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feat: Implement iOS-compatible selective padding for BLE messages #501

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feat: Implement iOS-compatible selective padding for BLE messages #501

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19 changes: 17 additions & 2 deletions app/src/main/java/com/bitchat/android/mesh/BluetoothPacketBroadcaster.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,17 @@ class BluetoothPacketBroadcaster(
nicknameResolver = resolver
}

/**
* iOS-compatible padding policy: only pad encrypted messages for BLE transmission
* Announce, message, leave, sync, fragment, and file transfer are sent unpadded over BLE
*/
private fun shouldPadForBLE(type: UByte): Boolean {
return when (MessageType.fromValue(type)) {
MessageType.NOISE_ENCRYPTED, MessageType.NOISE_HANDSHAKE -> true
else -> false
}
}

/**
* Debug logging helper - can be easily removed/disabled for production
*/
Expand Down Expand Up @@ -202,7 +213,9 @@ class BluetoothPacketBroadcaster(
characteristic: BluetoothGattCharacteristic?
): Boolean {
val packet = routed.packet
val data = packet.toBinaryData() ?: return false
// iOS-compatible: Use selective padding policy for BLE
val padForBLE = shouldPadForBLE(packet.type)
val data = packet.toBinaryData(padding = padForBLE) ?: return false
val isFile = packet.type == MessageType.FILE_TRANSFER.value
if (isFile) {
Log.d(TAG, "📤 Broadcasting FILE_TRANSFER: ${packet.payload.size} bytes")
Expand Down Expand Up @@ -285,7 +298,9 @@ class BluetoothPacketBroadcaster(
characteristic: BluetoothGattCharacteristic?
) {
val packet = routed.packet
val data = packet.toBinaryData() ?: return
// iOS-compatible: Use selective padding policy for BLE
val padForBLE = shouldPadForBLE(packet.type)
val data = packet.toBinaryData(padding = padForBLE) ?: return
val typeName = MessageType.fromValue(packet.type)?.name ?: packet.type.toString()
val senderPeerID = routed.peerID ?: packet.senderID.toHexString()
val incomingAddr = routed.relayAddress
Expand Down
16 changes: 9 additions & 7 deletions app/src/main/java/com/bitchat/android/protocol/BinaryProtocol.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -78,8 +78,8 @@ data class BitchatPacket(
ttl = ttl
)

fun toBinaryData(): ByteArray? {
return BinaryProtocol.encode(this)
fun toBinaryData(padding: Boolean = true): ByteArray? {
return BinaryProtocol.encode(this, padding = padding)
}

/**
Expand Down Expand Up @@ -189,7 +189,7 @@ object BinaryProtocol {
}
}

fun encode(packet: BitchatPacket): ByteArray? {
fun encode(packet: BitchatPacket, padding: Boolean = true): ByteArray? {
try {
// Try to compress payload if beneficial
var payload = packet.payload
Expand Down Expand Up @@ -275,11 +275,13 @@ object BinaryProtocol {
buffer.rewind()
buffer.get(result)

// Apply padding to standard block sizes for traffic analysis resistance
val optimalSize = MessagePadding.optimalBlockSize(result.size)
val paddedData = MessagePadding.pad(result, optimalSize)
// Apply padding if requested (iOS-compatible: selective padding for privacy)
if (padding) {
val optimalSize = MessagePadding.optimalBlockSize(result.size)
return MessagePadding.pad(result, optimalSize)
}

return paddedData
return result

} catch (e: Exception) {
Log.e("BinaryProtocol", "Error encoding packet type ${packet.type}: ${e.message}")
Expand Down
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