From b0b1a72ce76112725e6ac9f2e218c9a8c40ade79 Mon Sep 17 00:00:00 2001
From: Mike Marcacci <mike.marcacci@gmail.com>
Date: Sat, 21 Dec 2019 13:31:58 -0500
Subject: [PATCH] Add comments to stream example

---
 api/server.js | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/api/server.js b/api/server.js
index a745012..658a731 100644
--- a/api/server.js
+++ b/api/server.js
@@ -31,15 +31,27 @@ const storeUpload = async upload => {
 
   // Store the file in the filesystem.
   await new Promise((resolve, reject) => {
-    stream
-      .on('error', error => {
-        unlink(path, () => {
-          reject(error)
-        })
+    // Create a stream to which the upload will be written.
+    const writeStream = createWriteStream(path)
+
+    // When the upload is fully written, resolve the promise.
+    writeStream.on('finish', resolve)
+
+    // If there's an error writing the file, remove the partially written file
+    // and reject the promise.
+    writeStream.on('error', error => {
+      unlink(path, () => {
+        reject(error)
       })
-      .pipe(createWriteStream(path))
-      .on('error', reject)
-      .on('finish', resolve)
+    })
+
+    // In node <= 13, errors are not automatically propagated between piped
+    // streams. If there is an error receiving the upload, destroy the write
+    // stream with the corresponding error.
+    stream.on('error', error => writeStream.destroy(error))
+
+    // Pipe the upload into the write stream.
+    stream.pipe(writeStream)
   })
 
   // Record the file metadata in the DB.