Are nested or recursive HTTP/2 push streams possible?

[robbie-mac]

• Node.js Version: 9.7.0
• OS: Windows
• Scope (install, code, runtime, meta, other?): code
• Module (and version) (if relevant): HTTP/2

@jasnell or anybody else that would care to comment. I'm wondering a couple of things regarding HTTP/2 push streams:
If I understand things correctly, push streams are intended to proactively serve resources that are needed to get a page on screen as quickly as possible. Basically compressing the fetch-parse-fetch-parse loop.

So with that in mind, I though of this: index.htm needs a few resources, css and js. The js file needs a few resources, say some json data.

I want to push resources to a document served by a push stream.

So here is what I tried:

//server = http2.createSecureServer(); init code removed for brevity
server.addListener('stream', function (stream, headers) {
let resourcePath = path.join(serverRootPath, headers[HTTP2_HEADER_PATH]);
stream.respondWithFile(resourcePath, {
            'content-type': mimeTypes.get(resourcePath.match(mimeRegExp)[0]),
        });
}); 

Yay I have a static file server, except no push. So I modify to this:

//server = http2.createSecureServer(); init code removed for brevity
server.addListener('stream', function (stream, headers) {
let resourcePath = path.join(serverRootPath, headers[HTTP2_HEADER_PATH]);
stream.respondWithFile(resourcePath, {
            'content-type': mimeTypes.get(resourcePath.match(mimeRegExp)[0]),
        });
stream.pushStream({ ':path': pushResourcePath }, { 'parent': stream.id }, (err, stream, headers) => {
            stream.respondWithFile(path.join(serverRoot, pushResourcePath), {
                'content-type': mimeTypes.get(path.join(serverRoot,pushResourcePath).match(mimeRegExp)[0]),
            });
        });
}); 

Yay, I have a working push stream. Then I add a push stream inside of the push stream callback

//server = http2.createSecureServer(); init code removed for brevity
server.addListener('stream', function (stream, headers) {
    let resourcePath = path.join(serverRootPath, headers[HTTP2_HEADER_PATH]);
    stream.respondWithFile(resourcePath, {
        'content-type': mimeTypes.get(resourcePath.match(mimeRegExp)[0]),
    });
    stream.pushStream({ ':path': pushResourcePath }, { 'parent': stream.id }, (err, stream, headers) => {
        stream.respondWithFile(path.join(serverRoot, pushResourcePath), {
            'content-type': mimeTypes.get(path.join(serverRoot, pushResourcePath).match(mimeRegExp)[0]),
        });
        stream.pushStream({ ':path': subPushResourcePath }, { 'parent': stream.id }, (err, stream, headers) => {
            stream.respondWithFile(path.join(serverRoot, subPushResourcePath), {
                'content-type': mimeTypes.get(path.join(serverRoot, subPushResourcePath).match(mimeRegExp)[0]),
            });
        });
    });
}); 

The train derails here. I get an error stating an invalid argument for the nested push stream, and the json file is served through another get request.

What am I missing? The nested pushstream callback gets an error instead of a stream, but I don't understand why.

On a more design level curiosity, why was the stream.pushStream() function designed with a callback, and not as a promise? Given that pushStream generates a request Promise... or am I conflating two different uses of Promise?

[robbie-mac]

I realized it would make sense to provide the error:

{ Error [ERR_HTTP2_ERROR]: Invalid argument
at ServerHttp2Stream.pushStream (internal/http2/core.js:2095:17)
at file:///D:/http2_experimental_server/src/server.mjs:106:24
at process._tickCallback (internal/process/next_tick.js:114:19)
code: 'ERR_HTTP2_ERROR',
name: 'Error [ERR_HTTP2_ERROR]',
errno: -501 }

[robbie-mac]

The more I try to figure this out, the more I feel this might be a bug. Closing an moving to nodejs/node#19095