Revise paste distsys hw2

package main

import (
	"context"
	"fmt"
	"log"
	"net"
	"os"
	"sync"

pb "dagorokhov/messenger/proto"
	emptypb "google.golang.org/protobuf/types/known/emptypb"
	timestamppb "google.golang.org/protobuf/types/known/timestamppb"

grpc "google.golang.org/grpc"
)

type messengerServer struct {
	pb.UnimplementedMessengerServerServer
	channels []chan *pb.Message
	mutex    sync.Mutex
}

func (s *messengerServer) SendMessage(ctx context.Context, message *pb.Message) (*pb.Reply, error) {
	fmt.Println("got message", message)
	reply := pb.Reply{SendTime: timestamppb.Now()}
	message.SendTime = reply.SendTime

s.mutex.Lock()
	defer s.mutex.Unlock()

for _, channel := range s.channels {
		channel <- message
	}
	return &reply, nil
}

func (s *messengerServer) ReadMessages(_ *emptypb.Empty, stream grpc.ServerStreamingServer[pb.Message]) error {
	fmt.Println("connected to listen")
	s.mutex.Lock()
	s.channels = append(s.channels, make(chan *pb.Message))
	channel := s.channels[len(s.channels)-1]
	s.mutex.Unlock()

for message := range channel {
		fmt.Println("trying to send message", message)
		if err := stream.Send(message); err != nil {
			fmt.Println(err)
			return err
		}
	}

return nil
}

func main() {
	fmt.Println("starting server")
	port := os.Getenv("MESSENGER_SERVER_PORT")
	if port == "" {
		port = "51075"
	}

lis, err := net.Listen("tcp", fmt.Sprintf("localhost:%v", port))
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	var opts []grpc.ServerOption
	grpcServer := grpc.NewServer(opts...)

server := messengerServer{}
	pb.RegisterMessengerServerServer(grpcServer, &server)

grpcServer.Serve(lis)
}