dgram: implicit binds should be exclusive

Server sockets should be shared by default, and client sockets should be
exclusive by default. For net/TCP, this is how it is, for dgram/UDP, its
a little less clear what a client socket is, but a socket that is
auto-bound during a dgram.send() is not usefully shared among cluster
workers, any more than an outgoing TCP connection would be usefully
shared.

Since implicit binds become exclusive, implicit/client dgram sockets can
now be used with cluster on Windows. Before, neither explicit nor
implicitly bound sockets could be used, causing dgram to be completely
unsupported with cluster on Windows. After this change, they become half
supported.

PR-URL: https://github.com/joyent/node/pull/8643
Reviewed-by: Bert Belder <bertbelder@gmail.com>

lib/dgram.js

@@ -299,7 +299,7 @@ Socket.prototype.send = function(buffer,
   self._healthCheck();
 
   if (self._bindState == BIND_STATE_UNBOUND)
-    self.bind(0, null);
+    self.bind({port: 0, exclusive: true}, null);
 
   // If the socket hasn't been bound yet, push the outbound packet onto the
   // send queue and send after binding is complete.

test/parallel/test-dgram-exclusive-implicit-bind.js

@@ -0,0 +1,100 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var cluster = require('cluster');
+var dgram = require('dgram');
+
+// Without an explicit bind, send() causes an implicit bind, which always
+// generate a unique per-socket ephemeral port. An explicit bind to a port
+// number causes all sockets bound to that number to share a port.
+//
+// The 2 workers that call bind() will share a port, the two workers that do
+// not will not share a port, so master will see 3 unique source ports.
+
+// Note that on Windows, clustered dgram is not supported. Since explicit
+// binding causes the dgram to be clustered, don't fork the workers that bind.
+// This is a useful test, still, because it demonstrates that by avoiding
+// clustering, client (ephemeral, implicitly bound) dgram sockets become
+// supported while using cluster, though servers still cause the master to error
+// with ENOTSUP.
+
+var windows = process.platform === 'win32';
+
+if (cluster.isMaster) {
+  var pass;
+  var messages = 0;
+  var ports = {};
+
+  process.on('exit', function() {
+    assert.equal(pass, true);
+  });
+
+  var target = dgram.createSocket('udp4');
+
+  target.on('message', function(buf, rinfo) {
+    messages++;
+    ports[rinfo.port] = true;
+
+    if (windows && messages === 2) {
+      assert.equal(Object.keys(ports).length, 2);
+      done();
+    }
+
+    if (!windows && messages === 4) {
+      assert.equal(Object.keys(ports).length, 3);
+      done();
+    }
+
+    function done() {
+      pass = true;
+      cluster.disconnect();
+      target.close();
+    }
+  });
+
+  target.on('listening', function() {
+    cluster.fork();
+    cluster.fork();
+    if (!windows) {
+      cluster.fork({BOUND: 'y'});
+      cluster.fork({BOUND: 'y'});
+    }
+  });
+
+  target.bind({port: common.PORT, exclusive: true});
+
+  return;
+}
+
+var source = dgram.createSocket('udp4');
+
+if (process.env.BOUND === 'y') {
+  source.bind(0);
+} else {
+  // cluster doesn't know about exclusive sockets, so it won't close them. This
+  // is expected, its the same situation for timers, outgoing tcp connections,
+  // etc, which also keep workers alive after disconnect was requested.
+  source.unref();
+}
+
+source.send(Buffer('abc'), 0, 3, common.PORT, '127.0.0.1');