conn: robustly deliver response after channel read EOF #892
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Conn protocol closes the channel as soon as an EOF is received from a read request. This is at odds with a typical usage of conn, where separate programs are used to send a command and receive a result. We modify this behavior by calling moat `bal_f` only on genuine read errors. Furthermore, in conn.c we close the channel after processing the effect if we detect that the read end of the pipe has closed.
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This change also works well with standard |
mikolajpp
changed the title
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This change seems right for conn, but not the behavior we want for mars/urth IPC. In the long run, I don't think both of those things should use newt, but for now it'd be a bit of work to detangle them. I've pushed up a hacky workaround to preserve the old IPC behavior (see bcb965a), can you take a look and make sure it's still suitable for your needs? |
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I have tested with your changes, works just as good. |
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It is presently impossible to interface with conn using the typical pattern of sending a command using one program, and receiving the result with another through Unix pipes. Conn will eagerly close the connection as soon as it hears EOF from the read end of the pipe, which does not leave any chance to deliver an future result to the recipient. The only way to reliably receive results from conn in this situation is to set long timeouts in tools such as
netcatorsocat.This PR is (1) request for clarification about the protocol, whether the original behavior was intended, and (2) a first attempt to rectify this situation by:
newt.cThis PR requires an expert's look whether this change fits well with other IO drivers, given that
newt.cis used in many other places.With this PR applied, I have been able to successfully use
socatwith theclickscript to dramatically speedup interactions with an Urbit ship via conn.Our backend tests runner now completes in under
20s, while previously it took more than 4m to complete, due to a need for long timeouts at each interaction.