Two items are lost when HTTP sink client is reconnected

[olukas]

When HTTP sink is set up with accumulateItems and client is connected and then reconnected then 2 items are lost during reconnection.

Steps to reproduce:

1. Start pipeline:

Pipeline p = Pipeline.create();
StreamSource<Long> source = HttpListenerSources.builder()
        .type(Long.class)
        .build();
Sink<Object> sink = HttpListenerSinks.builder()
        .accumulateItems(500)
        .buildServerSent();
p.readFrom(source)
        .withoutTimestamps()
        .writeTo(sink);

2. Connect client for HTTP sink by curl -X GET http://localhost:8081
3. Send couple of messages by curl POST, all are processed correctly
4. Stop client for sink (from step 2)
5. Send couple of messages by curl POST, all are processed correctly
6. Connect again client for HTTP sink by curl -X GET http://localhost:8081
7. Send couple of messages by curl POST, first two messages sent after client was disconnected (i.e. messages from step 5) are missing

[gurbuzali]

The root cause of the issue is undertow does not figure out if the client is disconnected. First I thought that there is a timeout or somothing but after like 10 minutes undertow was still thinking that the client is alive. The only way that undertow declares a client dead and removes it is by sending 2 items to the connection, after sending the second item it immediately declares client dead.

I haven't been able to find a configuration parameter on undertow side which will trigger an immediate removal of the client