fix(rpc): better error handling

rpc/src/core/client.ts

@@ -1,6 +1,7 @@
 import type * as s from '@entityseven/fivem-rpc-shared-types'
 
 import { Emitter } from '../utils/emitter'
+import { RPCError } from '../utils/errors'
 import { generateUUID, parse, stringify, stringifyWeb } from '../utils/funcs'
 import {
 	NATIVE_CLIENT_EVENTS,
@@ -35,8 +36,11 @@ export class RPCInstanceClient extends Wrapper {
 		on(
 			`__cfx_nui:${RPCEvents.LISTENER_WEB}`,
 			async (data: RPCState, callback: (res: unknown) => void) => {
-				const res = await this._handleWeb(data)
-				callback(res)
+				try {
+					callback(await this._handleWeb(data))
+				} catch (e) {
+					callback(this.errorResponse(data, e))
+				}
 			},
 		)
 	}
@@ -47,7 +51,7 @@ export class RPCInstanceClient extends Wrapper {
 		try {
 			parse(payloadRaw)
 		} catch {
-			throw new Error(RPCErrors.INVALID_DATA)
+			throw new RPCError(RPCErrors.INVALID_DATA, RPCErrors.INVALID_DATA)
 		}
 		const payload = parse(payloadRaw)
 
@@ -59,23 +63,7 @@ export class RPCInstanceClient extends Wrapper {
 
 		if (payload.type === 'event') {
 			if (payload.calledTo === 'client') {
-				this.verifyEvent(this._emitterServer, payload)
-
-				const responseData = await this._emitterServer.emit(
-					payload.event,
-					...(payload.data && payload.data.length > 0 ? payload.data : []),
-				)
-
-				const response: RPCState = {
-					event: payload.event,
-					uuid: payload.uuid,
-					calledFrom: 'client',
-					calledTo: 'server',
-					error: null,
-					data: [responseData],
-					player: payload.player,
-					type: 'response',
-				}
+				const response = await this.dispatch(this._emitterServer, payload)
 
 				emitNet(RPCEvents.LISTENER_CLIENT, stringify(response))
 			}
@@ -87,8 +75,14 @@ export class RPCInstanceClient extends Wrapper {
 			}
 		}
 		if (payload.type === 'response') {
-			if (payload.calledTo === 'client' || payload.calledTo === 'webview') {
-				this.resolvePending(payload)
+			if (payload.calledTo === 'client') {
+				this.settle(payload)
+			}
+			if (payload.calledTo === 'webview') {
+				// relayed webview -> server call: the webview gets the whole response
+				if (!this._pending.resolve(payload.uuid, payload)) {
+					this.logIgnored(payload)
+				}
 			}
 		}
 	}
@@ -102,22 +96,19 @@ export class RPCInstanceClient extends Wrapper {
 
 		if (payload.type === 'event') {
 			if (payload.calledTo === 'client') {
-				return await this._emitterWeb.emit(
-					payload.event,
-					...(payload.data && payload.data.length > 0 ? payload.data : []),
-				)
+				return this.dispatch(this._emitterWeb, payload)
 			}
 			if (payload.calledTo === 'server') {
 				payload.player = GetPlayerServerId(PlayerId())
 				emitNet(RPCEvents.LISTENER_WEB, stringify(payload))
 
-				return this._pending.wait(payload.uuid)
+				return this._pending.wait<RPCState>(payload)
 			}
 		}
 
 		if (payload.type === 'response') {
 			if (payload.calledTo === 'client') {
-				this.resolvePending(payload)
+				this.settle(payload)
 
 				return { status: 'ok' }
 			}
@@ -182,7 +173,7 @@ export class RPCInstanceClient extends Wrapper {
 
 		emitNet(RPCEvents.LISTENER_CLIENT, stringify(payload))
 
-		return this._pending.wait<Awaited<Response>>(payload.uuid)
+		return this._pending.wait<Awaited<Response>>(payload)
 	}
 
 	// ===== WEBVIEW =====
@@ -239,7 +230,7 @@ export class RPCInstanceClient extends Wrapper {
 			data: payload,
 		})
 
-		return this._pending.wait<Awaited<Response>>(payload.uuid)
+		return this._pending.wait<Awaited<Response>>(payload)
 	}
 
 	// ===== SELF =====
@@ -297,7 +288,7 @@ export class RPCInstanceClient extends Wrapper {
 			)
 		}
 
