Re: Computing window sizes and adjustments

On Tue, 17 Jul 2007, JCA wrote:

> On 7/16/07, Damien Miller <djm@mindrot.org> wrote:
>
> > OpenSSH counts the data sent over a channel against the window, not
> > including the protocol-level framing used to send it.
>
> Thanks for the feedback. Let me see if I can pin things down.
>
> The structure of an SSHv2 packet is laid down in section 6 of RFC 4253:
>
> uint32 packet_length
> byte padding_length
> byte[n1] payload; n1 = packet_length - padding_length - 1
> byte[n2] random padding; n2 = padding_length
> byte[m] mac (Message Authentication Code - MAC); m = mac_length

This isn't included

> If I understand you correctly, the only field that is to be taken into
> account when adjusting the window size is the payload. Now only two
> packet types, namely, SSH_MSG_CHANNEL_DATA and
> SSH_MSG_CHANNEL_DATA_EXTENDED, consume window space. The structures of
> these packets are
>
> byte SSH_MSG_CHANNEL_DATA
> uint32 recipient channel

This isn't included

> string data

This is

> and
>
> byte SSH_MSG_CHANNEL_EXTENDED_DATA
> uint32 recipient channel
> uint32 data_type_code

This isn't included
> string data

This is

You can see the exact calculations by grepping for "window" in channels.c

-d
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