Added DownloadMediaMessage

src/WAClient/Messages.ts

@@ -17,7 +17,7 @@ import {
 } from './Constants'
 import { generateMessageID, sha256, hmacSign, aesEncrypWithIV, randomBytes } from '../WAConnection/Utils'
 import { WAMessageContent, WAMetric, WAFlag, WANode, WAMessage, WAMessageProto } from '../WAConnection/Constants'
-import { validateJIDForSending, generateThumbnail, getMediaKeys } from './Utils'
+import { validateJIDForSending, generateThumbnail, getMediaKeys, decodeMediaMessageBuffer } from './Utils'
 import { proto } from '../../WAMessage/WAMessage'
 
 export default class WhatsAppWebMessages extends WhatsAppWebGroups {
@@ -335,4 +335,19 @@ export default class WhatsAppWebMessages extends WhatsAppWebGroups {
             message: messageJSON as WAMessage
         } as WASendMessageResponse
     }
+    /**
+     * Securely downloads the media from the message. 
+     * Renews the download url automatically, if necessary.
+     */
+    async downloadMediaMessage (message: WAMessage) {
+        try {
+            return decodeMediaMessageBuffer (message.message)
+        } catch (error) {
+            if (error.toString().includes('Empty buffer returned')) {
+                await this.updateMediaMessage (message)
+                return decodeMediaMessageBuffer (message.message)
+            }
+            throw error
+        }
+    }
 }

src/WAClient/Tests.ts

@@ -52,7 +52,8 @@ WAClientTest('Messages', (client) => {
     it('should send a gif', async () => {
         const content = fs.readFileSync('./Media/ma_gif.mp4')
         const message = await sendAndRetreiveMessage(client, content, MessageType.video, { mimetype: Mimetype.gif })
-        const file = await decodeMediaMessage(message.message, './Media/received_vid')
+        const buffer = await client.downloadMediaMessage(message)
+        fs.writeFileSync ('./Media/received_vid.mp4', buffer)
     })
     it('should send an image', async () => {
         const content = fs.readFileSync('./Media/meme.jpeg')

src/WAClient/Utils.ts

@@ -133,7 +133,7 @@ export async function decodeMediaMessageBuffer(message: WAMessageContent) {
     const fetched = await fetch(messageContent.url, { headers: { Origin: 'https://web.whatsapp.com' } })
     const buffer = await fetched.buffer()
 
-    if (buffer.length === 0) {
+    if (buffer.length <= 10) {
         throw new Error ('Empty buffer returned. File has possibly been deleted from WA servers. Run `client.updateMediaMessage()` to refresh the url')
     }
 
@@ -148,11 +148,9 @@ export async function decodeMediaMessageBuffer(message: WAMessageContent) {
         const testBuff = Buffer.concat([mediaKeys.iv, file])
         const sign = hmacSign(testBuff, mediaKeys.macKey).slice(0, 10)
         // our sign should equal the mac
-        if (sign.equals(mac)) {
-            return aesDecryptWithIV(file, mediaKeys.cipherKey, mediaKeys.iv) // decrypt media
-        } else {
-            throw new Error()
-        }
+        if (!sign.equals(mac)) throw new Error()
+        
+        return aesDecryptWithIV(file, mediaKeys.cipherKey, mediaKeys.iv) // decrypt media
     }
     const allTypes = [type, ...Object.keys(HKDFInfoKeys)]
     for (let i = 0; i < allTypes.length;i++) {
@@ -165,7 +163,7 @@ export async function decodeMediaMessageBuffer(message: WAMessageContent) {
             if (i === 0) { console.log (`decryption of ${type} media with original HKDF key failed`) }
         }
     }
-    throw new Error('HMAC sign does not match for ' + buffer.length)
+    throw new Error('Decryption failed, HMAC sign does not match')
 }
 /**
  * Decode a media message (video, image, document, audio) & save it to the given file