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Wi-Fi bulk transport: AWDL data plane for large media with BLE fallback

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BLE stays the control plane: a sender with a queued file > 64 KiB to a
directly connected peer advertising the wifiBulk capability sends a
bulkTransferOffer (0x04) inside the established Noise session — transferID,
file size, payload SHA-256, a fresh 32-byte token, and a random per-transfer
Bonjour instance name. The receiver answers bulkTransferResponse (0x05) with
its own token half, then both sides meet on a per-transfer
_bitchat-bulk._tcp channel over peer-to-peer Wi-Fi (AWDL).

The TCP stream is secured independently of TLS: both tokens traveled inside
Noise, so only the two peers can derive the ChaChaPoly channel key
(HKDF-SHA256, domain "bitchat-bulk-v1", transferID as salt). Frames are
length-prefixed sealed boxes with structured direction+counter nonces; the
first frame must prove knowledge of the key or the client is disconnected,
and the final hash is verified against the offer before delivery.

Decline, timeout, or any mid-transfer error falls back to BLE fragmentation
exactly once, driving the same TransferProgressManager stream so the UI is
unchanged. Wi-Fi-negotiated transfers may carry up to 8 MiB (new
FileTransferLimits.maxWifiBulkPayloadBytes, enforced by the receiver from
the accepted offer); the BLE path keeps its existing caps.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
jack
2026-07-06 20:35:40 +02:00
co-authored by Claude Fable 5
parent 688b954fb8
commit e4b3cff5fa
21 changed files with 2614 additions and 21 deletions
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bitchat/Services/TransportConfig.swift
+15
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@@ -281,6 +281,21 @@ enum TransportConfig {
static let syncResponseRateLimitMaxResponses: Int = 8
static let syncResponseRateLimitWindowSeconds: TimeInterval = 30.0
// Wi-Fi bulk transport (peer-to-peer AWDL data plane for large media).
// BLE stays the control plane: offers/responses ride the Noise session,
// only the sealed chunk stream moves to TCP over AWDL.
static let wifiBulkEnabled: Bool = true
// Below this size BLE fragmentation is fast enough that negotiation
// overhead isn't worth it.
static let wifiBulkMinPayloadBytes: Int = 64 * 1024
static let wifiBulkChunkBytes: Int = 64 * 1024
// Offer unanswered for this long → fall back to BLE fragmentation.
static let wifiBulkOfferTimeoutSeconds: TimeInterval = 10.0
// Hard ceiling on how long the Bonjour listener/connection may live.
static let wifiBulkTransferWindowSeconds: TimeInterval = 60.0
static let wifiBulkServiceType: String = "_bitchat-bulk._tcp"
static let wifiBulkMaxConcurrentIncoming: Int = 4
// Courier store-and-forward
// Initial spray-and-wait budget per deposited envelope: each courier may
// hand half its remaining copies to another courier on encounter, so a