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Wi-Fi bulk transport: AWDL data plane for large media with BLE fallback
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>
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jack
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//
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// WifiBulkPolicyTests.swift
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// bitchatTests
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//
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// This is free and unencumbered software released into the public domain.
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// For more information, see <https://unlicense.org>
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//
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import BitFoundation
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import Foundation
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import Testing
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@testable import bitchat
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@Suite("WifiBulk policy")
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struct WifiBulkPolicyTests {
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private func candidate(
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payloadBytes: Int = 300_000,
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capabilities: PeerCapabilities = [.wifiBulk],
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direct: Bool = true,
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session: Bool = true
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) -> WifiBulkPolicy.SendCandidate {
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WifiBulkPolicy.SendCandidate(
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payloadBytes: payloadBytes,
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peerCapabilities: capabilities,
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isDirectlyConnected: direct,
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hasEstablishedNoiseSession: session
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)
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}
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@Test("Eligible large transfer to a direct wifiBulk peer is offered")
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func eligibleTransferOffered() {
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#expect(WifiBulkPolicy.shouldOffer(candidate(), enabled: true))
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}
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@Test("Fallback matrix: every failed gate keeps the transfer on BLE")
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func fallbackMatrix() {
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// Feature disabled.
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#expect(!WifiBulkPolicy.shouldOffer(candidate(), enabled: false))
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// Small file: negotiation overhead not worth it.
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#expect(!WifiBulkPolicy.shouldOffer(candidate(payloadBytes: 64 * 1024), enabled: true))
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// Peer doesn't advertise the capability.
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#expect(!WifiBulkPolicy.shouldOffer(candidate(capabilities: []), enabled: true))
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#expect(!WifiBulkPolicy.shouldOffer(candidate(capabilities: [.prekeys, .gateway]), enabled: true))
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// Multi-hop recipient (reachable but not directly connected).
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#expect(!WifiBulkPolicy.shouldOffer(candidate(direct: false), enabled: true))
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// No established Noise session to carry the offer.
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#expect(!WifiBulkPolicy.shouldOffer(candidate(session: false), enabled: true))
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// Payload beyond even the Wi-Fi ceiling.
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#expect(!WifiBulkPolicy.shouldOffer(
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candidate(payloadBytes: FileTransferLimits.maxWifiBulkPayloadBytes + 1),
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enabled: true
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))
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}
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@Test("Offer threshold is strictly greater than the minimum")
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func offerThresholdBoundary() {
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#expect(!WifiBulkPolicy.shouldOffer(
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candidate(payloadBytes: TransportConfig.wifiBulkMinPayloadBytes),
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enabled: true
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))
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#expect(WifiBulkPolicy.shouldOffer(
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candidate(payloadBytes: TransportConfig.wifiBulkMinPayloadBytes + 1),
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enabled: true
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))
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}
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private func offer(fileSize: UInt64) -> WifiBulkOffer {
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WifiBulkOffer(
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transferID: Data(repeating: 1, count: WifiBulkWire.transferIDLength),
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fileSize: fileSize,
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payloadHash: Data(repeating: 2, count: WifiBulkWire.hashLength),
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token: Data(repeating: 3, count: WifiBulkWire.tokenLength),
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serviceName: "0011223344556677"
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)
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}
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@Test("Receiver accepts an in-cap offer from a direct peer")
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func receiverAccepts() {
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#expect(WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: 1_000_000),
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senderIsDirectlyConnected: true,
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activeIncomingTransfers: 0,
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enabled: true
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))
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}
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@Test("Receiver enforces its own size cap, not the sender's word")
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func receiverSizeCap() {
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#expect(!WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: UInt64(FileTransferLimits.maxWifiBulkPayloadBytes) + 1),
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senderIsDirectlyConnected: true,
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activeIncomingTransfers: 0,
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enabled: true
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))
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#expect(WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: UInt64(FileTransferLimits.maxWifiBulkPayloadBytes)),
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senderIsDirectlyConnected: true,
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activeIncomingTransfers: 0,
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enabled: true
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))
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#expect(!WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: 0),
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senderIsDirectlyConnected: true,
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activeIncomingTransfers: 0,
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enabled: true
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))
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}
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@Test("Receiver declines when disabled, indirect, or saturated")
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func receiverDeclines() {
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#expect(!WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: 1000),
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senderIsDirectlyConnected: true,
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activeIncomingTransfers: 0,
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enabled: false
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))
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#expect(!WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: 1000),
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senderIsDirectlyConnected: false,
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activeIncomingTransfers: 0,
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enabled: true
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))
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#expect(!WifiBulkPolicy.shouldAccept(
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offer: offer(fileSize: 1000),
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senderIsDirectlyConnected: true,
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activeIncomingTransfers: TransportConfig.wifiBulkMaxConcurrentIncoming,
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enabled: true
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))
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}
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@Test("This build advertises the wifiBulk capability when enabled")
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func localCapabilityAdvertised() {
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#expect(PeerCapabilities.localSupported.contains(.wifiBulk) == TransportConfig.wifiBulkEnabled)
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}
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@Test("File packets above the BLE cap encode/decode only with the Wi-Fi limit")
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func filePacketWifiLimit() throws {
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let content = Data(repeating: 0x5A, count: 2 * 1024 * 1024) // 2 MiB
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let packet = BitchatFilePacket(fileName: "big.jpg", fileSize: UInt64(content.count), mimeType: "image/jpeg", content: content)
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// BLE cap unchanged.
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#expect(packet.encode() == nil)
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let encoded = try #require(packet.encode(limit: FileTransferLimits.maxWifiBulkPayloadBytes))
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#expect(BitchatFilePacket.decode(encoded) == nil) // BLE-cap decode still rejects
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let decoded = try #require(BitchatFilePacket.decode(encoded, limit: FileTransferLimits.maxWifiBulkPayloadBytes))
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#expect(decoded.content == content)
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#expect(decoded.fileName == "big.jpg")
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}
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}
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