Wrap up connection + in memory store

src/Utils/decode-wa-message.ts

@@ -0,0 +1,63 @@
+import { Boom } from '@hapi/boom'
+import BinaryNode from "../BinaryNode"
+import { aesDecrypt, hmacSign } from "./generics"
+import { DisconnectReason, WATag } from "../Types"
+
+export const decodeWAMessage = (
+    message: string | Buffer, 
+    auth: { macKey: Buffer, encKey: Buffer }, 
+    fromMe: boolean=false
+) => {
+
+    let commaIndex = message.indexOf(',') // all whatsapp messages have a tag and a comma, followed by the actual message
+    if (commaIndex < 0) throw new Boom('invalid message', { data: message }) // if there was no comma, then this message must be not be valid
+    
+    if (message[commaIndex+1] === ',') commaIndex += 1
+    let data = message.slice(commaIndex+1, message.length)
+    
+    // get the message tag.
+    // If a query was done, the server will respond with the same message tag we sent the query with
+    const messageTag: string = message.slice(0, commaIndex).toString()
+    let json: any
+    let tags: WATag
+    if (data.length > 0) {
+        if (typeof data === 'string') {
+            json = JSON.parse(data) // parse the JSON
+        } else {
+            const { macKey, encKey } = auth || {}
+            if (!macKey || !encKey) {
+                throw new Boom('recieved encrypted buffer when auth creds unavailable', { data: message, statusCode: DisconnectReason.badSession })
+            }
+            /* 
+                If the data recieved was not a JSON, then it must be an encrypted message.
+                Such a message can only be decrypted if we're connected successfully to the servers & have encryption keys
+            */
+            if (fromMe) {
+                tags = [data[0], data[1]]
+                data = data.slice(2, data.length)
+            }
+            
+            const checksum = data.slice(0, 32) // the first 32 bytes of the buffer are the HMAC sign of the message
+            data = data.slice(32, data.length) // the actual message
+            const computedChecksum = hmacSign(data, macKey) // compute the sign of the message we recieved using our macKey
+            
+            if (checksum.equals(computedChecksum)) {
+                // the checksum the server sent, must match the one we computed for the message to be valid
+                const decrypted = aesDecrypt(data, encKey) // decrypt using AES
+                json = BinaryNode.from(decrypted) // decode the binary message into a JSON array
+            } else {
+                throw new Boom('Bad checksum', {
+                    data: {
+                        received: checksum.toString('hex'),
+                        computed: computedChecksum.toString('hex'),
+                        data: data.slice(0, 80).toString(),
+                        tag: messageTag,
+                        message: message.slice(0, 80).toString()
+                    },
+                    statusCode: DisconnectReason.badSession
+                })
+            }
+        }   
+    }
+    return [messageTag, json, tags] as const
+}