-		this.verifyEvent(this._emitterLocal, payload)
+		this.assertListener(this._emitterLocal, payload.event)
 
 		return await this._emitterLocal.emit<Awaited<Response>>(
 			payload.event,
@@ -328,7 +319,7 @@ export class RPCInstanceClient extends Wrapper {
 		CallbackArguments extends Parameters<RPCNativeClientEvents[EventName]>,
 	>(eventName: EventName, cb: (...args: CallbackArguments) => void): this {
 		if (!NATIVE_CLIENT_EVENTS.includes(eventName)) {
-			throw new Error(RPCErrors.UNKNOWN_NATIVE)
+			throw new RPCError(RPCErrors.UNKNOWN_NATIVE, RPCErrors.UNKNOWN_NATIVE)
 		}
 
 		if (this.debug) {
@@ -347,7 +338,7 @@ export class RPCInstanceClient extends Wrapper {
 		>,
 	>(eventName: EventName, cb: (...args: CallbackArguments) => void): this {
 		if (!NATIVE_CLIENT_NETWORK_EVENTS.includes(eventName)) {
-			throw new Error(RPCErrors.UNKNOWN_NATIVE)
+			throw new RPCError(RPCErrors.UNKNOWN_NATIVE, RPCErrors.UNKNOWN_NATIVE)
 		}
 
 		if (this.debug) {

rpc/src/core/server.ts

@@ -1,6 +1,7 @@
 import type * as s from '@entityseven/fivem-rpc-shared-types'
 
 import { Emitter } from '../utils/emitter'
+import { RPCError } from '../utils/errors'
 import { generateUUID, parse, stringify } from '../utils/funcs'
 import { NATIVE_SERVER_EVENTS } from '../utils/native'
 import {
@@ -35,7 +36,7 @@ export class RPCInstanceServer extends Wrapper {
 		try {
 			parse(payloadRaw)
 		} catch {
-			throw new Error(RPCErrors.INVALID_DATA)
+			throw new RPCError(RPCErrors.INVALID_DATA, RPCErrors.INVALID_DATA)
 		}
 		const payload = parse(payloadRaw)
 
@@ -47,34 +48,27 @@ export class RPCInstanceServer extends Wrapper {
 
 		if (payload.calledFrom === 'client') {
 			if (payload.type === 'event') {
-				this.verifyEvent(this._emitterClient, payload)
 				if (payload.player === null || payload.player === -1) {
-					payload.error = RPCErrors.NO_PLAYER
-					this.triggerError(payload)
+					// nobody to reply to, the caller times out
+					this.console.error(
+						new RPCError(
+							RPCErrors.NO_PLAYER,
+							`${RPCErrors.NO_PLAYER}: "${payload.event}" from ${payload.calledFrom}`,
+						),
+					)
 					return
 				}
 
-				const responseData = await this._emitterClient.emit(
-					payload.event,
+				const response = await this.dispatch(
+					this._emitterClient,
+					payload,
 					payload.player,
-					...(payload.data && payload.data.length > 0 ? payload.data : []),
 				)
 
-				const response: RPCState = {
-					event: payload.event,
-					uuid: payload.uuid,
-					calledFrom: 'server',
-					calledTo: 'client',
-					error: null,
-					data: [responseData],
-					player: payload.player,
-					type: 'response',
-				}
-
 				emitNet(RPCEvents.LISTENER_SERVER, response.player, stringify(response))
 			}
 			if (payload.type === 'response') {
-				this.resolvePending(payload)
+				this.settle(payload)
 			}
 		}
 	}
@@ -83,7 +77,7 @@ export class RPCInstanceServer extends Wrapper {
 		try {
 			parse(payloadRaw)
 		} catch {
-			throw new Error(RPCErrors.INVALID_DATA)
+			throw new RPCError(RPCErrors.INVALID_DATA, RPCErrors.INVALID_DATA)
 		}
 		const payload = parse(payloadRaw)
 
@@ -95,34 +89,27 @@ export class RPCInstanceServer extends Wrapper {
 
 		if (payload.calledFrom === 'webview') {
 			if (payload.type === 'event') {
-				this.verifyEvent(this._emitterWeb, payload)
 				if (payload.player === null || payload.player === -1) {
-					payload.error = RPCErrors.NO_PLAYER
-					this.triggerError(payload)
+					// nobody to reply to, the caller times out
+					this.console.error(
+						new RPCError(
+							RPCErrors.NO_PLAYER,
+							`${RPCErrors.NO_PLAYER}: "${payload.event}" from ${payload.calledFrom}`,
+						),
+					)
 					return
 				}
 
