Add example for downloading message media

app.js

@@ -8,6 +8,9 @@ const fs = require('fs');
 const { phoneNumberFormatter } = require('./helpers/formatter');
 const fileUpload = require('express-fileupload');
 const axios = require('axios');
+const mime = require('mime-types');
+const { Z_ERRNO } = require('zlib');
+
 const port = process.env.PORT || 8000;
 
 const app = express();
@@ -73,6 +76,43 @@ client.on('message', msg => {
       }
     });
   }
+
+  // Downloading media
+  if (msg.hasMedia) {
+    msg.downloadMedia().then(media => {
+      // To better understanding
+      // Please look at the console what data we get
+      console.log(media);
+
+      if (media) {
+        // The folder to store: change as you want!
+        // Create if not exists
+        const mediaPath = './downloaded-media/';
+
+        if (!fs.existsSync(mediaPath)) {
+          fs.mkdirSync(mediaPath);
+        }
+
+        // Get the file extension by mime-type
+        const extension = mime.extension(media.mimetype);
+        
+        // Filename: change as you want! 
+        // I will use the time for this example
+        // Why not use media.filename? Because the value is not certain exists
+        const filename = new Date().getTime();
+
+        const fullFilename = mediaPath + filename + '.' + extension;
+
+        // Save to file
+        try {
+          fs.writeFileSync(fullFilename, media.data, { encoding: 'base64' }); 
+          console.log('File downloaded successfully!', fullFilename);
+        } catch (err) {
+          console.log('Failed to save the file:', err);
+        }
+      }
+    });
+  }
 });
 
 client.initialize();