Spring Web Reactive + Netty hangs on Windows when sending JSON [SPR-15108]

[spring-projects-issues]

Daniel Fernández opened SPR-15108 and commented

Scenario

A web application developed using Spring Boot 2.0 (snapshot) and Spring 5 Web Reactive using Netty as a server, outputs an amount of data in JSON format.

Implementation

The test-boot-netty-windows repository (tag spr15108) contains a test application initialised using http://start.spring.io.

It uses Spring Boot 2.0 and Spring 5 Web Reactive. The dependencies have been modified in order to use Netty as a server instead of Apache Tomcat.

The application contains a @RestController which has a controller method returning a Flux<Entity>.

The sample application can be started with mvn -U clean compile spring-boot:run, and it can be called like curl http://localhost:8080/list/SIZE, being SIZE the size of the list of elements to be returned.

Observed results

When running this application on Windows 10, if we request 41 elements everything goes alright, because the output size is 1969 bytes (less than 2 KBytes):

$ curl http://localhost:8080/list/41 > out
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1969    0  1969    0     0  63516      0 --:--:-- --:--:-- --:--:--  128k

...but if we request 50 elements:

$ curl http://localhost:8080/list/50 > out1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  2017    0  2017    0     0     13      0 --:--:--  0:02:28 --:--:--     0
^C (Interrupted)

Apparently, the server hangs when it needs to flush output data that exceeds 2048 bytes.

I've tested this on two different Windows 10 machines with the same result. Also, I've tested that this works OK on both MacOS 10.10 and Linux Ubuntu 16.

Note that, given this seems to involve the Netty output buffers, it might be related to #19662

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Affects: 5.0 M4

Reference URL: https://github.com/danielfernandez/test-boot-netty-windows/tree/spr15108

[spring-projects-issues]

Brian Clozel commented

Hi Daniel Fernández,

Indeed, there were a few identified reactor netty issues related to buffering and flushing of the response body; so I've waited for those to be resolved and checked again: everything works out now (tested on windows 7 against the latest Spring Boot SNAPSHOTs).

Thanks for raising this issue and sorry for the late reply!