feat(server): check that serverMode implementation is correct

lib/utils/getSocketServerImplementation.js

@@ -35,6 +35,43 @@ function getSocketServerImplementation(options) {
     );
   }
 
+  if (
+    !ServerImplementation.prototype.constructor ||
+    ServerImplementation.prototype.constructor.length < 1
+  ) {
+    throw new Error(
+      'serverMode must have a constructor that takes a single server argument and calls super(server) ' +
+        "on the superclass BaseServer, found via require('webpack-dev-server/lib/servers/BaseServer')"
+    );
+  }
+
+  if (
+    !ServerImplementation.prototype.send ||
+    ServerImplementation.prototype.send.length < 2
+  ) {
+    throw new Error(
+      'serverMode must have a send(connection, message) method that sends the message string to the provided client connection object'
+    );
+  }
+
+  if (
+    !ServerImplementation.prototype.close ||
+    ServerImplementation.prototype.close.length < 1
+  ) {
+    throw new Error(
+      'serverMode must have a close(connection) method that closes the provided client connection object'
+    );
+  }
+
+  if (
+    !ServerImplementation.prototype.onConnection ||
+    ServerImplementation.prototype.onConnection.length < 1
+  ) {
+    throw new Error(
+      'serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made'
+    );
+  }
+
   return ServerImplementation;
 }
 

test/server/utils/getSocketServerImplementation.test.js

@@ -1,10 +1,13 @@
 'use strict';
 
+/* eslint-disable constructor-super, no-empty-function, no-useless-constructor, no-unused-vars, class-methods-use-this */
+
 const getSocketServerImplementation = require('../../../lib/utils/getSocketServerImplementation');
+const BaseServer = require('../../../lib/servers/BaseServer');
 const SockJSServer = require('../../../lib/servers/SockJSServer');
 
 describe('getSocketServerImplementation util', () => {
-  it("should works with string serverMode ('sockjs')", () => {
+  it("should work with string serverMode ('sockjs')", () => {
     let result;
 
     expect(() => {
@@ -16,7 +19,7 @@ describe('getSocketServerImplementation util', () => {
     expect(result).toEqual(SockJSServer);
   });
 
-  it('should works with serverMode (SockJSServer class)', () => {
+  it('should work with serverMode (SockJSServer class)', () => {
     let result;
 
     expect(() => {
@@ -40,11 +43,87 @@ describe('getSocketServerImplementation util', () => {
     expect(result).toEqual(SockJSServer);
   });
 
-  it('should throws with serverMode (bad path)', () => {
+  it('should throw with serverMode (bad path)', () => {
     expect(() => {
       getSocketServerImplementation({
         serverMode: '/bad/path/to/implementation',
       });
-    }).toThrow(/serverMode must be a string/);
+    }).toThrow(/serverMode must be a string denoting a default implementation/);
+  });
+
+  it('should throw with serverMode (incorrect constructor)', () => {
+    expect(() => {
+      getSocketServerImplementation({
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor() {}
+        },
+      });
+    }).toThrow(
+      "serverMode must have a constructor that takes a single server argument and calls super(server) on the superclass BaseServer, found via require('webpack-dev-server/lib/servers/BaseServer')"
+    );
+  });
+
+  it('should throw with serverMode (no send method)', () => {
+    expect(() => {
+      getSocketServerImplementation({
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+        },
+      });
+    }).toThrow(
+      'serverMode must have a send(connection, message) method that sends the message string to the provided client connection object'
+    );
+  });
+
+  it('should throw with serverMode (incorrect send parameters)', () => {
+    expect(() => {
+      getSocketServerImplementation({
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+
+          send(connection) {}
+        },
+      });
+    }).toThrow(
+      'serverMode must have a send(connection, message) method that sends the message string to the provided client connection object'
+    );
+  });
+
+  it('should throw with serverMode (no close method)', () => {
+    expect(() => {
+      getSocketServerImplementation({
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+
+          send(connection, message) {}
+        },
+      });
+    }).toThrow(
+      'serverMode must have a close(connection) method that closes the provided client connection object'
+    );
+  });
+
+  it('should throw with serverMode (no onConnection method)', () => {
+    expect(() => {
+      getSocketServerImplementation({
+        serverMode: class ServerImplementation extends BaseServer {
+          constructor(server) {
+            super(server);
+          }
+
+          send(connection, message) {}
+
+          close(connection) {}
+        },
+      });
+    }).toThrow(
+      'serverMode must have a onConnection(f) method that calls f(connection) whenever a new client connection is made'
+    );
   });
 });