Rpcserver subscriber can hang when backsource unknown content length file

[NickYadance]

Bug report:

When backsource file with unknown content length, the remote peer will hang if the local peer didn't sync content length and total pieces with remote peer before sending the last piece.

Suppose file size=128MB, pieceSize=4MB, totalPieces=32. the local peer will send 32 pieces to remote peer, and total pieces=-1 in the last piece.

{"level":"info","ts":"2024-09-03 07:11:41.710","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.732","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.756","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.779","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.801","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.822","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.845","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.869","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.893","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.916","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.943","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.965","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:41.986","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.008","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.032","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.056","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.080","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.102","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.124","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.147","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.169","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.195","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.219","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.240","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.261","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.282","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.304","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.326","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.352","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}

This is due to the last piece(31) is sent before the content length is generated, and the remote peer will wait infinitiy since it didn't get the content length info.

{"level":"debug","ts":"2024-09-03 07:11:42.351","caller":"peer/piece_manager.go:262","msg":"piece 32 calculate digest","peer":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","task":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","component":"PeerTask","trace":"347dce459fee75f6b3ff19b0c985a745"}
{"level":"info","ts":"2024-09-03 07:11:42.352","caller":"rpcserver/subscriber.go:95","msg":"send ready piece 31","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.352","caller":"rpcserver/subscriber.go:99","msg":"sent 1 pieces, total: -1","taskID":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","localPeerID":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","remotePeerID":"xx-7-fef8e5f1-6c81-47b0-8e94-b0e5f4198b45"}
{"level":"info","ts":"2024-09-03 07:11:42.351","caller":"rpcserver/seeder.go:195","msg":"receive piece info, num: 31, ordered num: 31, finish: false","peer":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","task":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","component":"seedService"}
{"level":"info","ts":"2024-09-03 07:11:42.352","caller":"storage/local_storage.go:216","msg":"generated digest: c74f6296bec5d1f484ee54f2297461aff8e80b7a9675db36ab1dd0ed6d85ed31, total pieces: 32, content length: 134217728","task":"c5fad0a51a440ded9d2f27036b8a9bb4768b1caec402b94202a5821d8a8fa0d7","peer":"xx-1-ab92e31b-543c-48c3-b2ef-807b99491bd9_Seed","component":"localTaskStore"}

Root cause in code:

The last piece(32) size can be zero when file size aligns with piece size, so it didn't count into total pieces which is fine.

Dragonfly2/client/daemon/peer/piece_manager.go

Lines 556 to 563 in 75d6242

	// last piece, piece size maybe 0
	contentLength = int64(pieceSize)*int64(pieceNum) + n
	// when n == 0, content length is aligned at piece size, need ignore current piece
	if n == 0 {
	totalPieces = pieceNum
	} else {
	totalPieces = pieceNum + 1
	}

But when content length is updated, the real last piece(31) can already be sent, causing content length info missed.

Dragonfly2/client/daemon/peer/piece_manager.go

Lines 597 to 602 in 75d6242

	if result.Size == 0 {
	pt.SetTotalPieces(totalPieces)
	pt.SetContentLength(contentLength)
	log.Debugf("final piece is %d", pieceNum-1)
	break
	}

Expected behavior:

How to reproduce it:

Add a time.Sleep before updating content length, and download a 128MB file.

Dragonfly2/client/daemon/peer/piece_manager.go

Lines 597 to 602 in 75d6242

	if result.Size == 0 {
	pt.SetTotalPieces(totalPieces)
	pt.SetContentLength(contentLength)
	log.Debugf("final piece is %d", pieceNum-1)
	break
	}

Environment:

• Dragonfly version: v2.1.33
• OS: ubuntu
• Kernel (e.g. uname -a):
• Others: