go - gRPC下游的优雅关闭

Question

使用以下原型(prototype)缓冲区代码:

syntax = "proto3";

package pb;

message SimpleRequest {
    int64 number = 1;
}

message SimpleResponse {
    int64 doubled = 1;
}

// All the calls in this serivce preform the action of doubling a number.
// The streams will continuously send the next double, eg. 1, 2, 4, 8, 16.
service Test {
    // This RPC streams from the server only.
    rpc Downstream(SimpleRequest) returns (stream SimpleResponse);
}

我能够成功打开一个流，并不断从服务器获取下一个翻倍的数字。

我运行它的 go 代码如下所示:

ctxDownstream, cancel := context.WithCancel(ctx)
downstream, err := testClient.Downstream(ctxDownstream, &pb.SimpleRequest{Number: 1})
for {
    responseDownstream, err := downstream.Recv()
    if err != io.EOF {
        println(fmt.Sprintf("downstream response: %d, error: %v", responseDownstream.Doubled, err))

        if responseDownstream.Doubled >= 32 {
            break
        }
    }
}
cancel() // !!This is not a graceful shutdown
println(fmt.Sprintf("%v", downstream.Trailer()))

我遇到的问题是使用上下文取消意味着我的 downstream.Trailer() 响应为空。有没有办法从客户端优雅地关闭此连接并接收 downstream.Trailer()。

注意:如果我从服务器端关闭下游连接，我的预告片就会被填充。但是我无法指示我的服务器端关闭这个特定的流。因此必须有一种方法可以优雅地关闭流客户端。

谢谢。

根据请求的一些服务器代码:

func (b *binding) Downstream(req *pb.SimpleRequest, stream pb.Test_DownstreamServer) error {
    request := req

    r := make(chan *pb.SimpleResponse)
    e := make(chan error)
    ticker := time.NewTicker(200 * time.Millisecond)
    defer func() { ticker.Stop(); close(r); close(e) }()

    go func() {
        defer func() { recover() }()
        for {
            select {
            case <-ticker.C:
                response, err := b.Endpoint(stream.Context(), request)
                if err != nil {
                    e <- err
                }
                r <- response
            }
        }
    }()

    for {
        select {
        case err := <-e:
            return err
        case response := <-r:
            if err := stream.Send(response); err != nil {
                return err
            }
            request.Number = response.Doubled
        case <-stream.Context().Done():
            return nil
        }
    }
}

您仍然需要用一些信息填充预告片。我使用 grpc.StreamServerInterceptor 来执行此操作。

Answer 1

根据grpc go文档

Trailer returns the trailer metadata from the server, if there is any. It must only be called after stream.CloseAndRecv has returned, or stream.Recv has returned a non-nil error (including io.EOF).

因此，如果您想在客户端中阅读预告片，请尝试这样的操作

ctxDownstream, cancel := context.WithCancel(ctx)
defer cancel()
for {
  ...
  // on error or EOF
  break;
}
println(fmt.Sprintf("%v", downstream.Trailer()))

出现错误时从无限循环中跳出并打印预告片。 cancel 将在函数结束时被调用，因为它是延迟的。