HTTP Streaming and Server-Sent Events (SSE) [SPR-12212]

spring-projects-issues commented 10 years ago

Rossen Stoyanchev opened SPR-12212 and commented

Spring 4 SockJS support already provides an SEE transport that can be used even in browsers that don't support websocket.

The purpose of this ticket is to provide explicit support for Server-Sent Events in @RequestMapping methods in addition to the Callable and DeferredResult return types.

At present Callable and DeferredResult provide a simple way for a controller to produce a return value asynchronously once and then resume processing. This works for any annotated controller method and supports the full range of options, i.e. @ResponseBody or view resolution, handler interception, exception resolution, etc.

For SSE we'll need to support returning multiple values at different times. This will likely result very specifically in an HttpMessageConverter writing each value to the response.

Affects: 4.1 GA

Sub-tasks:

17271 Add documentation for Server-Sent Events support
17532 Add onTimeout() and onCompletion() callbacks to ResponseBodyEmitter

Issue Links:

16822 Support SSE / event-stream ("is duplicated by")
18994 Return type implementing DeferredResult is rejected with exception
18618 RxJava Observable/Single and Reactor Flux/Mono as Spring MVC handler method return types
17428 HTTP Streaming Directly to the OutputStream
INT-3625 Support for Server-Sent Events (SSE)
17209 Document how HandlerInterceptor should differentiate an ASYNC dispatch
17695 Add request timeout to ResponseBodyEmitter

Referenced from: commits https://github.com/spring-projects/spring-framework/commit/935ffc5827554d593e6fa8c148b4f3630dc2d918, https://github.com/spring-projects/spring-framework/commit/a32b5e61d0b5dff9c09cc3c7d7b8e5e68ac69ae5

5 votes, 12 watchers

spring-projects-issues commented 10 years ago

Marc Logemann commented

at the end the DeferredResult or DeferredStreamResult ;-) must be able to mimic the following behaviour (in Spring MVC, you will have DeferredResults in a list and not AsyncContexts as shown below)

for (AsyncContext asyncContext : queue) {
    ServletResponse response = asyncContext.getResponse();
    response.setContentType("text/event-stream"); //not good in a loop called multiple times
    PrintWriter out = response.getWriter();
    out.printf("data: 123\n\n");  
    out.flush();
}

spring-projects-issues commented 10 years ago

Marc Logemann commented

As a SSE feature bonus the Spring team might think about a special SSE bean (with attributes which mimic the SSE protocol like "data", "retry", "id" and others) and create a MessageConverter which serialize this into proper SSE wire protocol like:

data: xxxxx \n
id: yyyy \n
retry: i \n
\n

people then could simply use this bean in conjunction with the DeferredResult without bothering about the protocol itself like:

// somwhere in the controller
DeferredStreamResult<SseBean> dsResult = new DeferredStreamResult<>();
return dsResult;

// somewhere else which processes on all active DeferredResults 
SseBean sseBean = new SseBean("my Data");
dsResult.setResult(sseBean); //which keeps open the connection
dsResult.setResult(sse2Bean); // which should act on the same responsestream