# Protocol (proto = 11) Wire format only. Behavior (gate, clock, timeouts) is in [ARCHITECTURE.md](ARCHITECTURE.md). Source of truth: `packages/core/lib/src/protocol.dart` and `packages/server/lib/src/server_hub.dart`. Any wire change bumps `RelayConstants.protoVersion` and edits this file in the same commit. Changes are additive where possible; a client and server with different `proto` refuse each other at `hello` (`proto mismatch`). ## Transport - WebSocket at `/sync`, JSON text frames, each an object with a `t` field. - The first client frame must be `hello` within 10 s. Server pings every 5 s. - Match incoming frames by `t`, never by order: `welcome` can race `state`. - Failures: server sends `{"t":"err","message":...}` and closes. Messages: `bad hello: ...`, `proto mismatch: got X, want Y`, `wrong secret`, `rejected: ` (e.g. avatar too large), `bad message: ...` (a frame with a non-finite number, e.g. NaN position), `bad swap media`, `swap needs a url or the hosted file` (empty swap). - `GET /health` returns JSON (`ok`, `name`, `proto`, `viewers`, `bytesServed`, `uptimeSecs`; unauthenticated). `GET /m///` serves the host's file (Range table in ARCHITECTURE.md). `GET /j///` relays the current Jellyfin media (see "Jellyfin media" below). `/r///...` is the relay of a member's media (see "Relay" below). `GET /a///` serves a member's picture (see "Avatars" below), `GET /i///` the current media's art (see "Media art" below). ## Client to server ``` {"t":"hello","proto":11,"secret":"","user":{"name":"","avatar":""}, "media":{"name":"","size":0,"duration":0,"url":null},"hostKey":"...", "resume":""} {"t":"ready","ready":true,"source":"manual"} source: manual | auto {"t":"force","target":"all"|"","ready":true} {"t":"seek","position":123.4,"seq":3} {"t":"swap","media":{"name":"","size":0,"duration":0,"url":"..."}} {"t":"swap","media":{"name":"","size":0,"duration":0,"jellyfin":{}}} {"t":"swap","media":{"name":"","size":123,"duration":0,"url":"...","relay":{}}} {"t":"report","position":123.1,"buffered":6.2,"eventId":41, "duration":1440.5,"mediaId":2,"jf":{"":true}} {"t":"ping","c":1767225600000} {"t":"chat","text":"..."} {"t":"kick","target":"","reason":""} {"t":"profile","name":"...","avatar":""} {"t":"art","mediaId":2,"poster":"","banner":""} ``` Field notes: - `hello.secret`: the server password; a server with an empty secret is open. `hello.media` is carried but not used by the server today. - `hello.hostKey` (optional, omitted when empty): the hosting app generates a random key per hosting, gives it to its server and sends it from its own client. The member whose key equals the server's is the host and cannot be kicked. A server without a key (the dedicated server) has no host. Where the connection comes from does not matter. - `hello.resume` (optional, omitted when empty): the token from this client's previous `welcome`, sent on reconnect. If the server still has that member and it is not kicked, the connection takes it over: `welcome` returns the same `token` and `memberId`, the member keeps its flags, and there is no `join`/`leave` feed. Otherwise it is ignored and a new member joins. - `seek.seq` (optional, default 0): increasing per client; echoed in `state.seekSeq` so the sender recognises its own seek. - `report.duration` / `report.mediaId` (optional, omitted when 0): the open media's length in seconds and the `mediaId` it belongs to. The server takes the first one whose `mediaId` is current while its media duration is 0. - `report.jf` (optional): Jellyfin access per `ServerId`, `true` = this client plays the item with its own account, `false` = through the relay. Sticky: a report without `jf` keeps the last one. At most 8 entries, keys up to 64 characters; others are dropped. - `ping.c`: the client's clock in epoch ms; answered with `pong`. - `user.avatar`: base64 PNG, at most 256 KiB of characters (else `rejected: ...`). `name` is trimmed, empty becomes `?`, cut to 32 characters. - `profile`: changes this member's name and/or picture mid-session. A field that is absent (or null) stays as it is; `avatar: ""` removes the picture. Same rules as `hello.user`; a too large avatar gets `err` `rejected: avatar too large` (the socket stays open, nothing changes). - `art`: pictures of the current media (see "Media art"). - `chat.text` is cut to 500 characters. - `swap.media.url` is the link; `name`, `size`, `duration` are informational. `swap.media.jellyfin` makes it Jellyfin media (see below); then `url` is dropped. `swap.media.relay` makes it relayed media (see "Relay"). A swap keeps every member's `ready` and puts every fresh member in the set (`inSet`); clients that want to be unready for the new media send `ready` themselves (gate: ARCHITECTURE.md, "Ready gate"). - Frames before `welcome` (other than `hello`) are ignored; unparsable or unknown frames are ignored silently. ## Server to client ``` {"t":"welcome","token":"...","memberId":"m1","mediaUrl":"...","relayUrl":"...", "state":{}} {"t":"state","eventId":7,"transport":"playing"|"held"|"finished","position":12.3, "serverTime":"","mediaId":1, "media":{name,size,duration,url?,jellyfin?,relay?,swapBy?,art?}|absent, "members":[{"id","name","avatarHash"?,"ready","inSet","buffered","stale","jf"?, "host"?