[Qemu-devel] [PATCH] io: fix decoding when multiple websockets frames arrive at once

[Qemu-devel] [PATCH] io: fix decoding when multiple websockets frames arrive at once

[Daniel P. Berrange]

The qio_channel_websock_read_wire() method will read upto 4096
bytes off the socket and then decode the websockets header and
payload. The code was only decoding a single websockets frame,
even if the buffered data contained multiple frames. This meant
that decoding of subsequent frames was delayed until further
input arrived on the socket. This backlog of delayed frames
gets worse & worse over time.

Symptom was that when connecting to the VNC server via the
built-in websockets server, mouse/keyboard interaction would
start out fine, but slowly get more & more delayed until it
was unusable.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 io/channel-websock.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/io/channel-websock.c b/io/channel-websock.c
index e47279a..a06a4a8 100644
--- a/io/channel-websock.c
+++ b/io/channel-websock.c
@@ -570,21 +570,24 @@ static ssize_t qio_channel_websock_read_wire(QIOChannelWebsock *ioc,
         ioc->encinput.offset += ret;
     }
 
-    if (ioc->payload_remain == 0) {
-        ret = qio_channel_websock_decode_header(ioc, errp);
+    while (ioc->encinput.offset != 0) {
+        if (ioc->payload_remain == 0) {
+            ret = qio_channel_websock_decode_header(ioc, errp);
+            if (ret < 0) {
+                return ret;
+            }
+            if (ret == 0) {
+                ioc->io_eof = TRUE;
+                break;
+            }
+        }
+
+        ret = qio_channel_websock_decode_payload(ioc, errp);
         if (ret < 0) {
             return ret;
         }
-        if (ret == 0) {
-            return 0;
-        }
     }
-
-    ret = qio_channel_websock_decode_payload(ioc, errp);
-    if (ret < 0) {
-        return ret;
-    }
-    return ret;
+    return 1;
 }
 
 
@@ -642,9 +645,6 @@ static gboolean qio_channel_websock_flush(QIOChannel *ioc,
         if (ret < 0) {
             goto cleanup;
         }
-        if (ret == 0) {
-            wioc->io_eof = TRUE;
-        }
     }
 
  cleanup:
-- 
2.9.3

Re: [Qemu-devel] [PATCH] io: fix decoding when multiple websockets frames arrive at once

[Eric Blake]

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On 01/30/2017 04:51 AM, Daniel P. Berrange wrote:
> The qio_channel_websock_read_wire() method will read upto 4096

s/upto/up to/

> bytes off the socket and then decode the websockets header and
> payload. The code was only decoding a single websockets frame,
> even if the buffered data contained multiple frames. This meant
> that decoding of subsequent frames was delayed until further
> input arrived on the socket. This backlog of delayed frames
> gets worse & worse over time.
> 
> Symptom was that when connecting to the VNC server via the
> built-in websockets server, mouse/keyboard interaction would
> start out fine, but slowly get more & more delayed until it
> was unusable.
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  io/channel-websock.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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