-				const responseData = await this._emitterWeb.emit(
-					payload.event,
+				const response = await this.dispatch(
+					this._emitterWeb,
+					payload,
 					payload.player,
-					...(payload.data && payload.data.length > 0 ? payload.data : []),
 				)
 
-				const response: RPCState = {
-					event: payload.event,
-					uuid: payload.uuid,
-					calledFrom: 'server',
-					calledTo: 'webview',
-					error: null,
-					data: [responseData],
-					player: payload.player,
-					type: 'response',
-				}
-
 				emitNet(RPCEvents.LISTENER_SERVER, response.player, stringify(response))
 			}
 			if (payload.type === 'response') {
-				this.resolvePending(payload)
+				this.settle(payload)
 			}
 		}
 	}
@@ -183,7 +170,7 @@ export class RPCInstanceServer extends Wrapper {
 
 		emitNet(RPCEvents.LISTENER_SERVER, player, stringify(payload))
 
-		return this._pending.wait<Awaited<Response>>(payload.uuid)
+		return this._pending.wait<Awaited<Response>>(payload)
 	}
 
 	public async emitClientEveryone<
@@ -260,7 +247,7 @@ export class RPCInstanceServer extends Wrapper {
 
 		emitNet(RPCEvents.LISTENER_SERVER, player, stringify(payload))
 
-		return this._pending.wait<Awaited<Response>>(payload.uuid)
+		return this._pending.wait<Awaited<Response>>(payload)
 	}
 
 	// ===== SELF =====
@@ -318,7 +305,7 @@ export class RPCInstanceServer extends Wrapper {
 			)
 		}
 
-		this.verifyEvent(this._emitterLocal, payload)
+		this.assertListener(this._emitterLocal, payload.event)
 
 		return await this._emitterLocal.emit<Awaited<Response>>(
 			payload.event,
@@ -350,7 +337,7 @@ export class RPCInstanceServer extends Wrapper {
 		CallbackArguments extends Parameters<RPCNativeServerEvents[EventName]>,
 	>(eventName: EventName, cb: (...args: CallbackArguments) => void): this {
 		if (!NATIVE_SERVER_EVENTS.includes(eventName)) {
-			throw new Error(RPCErrors.UNKNOWN_NATIVE)
+			throw new RPCError(RPCErrors.UNKNOWN_NATIVE, RPCErrors.UNKNOWN_NATIVE)
 		}
 
 		if (this.debug) {

rpc/src/core/webview.ts

@@ -43,25 +43,9 @@ export class RPCInstanceWebview extends Wrapper {
 		}
 
 		if (payload.calledFrom === 'client' && payload.type === 'event') {
-			this.verifyEvent(this._emitterClient, payload)
+			const response = await this.dispatch(this._emitterClient, payload)
 
-			const responseData = await this._emitterClient.emit(
-				payload.event,
-				...(payload.data && payload.data.length > 0 ? payload.data : []),
-			)
-
-			const response: RPCState = {
-				event: payload.event,
-				uuid: payload.uuid,
-				calledFrom: 'webview',
-				calledTo: 'client',
-				error: null,
-				data: [responseData],
-				player: payload.player,
-				type: 'response',
-			}
-
-			await this._createHttpClientRequest(response).then()
+			await this._createHttpClientRequest(response)
 		}
 	}
 
@@ -73,23 +57,7 @@ export class RPCInstanceWebview extends Wrapper {
 		}
 
 		if (payload.calledFrom === 'server' && payload.type === 'event') {
-			this.verifyEvent(this._emitterServer, payload)
-
-			const responseData = await this._emitterServer.emit(
-				payload.event,
-				...(payload.data && payload.data.length > 0 ? payload.data : []),
-			)
-
-			const response: RPCState = {
-				event: payload.event,
-				uuid: payload.uuid,
-				calledFrom: 'webview',
-				calledTo: 'server',
-				error: null,
-				data: [responseData],
-				player: payload.player,
-				type: 'response',
-			}
+			const response = await this.dispatch(this._emitterServer, payload)
 
 			await this._createHttpClientRequest(response)
 		}
@@ -254,7 +222,7 @@ export class RPCInstanceWebview extends Wrapper {
 			)
 		}
 
