unclear docs: How to signal to StreamWriter that body is done?

[weissi]

StreamWriter's complete docs are

        /// Chunk provider.
        public struct StreamWriter {
            /// Write data to server.
            ///
            /// - parameters:
            ///     - data: `IOData` to write.
            public func write(_ data: IOData) -> EventLoopFuture<Void>
        }

I understand how I can provide chunks: by calling write but how do I tell the StreamWriter that I'm done sending request body bytes?

[adam-fowler]

@weissi You provide it with a length at the start and once you've supplied that data, it completes. I'm not a great fan of this interface. It is really confusing what is happening. Here is my attempt at implementing one https://github.com/swift-aws/aws-sdk-swift-core/blob/bdbac3768398b8387e2a81be193b6c42da75979e/Sources/AWSSDKSwiftCore/HTTP/AsyncHTTPClient.swift#L23

[weissi]

@adam-fowler but how do I do streaming? Ie. if I don't know the content length? Then chunked encoding should be selected...

[weissi]

CC @artemredkin

[adam-fowler]

@adam-fowler but how do I do streaming? Ie. if I don't know the content length? Then chunked encoding should be selected...

Yes that's a good question. That would be very useful.

[adam-fowler]

@weissi is this something that could be resolved for 1.2. It doesn't look like that complex a thing to do. Return an empty ByteBuffer() to indicate end or something like that and add a chunked header.

[adam-fowler]

Oh shit just thought this might be a breaking change. Although you could just add another version of the stream function.

[artemredkin]

@weissi answering your question, you just return succeeded future from write method:

.stream() { writer in
    writer.write()
    writer.write()
    ...
    writer.write()
    return eventLoop.makeSucceededFuture(())
}

I'm not a fan of this interface, it was designed mainly around how NonBlockingFileIO works...

[artemredkin]

Obviously, this example has absolutely no backpressure, so another alternative will be something like:

.stream() { writer in
    writer.write().flatMap {
        writer.write()
    }
}

[adam-fowler]

Sorry @artem I completely missed that. For some reason I had got it into my head you were required to pass in a content length

[artemredkin]

No worries, our docs in this area are not good, and API is not very clear at all. I'll try to improve streaming docs/API's after 1.2.0 release.

[weissi]

@artemredkin Hmm, I don't get it. A user gets handed a StreamWriter, they then call .write for every bit of data they have, how do they communicate that that's everything? So that there's nothing more coming?

[artemredkin]

user sets a body and passes it a closure, that has a singature:

(StreamWriter) -> EventLoopFuture<Void>

as soon as this future completes, we send .end

[adam-fowler]

@weissi I found it is a little confusing initially. I have a working version here, where you supply a stream function that returns ByteBuffers until you have finished streaming or have hit a specified size. https://github.com/swift-aws/aws-sdk-swift-core/blob/16cce9fe9fbc0f5949fb48a6fd7dce90b3645357/Sources/AWSSDKSwiftCore/HTTP/AsyncHTTPClient.swift#L78