The program creates a rpc server and a client and expose several methods via the rpc interface.
Several test functions testing one of the methods each.
The first test function register the rpc server:
RPCServer := new(RPCServer)
rpc.Register(RPCServer)
rpc.HandleHTTP()
Using a channel, each function wait for the server to signal that it is running and when the client finish, signal the server to shut down.
In the test function:
// start the server
ch := make(chan bool, 1)
go RunRPCServer(ch)
// wait for the server to start
<-ch
...Do Some Work...
// close the server
ch <- true
close(ch)
and in the server function:
listener, err := net.Listen("tcp4", "")
if err != nil {
log.Fatal("Could not open a listener port: ", err.Error())
}
wg := sync.WaitGroup{}
wg.Add(1)
// Start the server
rpcServer := http.Server{}
go func() {
go rpcServer.Serve(listener)
// signal that the server is running
ch <- true
// wait for the command to close the server
<-ch
<-ch
// shutdown server and exit
if err := rpcServer.Shutdown(context.Background()); err != nil {
log.Printf("HTTP server Shutdown: %v\n", err)
}
listener.Close()
wg.Done()
}()
wg.Wait()
It all works perfectly fine when running the tests once, or even several times with:
go test -count 1 ./src/rpcserver/
go test -count 1 ./src/rpcserver/
However, when running
go test -count 2 ./src/rpcserver/
An error is returned when the second run starts:
--- FAIL: TestRPCServer (0.00s)
panic: http: multiple registrations for /goRPC [recovered]
panic: http: multiple registrations for /goRPC
I wonder why
go test -count 2 ./src/rpcserver/
does not behave exactly as:
go test -count 1 ./src/rpcserver/
go test -count 1 ./src/rpcserver/
?
And what can be done in order to de-register the server between consecutive run of the tests?
Edit: Here is a full minimal example that illustrates the issue:
server.go:
package rpcserver
import (
"context"
"log"
"net"
"net/http"
"net/rpc"
)
type RPCServer int
// RPC: only methods that comply with the following scheme are exported:
// func (t *T) MethodName(argType T1, replyType *T2) error
// Since RPC-exposed methods must takes an argument.
type EmptyArg struct{}
// Expose several methods via the RPC interface:
func (RpcServer *RPCServer) Method_1(emptyArg EmptyArg, reply *string) error {
*reply = "This is Method_1"
return nil
}
func (RpcServer *RPCServer) Method_2(emptyArg EmptyArg, reply *string) error {
*reply = "This is Method_2"
return nil
}
func (RpcServer *RPCServer) Method_3(emptyArg EmptyArg, reply *string) error {
*reply = "This is Method_3"
return nil
}
// should be called only once per process
func RegisterRPCMethods() {
// Register the rpc methods
RpcServer := new(RPCServer)
rpc.Register(RpcServer)
rpc.HandleHTTP()
}
func RunRPCServer(ch chan struct{}) {
// Open a listener port
listener, err := net.Listen("tcp4", "127.0.0.1:38659")
if err != nil {
log.Fatal("listen error:", err)
}
// Print some data
log.Println("Server running")
log.Println("network:", listener.Addr().Network())
// Start the server
rpcServer := http.Server{}
go func() {
go rpcServer.Serve(listener)
// signal that the server is running
ch <- struct{}{}
// wait for the command to close the server
<-ch
// shutdown server and exit
if err := rpcServer.Shutdown(context.Background()); err != nil {
log.Printf("HTTP server Shutdown: %v\n", err)
}
listener.Close()
// signal that the server is closed
ch <- struct{}{}
}()
}
server_test.go:
package rpcserver
import (
"net/rpc"
"testing"
)
func TestMethod_1(t *testing.T) {
// call once.
