Ryosuke Kanda created SSHD-1287:
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Summary: Use the maximum packet size of the communication partner
Key: SSHD-1287
URL: https://issues.apache.org/jira/browse/SSHD-1287
Project: MINA SSHD
Issue Type: Bug
Affects Versions: 2.8.0
Reporter: Ryosuke Kanda
Attachments: ClientMain.java, ConsoleLog, ServerMain.java
It appears that SSHD may use the maximum packet size presented by the
communicating party to request reception.
RFC 4254 contains the following statement, where "maximum packet size" can be
read as "the maximum packet size that the sender is willing to accept" (as in
"initial window size").
{code:java}
Section 5.1 Opening a Channel
The 'maximum packet size' specifies the maximum size of
2an individual data packet that can be sent to the sender.{code}
The client/server must comply with its own declared maximum packet size.
I encountered this issue when I was using "freeSSHd" as an SFTP server.
The version of freeSSHd is 1.3.1.
The event is confirmed by creating a server with SSHD.
Attached are the client and server sources, as well as the client debug logs
(up to the first read request).
When communicating with these, the client knows that its maximum packet size is
"32768" and the server's maximum packet size is "65536".
{code:java}
// client window
[main] DEBUG org.apache.sshd.common.channel.Window -
init(Window[client/local](SftpChannelSubsystem[id=0,
recipient=-1]-ClientSessionImpl[user@localhost/127.0.0.1:10022][sftp]))
size=2097152, max=2097152, packet=32768
// server window
[sshd-SshClient[5702b3b1]-nio2-thread-3] DEBUG
org.apache.sshd.common.channel.Window -
init(Window[client/remote](SftpChannelSubsystem[id=0,
recipient=0]-ClientSessionImpl[user@localhost/127.0.0.1:10022][sftp]))
size=2097152, max=2097152, packet=65536 {code}
And when requesting to receive a file, it requests to read 65536 bytes at a
time. This means that it attempts to receive packets that exceed 32768 bytes.
{code:java}
[main] TRACE org.apache.sshd.sftp.client.impl.SftpInputStreamAsync -
sendRequests(SftpInputStreamAsync[ClientSessionImpl[user@localhost/127.0.0.1:10022]][/data4M.txt])
enqueue pending ack: SftpAckData[id=103, offset=0, length=65536] {code}
I hope this report is helpful.
I am doing machine translation, so please allow it to be unnatural.
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