fix(common): servers#listen() port number validation

Fixes hyperledger-cacti#383

Ensures that the when specifying port 0 the liste()
method does not throw an exception since it is
perfectly valid to bind to port zero in general.

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

packages/cactus-common/src/main/typescript/servers.ts

@@ -43,7 +43,10 @@ export class Servers {
 
     Checks.truthy(options, `${fnTag} arg options`);
     Checks.truthy(options.server, `${fnTag} arg options.server`);
-    Checks.truthy(options.port, `${fnTag} arg options.port`);
+    Checks.truthy(
+      options.port || options.port === 0,
+      `${fnTag} arg options.port`
+    );
     Checks.truthy(options.hostname, `${fnTag} arg options.hostname`);
     const { server, port, hostname } = options;
 

packages/cactus-common/src/test/typescript/unit/servers.test.ts

@@ -0,0 +1,41 @@
+import { createServer } from "http";
+
+import test, { Test } from "tape-promise/tape";
+
+import { Servers } from "../../../main/typescript/index";
+
+test("Servers", async (tParent: Test) => {
+  test("Servers#listen()", async (t: Test) => {
+    {
+      const server = createServer();
+      await t.rejects(
+        Servers.listen({ hostname: "x", port: "" as any, server }),
+        /options\.port/,
+        "Rejects when port specified as empty string OK"
+      );
+    }
+
+    {
+      const server = createServer();
+      await t.rejects(
+        Servers.listen({ hostname: "localhost", port: false as any, server }),
+        /options\.port/,
+        "Rejects when port specified as literal false boolean OK"
+      );
+      // await Servers.shutdown(server);
+    }
+
+    {
+      const server = createServer();
+      await t.doesNotReject(
+        Servers.listen({ hostname: "localhost", port: 0, server }),
+        "Does not rejects when port specified as zero OK"
+      );
+      await Servers.shutdown(server);
+    }
+
+    t.end();
+  });
+
+  tParent.end();
+});