Packet mumcord history

Part of the Plugin data protocol. Flow: Flow-History-Sync (read it for chunking, reassembly and timeouts).

Packet mumcord.history

Purpose. Mumble servers keep no chat history. When a Mumcord user joins or follows a channel, or asks for earlier messages, their client asks other Mumcord clients for the channel messages from before it started receiving the channel live, and fetches only what it is missing.

dataID	mumcord.history
Encoding	compact JSON header, optionally \n and a binary body
Version sent / accepted	1 / 1 and higher (below 1 is dropped)
Sent to	areq to everyone on the server; every other packet to one person
Feature gate	none (only Mumcord clients answer)
Defined in	crates/engine/src/history_sync/wire.rs, core.rs, hash.rs

Packet layout

{"v":1,"t":"part","r":7,"i":0,"last":false}\n<body bytes>

The header ends at the first \n; everything after it is the body. Packets without a body have no \n. A packet is at most 1000 bytes in total (PLUGIN_DATA_MAX), and the decoder rejects larger ones.

Header fields: v (version), t (packet type), r (request id chosen by the sender of the request, u32), plus the fields below. Times are Unix milliseconds. c is the Mumble channel id.

t	Direction	Header fields	Body	Meaning
areq	requester to everyone	r, c, from, to	none	Who holds messages of channel c in [from, to)?
avail	holder to requester	r, c, n, old, new	none	The holder has n messages, from old to new.
hreq	requester to holder	r, c, from, to	none	Send me the hashes of your messages in [from, to).
hashes	holder to requester	r, i, last	8-byte hashes, concatenated	Chunk i of the hash list, oldest first.
get	requester to holder	r	bitmap	Send the messages whose bits are set (bit k % 8 of byte k / 8, least significant bit first, is hash k).
part	holder to requester	r, i, last	slice of a JSON array	Chunk i of the message stream; join all chunks to get the array.
deny	holder to requester	r	none	The holder does not answer request r.

Field types: r u32, c u32, n u32, i u16, last boolean, from, to, old, new i64. Packets that must have no body (areq, avail, hreq, deny) are rejected if they carry one; a hashes body whose length is not a multiple of 8 is rejected.

Message stream (part bodies)

The bodies of all part packets of one request, joined in order of i, form one JSON array of messages:

Field	Type	Meaning
ts	integer	Time the holder received it, Unix milliseconds.
n	string	Sender name (kept up to 128 characters).
h	string	Sender's certificate hash, hex, at most 128 characters. Optional.
b	string	Message body as sanitized HTML, at most 8 KiB. The receiver sanitizes it again.

Examples

{"v":1,"t":"areq","r":7,"c":3,"from":1766620800000,"to":1767225600000}
{"v":1,"t":"avail","r":7,"c":3,"n":120,"old":1766700000000,"new":1767200000000}
{"v":1,"t":"hreq","r":8,"c":3,"from":1766620800000,"to":1767225600000}
{"v":1,"t":"hashes","r":8,"i":0,"last":true}\n<n x 8 bytes>
{"v":1,"t":"get","r":8}\n<bitmap, 1 bit per hash>
{"v":1,"t":"part","r":8,"i":0,"last":true}\n[{"ts":1767200000000,"n":"Alice","h":"0123456789abcdef0123456789abcdef01234567","b":"Hello &lt;3"}]
{"v":1,"t":"deny","r":8}

Hashes

A hash is the first 8 bytes (HASH_LEN) of SHA-1 over these parts, each followed by a zero byte: mumcord-history-v1, the channel path (channel names joined with /), the sender (cert:<hash> or name:<name>), the send time in whole seconds as a decimal string, and the normalized body (tags removed, common HTML entities decoded, whitespace collapsed). Because every client stamps messages with its own clock, comparisons also try the second before and after; messages from the same sender with the same text within 5 seconds (SKEW_MS) also count as duplicates. See hash.rs.

Limits

Limit	Value	Constant
Plugin data per packet	1000 bytes	PLUGIN_DATA_MAX
Body per packet	900 bytes	BODY_BUDGET
Hashes per hashes chunk	112	HASHES_PER_CHUNK
Messages per request	500	MAX_MESSAGES
Body of one message	8 KiB (larger ones, such as inline images, are not synced)	MAX_BODY
Message stream per answer	256 KiB	MAX_STREAM
Age	7 days	MAX_AGE_MS
Holders asked	3	MAX_HOLDERS
Answers prepared at once	3	MAX_SERVES
Requests per person	refill 0.2 per second, burst 6	PEER_RATE, PEER_BURST
Outgoing pace	3 packets per second, burst 10	SEND_RATE, SEND_BURST

Privacy

Carries chat messages, sender names and certificate hashes of a channel. Only answered for people the holder saw arrive in that channel, and only for messages from before they arrived. Holders answer only while the user has "share history" on, and never for private chats. Received bodies are untrusted HTML and must be sanitized before rendering.

Used in

Flow-History-Sync.