to the connection (h2c->conn) instead of the h2 connection
descriptor (h2c).
This patch must be backported to 1.8.
This removes the unused next_header_block and try_again labels
from mux_h2.c.
try_again is unused as of a76e4c21839cafd036fbe755416569206502c1d9,
which first appeared in haproxy 1.8.0.
next_header_block is unused as of 872855998bd03d5224e0e5cd6aef9b91e2a6de1d,
which was backported to haproxy 1.8.0 as
59fcb216085a7aa9744cffe39567c80de4ebd6bf.
Instead of looking for CO_FL_EARLY_DATA to know if we have to try to wake
up a stream, because it is waiting for a SSL handshake, instead add a new
conn_stream flag, CS_FL_WAIT_FOR_HS. This way we don't have to rely on
CO_FL_EARLY_DATA, and we will only wake streams that are actually waiting.
Peter Lindegaard Hansen reported a problem affecting some POST requests
sent by MSIE on 1.8.3. Lukas found that we incorrectly dealt with the
END_STREAM flag on empty DATA frames.
What happens in fact is that while we correctly report that we've read a
zero-byte frame, since commit 8fc016d ("BUG/MEDIUM: h2: support uploading
partial DATA frames") backported into 1.8.2, we've been able to return
without updating the parser's state nor checking the frame flags in this
case.
The fix is trival, we just need not to return too early.
This fix must be backported to 1.8.
During a reload operation, instead of keeping the H2 connections opened
forever causing confusion during configuration changes, let's send a
graceful shutdown so that the client knows that it would better open a
new connection for future requests. We can't really catch the signal
from H2, but we can advertise this graceful shutdown upon the next I/O
event (eg: a WINDOW_UPDATE from the client or a new request). One of
the visible effect is that the old process quits much faster.
This patch should be backported to 1.8 since it is affected by this
problem.
The recent patch introducing the H2_CS_FRAME_E state to emit stream
resets was not totally correct in that in the rare case where there is
no room left to emit the reset, the next call to process it later could
use an uninitialized stream. This only affects responses to frames that
are sent on closed streams though.
This fix must be backported to 1.8.
The h2spec utility found certain situations where we're returning an
RST_STREAM while a GOAWAY is expected. While we can't always reliably
decide which one to use (eg: after a stream has been closed for a long
time), in practice we often still have the stream available until it's
destroyed at the application level. This provides the flags we need to
verify the conditions that led to its closure, namely if RST was sent
or received, or if it was regularly closed using a double ES.
The first step consists in marking all closed streams as having already
sent an RST_STREAM frame. This will ensure that we can send an RST_STREAM
for a late transmission on a stream we have forgotten about instead of
risking to break the connection. The next steps consist in re-arranging
the H2_SS_CLOSED checks so that we can deliver a GOAWAY frame for the
few cases where an unexpected frame was received after a double ES.
By carefully taking care of these specificities, we can reduce by 4 the
number of remaining compliance issues.
Note: some tests start to become a bit long and to be repeated at various
places. Probably that adding a bitmask of allowed/forbidden frame types
per state and/or per situation could significantly help. It's likely
that some deeper tests in the frame handlers could also be removed now
as they can't be triggered anymore.
This fix should be backported to 1.8.
Some stream errors applied to half-closed and closed streams are not
properly reported, especially after the stream transistions to the
closed state. The reason is that the code checks for this "error"
stream state in order to send an RST frame. But if the stream was
just closed or was already closed, there's no way to validate this
condition, and the error is never reported to the peer.
In order to address this situation, we'll add a new FRAME_E demux state
which indicates that the previously parsed frame triggered a stream error
of type STREAM CLOSED that needs to be reported. Proceeding like this
will ensure that we don't lose that information even if we can't
immediately send the message. It also removes the confusion where FRAME_A
could be used either for ACKs or for RST.
The state transition has been added after every h2s_error() on the demux
path. It seems that we might need to have two distinct h2s_error()
functions, one for the mux and another one for the demux, though it
would provide little benefit. It also becomes more apparent that the
H2_SS_ERROR state is only used to detect the need to report an error
on the mux direction. Maybe this will have to be revisited later.
This simple change managed to eliminate 5 bugs reported by h2spec.
This fix must be backported to 1.8.
This new field will be used to describe certain properties of some
muxes. For now we only add MX_FL_CLEAN_ABRT to indicate that a mux
is able to unambiguously report aborts using CS_FL_ERROR contrary
to others who may only report it via a read0. This will be used to
improve handling of the abortonclose option with H2. Other flags
may come later to report multiplexing capabilities or not, support
of client/server sides etc.
Commit 4974561 ("BUG/MEDIUM: h2: enforce the per-connection stream limit")
implemented a stream limit enforcement on the connection but it was not
correctly done as it would count streams still known by the connection,
which includes the lingering ones that are already marked close. We need
to count only the non-closed ones, which this patch does. The effect is
that some streams are rejected a bit before the limit.
This fix needs to be backported to 1.8.
Tunnelled responses are those without a content-length nor a chunked
encoding. They are specially dealt with in the current code but the
behaviour is not correct. The fact that the chunk size is left to zero
with a state artificially set to CHUNK_SIZE validates the test on
whether or not to set the end of stream flag. Thus the first DATA
frame always carries the ES flag and subsequent ones remain blocked.