-		this.verifyEvent(this._emitterLocal, payload)
+		this.assertListener(this._emitterLocal, payload.event)
 
 		return await this._emitterLocal.emit<Awaited<Response>>(
 			payload.event,
@@ -266,9 +234,9 @@ export class RPCInstanceWebview extends Wrapper {
 
 	/** Sends an event to the client and waits for its response (with timeout) */
 	private _request<R>(payload: RPCState): Promise<R> {
-		const response = this._pending.wait<R>(payload.uuid)
-		this._createHttpClientRequest(payload).then(
-			data => this._pending.resolve(payload.uuid, data),
+		const response = this._pending.wait<R>(payload)
+		this._createHttpClientRequest<RPCState>(payload).then(
+			res => this.settle(res),
 			(error: Error) => this._pending.reject(payload.uuid, error),
 		)
 		return response

rpc/src/core/wrapper.ts

@@ -1,12 +1,15 @@
 import { Emitter } from '../utils/emitter'
-import { parse } from '../utils/funcs'
+import {
+	handlerErrorMessage,
+	notRegisteredMessage,
+	RPCError,
+} from '../utils/errors'
 import { Pending } from '../utils/pending'
 import {
 	type RPCConfig,
 	type RPCEnvironment,
 	RPCErrors,
 	type RPCState,
-	type RPCStateRaw,
 } from '../utils/types'
 
 export class Wrapper {
@@ -24,41 +27,104 @@ export class Wrapper {
 		this.console = console
 	}
 
-	/** Settles the call waiting for this response; ignores late or unexpected ones */
-	protected resolvePending(payload: RPCState): void {
-		const found = this._pending.resolve(payload.uuid, payload.data?.[0])
-		if (!found && this.debug) {
-			this.console.log(
-				`[RPC]:ignored response ${payload.event} ${payload.uuid} (no pending call, possibly timed out)`,
+	/**
+	 * Runs the listener for `request` and builds the response to send back.
+	 * Never throws: a missing listener or a thrown error ends up in `error`.
+	 *
+	 * @param prefix - arguments passed before the request data (server: player)
+	 */
+	protected async dispatch(
+		emitter: Emitter,
+		request: RPCState,
+		...prefix: unknown[]
+	): Promise<RPCState> {
+		if (!emitter.has(request.event)) {
+			return this.errorResponse(
+				request,
+				new RPCError(
+					RPCErrors.EVENT_NOT_REGISTERED,
+					notRegisteredMessage(request.event, this.env, request.calledFrom),
+				),
+			)
+		}
+
+		try {
+			const data = await emitter.emit(
+				request.event,
+				...prefix,
+				...(request.data ?? []),
+			)
+			return this.response(request, [data], null)
+		} catch (e) {
+			// keep the stack visible where the listener lives
+			this.console.error(e)
+			return this.errorResponse(
+				request,
+				new RPCError(
+					RPCErrors.HANDLER_ERROR,
+					handlerErrorMessage(request.event, this.env, e),
+				),
 			)
 		}
 	}
 
-	protected verifyEvent(state: Emitter, data: RPCStateRaw | RPCState) {
-		const rpcData = typeof data === 'string' ? parse(data) : data
+	/** Builds the response to `request` carrying `error` */
+	protected errorResponse(request: RPCState, error: unknown): RPCState {
+		const rpcError =
+			error instanceof RPCError
+				? error
+				: new RPCError(
+						RPCErrors.HANDLER_ERROR,
+						handlerErrorMessage(request.event, this.env, error),
+					)
+		return this.response(request, null, {
+			code: rpcError.code,
+			message: rpcError.message,
+		})
+	}
 
-		if (!state.has(rpcData.event)) {
-			rpcData.error = RPCErrors.EVENT_NOT_REGISTERED
-			this.triggerError(rpcData)
+	/** Settles the call waiting for `response`; ignores late or unexpected ones */
+	protected settle(response: RPCState): void {
+		const found = response.error
+			? this._pending.reject(response.uuid, RPCError.fromResponse(response))
+			: this._pending.resolve(response.uuid, response.data?.[0])
+
+		if (!found) this.logIgnored(response)
+	}
+
+	/** Throws if no local listener is registered for `event` */
+	protected assertListener(emitter: Emitter, event: string): void {
+		if (!emitter.has(event)) {
+			throw new RPCError(
+				RPCErrors.EVENT_NOT_REGISTERED,
+				notRegisteredMessage(event, this.env, this.env),
+				{ event, uuid: '', from: this.env, to: this.env },
+			)
 		}
 	}
 
