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import { nanoid } from 'nanoid'
import { isEqual } from 'lodash'
import { Runtime, runtime } from 'webextension-polyfill'
import { serializeError, isErrorLike, type ErrorObject, deserializeError } from 'serialize-error'
import type { JsonObject } from 'type-fest'
export type ChannelContext = 'background' | 'content-script' | 'popup' | 'devtools' | 'options'
export type OnMessageCallback<T extends JsonObject> = (sender: ChannelContext, payload: any) => Promise<T>
export interface ClientChannel {
sendMessage<TSource extends JsonObject, TResult extends JsonObject>(name: string, message: TSource): Promise<TResult>
disconnect(): void
}
export interface ListenerChannel {
onMessage<T extends JsonObject>(name: string, onMessage: OnMessageCallback<T>): () => void
onDisconnected(cb: () => void): void
}
export interface MessageChannel{
openChannel(): ClientChannel
openOnMessageChannel(): ListenerChannel
}
interface InternalChannelMessage{
readonly transactionId: string
readonly payload: JsonObject
readonly srcContext: ChannelContext
readonly destContext: ChannelContext
readonly handlerName: string
}
interface InternalChannelMessageResponse{
readonly request: InternalChannelMessage
readonly response: JsonObject | undefined
readonly error?: ErrorObject
}
interface SendMessageToken<T extends JsonObject> {
readonly request: InternalChannelMessage;
resolve(response: T): void;
reject(error: Error): void
}
interface RxChannelState{
addHandler(name:string, handler: OnMessageCallback<any>): () => void
removeHandler(name:string, handler: OnMessageCallback<any>): void
handlePortMessage(message: InternalChannelMessage, port: Runtime.Port): void
onDisconnected(): void
}
export const createMessageChannel = (localContext: ChannelContext, randomIdSize = 32): MessageChannel => {
const createRxChannel = (): RxChannelState => {
const createPortResponse = (request: InternalChannelMessage, response?: JsonObject, error?: ErrorObject)
: InternalChannelMessageResponse => {
return { request, response, error }
}
//Stores open messages
const handlerMap = new Map<string, OnMessageCallback<any>>()
const handleMessageInternal = async (message: InternalChannelMessage): Promise<any> => {
//OnMessage hanlders will always respond to a destination context
if (!isEqual(message.destContext, localContext)) {
throw new Error(`Invalid destination context ${message.destContext}`)
}
switch (message.srcContext) {
case 'background':
throw new Error('Background context is not supported as a source')
case 'content-script':
case 'popup':
case 'devtools':
case 'options':
break;
default:
throw new Error(`Invalid source context ${message.srcContext}`)
}
//Try to get the handler
const handler = handlerMap.get(message.handlerName)
if (handler === undefined) {
throw new Error(`No handler for ${message.handlerName}`)
}
return handler(message.srcContext, message.payload);
}
return {
addHandler(name: string, handler: OnMessageCallback<any>) {
handlerMap.set(name, handler)
//Return a function to remove the handler
return () => handlerMap.delete(name)
},
removeHandler(name: string) {
handlerMap.delete(name)
},
async handlePortMessage(message: InternalChannelMessage, port: Runtime.Port) {
let isConnected = true
const onDisconnected = () => {
isConnected = false
}
//Add disconnect handler so we can know if the port has disconnected
port.onDisconnect.addListener(onDisconnected)
try {
//Invoke internal message handler and convert to promise response
const response = await handleMessageInternal(message);
if (!isConnected) {
return
}
port.postMessage(
createPortResponse(message, response)
)
}
catch (err: unknown) {
if (!isConnected) {
return
}
//try to serialize the error
const handlerError = isErrorLike(err) ? serializeError(err) : err as ErrorObject
//Send the error back to the port
port.postMessage(
createPortResponse(message, undefined, handlerError)
)
}
finally {
//remove disconnect handler
port.onDisconnect.removeListener(onDisconnected)
}
},
onDisconnected() {
}
}
}
const createTxChannel = (destContext: ChannelContext) => {
const handlerMap = new Map<string, SendMessageToken<any>>()
return {
sendMessage: (port: Runtime.Port) => {
return <T extends JsonObject>(name: string, message: JsonObject): Promise<T> => {
//unique transaction id for message, used to match in response map
const transactionId = nanoid(randomIdSize)
//Create itnernal request wrapper
const request: InternalChannelMessage = {
transactionId,
payload: message,
srcContext: localContext,
destContext,
handlerName: name
}
//Create promise
const promise = new Promise<T>((resolve, reject) => {
//Add to handler map
handlerMap.set(transactionId, { request, resolve, reject })
})
//Send request
port.postMessage(request)
//Return promise
return promise
}
},
onMessage: (message: InternalChannelMessageResponse) => {
const { transactionId } = message.request
//Get the handler
const handler = handlerMap.get(transactionId)
if (handler === undefined) {
throw new Error(`No waiting response handler for ${transactionId}`)
}
//Remove the handler
handlerMap.delete(transactionId)
//Check for error
if (message.error !== undefined) {
//Deserialize error
const err = deserializeError(message.error)
handler.reject(err)
}
else {
handler.resolve(message.response)
}
},
onReconnect: (port: Runtime.Port) => {
//resend pending messages
handlerMap.forEach((token, _) => port.postMessage(token.request))
}
}
}
return {
openChannel(): ClientChannel {
//Open the transmission channel
const { sendMessage, onReconnect, onMessage } = createTxChannel('background');
let port: Runtime.Port;
/**
* Creates a persistent connection to the background script.
* When the port closes, it is reopend and all pending messages
* are resent
*/
const connect = () => {
port = runtime.connect()
port.onMessage.addListener(onMessage)
//reconnect on disconnect
port.onDisconnect.addListener(connect)
//resend pending messages
onReconnect(port)
}
if (localContext === 'background') {
throw new Error('Send channels are not currently supported by ')
}
connect()
return {
//Init send-message handler
sendMessage: sendMessage(port!),
disconnect: port!.disconnect
}
},
openOnMessageChannel(): ListenerChannel {
const { addHandler, handlePortMessage, onDisconnected } = createRxChannel()
const onDisconnectedHandlers = new Set<() => void>()
//Listen for new connections
runtime.onConnect.addListener((port: Runtime.Port) => {
port.onMessage.addListener(handlePortMessage);
port.onDisconnect.addListener(onDisconnected);
//Call all local handlers on on disconnect
port.onDisconnect.addListener(() => {
onDisconnectedHandlers.forEach(cb => cb())
})
})
return {
onMessage: addHandler,
//add to onDisconnectedHandlers
onDisconnected: onDisconnectedHandlers.add,
}
}
}
}
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