fix: validate parsed user metadata shape

src/http/routes/object/getSignedUploadURL.ts

@@ -78,8 +78,6 @@ export default async function routes(fastify: FastifyInstance) {
       const customMd = request.headers['x-metadata']
 
       if (typeof customMd === 'string') {
-        // TODO: parseUserMetadata casts to Record<string, string> but values could be anything;
-        // validation should be added in a follow-up
         userMetadata = parseUserMetadata(customMd)
       }
 

src/storage/uploader.test.ts

@@ -33,6 +33,7 @@ import { FileStore } from './protocols/tus/file-store'
 import { UploadId } from './protocols/tus/upload-id'
 import { AssetRenderer } from './renderer/asset'
 import { Storage } from './storage'
+import { parseUserMetadata } from './uploader'
 
 type SavedObject = Parameters<Database['upsertObject']>[0] & { id: string }
 
@@ -588,3 +589,34 @@ describe('multipart fields after the file', () => {
     expect(fixture.saved?.metadata?.contentEncoding).toBe(contentEncoding)
   })
 })
+
+describe('parseUserMetadata', () => {
+  const encode = (value: unknown) => Buffer.from(JSON.stringify(value)).toString('base64')
+
+  test('parses a metadata object with arbitrary JSON values', () => {
+    const metadata = {
+      source: 'client',
+      processed: true,
+      attempts: 3,
+      labels: ['invoice', 'paid'],
+      nested: { system: 'erp' },
+      empty: null,
+    }
+
+    expect(parseUserMetadata(encode(metadata))).toEqual(metadata)
+  })
+
+  test.each([
+    ['null', null],
+    ['an array', ['invoice', 'paid']],
+    ['a string', 'client'],
+    ['a number', 3],
+    ['a boolean', true],
+  ])('rejects %s as top-level metadata', (_description, metadata) => {
+    expect(parseUserMetadata(encode(metadata))).toBeUndefined()
+  })
+
+  test('rejects malformed metadata', () => {
+    expect(parseUserMetadata(Buffer.from('{invalid-json').toString('base64'))).toBeUndefined()
+  })
+})

src/storage/uploader.ts

@@ -565,10 +565,16 @@ export async function fileUploadFromRequest(
   }
 }
 
-export function parseUserMetadata(metadata: string) {
+export function parseUserMetadata(metadata: string): Record<string, unknown> | undefined {
   try {
     const json = Buffer.from(metadata, 'base64').toString('utf8')
-    return JSON.parse(json) as Record<string, string>
+    const parsed: unknown = JSON.parse(json)
+
+    if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) {
+      return undefined
+    }
+
+    return parsed as Record<string, unknown>
   } catch {
     // no-op
     return undefined