Clarify comments + add field handler to multipart sample (#609)

* Clarify comments + add field handler to multipart sample

* Address comments

Author: Ace Nassri

functions/http/index.js

@@ -147,21 +147,32 @@ const Busboy = require('busboy');
 exports.uploadFile = (req, res) => {
   if (req.method === 'POST') {
     const busboy = new Busboy({ headers: req.headers });
+    const tmpdir = os.tmpdir();
+
+    // This object will accumulate all the fields, keyed by their name
+    const fields = {};
 
     // This object will accumulate all the uploaded files, keyed by their name.
     const uploads = {};
-    const tmpdir = os.tmpdir();
 
-    // This callback will be invoked for each file uploaded.
+    // This code will process each non-file field in the form.
+    busboy.on('field', (fieldname, val) => {
+      // TODO(developer): Process submitted field values here
+      console.log(`Processed field ${fieldname}: ${val}.`);
+      fields[fieldname] = val;
+    });
+
+    // This code will process each file uploaded.
     busboy.on('file', (fieldname, file, filename) => {
       // Note: os.tmpdir() points to an in-memory file system on GCF
       // Thus, any files in it must fit in the instance's memory.
+      console.log(`Processed file ${filename}`);
       const filepath = path.join(tmpdir, filename);
       uploads[fieldname] = filepath;
       file.pipe(fs.createWriteStream(filepath));
     });
 
-    // This callback will be invoked after all uploaded files are saved.
+    // This event will be triggered after all uploaded files are saved.
     busboy.on('finish', () => {
       // TODO(developer): Process uploaded files here
       for (const name in uploads) {