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io: simplify websocket ping reply handling

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We must ensure we don't get flooded with ping replies if the outbound
channel is slow. Currently we do this by keeping the ping reply in a
separate temporary buffer and only writing it if the encoutput buffer
is completely empty. This is overly pessimistic, as it is reasonable
to add a ping reply to the encoutput buffer even if it has previous
data in it, as long as that previous data doesn't include a ping
reply.

To track this better, put the ping reply directly into the encoutput
buffer, and then record the size of encoutput at this time in
pong_remain. As we write encoutput to the underlying channel, we
can decrement the pong_remain counter. Once it hits zero, we can
accept further ping replies for transmission.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrange 2017-10-09 15:34:06 +01:00
parent a7b20a8efa
commit 57b0cdf152
2 changed files with 16 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/io/channel-websock.h
View File

@ -60,8 +60,8 @@ struct QIOChannelWebsock {
Buffer encoutput;
Buffer rawinput;
Buffer rawoutput;
Buffer ping_reply;
size_t payload_remain;
size_t pong_remain;
QIOChannelWebsockMask mask;
guint io_tag;
Error *io_err;

28
io/channel-websock.c
View File

@ -825,11 +825,14 @@ static int qio_channel_websock_decode_payload(QIOChannelWebsock *ioc,
}
return -1;
} else if (ioc->opcode == QIO_CHANNEL_WEBSOCK_OPCODE_PING) {
/* ping frames produce an immediate reply */
buffer_reset(&ioc->ping_reply);
qio_channel_websock_encode_buffer(
ioc, &ioc->ping_reply, QIO_CHANNEL_WEBSOCK_OPCODE_PONG,
&ioc->encinput);
/* ping frames produce an immediate reply, as long as we've not still
* got a previous pong queued, in which case we drop the new pong */
if (ioc->pong_remain == 0) {
qio_channel_websock_encode_buffer(
ioc, &ioc->encoutput, QIO_CHANNEL_WEBSOCK_OPCODE_PONG,
&ioc->encinput);
ioc->pong_remain = ioc->encoutput.offset;
}
} /* pong frames are ignored */
if (payload_len) {
@ -888,7 +891,6 @@ static void qio_channel_websock_finalize(Object *obj)
buffer_free(&ioc->encoutput);
buffer_free(&ioc->rawinput);
buffer_free(&ioc->rawoutput);
buffer_free(&ioc->ping_reply);
object_unref(OBJECT(ioc->master));
if (ioc->io_tag) {
g_source_remove(ioc->io_tag);
@ -946,12 +948,7 @@ static ssize_t qio_channel_websock_write_wire(QIOChannelWebsock *ioc,
ssize_t ret;
ssize_t done = 0;
/* ping replies take priority over binary data */
if (!ioc->ping_reply.offset) {
qio_channel_websock_encode(ioc);
} else if (!ioc->encoutput.offset) {
buffer_move_empty(&ioc->encoutput, &ioc->ping_reply);
}
qio_channel_websock_encode(ioc);
while (ioc->encoutput.offset > 0) {
ret = qio_channel_write(ioc->master,
@ -968,6 +965,11 @@ static ssize_t qio_channel_websock_write_wire(QIOChannelWebsock *ioc,
}
buffer_advance(&ioc->encoutput, ret);
done += ret;
if (ioc->pong_remain < ret) {
ioc->pong_remain = 0;
} else {
ioc->pong_remain -= ret;
}
}
return done;
}
@ -1026,7 +1028,7 @@ static void qio_channel_websock_set_watch(QIOChannelWebsock *ioc)
return;
}
if (ioc->encoutput.offset || ioc->ping_reply.offset) {
if (ioc->encoutput.offset) {
cond |= G_IO_OUT;
}
if (ioc->encinput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER &&