dgram: support dgram.send with multiple buffers

Added ability to dgram.send to send multiple buffers, _writev style.
The offset and length parameters in dgram.send are now optional.
Refactored the dgram benchmarks, and seperated them from net.
Added docs for the new signature.

Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
Fixes: nodejs#4302
PR-URL: nodejs#4374

Makefile

@@ -501,7 +501,10 @@ bench-events: all
 bench-util: all
 	@$(NODE) benchmark/common.js util
 
-bench-all: bench bench-misc bench-array bench-buffer bench-url bench-events
+bench-dgram: all
+	@$(NODE) benchmark/common.js dgram
+
+bench-all: bench bench-misc bench-array bench-buffer bench-url bench-events bench-dgram bench-util
 
 bench: bench-net bench-http bench-fs bench-tls
 

benchmark/dgram/array-vs-concat.js

@@ -0,0 +1,80 @@
+// test UDP send throughput with the multi buffer API against Buffer.concat
+'use strict';
+
+const common = require('../common.js');
+const PORT = common.PORT;
+
+// `num` is the number of send requests to queue up each time.
+// Keep it reasonably high (>10) otherwise you're benchmarking the speed of
+// event loop cycles more than anything else.
+var bench = common.createBenchmark(main, {
+  len: [64, 256, 512, 1024],
+  num: [100],
+  chunks: [1, 2, 4, 8],
+  type: ['concat', 'multi'],
+  dur: [5]
+});
+
+var dur;
+var len;
+var num;
+var type;
+var chunk;
+var chunks;
+var encoding;
+
+function main(conf) {
+  dur = +conf.dur;
+  len = +conf.len;
+  num = +conf.num;
+  type = conf.type;
+  chunks = +conf.chunks;
+
+  chunk = []
+  for (var i = 0; i < chunks; i++) {
+    chunk.push(new Buffer(Math.round(len / chunks)));
+  }
+
+  server();
+}
+
+var dgram = require('dgram');
+
+function server() {
+  var sent = 0;
+  var received = 0;
+  var socket = dgram.createSocket('udp4');
+
+  var onsend = type === 'concat' ? onsendConcat : onsendMulti;
+
+  function onsendConcat() {
+    if (sent++ % num == 0)
+      for (var i = 0; i < num; i++) {
+        socket.send(Buffer.concat(chunk), PORT, '127.0.0.1', onsend);
+      }
+  }
+
+  function onsendMulti() {
+    if (sent++ % num == 0)
+      for (var i = 0; i < num; i++) {
+        socket.send(chunk, PORT, '127.0.0.1', onsend);
+      }
+  }
+
+  socket.on('listening', function() {
+    bench.start();
+    onsend();
+
+    setTimeout(function() {
+      var bytes = sent * len;
+      var gbits = (bytes * 8) / (1024 * 1024 * 1024);
+      bench.end(gbits);
+    }, dur * 1000);
+  });
+
+  socket.on('message', function(buf, rinfo) {
+    received++;
+  });
+
+  socket.bind(PORT);
+}

benchmark/dgram/multi-buffer.js

@@ -0,0 +1,70 @@
+// test UDP send/recv throughput with the multi buffer API
+'use strict';
+
+const common = require('../common.js');
+const PORT = common.PORT;
+
+// `num` is the number of send requests to queue up each time.
+// Keep it reasonably high (>10) otherwise you're benchmarking the speed of
+// event loop cycles more than anything else.
+var bench = common.createBenchmark(main, {
+  len: [64, 256, 1024],
+  num: [100],
+  chunks: [1, 2, 4, 8],
+  type: ['send', 'recv'],
+  dur: [5]
+});
+
+var dur;
+var len;
+var num;
+var type;
+var chunk;
+var chunks;
+var encoding;
+
+function main(conf) {
+  dur = +conf.dur;
+  len = +conf.len;
+  num = +conf.num;
+  type = conf.type;
+  chunks = +conf.chunks;
+
+  chunk = []
+  for (var i = 0; i < chunks; i++) {
+    chunk.push(new Buffer(Math.round(len / chunks)));
+  }
+
+  server();
+}
+
+var dgram = require('dgram');
+
+function server() {
+  var sent = 0;
+  var received = 0;
+  var socket = dgram.createSocket('udp4');
+
+  function onsend() {
+    if (sent++ % num == 0)
+      for (var i = 0; i < num; i++)
+        socket.send(chunk, PORT, '127.0.0.1', onsend);
+  }
+
+  socket.on('listening', function() {
+    bench.start();
+    onsend();
+
+    setTimeout(function() {
+      var bytes = (type === 'send' ? sent : received) * len;
+      var gbits = (bytes * 8) / (1024 * 1024 * 1024);
+      bench.end(gbits);
+    }, dur * 1000);
+  });
+
+  socket.on('message', function(buf, rinfo) {
+    received++;
+  });
+
+  socket.bind(PORT);
+}

benchmark/net/dgram.js → benchmark/dgram/offset-length.js

@@ -1,7 +1,8 @@
-// test UDP send/recv throughput
+// test UDP send/recv throughput with the "old" offset/length API
+'use strict';
 