-	protected triggerError(rpcData: RPCState, error?: string): Error {
-		const errorMessage = [
-			`${rpcData.error}`,
-			`Event: ${rpcData.event}`,
-			`Uuid: ${rpcData.uuid}`,
-			`From: ${rpcData.calledFrom}`,
-			`To: ${rpcData.calledTo}`,
-			`Player: ${rpcData.player}`,
-			`Type: ${rpcData.type}`,
-			`Data: ${rpcData.data}`,
-		]
-
-		if (error) {
-			errorMessage.push(`Info: ${error}`)
+	protected logIgnored(response: RPCState): void {
+		if (this.debug) {
+			this.console.log(
+				`[RPC]:ignored response ${response.event} ${response.uuid} (no pending call, possibly timed out)`,
+			)
+		}
 	}
 
-		throw new Error(errorMessage.join('\n | '))
+	private response(
+		request: RPCState,
+		data: RPCState['data'],
+		error: RPCState['error'],
+	): RPCState {
+		return {
+			event: request.event,
+			uuid: request.uuid,
+			calledFrom: this.env,
+			calledTo: request.calledFrom,
+			error,
+			data,
+			player: request.player,
+			type: 'response',
+		}
 	}
 }

rpc/src/index.ts

@@ -2,6 +2,7 @@ import { RPCInstanceClient } from './core/client'
 import { RPCInstanceServer } from './core/server'
 import { RPCInstanceWebview } from './core/webview'
 import { Wrapper } from './core/wrapper'
+import { RPCError } from './utils/errors'
 import {
 	type RPCConfig,
 	type RPCEnvironment,
@@ -54,7 +55,10 @@ class RPCFactory<T extends RPCEnvironment> extends Wrapper {
 				this.operator = new RPCInstanceWebview(opts as RPCConfig<'webview'>)
 				break
 			default:
-				throw new Error(RPCErrors.UNKNOWN_ENVIRONMENT)
+				throw new RPCError(
+					RPCErrors.UNKNOWN_ENVIRONMENT,
+					RPCErrors.UNKNOWN_ENVIRONMENT,
+				)
 		}
 	}
 
@@ -65,6 +69,7 @@ class RPCFactory<T extends RPCEnvironment> extends Wrapper {
 
 export { RPCFactory }
 export * from './utils/types'
+export { RPCError, type RPCErrorDetails } from './utils/errors'
 export * from './utils/native'
 export type * from './core/server'
 export type * from './core/client'

