Response not sent when client sends "Expect: 100-continue" request header

[bclozel]

Consider the following sample server:

// this server reads the request body then replies with "test"
NettyContext context = HttpServer
	.create(8080)
	.newHandler((req, res) -> {
		return req.receiveContent()
			.then(res.sendString(Mono.just("test")).then());
	})
	.block();

When an HTTP client sends the following request, things work as expected:

curl --data "Test" http://localhost:8080/demo --header "Content-Type: text/plain" --header "Expect:" -vvv
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> POST /demo HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
> Content-Type: text/plain
> Content-Length: 4
>
* upload completely sent off: 4 out of 4 bytes
< HTTP/1.1 200 OK
< transfer-encoding: chunked
<
* Connection #0 to host localhost left intact
test%

Some HTTP clients, when sending a large request body, can send "Expect: 100-continue" request headers (see this article for more on that).

Expected behavior

With the following command:

curl --data "Test" http://localhost:8080/demo --header "Content-Type: text/plain" --header "Expect: 100-continue"

I expect the server:

1. to answer HTTP/1.1 100 Continue
2. to read the request body
3. reply with HTTP/1.1 200 Continue and the "test" response body

Actual behavior

Instead, the HTTP client get no reply once it's sent the request body - it's hanged:

curl --data "Test" http://localhost:8080/demo --header "Content-Type: text/plain" --header "Expect: 100-continue" -vvv
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> POST /demo HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
> Content-Type: text/plain
> Expect: 100-continue
> Content-Length: 4
>
< HTTP/1.1 100 Continue
* We are completely uploaded and fine

On the server side, we can read the following:

         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 50 4f 53 54 20 2f 64 65 6d 6f 20 48 54 54 50 2f |POST /demo HTTP/|
|00000010| 31 2e 31 0d 0a 48 6f 73 74 3a 20 6c 6f 63 61 6c |1.1..Host: local|
|00000020| 68 6f 73 74 3a 38 30 38 30 0d 0a 55 73 65 72 2d |host:8080..User-|
|00000030| 41 67 65 6e 74 3a 20 63 75 72 6c 2f 37 2e 35 34 |Agent: curl/7.54|
|00000040| 2e 30 0d 0a 41 63 63 65 70 74 3a 20 2a 2f 2a 0d |.0..Accept: */*.|
|00000050| 0a 43 6f 6e 74 65 6e 74 2d 54 79 70 65 3a 20 74 |.Content-Type: t|
|00000060| 65 78 74 2f 70 6c 61 69 6e 0d 0a 45 78 70 65 63 |ext/plain..Expec|
|00000070| 74 3a 20 31 30 30 2d 63 6f 6e 74 69 6e 75 65 0d |t: 100-continue.|
|00000080| 0a 43 6f 6e 74 65 6e 74 2d 4c 65 6e 67 74 68 3a |.Content-Length:|
|00000090| 20 34 0d 0a 0d 0a                               | 4....          |
+--------+-------------------------------------------------+----------------+
20:44:58.347 [reactor-http-nio-4] DEBUG r.i.n.h.server.HttpServerOperations - Increasing pending responses, now 1
20:44:58.347 [reactor-http-nio-4] DEBUG r.ipc.netty.http.server.HttpServer - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] READ COMPLETE
20:44:58.347 [reactor-http-nio-4] DEBUG r.i.netty.channel.ChannelOperations - [HttpServer] [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] handler is being applied: reactor.ipc.netty.http.server.DummyTest$$Lambda$7/1182461167@2c155cf3
20:44:58.347 [reactor-http-nio-4] DEBUG r.i.n.c.ChannelOperationsHandler - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] Writing object DefaultFullHttpResponse(decodeResult: success, version: HTTP/1.1, content: EmptyByteBufBE)
HTTP/1.1 100 Continue
20:44:58.348 [reactor-http-nio-4] DEBUG r.ipc.netty.http.server.HttpServer - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] WRITE: 25B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 54 54 50 2f 31 2e 31 20 31 30 30 20 43 6f 6e |HTTP/1.1 100 Con|
|00000010| 74 69 6e 75 65 0d 0a 0d 0a                      |tinue....       |
+--------+-------------------------------------------------+----------------+
20:44:58.348 [reactor-http-nio-4] DEBUG r.ipc.netty.http.server.HttpServer - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] USER_EVENT: [Handler Terminated]
20:44:58.348 [reactor-http-nio-4] DEBUG r.i.n.c.ChannelOperationsHandler - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] Disposing context reactor.ipc.netty.channel.ServerContextHandler@3ac7f46c
20:44:58.348 [reactor-http-nio-4] DEBUG r.ipc.netty.http.server.HttpServer - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] FLUSH
20:44:58.348 [reactor-http-nio-4] DEBUG r.ipc.netty.http.server.HttpServer - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] READ: 4B
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 54 65 73 74                                     |Test            |
+--------+-------------------------------------------------+----------------+
20:44:58.349 [reactor-http-nio-4] DEBUG r.i.n.c.ChannelOperationsHandler - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] No ChannelOperation attached. Dropping: Test
20:44:58.349 [reactor-http-nio-4] DEBUG r.ipc.netty.http.server.HttpServer - [id: 0xe1bb4076, L:/0:0:0:0:0:0:0:1:8080 - R:/0:0:0:0:0:0:0:1:53272] READ COMPLETE

Steps to reproduce

These curl commands are quite artificial, but you can reproduce this behavior naturally with curl, when sending large files like:

curl --data @bigint.txt http://localhost:8080/demo --header "Content-Type: text/plain"

Reactor Netty version

master branch, 0.7.5.BUILD-SNAPSHOT

JVM version (e.g. java -version)

java version "1.8.0_162"
Java(TM) SE Runtime Environment (build 1.8.0_162-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.162-b12, mixed mode)

OS version (e.g. uname -a)

17.4.0 Darwin Kernel Version 17.4.0: Sun Dec 17 09:19:54 PST 2017; root:xnu-4570.41.2~1/RELEASE_X86_64 x86_64