在Go中关闭grpc服务器时如何检测错误？

Question

I'm trying to detect the gRPC server shutdown in Go gRPC client code like

import (
     pb "mysample.com/api/rpc"
     "google.golang.org/grpc"
)
var stream pb.SearchProductService_MarketStreamClient
for {
    r, err := stream.Recv()
    if err == io.EOF {
        log.Println("Info: server close")
        break
    } else if err != nil {
        log.Println("Err: grpc code:", grpc.Code(err))
        if err != nil {
          log.Fatal(err)
        }
    }
    outs := printOrderbook(r)
    fmt.Println(outs)
    if outf != nil {
        outf.WriteString(time.Now().Format("030405.000 ") +
            outs + "
")
    }
}

The output message is

mysample.go:122: Err: grpc code: Unavailable
panic: rpc error: code = Unavailable desc = transport is closing

I'm trying to search 'transport is closing' in Go's source and $GOPATH/src/, but I can't not found such phrase. Is there any smart method to handle such deeper error?

Answer 1

gRPC always need to return errors properly, if you do not handle errors the connection will go into TRANSIENT_FAILURE state and you cannot request any query with this client connection. Catch the error properly and return it using grpc error codes. You can find deeper insites here https://www.grpc.io/docs/guides/error/ and use this inbuilt package grpc: google.golang.org/grpc/status

conn *grpc.ClientConn conn.GetState() will give the current connection state