// (test functions are executed in-order)
RegisterRPCMethods()
// start the server
ch := make(chan struct{})
go RunRPCServer(ch)
// wait for the server to start
<-ch
// Dial to the rpc server
client, err := rpc.DialHTTP("tcp", "127.0.0.1:38659")
if err != nil {
t.Errorf("Could not dial %s: %s", "127.0.0.1:38659", err.Error())
}
// the called function allready asserting type.
reply := ""
err = client.Call("RPCServer.Method_1", EmptyArg{}, &reply)
if err != nil {
t.Error(err)
}
// close the server
ch <- struct{}{}
// wait for the server to close
<-ch
close(ch)
}
func TestMethod_2(t *testing.T) {
// start the server
ch := make(chan struct{})
go RunRPCServer(ch)
// wait for the server to start
<-ch
// Dial to the rpc server
client, err := rpc.DialHTTP("tcp", "127.0.0.1:38659")
if err != nil {
t.Errorf("Could not dial %s: %s", "127.0.0.1:38659", err.Error())
}
// the called function allready asserting type.
reply := ""
err = client.Call("RPCServer.Method_2", EmptyArg{}, &reply)
if err != nil {
t.Error(err)
}
// close the server
ch <- struct{}{}
// wait for the server to close
<-ch
close(ch)
}
func TestMethod_3(t *testing.T) {
// start the server
ch := make(chan struct{})
go RunRPCServer(ch)
// wait for the server to start
<-ch
// Dial to the rpc server
client, err := rpc.DialHTTP("tcp", "127.0.0.1:38659")
if err != nil {
t.Errorf("Could not dial %s: %s", "127.0.0.1:38659", err.Error())
}
// the called function allready asserting type.
reply := ""
err = client.Call("RPCServer.Method_3", EmptyArg{}, &reply)
if err != nil {
t.Error(err)
}
// close the server
ch <- struct{}{}
// wait for the server to close
<-ch
close(ch)
}
When running:
go test -v -count 1 ./src/server/...
The output is as expected:
=== RUN TestMethod_1
2022/05/11 10:59:49 Server running
2022/05/11 10:59:49 network: tcp
--- PASS: TestMethod_1 (0.00s)
=== RUN TestMethod_2
2022/05/11 10:59:49 Server running
2022/05/11 10:59:49 network: tcp
--- PASS: TestMethod_2 (0.00s)
=== RUN TestMethod_3
2022/05/11 10:59:49 Server running
2022/05/11 10:59:49 network: tcp
--- PASS: TestMethod_3 (0.00s)
PASS
ok lsfrpc/src/server 0.008s
And when running
go test -v -count 1 ./src/server/...
go test -v -count 1 ./src/server/...
Everything working fine (the output above, twice)
However, when running:
go test -v -count 2 ./src/server/...
There is an error at the beginning of the second run:
=== RUN TestMethod_1
2022/05/11 10:59:52 Server running
2022/05/11 10:59:52 network: tcp
--- PASS: TestMethod_1 (0.00s)
=== RUN TestMethod_2
2022/05/11 10:59:52 Server running
2022/05/11 10:59:52 network: tcp
--- PASS: TestMethod_2 (0.00s)
=== RUN TestMethod_3
2022/05/11 10:59:52 Server running
2022/05/11 10:59:52 network: tcp
--- PASS: TestMethod_3 (0.00s)
=== RUN TestMethod_1
--- FAIL: TestMethod_1 (0.00s)
panic: http: multiple registrations for /goRPC [recovered]
panic: http: multiple registrations for /goRPC
goroutine 63 [running]:
testing.tRunner.func1.2({0x7b9f20, 0xc0002927f0})
/home/sivsha01/go/src/testing/testing.go:1389 +0x24e
testing.tRunner.func1()
/home/sivsha01/go/src/testing/testing.go:1392 +0x39f
panic({0x7b9f20, 0xc0002927f0})
/home/sivsha01/go/src/runtime/panic.go:838 +0x207
net/http.(*ServeMux).Handle(0xb2e160, {0x83449c, 0x8}, {0x8dc3c0?, 0xc000198000})
Same as I described above. This seems as a wrong behavior to me.
A reduced version to reproduce the issue:
package rpcserver
import (
"net/http"
"os"
"testing"
)
func TestRegister(t *testing.T) {
t.Logf("pid: %d", os.Getpid())
register()
}
func register() {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {})
}
When you run the test with: go test -count 2 -v, you will find that the 2 tests running in the same process. As what is stated in your comment: RegisterRPCMethods() should be called only once per process.
You can use sync.Once to make sure it's just called once:
package rpcserver
import (
"net/http"
"os"
"sync"
"testing"
)
func TestRegister(t *testing.T) {
t.Logf("pid: %d", os.Getpid())
register()
}
var registerOnce sync.Once
func register() {
registerOnce.Do(func() {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {})
})
}
What's more, your tests won't depend on the execution order of the tests any longer. And all the tests can be run alone.