-var common = require('../common.js');
-var PORT = common.PORT;
+const common = require('../common.js');
+const PORT = common.PORT;
 
 // `num` is the number of send requests to queue up each time.
 // Keep it reasonably high (>10) otherwise you're benchmarking the speed of

benchmark/dgram/single-buffer.js

@@ -0,0 +1,62 @@
+// test UDP send/recv throughput with the new single Buffer API
+'use strict';
+
+const common = require('../common.js');
+const PORT = common.PORT;
+
+// `num` is the number of send requests to queue up each time.
+// Keep it reasonably high (>10) otherwise you're benchmarking the speed of
+// event loop cycles more than anything else.
+var bench = common.createBenchmark(main, {
+  len: [1, 64, 256, 1024],
+  num: [100],
+  type: ['send', 'recv'],
+  dur: [5]
+});
+
+var dur;
+var len;
+var num;
+var type;
+var chunk;
+var encoding;
+
+function main(conf) {
+  dur = +conf.dur;
+  len = +conf.len;
+  num = +conf.num;
+  type = conf.type;
+  chunk = new Buffer(len);
+  server();
+}
+
+var dgram = require('dgram');
+
+function server() {
+  var sent = 0;
+  var received = 0;
+  var socket = dgram.createSocket('udp4');
+
+  function onsend() {
+    if (sent++ % num == 0)
+      for (var i = 0; i < num; i++)
+        socket.send(chunk, PORT, '127.0.0.1', onsend);
+  }
+
+  socket.on('listening', function() {
+    bench.start();
+    onsend();
+
+    setTimeout(function() {
+      var bytes = (type === 'send' ? sent : received) * chunk.length;
+      var gbits = (bytes * 8) / (1024 * 1024 * 1024);
+      bench.end(gbits);
+    }, dur * 1000);
+  });
+
+  socket.on('message', function(buf, rinfo) {
+    received++;
+  });
+
+  socket.bind(PORT);
+}

doc/api/dgram.markdown

@@ -185,9 +185,10 @@ never have reason to call this.
 If `multicastInterface` is not specified, the operating system will attempt to
 drop membership on all valid interfaces.
 
-### socket.send(buf, offset, length, port, address[, callback])
+### socket.send(buf, [offset, length,] port, address[, callback])
 
-* `buf` Buffer object or string.  Message to be sent
+* `buf` Buffer object, string, or an array of either. Message to be
+  sent.
 * `offset` Integer. Offset in the buffer where the message starts.
 * `length` Integer. Number of bytes in the message.
 * `port` Integer. Destination port.
@@ -224,17 +225,36 @@ The only way to know for sure that the datagram has been sent is by using a
 passed as the first argument to the `callback`. If a `callback` is not given,
 the error is emitted as an `'error'` event on the `socket` object.
 
+Offset and length are optional, but if you specify one you would need to
+specify the other. Also, they are supported only when the first
+argument is a `Buffer`.
+
 Example of sending a UDP packet to a random port on `localhost`;
 
 ```js
 const dgram = require('dgram');
 const message = new Buffer('Some bytes');
 const client = dgram.createSocket('udp4');
-client.send(message, 0, message.length, 41234, 'localhost', (err) => {
+client.send(message, 41234, 'localhost', (err) => {
+  client.close();
+});
+```
+
+Example of sending a UDP packet composed of multiple buffers to a random port on `localhost`;
+
+```js
+const dgram = require('dgram');
+const buf1 = new Buffer('Some ');
+const buf2 = new Buffer('bytes');
+const client = dgram.createSocket('udp4');
+client.send([buf1, buf2], 41234, 'localhost', (err) => {
   client.close();
 });
 ```
 
+Sending multiple buffers might be faster or slower depending on your
+application and operating system: benchmark it. Usually it is faster.
+
 **A Note about UDP datagram size**
 
 The maximum size of an `IPv4/v6` datagram depends on the `MTU`