bitchat-protocol

BitChat binary protocol encode/decode for Python.

Implements the wire format from the BitChat mesh networking protocol: binary packet encode/decode, TLV codec for announcement and private message structures, and peer ID derivation utilities.

Installation

pip install bitchat-protocol

Requires Python 3.10+.

Quick Start

from bitchat_protocol import (
    encode, decode,
    BitchatPacket, MessageType,
    encode_announcement, decode_announcement,
    AnnouncementPacket,
    peer_id_from_noise_key,
)

# Encode a broadcast message
import time
packet = BitchatPacket(
    version=1,
    type=int(MessageType.MESSAGE),
    ttl=7,
    timestamp=int(time.time() * 1000),
    flags=0,
    sender_id=bytes.fromhex('abcdef0123456789'),
    payload='Hello, BitChat!'.encode(),
)
wire = encode(packet, padding=True)   # padded for BLE transmission

# Decode from bytes received over BLE or Nostr relay
decoded = decode(wire)
if decoded:
    print('type:', decoded.type)
    print('payload:', decoded.payload.decode())

API

Packet Encode/Decode

encode(packet: BitchatPacket, *, padding: bool = False) -> bytes
decode(data: bytes) -> BitchatPacket | None

decode() returns None (never raises) on invalid or truncated input.

TLV: AnnouncementPacket

encode_announcement(packet: AnnouncementPacket) -> bytes
decode_announcement(data: bytes) -> AnnouncementPacket | None

Decoder is lenient: unknown TLV tags are skipped (forward-compatible).

TLV: PrivateMessagePacket

encode_private_message(packet: PrivateMessagePacket) -> bytes
decode_private_message(data: bytes) -> PrivateMessagePacket | None

Decoder is strict: returns None on any unknown TLV tag.

TLV: RequestSyncPacket

REQUEST_SYNC gossip-sync payloads carrying GCS filter parameters. Unlike the TLVs above, these use 16-bit big-endian lengths.

encode_request_sync(packet: RequestSyncPacket) -> bytes
decode_request_sync(data: bytes, max_accept_bytes: int = MAX_ACCEPT_FILTER_BYTES) -> RequestSyncPacket | None

@dataclass
class RequestSyncPacket:
    p: int                                    # Golomb-Rice parameter (decode accepts 1..=MAX_P = 32)
    m: int                                    # hash range M = N * 2^P (uint32)
    data: bytes                               # GR bitstream bytes (MSB-first)
    types: int | None = None                  # sync-type flags bitmask
    since_timestamp: int | None = None        # only sync packets newer than this (ms, uint64)
    fragment_id_filter: str | None = None     # restrict sync to one fragment ID

from bitchat_protocol import (
    MessageType, RequestSyncPacket,
    encode_request_sync, decode_request_sync, sync_type_flags_from_message_types,
)

wire = encode_request_sync(RequestSyncPacket(
    p=19,
    m=1 << 19,
    data=gcs_filter_bytes,
    types=sync_type_flags_from_message_types([MessageType.ANNOUNCE, MessageType.MESSAGE]),
))
request = decode_request_sync(wire)  # None on any invalid input

The decoder is lenient about unknown tags (forward-compatible — the optional types/since_timestamp/fragment_id_filter TLVs are iOS-side extensions that older decoders skip) and strict about validity: it rejects p outside 1..=MAX_P (32), m = 0, missing required fields, and filter data larger than max_accept_bytes (default MAX_ACCEPT_FILTER_BYTES = 1024, a DoS guard).

Helpers: sync_type_flags_from_message_types(types) / sync_type_flags_to_message_types(flags) convert between list[MessageType] and the flags bitmask.

Peer ID Utilities

peer_id_from_noise_key(noise_public_key: bytes) -> str   # 16-char hex
peer_id_to_bytes(peer_id: str) -> bytes                  # 8 bytes
peer_id_from_bytes(data: bytes) -> str                   # 16-char hex
nostr_geo_dm_peer_id(nostr_pubkey_hex: str) -> str       # "nostr_" + prefix
nostr_geo_chat_peer_id(nostr_pubkey_hex: str) -> str     # "nostr:" + prefix

Utilities

hex_to_bytes(hex_str: str) -> bytes
bytes_to_hex(data: bytes) -> str

Wire Format

v1 Header (14 bytes)

[version:1][type:1][ttl:1][timestamp:8 BE uint64][flags:1][payloadLen:2 BE uint16]
[senderID:8]
[recipientID:8]         — if flags & HAS_RECIPIENT
[payload:payloadLen]
[signature:64]          — if flags & HAS_SIGNATURE

v2 Header (16 bytes)

Same but payloadLen is 4 bytes (BE uint32) and source routing is supported.

Flags Byte

Bit	Value	Name
0	0x01	HAS_RECIPIENT
1	0x02	HAS_SIGNATURE
2	0x04	IS_COMPRESSED
3	0x08	HAS_ROUTE (v2+ only)
4	0x10	IS_RSR

Running Tests

pip install -e ".[dev]"
pytest

Compatibility

This package implements the same binary wire format as:

• ios/bitchat/Protocols/BinaryProtocol.swift
• android/.../BinaryProtocol.kt

Cross-language compatibility is verified against the bitchat-sdk/spec-tests golden fixture suite. Clone that repo as a sibling of this one, then pytest runs all cross-language vectors automatically — without it, the fixture suite silently skips.

License

Unlicense — public domain.