fix(files): read HEIF compatible brands, not just the major brand

A standards-valid HEIF may carry a generic major brand such as isom and
declare heic, heix or mif1 only among the compatible brands that follow the
minor_version at offset 12. Reading bytes 8-11 alone classified those as
non-HEIF, skipping the fallback decode and leaving a small undecodable file
to reach the model as raw bytes.

Author: waleedlatif1

apps/sim/lib/uploads/server/heic.test.ts

@@ -4,12 +4,17 @@
 import { describe, expect, it } from 'vitest'
 import { isHeifContainer, transcodeHeicToJpeg } from '@/lib/uploads/server/heic'
 
-/** An ISO-BMFF header: 4-byte box size, the `ftyp` marker, then the major brand. */
-function ftypHeader(brand: string): Buffer {
-  const header = Buffer.alloc(16)
-  header.writeUInt32BE(16, 0)
+/**
+ * An ISO-BMFF `ftyp` box: 4-byte size, the `ftyp` marker, the major brand, a
+ * 4-byte minor version, then any compatible brands.
+ */
+function ftypHeader(brand: string, compatible: string[] = []): Buffer {
+  const size = 16 + compatible.length * 4
+  const header = Buffer.alloc(size)
+  header.writeUInt32BE(size, 0)
   header.write('ftyp', 4, 'ascii')
   header.write(brand, 8, 'ascii')
+  compatible.forEach((entry, index) => header.write(entry, 16 + index * 4, 'ascii'))
   return header
 }
 
@@ -48,6 +53,22 @@ describe('isHeifContainer', () => {
     expect(isHeifContainer(ftypHeader('qt  '))).toBe(false)
   })
 
+  it('detects a HEIF brand declared only among the compatible brands', () => {
+    // Standards-valid: a generic major brand with the HEIF brand listed after it.
+    expect(isHeifContainer(ftypHeader('isom', ['iso2', 'heic', 'mif1']))).toBe(true)
+    expect(isHeifContainer(ftypHeader('mp42', ['heix']))).toBe(true)
+  })
+
+  it('rejects a box whose compatible brands are all non-HEIF', () => {
+    expect(isHeifContainer(ftypHeader('isom', ['iso2', 'mp41', 'mp42']))).toBe(false)
+  })
+
+  it('does not read compatible brands past the declared box size', () => {
+    const truncated = ftypHeader('isom', ['heic'])
+    truncated.writeUInt32BE(16, 0)
+    expect(isHeifContainer(truncated)).toBe(false)
+  })
+
   it('rejects buffers too short to carry a brand', () => {
     expect(isHeifContainer(Buffer.alloc(0))).toBe(false)
     expect(isHeifContainer(ftypHeader('heic').subarray(0, 11))).toBe(false)

apps/sim/lib/uploads/server/heic.ts

@@ -34,7 +34,18 @@ const HEIF_BRANDS = new Set([
 export function isHeifContainer(buffer: Buffer): boolean {
   if (buffer.length < 12) return false
   if (buffer.toString('ascii', 4, 8) !== 'ftyp') return false
-  return HEIF_BRANDS.has(buffer.toString('ascii', 8, 12))
+  if (HEIF_BRANDS.has(buffer.toString('ascii', 8, 12))) return true
+
+  // A standards-valid HEIF may carry a generic major brand such as `isom` and name
+  // the HEIF brand only among the compatible brands, which follow the 4-byte
+  // minor_version at offset 12 and run to the end of the box. A declared size of 0
+  // or 1 (the ISO-BMFF size escapes, which `ftyp` does not use) leaves `end` below
+  // the loop's start, so those simply do not scan.
+  const end = Math.min(buffer.readUInt32BE(0), buffer.length)
+  for (let offset = 16; offset + 4 <= end; offset += 4) {
+    if (HEIF_BRANDS.has(buffer.toString('ascii', offset, offset + 4))) return true
+  }
+  return false
 }
 
 /**