fix(webdav): read ahead for mounted media ranges

server/routes/webdav.integration.test.ts

@@ -489,6 +489,34 @@ describe('WebDAV API', () => {
     expect(S3Service.prototype.getObjectBytes).not.toHaveBeenCalled()
   })
 
+  it('expands tiny WebDAVFS ranges for mounted media reads', async () => {
+    const { app, db, auth } = await createTestApp()
+    await authedHeaders(app)
+    await seedStorage(db)
+    const workspace = await org(db)
+    const account = await userAccount(db)
+    const key = await apiKey(auth, account.id, { webdav: ['read'] })
+    await file(db, workspace.id, { id: 'mounted-media', name: 'audio.mp3', size: 2 * 1024 * 1024 })
+    vi.mocked(S3Service.prototype.getObjectBody).mockResolvedValueOnce(streamBody('chunk'))
+
+    const partial = await app.request(`/dav/${workspace.slug}/audio.mp3`, {
+      method: 'GET',
+      headers: basicHeaders(account.email, key, {
+        Range: 'bytes=419430-419430',
+        'User-Agent': 'WebDAVFS/3.0.0 (03008000) Darwin/24.6.0 (arm64)',
+      }),
+    })
+
+    expect(partial.status).toBe(206)
+    expect(partial.headers.get('Content-Range')).toBe('bytes 419430-1468005/2097152')
+    expect(partial.headers.get('Content-Length')).toBe('1048576')
+    expect(S3Service.prototype.getObjectBody).toHaveBeenCalledWith(
+      expect.objectContaining({ id: storage.id }),
+      'objects/mounted-media.txt',
+      'bytes=419430-1468005',
+    )
+  })
+
   it('GET ignores unsupported ranges and honors If-Range validators', async () => {
     const { app, db, auth } = await createTestApp()
     await authedHeaders(app)

server/routes/webdav.ts

@@ -261,6 +261,8 @@ interface ByteRange {
   end: number
 }
 
+const WEBDAVFS_READ_AHEAD_BYTES = 1024 * 1024
+
 type RangeRequest = { action: 'none' | 'ignore' } | { action: 'serve'; range: ByteRange } | { action: 'reject' }
 
 function parseRangeRequest(header: string | undefined, size: number): RangeRequest {
@@ -298,6 +300,12 @@ function rangeNotSatisfiable(size: number): Response {
   return new Response(null, { status: 416, headers: { 'Content-Range': `bytes */${size}` } })
 }
 
+function webDavFsReadAheadRange(c: DavContext, range: ByteRange, size: number): ByteRange {
+  if (!c.req.header('User-Agent')?.startsWith('WebDAVFS/')) return range
+  if (range.end - range.start + 1 >= WEBDAVFS_READ_AHEAD_BYTES) return range
+  return { start: range.start, end: Math.min(size - 1, range.start + WEBDAVFS_READ_AHEAD_BYTES - 1) }
+}
+
 function ifRangeMatches(header: string | undefined, matter: NonNullable<WebDavTarget['matter']>): boolean {
   if (!header) return true
   const value = header.trim()
@@ -622,7 +630,7 @@ async function readFile(c: DavContext, auth: DavAuth): Promise<Response> {
 
     if (rangeRequest.action === 'reject') return rangeNotSatisfiable(size)
     if (rangeRequest.action !== 'serve') throw new Error('Unexpected range request action')
-    const range = rangeRequest.range
+    const range = webDavFsReadAheadRange(c, rangeRequest.range, size)
     const body = await s3.getObjectBody(storage, matter.object, `bytes=${range.start}-${range.end}`)
     headers.set('Content-Length', String(range.end - range.start + 1))
     headers.set('Content-Range', `bytes ${range.start}-${range.end}/${size}`)