Remove a customer's video from disk once its frame is read

attachments.js

@@ -178,12 +178,17 @@ function extractVideoFrame(buf) {
   const os = require('os');
   const path = require('path');
   const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'vec-'));
-  const input = path.join(dir, 'clip.bin');
-  const output = path.join(dir, 'frame.png');
-  fs.writeFileSync(input, buf);
-  const result = spawnSync(ffmpeg, ['-y', '-ss', '1', '-i', input, '-frames:v', '1', output], { timeout: 8000 });
-  if (result.status !== 0 || !fs.existsSync(output)) return null;
-  return fs.readFileSync(output);
+  try {
+    const input = path.join(dir, 'clip.bin');
+    const output = path.join(dir, 'frame.png');
+    fs.writeFileSync(input, buf);
+    const result = spawnSync(ffmpeg, ['-y', '-ss', '1', '-i', input, '-frames:v', '1', output], { timeout: 8000 });
+    if (result.status !== 0 || !fs.existsSync(output)) return null;
+    return fs.readFileSync(output);
+  } finally {
+    // The clip and its frame are a customer's attachment. They do not stay on disk.
+    fs.rmSync(dir, { recursive: true, force: true });
+  }
 }
 
 async function videoErrorLines(attachments, { fetchImpl, extractFrame, recognize } = {}) {

test/attachments.test.js

@@ -315,3 +315,19 @@ test('a video frame keeps the error line and the clip is not sent on', async ()
     { video: true }
   ), false);
 });
+
+test('a customer video is not left on disk after its frame is read', async () => {
+  const fs = require('node:fs');
+  const os = require('node:os');
+  const leftovers = () => fs.readdirSync(os.tmpdir()).filter((name) => name.startsWith('vec-'));
+  const before = new Set(leftovers());
+  const lines = await videoErrorLines(
+    [{ name: 'clip.mp4', contentType: 'video/mp4', url: 'https://cdn.example/clip.mp4' }],
+    {
+      fetchImpl: async () => ({ ok: true, arrayBuffer: async () => Buffer.from('not a real video') }),
+      recognize: async () => 'server_error 1011',
+    }
+  );
+  assert.equal(lines, '');
+  assert.deepEqual(leftovers().filter((name) => !before.has(name)), []);
+});