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// License: https://github.com/phoenixframework/phoenix/blob/master/LICENSE.md
export type Msg<T> = {
join_ref?: string | null
ref?: string | null
topic: string
event: string
payload: T
}
export default class Serializer {
HEADER_LENGTH = 1
USER_BROADCAST_PUSH_META_LENGTH = 6
KINDS = { userBroadcastPush: 3, userBroadcast: 4 }
BINARY_ENCODING = 0
JSON_ENCODING = 1
BROADCAST_EVENT = 'broadcast'
allowedMetadataKeys: string[] = []
constructor(allowedMetadataKeys?: string[] | null) {
this.allowedMetadataKeys = allowedMetadataKeys ?? []
}
encode(msg: Msg<{ [key: string]: any }>, callback: (result: ArrayBuffer | string) => any) {
if (
msg.event === this.BROADCAST_EVENT &&
!(msg.payload instanceof ArrayBuffer) &&
typeof msg.payload.event === 'string'
) {
return callback(
this._binaryEncodeUserBroadcastPush(msg as Msg<{ event: string } & { [key: string]: any }>)
)
}
let payload = [msg.join_ref, msg.ref, msg.topic, msg.event, msg.payload]
return callback(JSON.stringify(payload))
}
private _binaryEncodeUserBroadcastPush(message: Msg<{ event: string } & { [key: string]: any }>) {
if (this._isArrayBuffer(message.payload?.payload)) {
return this._encodeBinaryUserBroadcastPush(message)
} else {
return this._encodeJsonUserBroadcastPush(message)
}
}
private _encodeBinaryUserBroadcastPush(message: Msg<{ event: string } & { [key: string]: any }>) {
const userPayload = message.payload?.payload ?? new ArrayBuffer(0)
return this._encodeUserBroadcastPush(message, this.BINARY_ENCODING, userPayload)
}
private _encodeJsonUserBroadcastPush(message: Msg<{ event: string } & { [key: string]: any }>) {
const userPayload = message.payload?.payload ?? {}
const encoder = new TextEncoder()
const encodedUserPayload = encoder.encode(JSON.stringify(userPayload)).buffer
return this._encodeUserBroadcastPush(message, this.JSON_ENCODING, encodedUserPayload)
}
private _encodeUserBroadcastPush(
message: Msg<{ event: string } & { [key: string]: any }>,
encodingType: number,
encodedPayload: ArrayBuffer
) {
// Encode each header field as UTF-8. The length prefixes are byte counts and
// the decode side uses TextDecoder (UTF-8), so measuring with String.length
// and writing with charCodeAt would corrupt any multi-byte character (e.g.
// accents or emoji) and desynchronize the buffer.
const encoder = new TextEncoder()
const topic = encoder.encode(message.topic)
const ref = encoder.encode(message.ref ?? '')
const joinRef = encoder.encode(message.join_ref ?? '')
const userEvent = encoder.encode(message.payload.event)
// Filter metadata based on allowed keys
const rest = this.allowedMetadataKeys
? this._pick(message.payload, this.allowedMetadataKeys)
: {}
const metadata = encoder.encode(Object.keys(rest).length === 0 ? '' : JSON.stringify(rest))
// Validate byte lengths don't exceed uint8 max value (255)
if (joinRef.length > 255) {
throw new Error(`joinRef length ${joinRef.length} exceeds maximum of 255`)
}
if (ref.length > 255) {
throw new Error(`ref length ${ref.length} exceeds maximum of 255`)
}
if (topic.length > 255) {
throw new Error(`topic length ${topic.length} exceeds maximum of 255`)
}
if (userEvent.length > 255) {
throw new Error(`userEvent length ${userEvent.length} exceeds maximum of 255`)
}
if (metadata.length > 255) {
throw new Error(`metadata length ${metadata.length} exceeds maximum of 255`)
}
const metaLength =
this.USER_BROADCAST_PUSH_META_LENGTH +
joinRef.length +
ref.length +
topic.length +
userEvent.length +
metadata.length
const header = new ArrayBuffer(this.HEADER_LENGTH + metaLength)
const view = new DataView(header)
const bytes = new Uint8Array(header)
let offset = 0
view.setUint8(offset++, this.KINDS.userBroadcastPush) // kind
view.setUint8(offset++, joinRef.length)
view.setUint8(offset++, ref.length)
view.setUint8(offset++, topic.length)
view.setUint8(offset++, userEvent.length)
view.setUint8(offset++, metadata.length)
view.setUint8(offset++, encodingType)
bytes.set(joinRef, offset)
offset += joinRef.length
bytes.set(ref, offset)
offset += ref.length
bytes.set(topic, offset)
offset += topic.length
bytes.set(userEvent, offset)
offset += userEvent.length
bytes.set(metadata, offset)
offset += metadata.length
var combined = new Uint8Array(header.byteLength + encodedPayload.byteLength)
combined.set(new Uint8Array(header), 0)
combined.set(new Uint8Array(encodedPayload), header.byteLength)
return combined.buffer
}
decode(rawPayload: ArrayBuffer | string, callback: Function) {
if (this._isArrayBuffer(rawPayload)) {
let result = this._binaryDecode(rawPayload as ArrayBuffer)
return callback(result)
}
if (typeof rawPayload === 'string') {
const jsonPayload = JSON.parse(rawPayload)
const [join_ref, ref, topic, event, payload] = jsonPayload
return callback({ join_ref, ref, topic, event, payload })
}
return callback({})
}
private _binaryDecode(buffer: ArrayBuffer) {
const view = new DataView(buffer)
const kind = view.getUint8(0)
const decoder = new TextDecoder()
switch (kind) {
case this.KINDS.userBroadcast:
return this._decodeUserBroadcast(buffer, view, decoder)
}
}
private _decodeUserBroadcast(
buffer: ArrayBuffer,
view: DataView,
decoder: TextDecoder
): {
join_ref: null
ref: null
topic: string
event: string
payload: { [key: string]: any }
} {
const topicSize = view.getUint8(1)
const userEventSize = view.getUint8(2)
const metadataSize = view.getUint8(3)
const payloadEncoding = view.getUint8(4)
let offset = this.HEADER_LENGTH + 4
const topic = decoder.decode(buffer.slice(offset, offset + topicSize))
offset = offset + topicSize
const userEvent = decoder.decode(buffer.slice(offset, offset + userEventSize))
offset = offset + userEventSize
const metadata = decoder.decode(buffer.slice(offset, offset + metadataSize))
offset = offset + metadataSize
const payload = buffer.slice(offset, buffer.byteLength)
const parsedPayload =
payloadEncoding === this.JSON_ENCODING ? JSON.parse(decoder.decode(payload)) : payload
const data: { [key: string]: any } = {
type: this.BROADCAST_EVENT,
event: userEvent,
payload: parsedPayload,
}
// Metadata is optional and always JSON encoded
if (metadataSize > 0) {
data['meta'] = JSON.parse(metadata)
}
return { join_ref: null, ref: null, topic: topic, event: this.BROADCAST_EVENT, payload: data }
}
private _isArrayBuffer(buffer: any): boolean {
return buffer instanceof ArrayBuffer || buffer?.constructor?.name === 'ArrayBuffer'
}
private _pick(obj: Record<string, any> | null | undefined, keys: string[]): Record<string, any> {
if (!obj || typeof obj !== 'object') {
return {}
}
return Object.fromEntries(Object.entries(obj).filter(([key]) => keys.includes(key)))
}
}
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