fix: try to use next available port

closes #15

Author: fengmk2

lib/detect-port.js

@@ -8,26 +8,40 @@ module.exports = (port, callback) => {
     callback = port;
     port = null;
   }
+  port = parseInt(port) || 0;
+  let maxPort = port + 10;
+  if (maxPort > 65535) {
+    maxPort = 65535;
+  }
+  debug('detect free port between [%s, %s)', port, maxPort);
   if (typeof callback === 'function') {
-    return tryListen(port, callback);
+    return tryListen(port, maxPort, callback);
   }
   // promise
   return new Promise(resolve => {
-    tryListen(port, (_, realPort) => {
+    tryListen(port, maxPort, (_, realPort) => {
       resolve(realPort);
     });
   });
 };
 
-function tryListen(port, callback) {
-  port = parseInt(port) || 0;
+function tryListen(port, maxPort, callback) {
   const server = new net.Server();
 
   server.on('error', err => {
     debug('listen %s error: %s', port, err);
-    port = 0;
+    if (port === 0) {
+      return callback(err);
+    }
+
+    port++;
+    if (port >= maxPort) {
+      debug('port: %s >= maxPort: %s, give up and use random port', port, maxPort);
+      port = 0;
+      maxPort = 0;
+    }
     server.close();
-    return tryListen(port, callback);
+    return tryListen(port, maxPort, callback);
   });
 
   server.listen({ port }, () => {

package.json

@@ -23,7 +23,8 @@
     "egg-bin": "^2.0.0",
     "egg-ci": "^1.1.0",
     "eslint": "^3.13.1",
-    "eslint-config-egg": "^3.1.0"
+    "eslint-config-egg": "^3.1.0",
+    "pedding": "^1.1.0"
   },
   "scripts": {
     "test": "egg-bin test",

test/detect-port.test.js

@@ -2,16 +2,24 @@
 
 const assert = require('assert');
 const net = require('net');
+const pedding = require('pedding');
 const detectPort = require('..');
 
 describe('detect port test', () => {
-  let server;
+  const servers = [];
   before(done => {
-    server = new net.Server();
-    server.listen(7001, done);
+    done = pedding(11, done);
+    const server = new net.Server();
+    server.listen(3000, done);
+    servers.push(server);
+    for (let port = 7000; port < 7010; port++) {
+      const server = new net.Server();
+      server.listen(port, done);
+      servers.push(server);
+    }
   });
   after(() => {
-    server.close();
+    servers.forEach(server => server.close());
   });
 
   it('get random port', done => {
@@ -29,11 +37,18 @@ describe('detect port test', () => {
     });
   });
 
-  it('work with listening port', done => {
-    const port = 7001;
+  it('work with listening next port 3001', done => {
+    const port = 3000;
     detectPort(port, (_, realPort) => {
-      assert(realPort !== 7001);
-      assert(realPort > 0);
+      assert(realPort === 3001);
+      done();
+    });
+  });
+
+  it('work with listening random port when try port hit maxPort', done => {
+    const port = 7000;
+    detectPort(port, (_, realPort) => {
+      assert(realPort < 7000 || realPort > 7009);
       done();
     });
   });