| 1 | // fixtures/frames.mjs — the updates wire's framing (spec plan, Global |
| 2 | // Constraints: "each update framed as a 4-byte big-endian length then |
| 3 | // the bytes, in seq order"). live.go's updatesGet writes it; this reads |
| 4 | // it back into the individual Yjs updates Y.applyUpdate takes one at a |
| 5 | // time. |
| 6 | // |
| 7 | // Docs' endpoint concatenates updates with no framing and its client |
| 8 | // loops Y.readUpdate over one decoder; Slides frames them so the |
| 9 | // client never has to know how a Yjs update finds its own end, and so |
| 10 | // a snapshot (one large update) and a tail (many small ones) travel the |
| 11 | // same way. Pure bytes in, bytes out, so it is tested under plain Node. |
| 12 | |
| 13 | /** The frames a body carries, in order. Throws on a body that does not divide cleanly. */ |
| 14 | export function parseFrames (bytes) { |
| 15 | const out = [] |
| 16 | let at = 0 |
| 17 | while (at < bytes.length) { |
| 18 | if (bytes.length - at < 4) throw new Error(`frame: ${bytes.length - at} trailing bytes with no length prefix`) |
| 19 | const n = ((bytes[at] << 24) >>> 0) + (bytes[at + 1] << 16) + (bytes[at + 2] << 8) + bytes[at + 3] |
| 20 | at += 4 |
| 21 | if (bytes.length - at < n) throw new Error(`frame: a frame claims ${n} bytes and ${bytes.length - at} remain`) |
| 22 | out.push(bytes.subarray(at, at + n)) |
| 23 | at += n |
| 24 | } |
| 25 | return out |
| 26 | } |
| 27 | |
| 28 | /** One frame: the length prefix then the bytes (what a test or a beacon builds). */ |
| 29 | export function frame (update) { |
| 30 | const out = new Uint8Array(4 + update.length) |
| 31 | out[0] = (update.length >>> 24) & 255 |
| 32 | out[1] = (update.length >>> 16) & 255 |
| 33 | out[2] = (update.length >>> 8) & 255 |
| 34 | out[3] = update.length & 255 |
| 35 | out.set(update, 4) |
| 36 | return out |
| 37 | } |
| 38 | |
amadan