}], "seekBy":"m1","seekSeq":3,"relay":true} {"t":"pong","c":1767225600000,"s":1767225600012} {"t":"feed","actor":"","action":"","target":"","reason":"","at":""} {"t":"chat","text":"...","from":""} {"t":"kicked","reason":""} {"t":"err","message":""} ``` - `welcome.token` is private to its owner and appears only in that member's media URL. `mediaUrl` is omitted when there is no media; it is a built `/m/...` URL for a host file (host part = what the client dialled), otherwise the shared link. `welcome.state` has the same shape as `state`. `relayUrl` is present only when `state.relay` is: this member's `/j/...` URL for the current Jellyfin media (private like `token`). - `state` is sent every second and on every change. `position` is the value at `serverTime` (server clock); clients extrapolate while `transport` is `playing`, on the server's clock (see `pong`). `finished`: the media reached its end (`position` = duration); it stays until a seek or swap. `eventId` increases on seek, swap and transport changes. `mediaId` increases on swap. `media.relay` is present for relayed media (see "Relay"). `media.duration` is 0 until a client reports it. `media.swapBy`: member id of who swapped it in (omitted once that member left, and for the media the server started with). `media.art`: see "Media art". `seekBy` (member id) and `seekSeq` are present only while the current `eventId` came from a seek. `relay` (omitted when false): the server can relay the current Jellyfin media. `members[].jf` is the member's last `report.jf`, omitted when it never sent one. `members[].avatarHash` (omitted when the member has no picture) names the picture's bytes (see "Avatars"). `members[].host` (omitted when false): the member sent the server's `hostKey` (see `hello.hostKey`). - `pong.c` echoes the ping's `c`; `pong.s` is the server's clock in epoch ms (the clock `serverTime` uses). With `t3` the local receive time, the offset is `s - (c + t3) / 2`, accurate to half the round trip. - `feed.action` values: `ready`, `unready`, `force-ready`, `force-unready`, `force-play`, `force-hold`, `kick`, `join`, `leave`, `stale`, `swap`, `seek`, `pause`, `resume`, `finished`, `chat`, `rename`, `avatar`. `target` and `reason` are optional; `reason` carries `auto`/`manual` for ready and `silent too long` or `no signal` for leave/stale. `rename`: `actor` is the new name, `target` the old one. `avatar`: the actor changed only the picture. - Chat is delivered twice: a `chat` frame with the text and a textless `feed` with `action:"chat"`. Render the `chat` frame only; the reference client drops the textless feed entry. ## Avatars - The picture is sent as base64 in `hello.user.avatar` or `profile.avatar`; `state` carries only its hash: the first 16 hex characters of the sha256 of the decoded bytes. An avatar that is not valid base64, or whose bytes are not a PNG, JPEG, WebP or GIF (by magic bytes), counts as none. - `GET /a///`: the bytes with their image content type, `cache-control: private, max-age=31536000, immutable` (a hash names fixed bytes; clients fetch each hash once, from the host they dialled). Errors: 401 bad token, 403 kicked, 404 no current member has that picture, 410 unknown session. Pictures go with their member (leave, change, removal). ## Media art ``` client {"t":"art","mediaId":2,"poster":"","banner":""} state media.art = {"poster":"","banner":""} ``` - A portrait poster and a wide banner for the current media, so every member (guests without Jellyfin included) can show them. Sent by the member who made the current swap (`media.swapBy`) or the host, for the current `mediaId`; from anyone else, or for another `mediaId`, it is ignored. Each field is optional; one that is not a picture (same check as avatars) or larger than its cap (poster 256 KiB, banner 768 KiB of decoded bytes) counts as none. A later `art` replaces the earlier one whole; any swap clears it. - `media.art` carries hashes like `avatarHash`; a key is omitted when that picture is absent, `art` when both are. - `GET /i///`: as `/a/` (see "Avatars"); 404 when the current media has no such art. ## Jellyfin media ``` = {"serverId":"","itemId":"<32 hex>", "mediaSourceId":"...","title":"Pilot","subtitle":"Show - S01E01", "runtimeSecs":1440.5} ``` - `serverId`, `itemId` required; `mediaSourceId`, `subtitle`, `runtimeSecs` optional (omitted when absent); `title` always sent (may be empty). `runtimeSecs` is informational: the sync clock still uses the duration a client reports. - The server keeps only the ref: for Jellyfin media no URL or token is stored or broadcast (a `url` sent along is dropped). `serverId`, `itemId` and `mediaSourceId` must match `[A-Za-z0-9-]{1,64}`, otherwise `bad swap media`. `media.name` is the swap's name, else the ref's `title`; names are sanitized like link names. - Each client resolves the ref with its own account on that server. A client without one plays the relay URL when `state.relay` is true: `welcome.relayUrl`, or after a swap built like the `/m` one from the host it dialled: `http:///j/default//`. - `GET /j///`: the server fetches `/Videos//stream?static=true&mediaSourceId=` (the original file) with its own credential and streams it through. `Range` is forwarded as