akka/akka-http

Special handling of Expect: 100-Continue may not be appropriate in a proxy

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#514 opened on Nov 11, 2016

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Description

I'm using Akka HTTP (3.0.0-RC1) to create a reverse-http-proxy. The special handling of Expect: 100-Continue looks like it's causing weirdness in this case. In wireshark, here's what I see:

Proxy  -> RSP: 100 Continue -> Client
Client -> REQ -> Proxy
Server -> RSP: 100 Continue -> Proxy
Proxy  -> REQ -> Server
Server -> 200 -> Proxy
Proxy  -> 200 -> Client

In the production logs (not in an attempt at a clean room reproduction) we see a number of these messages:

Sending an 2xx 'early' response before end of request was received...

It's not 100% clear that these are related to the special handling of 100, but they do seem to coincide a lot. It feels like the special handling should be avoided when akka-http is operating as a proxy, leaving the handling logic up to the server to which we're proxying.

Contributor guide

Research direction
Investigate the handling of the 'Expect: 100 Continue' header in the Akka HTTP server, particularly when acting as a proxy. Trace the code path that creates the initial '100 Continue' response and see if it can be disabled when proxying to allow the upstream server to handle it.
Tech stack
scala
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
ScalaHTTP
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65