From 7fd4c589dfa87b743047c617bcb036f01b48c0d6 Mon Sep 17 00:00:00 2001
From: hippoz <paperplanelive@gmail.com>
Date: Tue, 2 Feb 2021 10:17:49 +0200
Subject: [PATCH] implement basic parsing

---
 lib/Parser.js | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/Socket.js |   7 +++-
 2 files changed, 107 insertions(+), 1 deletion(-)
 create mode 100644 lib/Parser.js

diff --git a/lib/Parser.js b/lib/Parser.js
new file mode 100644
index 0000000..6a7ed20
--- /dev/null
+++ b/lib/Parser.js
@@ -0,0 +1,101 @@
+class WebsocketFrame {
+    constructor() {
+        // Just defining the structure of the WebsocketFrame,
+        // I could actually just use a normal object but I
+        // might need to add some methods to this in the future
+        // so it's good enough
+
+        // 1 byte - first byte
+        this.FIN = undefined;
+        this.RSVx = undefined;
+        this.Opcode = undefined;
+        
+        // 1 byte - second byte
+        this.MASK = undefined;
+        this.PayloadLen = undefined;
+
+        // 4 bytes - masking key
+        this.MaskingKey = undefined;
+
+        // (Extension Data + Application Data[PayloadLen]) (kind of) - payload data
+        // TODO: Separate extension data from application data
+        this.PayloadData = undefined;
+    }
+}
+
+const parseWebsocketFrame = (data) => {
+    const firstByte = data.getUint8(0);
+    const secondByte = data.getUint8(1);
+
+    const frame = new WebsocketFrame();
+
+    // 1 byte - first byte
+    frame.FIN = (firstByte & 0x01); // 0x01[0b10000000] - Get most significant bit (FIN)
+    frame.RSVx = (firstByte & 0x70) // 0x70[0b01110000] - Get the 3 bits after the most significant bit (RSVx)
+    frame.Opcode = (firstByte & 0x0F) // 0xF[0b00001111] - Get the last 4 bits (Opcode)
+
+    // 1 byte - second byte
+    frame.MASK = (secondByte & 0x01) // 0x01[0b10000000] - Get most significant bit (MASK)
+    frame.PayloadLen = (secondByte & 0x7F) // 0x7F[0b01111111] - Get last 7 bits (Payload len)
+
+    let maskingKeyOffset = 2; // By default, theres a 2 byte offset. We will modify this in the cases below.
+
+    // Handle Payload len cases and set the masking key offset
+    if (frame.PayloadLen === 126) {
+        frame.PayloadLen = data.getUint16(2);
+        maskingKeyOffset = 4; // 4 byte offset, because we also read 2 bytes with getUint16 above (2 bytes (normal size) + 2 bytes)
+    } else if (frame.PayloadLen === 127) {
+        frame.PayloadLen = data.getBigUint64(2);
+        maskingKeyOffset = 10; // 10 byte offset, because we also read 8 bytes with getBigUint64 above (2 bytes (normal size) + 8 bytes)
+    }
+    
+    const maskingKeyEnd = maskingKeyOffset + 4; // (4 bytes because it is a 32 bit value)
+    if (frame.MASK) frame.MaskingKey = data.buffer.slice(maskingKeyOffset, maskingKeyEnd); // Create a new buffer starting at the masking key offset and ending at the masking key end (duh).
+
+    // TODO: Separate extension data from application data
+    frame.PayloadData = data.buffer.slice(maskingKeyEnd, maskingKeyEnd + frame.PayloadLen); // Create a new buffer that starts at the end of the masking key and ends at (the end of the masking key + payload length)
+
+    // TODO: implement unmasked string decoding
+    if (frame.MASK) {
+        switch (frame.Opcode) {
+            case 1: { // Denotes a text frame   
+                const payloadDataView = new DataView(frame.PayloadData);
+                const maskingKeyView = new DataView(frame.MaskingKey);
+    
+                let decoded = '';
+    
+                for (let i = 0; i < frame.PayloadData.byteLength; i++) {
+                    decoded += (String.fromCharCode(payloadDataView.getUint8(i) ^ maskingKeyView.getUint8(i % 4)));
+                }
+                
+                frame.DecodedPayloadData = decoded;
+
+                break;
+            }
+    
+            case 2: { // Denotes a binary frame
+                // TODO: untested
+                const payloadDataView = new DataView(frame.PayloadData);
+                const maskingKeyView = new DataView(frame.MaskingKey);
+    
+                const decoded = [];
+    
+                for (let i = 0; i < frame.PayloadData.byteLength; i++) {
+                    decoded.push(payloadDataView.getUint8(i) ^ maskingKeyView.getUint8(i % 4));
+                }
+                
+                frame.DecodedPayloadData = decoded;
+
+                break;
+            }
+        }
+    }
+
+    return frame;
+}
+
+module.exports = {
+    WebsocketFrame,
+
+    parseWebsocketFrame
+};
\ No newline at end of file
diff --git a/lib/Socket.js b/lib/Socket.js
index 8399329..c51f080 100644
--- a/lib/Socket.js
+++ b/lib/Socket.js
@@ -1,4 +1,5 @@
 const constants = require("./constants");
+const parser = require('./Parser');
 
 class Socket {
     constructor({ initialState='CONNECTING', socket }) {
@@ -10,11 +11,15 @@ class Socket {
         this._socket.on('data', (e) => {
             if (this._state !== constants.states.OPEN) return;
 
-            console.log(e.toString());
+            this._decodePayload(e.buffer);
         });
     }
 }
 
+Socket.prototype._decodePayload = function(payload) {
+    console.log(parser.parseWebsocketFrame(new DataView(payload)));
+};
+
 Socket.prototype._setConnectionState = function(state) {
     this._state = state;
 };