(guix build download) uses ‘session-record-port’ from (gnutls), which returns a port to conveniently write to/read from the TLS session’s “record” layer.
The problem is that every write to the port, that is, every call to ‘write_to_session_record_port’ in the GnuTLS bindings, leads to the creation of one “Application Data” packet. For instance, when (web requests) writes an HTTP GET request, it roughly does: (display "GET" port) (display " " port) (display uri port) (display "\n\r" port) … it ends up creating a lot of small Application Data packets. When debugging is enabled in (guix build download), that translates to things like: gnutls: [14594|5] REC[0x152c9c0]: Preparing Packet Application Data(23) with length: 1 and min pad: 0 gnutls: [14594|9] ENC[0x152c9c0]: cipher: AES-128-GCM, MAC: AEAD, Epoch: 1 gnutls: [14594|5] REC[0x152c9c0]: Sent Packet[4] Application Data(23) in epoch 1 and length: 30 Terribly suboptimal. The difficulty is that the session record port doesn’t do any caching by itself, and it shouldn’t, because it’s the application’s responsibility. So we might have to do our own caching and/or use ‘record-send’ and ‘record-receive!’ instead of ‘session-record-port’. Ludo’.
