#2116: Application layer protocol for transfering RPC messages + utf8
decoding
error
-------------------+--------------------------------------------------------
Reporter: bro | Owner:
Type: patch | Status: new
Priority: major | Milestone: Future
Component: other | Version: 1.3.5
Keywords: |
-------------------+--------------------------------------------------------
== Introduction ==
After upgrading my FreeBSD server I suddenly had problems getting the GTK
client to show the torrent list (as well as the states and trackers info
to the left.). The CLI client wouldn't show the torrents with the ''info''
command. It was pretty much the same symptoms as these bug reports:
http://dev.deluge-torrent.org/ticket/1531 http://dev.deluge-
torrent.org/ticket/2095 which I presume have encountered the same bug.
Some that reported this problem in the bug reports have a lot of torrents
(many hundreds), and I have about 1600 myself, so it looked like this
would be a problem only for those with a lot of torrents.
What happens is that the client can see the daemon being online, but when
connecting, it will fail to populate the torrent list.
''If'' the torrent list is successfully populated, it continues to work
with no problems.
After a lot of testing, expecting it was a problem with corruption of the
state files, I eventually found the cause, which of course, had nothing to
do with the state files ;-)
The problem actually turned out to be twofold.
== Problem one - Application layer protocol for transferring data ==
The first problem has to do with the application layer protocol, or the
lack of such a protocol when it comes to transferring the data over the
network. When RPC commands are sent over the network, they're usually
successfully decompressed by ''zlib'' on the receiver, but not always.
When transferring one command (say 20 bytes), with a big enough delay
until the next command is sent, the 20 bytes are received on the other
side, and the data is decompressed and decoded (by rencode).
When transferring multiple messages within a short time period, these
messages might be received as ''one'' on the other side. So when
transferring two messages at the same time, one of 20 bytes, and one of 40
bytes, the receiver might receive 60 bytes, and has no idea that it's
actually two messages.
The current protocol trusts that the ''zlib'' library will successfully
decompress compressed messages that are concatenated by TCP when
transfered. Usually it will successfully decompress the first message, but
subsequent messages aren't successfully decompressed as far as I've been
able to test.
Most messages are received separately, so that is why this bug shows it's
ugly face only in rare cases.
The '''big''' problem is that in some cases, the torrent list being
transferred isn't successfully decompressed, and thereby lost to the
client.
The current deluge protocol will add newly received data onto the current
buffer of old (but not successfully decompressed) data and then it tries
to decompress the whole buffer. If this fails it will wait for more data.
What happens when the torrent list is never populated, is that it fails to
decompress the data in the buffer even after the whole torrent list has
been transferred. The result is that it just keeps appending incoming data
onto the buffer which results in no messages being received at all.
I'm not sure if this is because the torrent list is received as the second
message (i.e. it has been concatenated onto the data of another message on
arrival), or if there is another reason the torrent list message fails to
be decompressed.
As far as I can see, the only way to solve this is to use an application
layer protocol that knows how to separate messages.
== Problem two - Decoding error with rencode ==
After implementing a simple application layer protocol it turned out the
torrent list still wouldn't load, because the ''rencode'' library fails to
decode the transferred data with a
{{{
UnicodeDecodeError: 'utf8' codec can't decode byte 0xe8 in position 54:
invalid continuation byte
}}}
This problem was easily fixed by replacing ''rencode'' with
[http://docs.python.org/library/pickle.html ''pickle''].
Other advantages of ''pickle'' (or more precisely cPickle) compared to
''rencode'' is especially speed, but also size (somewhat):
{{{
~/test$ ./pickle_test.py
Data size: 5125267 bytes
pickle dumps time: 0:00:00.939099
pickle dump size: 3470949
cPickle dumps time: 0:00:00.203606
cPickle dump size: 3426268
rencode dumps time: 0:00:00.448616
rencode dymp size: 4033409
pickle loads time: 0:00:00.673550
cPickle loads time: 0:00:00.162311
rencode loads time: 0:00:00.690657
}}}
These are test results from the actual data of the torrent list
transferred from my server (1600 torrents).
== Patch ==
I've implemented a class ''!DelugeTransferProtocol'' which fixes the
issues I had, though I cant guarantee that it fixes the issues others have
reported, or that it doesn't introduce other bugs ;-)
This patch will render the client unable to communicate with any unpatched
daemons.
I've also implemented tests to verify sending and receiving of messages
through the transfer protocol.
> kunjungi sayank
>
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> long life
>
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