StreamWriter expects to be called on some internal EventLoop

[weissi]

The HTTPClient.Body.StreamWriter that you get when using the default .stream(length: contentLength, { thisStreamWriterHere in }) expects to be called on the internal EventLoop that belongs to the underlying Channel. The user however doesn't get access to that Channel at all so it's impossible to use this API :(.

This needs a fix really soon.

[weissi]

After a chat with @ktoso, I noticed that this ticket isn't clear enough. The rules should be:

• All callouts (delegate, futures, callbacks, ...) AHC makes to the user should be on the preferred EL, no matter where the Channel lives
• All callins (returned futures, callins, ...) from the user must be tolerated on any thread.

IMHO fixing this issue is blocking 1.2.0, we cannot possibly release it as on master as it's impossible to use right now.

[ktoso]

I started looking into this a bit btw, may have more time soon to dedicate to this.

[artemredkin]

It seems that this is more about API design, than a programming model, no? Even if I fix #192 in #215 , it will still not solve this issue if I don't want to specify task EL myself, right?

[weissi]

@artemredkin Not sure, the write API for StreamWriter can stay as is but it can't make the assumption it makes today because that makes it impossible to use with the connection pool.
In theory, we could mandate that the user calls us back on the delegate's EL but that would be of no benefit to us because we need to hop EL's to the Channel's EL anyway so we should just accept callins on any EL.

[weissi]

when this gets fixed, we also need to undo this hack: https://github.com/swift-server/async-http-client/pull/219/files#diff-bd03a2521c79f3da4bd5825512ca9979R1739-R1741