sent; status, `Content-Range`, `Content-Length`, `Content-Type` and `Accept-Ranges` come back as Jellyfin sent them. Errors: 401 bad token, 403 kicked or not the current item, 404 no relay for the current media, 410 unknown session, 502 Jellyfin unreachable or rejecting the server's credential. Bytes count toward `bytesServed`. - Pasted Jellyfin links sent as plain `url` stay plain links. ## Relay Media whose bytes go through the server's buffer: a file on a member's computer, a link passed on by a member, a link the server fetches itself, or a Jellyfin item for viewers without an account. Behavior (buffer, flow control, cases) is in [ARCHITECTURE.md](ARCHITECTURE.md), "Relay". ``` swap media.relay = {} the swapper's machine serves the bytes media.relay = {"tracks":[{"kind":"video"},{"kind":"audio"}]} the same, as two tracks played together media.relay = {"fetch":true} the server reads media.url itself state media.relay = {"source":"m2","live":true} or {"fetch":true,"live":true} media.relay = {"fetch":true,"live":true,"tracks":[{"kind":"video"},{"kind":"audio"}]} ``` Tracks: a relayed media is one file, or several byte tracks (a page's separate video and audio files) that viewers play as one. `tracks` lists them in order, 2 to 4 entries of `kind` `video` or `audio`; absent (or anything else) means one file. Every track is a Range-readable byte stream; other kinds of track (e.g. segmented playlists) would add a field to the entry. - `swap`: `relay` with `jellyfin` keeps the ref (the swapper serves it to viewers without an account; `fetch` is ignored there). `relay` without `jellyfin`: no URL is stored or broadcast; `fetch` needs an http(s) `url` (else `relay fetch needs an http(s) url`), which the server keeps to itself, and a server with a password (else `server fetch needs a server password`: an open server would fetch any address it can reach for anyone). A web page `url` is read through the server's yt-dlp; when the server cannot read the link, the swapper later gets `The server can't fetch this link: `. Any later swap ends the relay. `tracks` on a member's swap names the tracks its source will serve; the server ignores it with `fetch` and with `jellyfin`. - `state.media.relay.source`: member id of the source (absent with `fetch`). `live` (omitted when false): bytes can flow (the source's channel is connected, or the server could read the link). `tracks`: as the swap named them, or, with `fetch`, set once the server has read the link (together with `live`). - `welcome.mediaUrl` for relayed media without `jellyfin`: this member's `/r/` URL; absent for the source itself (it plays its own copy) and for a fetched link the server has not read yet (clients open it on `live`). Clients build it after a swap like the `/m` one: `http:///r/default///` (name with `/` and `\` made `_`, then URL-encoded; the server ignores it). With `tracks`, it is an mpv EDL of every track's URL `http:///r/default////`, each framed by its byte length: `edl://!no_clip;%%;!new_stream;!no_clip;%%`. - `GET /r////`: the media (one file), Range table as for `/m`. `GET /r/////`: track `i` (from 0) of a media with `tracks` (track 0 of a one-file media too). Errors: 401 bad token, 403 kicked, 404 not the current relayed media (a player still on an older `mediaId` gets 404, never the new bytes) or no such track (the one-file URL of a media with `tracks`), 410 unknown session, 503 + `retry-after` the source never connected or the server could not read the link (60 s). A request whose bytes do not arrive within 60 s ends early. Bytes count toward `bytesServed`. - `GET /r///source` (WebSocket): the source's relay channel, dialled by the source (works behind NAT). Only the current source's token is accepted; anyone else, or the source after the next swap, is closed with code 4001 (the source stops instead of reconnecting). Frames: ``` source -> server {"t":"info","size":} first frame, one file {"t":"info","tracks":[{"kind":"video","size":}, {"kind":"audio","size":}]} first frame, tracks binary: [u32 big-endian pull id][bytes] in order per pull {"t":"end","id":1} {"t":"fail","id":1,"reason":"..."} server -> source {"t":"pull","id":1,"track":0,"start":0,"end":1048575} inclusive; no track: 0 {"t":"ack","id":1,"n":65536} bytes arrived {"t":"cancel","id":1} stop that pull ``` Pull ids are unique across the tracks of a connection; `track` is sent only for a media with `tracks`. An `info` whose track count differs from the swap's `tracks` closes the channel with 4001. A track `size` different from the one before (a reconnect) drops that track's buffer. ## Join and reconnect `hello` then `welcome`, then the app opens `mediaUrl`, seeks to the server position and buffers. A joining member is `ready=false`; it is `inSet` at once unless the server is `playing`, then from its first `ready` (members present at a swap are put in the set by it). A socket the server sees close loses its token; reconnect is a fresh `hello` (with `resume` = the old token), after which the client re-sends its prior ready flag. If the old member was still there (unclean drop), `resume` takes it over and the token and media URL stay the same. ## Reserved, not implemented Server-held queue (`queue-add`, `queue-skip`) would auto-advance like a swap.