serve: Add rc control for serve commands #4505

This adds the framework for serving. The individual servers will be
added in separate commits.

cmd/serve/servetest/rc.go

@@ -0,0 +1,77 @@
+package servetest
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/rclone/rclone/fs/rc"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// GetEphemeralPort opens a listening port on localhost:0, closes it,
+// and returns the address as "localhost:port".
+func GetEphemeralPort(t *testing.T) string {
+	listener, err := net.Listen("tcp", "localhost:0") // Listen on any available port
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, listener.Close())
+	}()
+	return listener.Addr().String()
+}
+
+// checkTCP attempts to establish a TCP connection to the given address,
+// and closes it if successful. Returns an error if the connection fails.
+func checkTCP(address string) error {
+	conn, err := net.DialTimeout("tcp", address, 5*time.Second)
+	if err != nil {
+		return fmt.Errorf("failed to connect to %s: %w", address, err)
+	}
+
+	err = conn.Close()
+	if err != nil {
+		return fmt.Errorf("failed to close connection to %s: %w", address, err)
+	}
+
+	return nil
+}
+
+// TestRc tests the rc interface for the servers
+//
+// in should contain any options necessary however this code will add
+// "fs", "addr".
+func TestRc(t *testing.T, in rc.Params) {
+	ctx := context.Background()
+	dir := t.TempDir()
+	serveStart := rc.Calls.Get("serve/start")
+	serveStop := rc.Calls.Get("serve/stop")
+	name := in["type"].(string)
+	addr := GetEphemeralPort(t)
+
+	// Start the server
+	in["fs"] = dir
+	in["addr"] = addr
+	out, err := serveStart.Fn(ctx, in)
+	require.NoError(t, err)
+	id := out["id"].(string)
+	assert.True(t, strings.HasPrefix(id, name+"-"))
+	gotAddr := out["addr"].(string)
+	assert.Equal(t, addr, gotAddr)
+
+	// Check we can make a TCP connection to the server
+	t.Logf("Checking connection on %q", addr)
+	err = checkTCP(addr)
+	assert.NoError(t, err)
+
+	// Stop the server
+	_, err = serveStop.Fn(ctx, rc.Params{"id": id})
+	require.NoError(t, err)
+
+	// Check we can make no longer make connections to the server
+	err = checkTCP(addr)
+	assert.Error(t, err)
+}