orca/src/shared/terminal-stream-protocol.ts

import { assertJsonTextStructureWithinLimits } from './json-text-structure-limit'

const TERMINAL_STREAM_KIND = 0x74
const TERMINAL_STREAM_VERSION = 1
const HEADER_BYTES = 16
export const TERMINAL_STREAM_JSON_MAX_BYTES = 8 * 1024 * 1024
export const TERMINAL_STREAM_JSON_STRUCTURE_LIMITS = {
  structuralTokens: 256 * 1024,
  nestingDepth: 32
} as const

export enum TerminalStreamOpcode {
  Output = 1,
  SnapshotStart = 2,
  SnapshotChunk = 3,
  SnapshotEnd = 4,
  Resized = 5,
  Error = 6,
  Input = 7,
  Resize = 8,
  Subscribe = 9,
  Unsubscribe = 10,
  SnapshotRequest = 11,
  Metadata = 12,
  // Why 13: Metadata=12 shipped to mobile clients in v1.4.120; Ack (branch-only
  // remote-multiplex flow control) renumbers to stay wire-compatible.
  Ack = 13,
  // Why 14: Ack already occupies 13 on current clients; older runtimes ignore
  // this opcode and still receive the compatibility Resize frame behind it.
  ClaimViewport = 14,
  OutputSpan = 15,
  // Negotiated per stream; older hosts reject unknown opcodes, so clients send only after capability confirmation.
  SetOutputPaused = 16,
  // Negotiated per stream because older clients reject unknown opcodes.
  WriteUnavailable = 17,
  // Host->client; `seq` is the cumulative input sequence the host applied (see encodeTerminalInputAck). Sent only after `inputAck` negotiation.
  InputAck = 18,
  // Host->client, empty payload; at most once per pause, when the host first discards output for a paused stream. Sent only after `outputPauseDropNotice` negotiation.
  PausedOutputDropped = 19
}

export type TerminalInputAckKind = 'applied' | 'delivery-unknown' | 'resend'

const INPUT_ACK_FLAGS: Record<TerminalInputAckKind, number> = {
  applied: 0,
  // The write at `seq` may have reached the terminal; the client must not resend it.
  'delivery-unknown': 1,
  // A refusal or gap: the host needs everything after `seq` sent again, in order.
  resend: 2
}

/** InputAck payload; `seq` is the host's cumulative applied input sequence. */
export function encodeTerminalInputAck(kind: TerminalInputAckKind): Uint8Array {
  return kind === 'applied' ? new Uint8Array() : Uint8Array.of(INPUT_ACK_FLAGS[kind])
}

export function decodeTerminalInputAck(payload: Uint8Array): TerminalInputAckKind {
  return payload[0] === INPUT_ACK_FLAGS.resend
    ? 'resend'
    : payload[0] === INPUT_ACK_FLAGS['delivery-unknown']
      ? 'delivery-unknown'
      : 'applied'
}

export type TerminalStreamFrame = {
  opcode: TerminalStreamOpcode
  streamId: number
  seq: number
  payload: Uint8Array
}

export function encodeTerminalStreamFrame(frame: TerminalStreamFrame): Uint8Array {
  const out = new Uint8Array(HEADER_BYTES + frame.payload.length)
  const view = new DataView(out.buffer, out.byteOffset, out.byteLength)
  view.setUint8(0, TERMINAL_STREAM_KIND)
  view.setUint8(1, TERMINAL_STREAM_VERSION)
  view.setUint8(2, frame.opcode)
  view.setUint8(3, 0)
  view.setUint32(4, frame.streamId, true)
  const seq = Math.max(0, Math.floor(frame.seq))
  view.setUint32(8, Math.floor(seq / 0x100000000), true)
  view.setUint32(12, seq >>> 0, true)
  out.set(frame.payload, HEADER_BYTES)
  return out
}

export function decodeTerminalStreamFrame(bytes: Uint8Array): TerminalStreamFrame | null {
  if (bytes.length < HEADER_BYTES) {
    return null
  }
  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength)
  if (view.getUint8(0) !== TERMINAL_STREAM_KIND || view.getUint8(1) !== TERMINAL_STREAM_VERSION) {
    return null
  }
  const opcode = view.getUint8(2)
  if (!isTerminalStreamOpcode(opcode)) {
    return null
  }
  const high = view.getUint32(8, true)
  const low = view.getUint32(12, true)
  return {
    opcode,
    streamId: view.getUint32(4, true),
    seq: high * 0x100000000 + low,
    payload: bytes.slice(HEADER_BYTES)
  }
}

/** The stream id in a terminal frame's header, or null when the bytes are not a terminal frame. */
export function readTerminalStreamFrameId(bytes: Uint8Array): number | null {
  if (
    bytes.length < HEADER_BYTES ||
    bytes[0] !== TERMINAL_STREAM_KIND ||
    bytes[1] !== TERMINAL_STREAM_VERSION
  ) {
    return null
  }
  return new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength).getUint32(4, true)
}

/** Overwrites the stream id of a frame `readTerminalStreamFrameId` accepted. */
export function writeTerminalStreamFrameId(bytes: Uint8Array, streamId: number): void {
  new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength).setUint32(4, streamId, true)
}

export function encodeTerminalStreamJson(value: unknown): Uint8Array {
  return new TextEncoder().encode(JSON.stringify(value))
}

export function decodeTerminalStreamJson<T>(payload: Uint8Array): T | null {
  if (payload.byteLength > TERMINAL_STREAM_JSON_MAX_BYTES) {
    return null
  }
  try {
    const content = new TextDecoder().decode(payload)
    assertJsonTextStructureWithinLimits(content, TERMINAL_STREAM_JSON_STRUCTURE_LIMITS)
    return JSON.parse(content) as T
  } catch {
    return null
  }
}

export function encodeTerminalStreamText(value: string): Uint8Array {
  return new TextEncoder().encode(value)
}

export function decodeTerminalStreamText(payload: Uint8Array): string {
  return new TextDecoder().decode(payload)
}

function isTerminalStreamOpcode(value: number): value is TerminalStreamOpcode {
  return (
    value === TerminalStreamOpcode.Output ||
    value === TerminalStreamOpcode.SnapshotStart ||
    value === TerminalStreamOpcode.SnapshotChunk ||
    value === TerminalStreamOpcode.SnapshotEnd ||
    value === TerminalStreamOpcode.Resized ||
    value === TerminalStreamOpcode.Error ||
    value === TerminalStreamOpcode.Input ||
    value === TerminalStreamOpcode.Resize ||
    value === TerminalStreamOpcode.Subscribe ||
    value === TerminalStreamOpcode.Unsubscribe ||
    value === TerminalStreamOpcode.SnapshotRequest ||
    value === TerminalStreamOpcode.Metadata ||
    value === TerminalStreamOpcode.Ack ||
    value === TerminalStreamOpcode.ClaimViewport ||
    value === TerminalStreamOpcode.OutputSpan ||
    value === TerminalStreamOpcode.SetOutputPaused ||
    value === TerminalStreamOpcode.WriteUnavailable ||
    value === TerminalStreamOpcode.InputAck ||
    value === TerminalStreamOpcode.PausedOutputDropped
  )
}