From 0c6ba4c1a866b0cf34330cc5d94ee3e34671067d Mon Sep 17 00:00:00 2001
From: Brian Gough <brian.gough@overleaf.com>
Date: Tue, 16 Jul 2019 14:02:52 +0100
Subject: [PATCH] monkeypatch socket.io to fix frame handler in v0.9.16

---
 services/real-time/app.coffee         |  3 ++
 services/real-time/socket.io.patch.js | 43 +++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 services/real-time/socket.io.patch.js

diff --git a/services/real-time/app.coffee b/services/real-time/app.coffee
index 4effc386df..7b53730ce6 100644
--- a/services/real-time/app.coffee
+++ b/services/real-time/app.coffee
@@ -23,6 +23,9 @@ CookieParser = require("cookie-parser")
 DrainManager = require("./app/js/DrainManager")
 HealthCheckManager = require("./app/js/HealthCheckManager")
 
+# work around frame handler bug in socket.io v0.9.16
+require("./socket.io.patch.js") 
+
 # Set up socket.io server
 app = express()
 Metrics.injectMetricsRoute(app)
diff --git a/services/real-time/socket.io.patch.js b/services/real-time/socket.io.patch.js
new file mode 100644
index 0000000000..21a9608133
--- /dev/null
+++ b/services/real-time/socket.io.patch.js
@@ -0,0 +1,43 @@
+var io = require("socket.io");
+
+if (io.version === "0.9.16") {
+  console.log("patching socket.io hybi-16 transport frame prototype");
+  var transports = require("socket.io/lib/transports/websocket/hybi-16.js");
+  transports.prototype.frame = patchedFrameHandler;
+  // file hybi-07-12 has the same problem but no browsers are using that protocol now
+}
+
+function patchedFrameHandler(opcode, str) {
+  var dataBuffer = new Buffer(str),
+    dataLength = dataBuffer.length,
+    startOffset = 2,
+    secondByte = dataLength;
+  if (dataLength === 65536) {
+    console.log("fixing invalid frame length in socket.io");
+  }
+  if (dataLength > 65535) {
+    // original code had > 65536
+    startOffset = 10;
+    secondByte = 127;
+  } else if (dataLength > 125) {
+    startOffset = 4;
+    secondByte = 126;
+  }
+  var outputBuffer = new Buffer(dataLength + startOffset);
+  outputBuffer[0] = opcode;
+  outputBuffer[1] = secondByte;
+  dataBuffer.copy(outputBuffer, startOffset);
+  switch (secondByte) {
+    case 126:
+      outputBuffer[2] = dataLength >>> 8;
+      outputBuffer[3] = dataLength % 256;
+      break;
+    case 127:
+      var l = dataLength;
+      for (var i = 1; i <= 8; ++i) {
+        outputBuffer[startOffset - i] = l & 0xff;
+        l >>>= 8;
+      }
+  }
+  return outputBuffer;
+}