Add backpressure example

examples/Backpressure.js

@@ -0,0 +1,73 @@
+/* A few users have reported having issues understanding backpressure and how to deal with it.
+ *
+ * Backpressure is the buildup of unacknowledged data; you can't just call ws.send without checking for backpressure.
+ * Data doesn't just, poof, immediately jump from your server to the receiver - the receiver has to actually... receive it.
+ * That happens with ACKs, controlling the transmission window.
+ *
+ * This applies to _EVERYTHING_ computer science (not just uWS); files, sockets, queues, and so on. If you're building
+ * web services without taking backpressure into account you're not developing proper solutions - you're fucking around.
+ *
+ * Any slow receiver can wreck your whole server if you're not taking backpressure into account.
+ *
+ * The following is a (preposterous) example of how data can be pushed according to backpressure.
+ * Do not take this as a way to actually write code, this is horrible, but it shows the concept clearly.
+ *
+ */
+
+/* Number between thumb and index finger */
+const backpressure = 1024;
+
+/* Used for statistics */
+let messages = 0;
+let messageNumber = 0;
+
+const uWS = require('../dist/uws.js');
+const port = 9001;
+
+const app = uWS./*SSL*/App({
+  key_file_name: 'misc/key.pem',
+  cert_file_name: 'misc/cert.pem',
+  passphrase: '1234'
+}).ws('/*', {
+  /* Options */
+  compression: 0,
+  maxPayloadLength: 16 * 1024 * 1024,
+  /* We need a slightly higher timeout for this crazy example */
+  idleTimeout: 60,
+  /* Handlers */
+  open: (ws, req) => {
+    console.log('A WebSocket connected via URL: ' + req.getUrl() + '! Pushing data now!');
+    /* We begin our example by sending until we have backpressure */
+    while (ws.getBufferedAmount() < backpressure) {
+        ws.send("This is a message, let's call it " + messageNumber);
+        messageNumber++;
+        messages++;
+    }
+  },
+  drain: (ws) => {
+    /* Continue sending when we have drained (some) */
+    while (ws.getBufferedAmount() < backpressure) {
+      ws.send("This is a message, let's call it " + messageNumber);
+      messageNumber++;
+      messages++;
+    }
+  },
+  close: (ws, code, message) => {
+    console.log('WebSocket closed');
+  }
+}).any('/*', (res, req) => {
+  res.end('Nothing to see here!');
+}).listen(port, (token) => {
+  if (token) {
+    console.log('Listening to port ' + port);
+  } else {
+    console.log('Failed to listen to port ' + port);
+  }
+});
+
+/* Start a timer to check how fast we end up sending.
+ * Not a benchmark, just statistics. */
+setInterval(() => {
+    console.log("Sent " + messages + " messages last second");
+    messages = 0;
+}, 1000);