rpc/src/utils/errors.ts

@@ -0,0 +1,90 @@
+import { type RPCEnvironment, RPCErrors, type RPCState } from './types'
+
+/** Where a failed call was going, when the error comes from a call */
+export type RPCErrorDetails = {
+	event: string
+	uuid: string
+	/** Environment that made the call */
+	from: RPCEnvironment
+	/** Environment that was called */
+	to: RPCEnvironment
+}
+
+/**
+ * Error thrown or rejected by this library. Check `code` against `RPCErrors`.
+ *
+ * @example
+ * try {
+ * 	await rpc.emitServer('buyItem', 'water')
+ * } catch (e) {
+ * 	if (e instanceof RPCError && e.code === RPCErrors.TIMEOUT) {
+ * 		// server did not answer in time
+ * 	}
+ * }
+ */
+export class RPCError extends Error {
+	public readonly code: RPCErrors
+	public readonly details: RPCErrorDetails | undefined
+
+	constructor(code: RPCErrors, message: string, details?: RPCErrorDetails) {
+		super(message)
+		this.name = 'RPCError'
+		this.code = code
+		this.details = details
+	}
+
+	/** **Internal** Rebuilds the error a receiver sent back in a response */
+	static fromResponse(response: RPCState): RPCError {
+		return new RPCError(
+			response.error?.code ?? RPCErrors.HANDLER_ERROR,
+			response.error?.message ?? 'Unknown error',
+			{
+				event: response.event,
+				uuid: response.uuid,
+				from: response.calledTo,
+				to: response.calledFrom,
+			},
+		)
+	}
+}
+
+/** **Internal** Name of the method that listens on `receiver` for calls from `sender` */
+export function listenerName(
+	receiver: RPCEnvironment,
+	sender: RPCEnvironment,
+): string {
+	if (receiver === sender) return 'onSelf'
+	return `on${sender[0]?.toUpperCase()}${sender.slice(1)}`
+}
+
+/** **Internal** */
+export function notRegisteredMessage(
+	event: string,
+	receiver: RPCEnvironment,
+	sender: RPCEnvironment,
+): string {
+	return `No listener for "${event}" on ${receiver}. Register it with rpc.${listenerName(receiver, sender)}("${event}", ...) in ${receiver} code.`
+}
+
+/** **Internal** */
+export function handlerErrorMessage(
+	event: string,
+	receiver: RPCEnvironment,
+	cause: unknown,
+): string {
+	const reason =
+		cause instanceof Error || (cause as Error | undefined)?.message
+			? (cause as Error).message
+			: String(cause)
+	return `Listener for "${event}" on ${receiver} threw: ${reason}`
+}
+
+/** **Internal** */
+export function timeoutMessage(
+	event: string,
+	receiver: RPCEnvironment,
+	sender: RPCEnvironment,
+	timeout: number,
+): string {
+	return `No response for "${event}" from ${receiver} within ${timeout} ms. Check that ${receiver} registered rpc.${listenerName(receiver, sender)}("${event}", ...) and that it returns, or raise RPCConfig.timeout (0 disables it).`
+}

rpc/src/utils/pending.ts

@@ -1,4 +1,5 @@
-import { RPCErrors } from './types'
+import { RPCError, timeoutMessage } from './errors'
+import { RPCErrors, type RPCState } from './types'
 
 type Call = {
 	resolve: (data: unknown) => void
@@ -13,17 +14,18 @@ export class Pending {
 	/** @param timeout - ms before a call rejects, `0` or less disables it */
 	constructor(private readonly _timeout: number) {}
 
-	public wait<R>(uuid: string): Promise<R> {
+	/** Waits for the response to `request`, rejects with `RPCErrors.TIMEOUT` */
+	public wait<R>(request: RPCState): Promise<R> {
 		return new Promise<R>((resolve, reject) => {
 			const timer =
 				this._timeout > 0
 					? setTimeout(
-							() => this.reject(uuid, new Error(RPCErrors.TIMEOUT)),
+							() => this.reject(request.uuid, this._timeoutError(request)),
 							this._timeout,
 						)
 					: undefined
 
-			this._calls.set(uuid, {
+			this._calls.set(request.uuid, {
 				resolve: resolve as (data: unknown) => void,
 				reject,
 				timer,
@@ -53,4 +55,22 @@ export class Pending {
 		}
 		return call
 	}
+
+	private _timeoutError(request: RPCState): RPCError {
+		return new RPCError(
+			RPCErrors.TIMEOUT,
+			timeoutMessage(
+				request.event,
+				request.calledTo,
+				request.calledFrom,
+				this._timeout,
+			),
+			{
+				event: request.event,
+				uuid: request.uuid,
+				from: request.calledFrom,
+				to: request.calledTo,
+			},
+		)
+	}
 }

rpc/src/utils/types.ts

@@ -46,12 +46,18 @@ export type RPCState = {
 	uuid: string
 	calledFrom: RPCEnvironment
 	calledTo: RPCEnvironment
-	error: string | null
+	error: RPCErrorPayload | null
 	data: unknown[] | null
 	player: number | null
 	type: RPCEventType
 }
 
+/** **Internal** Error sent back in a response, rebuilt as `RPCError` by the caller */
+export type RPCErrorPayload = {
+	code: RPCErrors
+	message: string
+}
+
 /**
  * **Internal**
  *
@@ -93,6 +99,7 @@ export enum RPCErrors {
 	UNKNOWN_NATIVE = 'Unknown native event (if you are sure this exists - use native handler)',
 	UNKNOWN_ENVIRONMENT = 'Unknown environment (must be either "server", "client" or "webview")',
 	TIMEOUT = 'Timed out waiting for response',
+	HANDLER_ERROR = 'Listener threw an error',
 }
 
 /**