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SSHv2 doesn't actually have compression levels

From: Tobias Geerinckx-Rice
Subject: SSHv2 doesn't actually have compression levels
Date: Tue, 30 Jul 2019 03:58:32 +0200


While reading (guix scripts offload) in a (failed) attempt to get offloading working, the following comment caught my eye:

;; We rely on protocol-level compression from libssh to optimize large data
 ;; transfers.  Warn if it's missing.

which means that we're not currently doing our own compression inside the tunnel.

This is significant, because it means that the COMPRESS-LEVEL field of BUILD-MACHINE is completely bogus[0], and probably always was - unless it once supported SSHv1, which I think we can agree is not something we want to support today. Nobody's offloading libreoffice to that old router in the attic.

I'd like to undocument the option, and add a comment noting its lack of any useful effect to the code, by next week.

Kind regards,


[0]: Take a look at OpenSSH's readconf.c, packet.c, and all calls to start_compression_out().

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