Golang RCP call hanging - go

Question

I have a back-end app and a front-end, both in Go. I am trying to make them talk via rpc.
back-end main.go
package main
import (
"fmt"
"log"
"net"
"net/http"
"net/rpc"
"time"
)
type Application struct {
config struct {
server struct {
port int
network string
}
}
}
type MusicProject struct {
Id string
CreatedTime time.Time
LastEditedTime time.Time
Title string
Year int
Status string
Description string
ChoirRollup string
}
func main() {
var app Application
app.config.server.port = 5002
app.config.server.network = "tcp"
if err := rpc.Register(new(Application)); err != nil {
log.Fatal(err)
}
rpc.HandleHTTP()
// start the rpc server
log.Println("Starting server port", app.config.server.port)
l, err := net.Listen("tcp", fmt.Sprintf(":%v", app.config.server.port))
if err != nil {
log.Fatal(err)
}
if err = http.Serve(l, nil); err != nil {
log.Fatal(err)
}
}
func (app *Application) GetMusicProjectById(id string, model *MusicProject) error {
musicProject := MusicProject{
Id: id,
CreatedTime: time.Now(),
LastEditedTime: time.Now(),
Title: "Test Project",
Year: 2020,
Status: "Completed",
Description: "Short project Description",
ChoirRollup: "Best Choir",
}
model = &musicProject
return nil
}
front-end rpc call
package main
import (
"log"
"net/rpc"
"time"
)
type MusicProject struct {
Id string
CreatedTime time.Time
LastEditedTime time.Time
Title string
Year int
Status string
Description string
ChoirRollup string
}
func main() {
dial, err := rpc.Dial("tcp", "localhost:5002")
if err != nil {
log.Println(err)
}
projectID := "some_id_123"
var musicProject MusicProject
err = dial.Call("Application.GetMusicProjectById", projectID, &musicProject)
if err != nil {
log.Println(err)
}
log.Println(musicProject)
}
Once the client method is call, the call hanged indefinite with out sending back any error, so quite difficult to debug.
Do you have any suggestion for debugging? Do you see anything wrong in my code?
Thank you for your help!

Answer 1

Your server is serving HTTP:
if err = http.Serve(l, nil); err != nil {
log.Fatal(err)
}
But your client is using straight TCP (HTTP runs over TCP but adds another layer):
err = dial.Call("Application.GetMusicProjectById", projectID, &musicProject)
So to fix your issue you need to change one side or the other. For example change the server to:
rpc.Accept(l)
(alternatively you could use rpc.DialHTTP in the client)
There are a couple of other issues with your code (the main one being the way you set the response in the back-end). The following works for me (have not put much effort into making it tidy or testing!).
server
package main
import (
"fmt"
"log"
"net"
"net/rpc"
"time"
)
type MusicProject struct {
Id string
CreatedTime time.Time
LastEditedTime time.Time
Title string
Year int
Status string
Description string
ChoirRollup string
}
type Application struct {
}
func (app *Application) GetMusicProjectById(id string, model *MusicProject) error {
*model = MusicProject{
Id: id,
CreatedTime: time.Now(),
LastEditedTime: time.Now(),
Title: "Test Project",
Year: 2020,
Status: "Completed",
Description: "Short project Description",
ChoirRollup: "Best Choir",
}
return nil
}
func main() {
const port = 5002
if err := rpc.Register(new(Application)); err != nil {
log.Fatal(err)
}
// start the rpc server
log.Println("Starting server on port:", port)
l, err := net.Listen("tcp", fmt.Sprintf(":%d", port))
if err != nil {
log.Fatal(err)
}
rpc.Accept(l)
}
client
package main
import (
"log"
"net/rpc"
"time"
)
type MusicProject struct {
Id string
CreatedTime time.Time
LastEditedTime time.Time
Title string
Year int
Status string
Description string
ChoirRollup string
}
func main() {
dial, err := rpc.Dial("tcp", "localhost:5002")
if err != nil {
log.Fatal(err)
}
projectID := "some_id_123"
var musicProject MusicProject
err = dial.Call("Application.GetMusicProjectById", projectID, &musicProject)
if err != nil {
log.Fatal("error:", err)
}
log.Println(musicProject)
}