Allow clients to use the already used port on a standalone server

src/client/mockttp-client.ts

@@ -166,7 +166,7 @@ export default class MockttpClient extends AbstractMockttp implements Mockttp {
     }
 
     async start(port?: number): Promise<void> {
-        if (this.mockServerConfig) throw new Error('Server is already started');
+        if (this.mockServerConfig && !this.mockServerOptions.allowMultiClientsOnPort) throw new Error('Server is already started');
 
         const path = port ? `/start?port=${port}` : '/start';
         let mockServerConfig = await this.requestFromStandalone<MockServerConfig>(path, {

src/mockttp.ts

@@ -167,6 +167,7 @@ export interface Mockttp {
 }
 
 export interface MockttpOptions {
+    allowMultiClientsOnPort?: boolean;
     cors?: boolean;
     debug?: boolean;
     https?: CAOptions;

src/standalone/mockttp-standalone.ts

@@ -29,6 +29,7 @@ import { MockttpOptions } from '../mockttp';
 import { Duplex, PassThrough } from 'stream';
 
 export interface StandaloneServerOptions {
+    allowMultiClientsOnPort?: boolean;
     debug?: boolean;
     serverDefaults?: MockttpOptions;
 }
@@ -60,9 +61,14 @@ export class MockttpStandalone {
                 );
 
                 if (port != null && this.routers[port] != null) {
-                    res.status(409).json({
-                        error: `Cannot start: mock server is already running on port ${port}`
-                    });
+                    if(options.allowMultiClientsOnPort) {
+                        res.status(200).json(this.getMockServerConfigForPort(port));
+                    } else {
+                        res.status(409).json({
+                            error: `Cannot start: mock server is already running on port ${port}`
+                        });
+                    }
+
                     return;
                 }
 
@@ -133,6 +139,21 @@ export class MockttpStandalone {
         });
     }
 
+    private getMockServerConfigForPort(port: number) {
+        const mockServerOnPort = this.mockServers.find(server => server.port === port);
+
+        if(mockServerOnPort) {
+            return {
+                mockRoot: mockServerOnPort.url,
+                port,
+            }
+        }
+
+        return {
+            port,
+        }
+    }
+
     private routers: { [port: number]: express.Router } = { };
     private subscriptionServers: { [port: number]: SubscriptionServer } = { };
     private streamServers: { [port: number]: ws.Server } = { };