This patch fixes it in two ways :
- update h1m->curr_len to the size of the current buffer so that it
is properly subtracted later to find the real end ;
- don't set the state to CHUNK_SIZE when there's no content-length
and instead set it to CHUNK_SIZE only when there's chunking.
This fix needs to be backported to 1.8.
We used to switch the stream's state to HREM when seeing and ES bit on
the DATA frame before actually being able to process that frame, possibly
resulting in the DATA frame being processed after the stream was seen as
half-closed and possibly being rejected. The state must not change before
the frame is really processed.
Also fixes a harmless typo in the flag name which should have DATA and
not HEADERS in its name (but all values are equal).
Must be backported to 1.8.
Since last commit it's not required that the DATA frames are complete anymore
so better start with what we have. Only the HEADERS frame requires this. This
may be backported as part of the upload fixes.
We currently have a problem with DATA frames when they don't fit into
the destination buffer. While it was imagined that in theory this never
happens, in practice it does when "option http-buffer-request" is set,
because the headers don't leave the target buffer before trying to read
so if the frame is full, there's never enough room.
This fix consists in reading what can be read from the frame and advancing
the input buffer. Once the contents left are only the padding, the frame
is completely processed. This also solves another problem we had which is
that it was possible to fill a request buffer beyond its reserve because
the <count> argument was not respected in h2_rcv_buf(). Thus it's possible
that some POST requests sent at once with a headers+body filling exactly a
buffer could result in "400 bad req" when trying to add headers.
This fix must be backported to 1.8.
We'll try to process partial frames and for this we need to know the
padding length. The first step requires to extract it during the parsing
and store it in the demux context in the connection. Till now it was only
processed at once.
Even after previous commit ("BUG/MEDIUM: h2: work around a connection
API limitation") there is still a problem with some requests. Sometimes
when polling for more request data while some pending data lies in the
buffer, there's no way to enter h2_recv() because the FD is not marked
ready for reading.
We need to slightly change the approach and make h2_recv() only receive
from the buffer and h2_wake() always attempt to demux if the demux is not
blocked.
However, if the connection is already being polled for reading, it will
not wake up from polling. For this reason we need to cheat and also
pretend a request for sending data, which ensures that as soon as any
direction may move, we can continue to demux. This shows that in the
long term we probably need a better way to resume an interrupted
operation at the mux level.
With this fix, no more hangups happen during uploads. Note that this
time the setup required to provoke the hangups was a bit complex :
- client is "curl" running on local host, uploading 1.7 MB of
data via haproxy
- haproxy running on local host, forwarding to a remote server
through a 100 Mbps only switch
- timeouts disabled on haproxy
- remote server made of thttpd executing a cgi reading request data
through "dd bs=10" to slow down everything.
With such a setup, around 3-5% of the connections would hang up.
This fix needs to be backported to 1.8.
The connection API permits us to enable or disable receiving on a
connection. The underlying FD layer arranges this with the polling
and the fd cache. In practice, if receiving was allowed and an end
of buffer was reached, the FD is subscribed to the polling. If later
we want to process pending data from the buffer, we have to enable
receiving again, but since it's already enabled (in polled mode),
nothing happens and the pending data remain stuck until a new event
happens on the connection to wake the FD up. This is a limitation of
the internal connection API which is not very friendly to the new mux
architecture.
The visible effect is that certain uploads to slow servers experience
truncation on timeout on their last blocks because nothing new comes
from the connection to wake it up while it's being polled.
In order to work around this, there are two solutions :
- either cheat on the connection so that conn_update_xprt_polling()
always performs a call to fd_may_recv() after fd_want_recv(), that
we can trigger from the mux by always calling conn_xprt_stop_recv()
before conn_xprt_want_recv(), but that's a bit tricky and may have
side effects on other parts (eg: SSL)
- or we refrain from receiving in the mux as soon as we're busy on
anything else, regardless of whether or not some room is available
in the receive buffer.
This patch takes the second approach above. This way once we read some
data, as soon as we detect that we're stuck, we immediately stop receiving.
This ensures the event doesn't go into polled mode for this period and
that as soon as we're unstuck we can continue. In fact this guarantees
that we can only wait on one side of the mux for a given direction. A
future improvement of the connection layer should make it possible to
resume processing of an interrupted receive operation.
This fix must be backported to 1.8.
In order to allow demuxing when the dmux buffer is full, we need to
enable data receipt in multiple conditions. Since the conditions are a
bit complex, they have been delegated to a new function h2_recv_allowed()
which follows these rules :
- if an error or a shutdown was detected on the connection and the buffer
is empty, we must not attempt to receive
- if the demux buf failed to be allocated, we must not try to receive and
we know there is nothing pending
- if the buffer is not full, we may attempt to receive
- if no flag indicates a blocking condition, we may attempt to receive
- otherwise must may not attempt
No more truncated payloads are detected in tests anymore, which seems to
indicate that the issue was worked around. A better connection API will
have to be created for new versions to make this stuff simpler and more
intuitive.
This fix needs to be backported to 1.8 along with the rest of the patches
related to CS_FL_RCV_MORE.
If we can't demux pending data due to a stream buffer full condition, we
now set CS_FL_RCV_MORE on the conn_stream so that the stream layer knows
it must call back as soon as possible to restart demuxing. Without this,
some uploaded payloads are truncated if the server does not consume them
fast enough and buffers fill up.
Note that this is still not enough to solve the problem, some changes are
required on the recv() and update_poll() paths to allow to restart reading
even with a buffer full condition.
This patch must be backported to 1.8.
