Flush stdout buffer when writing data

[gsabran]

Flush stdout buffer when writing data. I noticed that without an extra line break, the receiver was not getting the message written to stdout.

As a nit (happy to revert) I thought that stdio was clearer that stdioPipe as afaik piping is specific to shell scripts, and stdin can be written to in other contexts.

[mattmassicotte]

I'm afraid this isn't a safe change. Introducing new data like this will break some existing communication protocols. However! I do think the underlying problem you discovered should still be fixed. Perhaps we can do it another way?

(and yes I 100% agree with your nit, thanks for calling that out!)

[gsabran]

Introducing new data like this will break some existing communication protocols.

This only applies to when using the process' stdio though. ie other communication protocols (for ex websocket) are not impacted.

As an alternative, what do you think of

@available(*, deprecated, renamed: "stdio", message: "Use stdio instead")
public static func stdioPipe() -> DataChannel {
  stdio(flushOnWrite: false)
}

public static func stdio(flushOnWrite: Bool = true) -> DataChannel { ... }

[mattmassicotte]

This only applies to when using the process' stdio though. ie other communication protocols (for ex websocket) are not impacted.

That's true! This transport just happens to be really important for my own uses.

I think it is critical that transports faithfully write only the data that a user actually intends. I'm much more inclined to use an out-of-band mechanism here like fflush. This would have the exact same behavior but not alter the data stream in any way.

What do you think about keeping non-flushing behavior the default, so existing clients continue to work, and look into using fflush?