Handle unread body from request

[bartlomieju]

Follow up #22 #49.

This PR provides most basic implementation that handles unread request body without reading all data to memory. As discussed in #49 it follows Golang's implementation.

[bartlomieju]

@ry you said that closeWriteAndWait is what we need. I don't fully understand it's purpose. Could you follow up?

[bartlomieju]

I'll wait on #188 before finishing this

[bartlomieju]

I've tried to rebase my branch against master, but given latest changes in #188 it's pretty hard.

Main loop in serve has:

for (const { req, conn } of queueToProcess) {
      if (req) {
        const res = createResponder(conn);
        yield { req, res };
      }
      serveConn(env, conn);
}

request and response are completely decoupled, which gives no easy way to check if request's body was fully read before responding, which leaves #49 unresolved

Maybe we could talk about rewriting it to something like this:

for (const { req, conn } of queueToProcess) {
      if (req) {
        // iterator should return response
        const res = yield req;

        // close connection if request body 
        // hasn't been consumed
        writeResponse(res, req);
      }

      // check if connection can be reused
      // get closed() should be added to `Conn` 
      if (!conn.closed) {
        serveConn(env, conn);
      }
}

CC @ry @kevinkassimo

[keroxp]

@bartlomieju

Isn't code like this enough? After #188, req.body is one of instance of BodyReader or ChunkedBodyReader. It can consume body to exactly end of the stream. If body was consumed entirely by user, no additional io operations happen.

for (const { req, conn } of queueToProcess) {
  if (req) {
    const res = createResponder(conn);
    yield { req, res };
    await copy({
      write: async p => p.byteLength
    }, req.body)
  }
  serveConn(env, conn);
}

[bartlomieju]

@keroxp agreed, however logic deciding whether or not it should be consumed or connection closed is much more complicated. We wanted to base it on Golang's implementation, here's old PR with discussion for context: #49