.NET 4.5 ASP.NET WebApi如何转发Spring服务的Server-Sent-Events

我有一个基于.NET 4.5的ASP.NET WebApi应用，需要在控制器中创建两个端点调用基于Spring Web的Java服务。其中一个端点需要实时转发Spring服务发送的Server-Sent-Events（SSE），但尝试了两种C#实现方式均失败。

需求说明：Spring服务在执行操作时会流式输出文本，需要将这些文本实时转发给前端展示操作进度，希望避免通过轮询获取状态的方式。

尝试的两种C#实现 #

第一种实现（返回HttpResponseMessage） #

[HttpPost]
[Route("api/myApp/myEndpoint")]
public async Task<HttpResponseMessage> myEndpoint([FromBody] MyEndpointParams params)
{
    try
    {
        using (var client = new HttpClient(new HttpClientHandler
        {
            AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate
        }))
        {
            string uri = "https://theServer/theSpringApp/api/theServerEventsSendingEndpoint";
            StringContent content = new StringContent(JsonConvert.SerializeObject(params), Encoding.UTF8, "application/json");
            HttpRequestMessage request = new HttpRequestMessage()
            {
                Method = HttpMethod.Post,
                RequestUri = new Uri(uri),
                Content = content
            };

            return await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
        }
    }
    catch (Exception ex)
    {
        log.Error("[myEndpoint] Error", ex);
        return new HttpResponseMessage(HttpStatusCode.InternalServerError);
    }
}

第二种实现（返回IDisposable） #

[HttpPost]
[Route("api/myApp/myEndpoint")]
public async Task<IDisposable> myEndpoint([FromBody] MyEndpointParams params)
{
    try
    {
        using (var client = new HttpClient(new HttpClientHandler
        {
            AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate
        }))
        {
            string uri = "https://theServer/theSpringApp/api/theServerEventsSendingEndpoint";
            StringContent content = new StringContent(JsonConvert.SerializeObject(params), Encoding.UTF8, "application/json");
            HttpRequestMessage request = new HttpRequestMessage()
            {
                Method = HttpMethod.Post,
                RequestUri = new Uri(uri),
                Content = content
            };

            var response = client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
            return await response.Result.Content.ReadAsStreamAsync();
        }
    }
    catch (Exception ex)
    {
        log.Error("[myEndpoint] Error", ex);
        return new HttpResponseMessage(HttpStatusCode.InternalServerError);
    }
}

Spring服务端点核心代码 #

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

...

private ExecutorService executorService = Executors.newCachedThreadPool();

...

@PostMapping(path = "/api/theServerEventsSendingEndpoint", produces = MediaType.TEXT_PLAIN_VALUE)
public SseEmitter sendTheServerEvents(@RequestBody(required = true) MyEndpointParams params) {

    SseEmitter emitter = new SseEmitter();
    executorService.execute(() -> {
        // 循环执行操作，每次循环执行：
        emitter.send("some text that depends on the operation it's doing");

        // 操作结束后：
        emitter.complete();
            
        // 省略了错误处理代码
    });
    return emitter;
}

内容的提问来源于stack exchange，提问作者nonzaprej