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server_sent_event.ts
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server_sent_event.ts
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// Copyright 2018-2022 the oak authors. All rights reserved. MIT license.
import type { Context } from "./context.ts";
import { assert } from "./util.ts";
const encoder = new TextEncoder();
const DEFAULT_KEEP_ALIVE_INTERVAL = 30_000;
export interface ServerSentEventInit extends EventInit {
/** An optional `id` which will be sent with the event and exposed in the
* client `EventSource`. */
id?: number;
/** The replacer is passed to `JSON.stringify` when converting the `data`
* property to a JSON string. */
replacer?:
| (string | number)[]
// deno-lint-ignore no-explicit-any
| ((this: any, key: string, value: any) => any);
/** Space is passed to `JSON.stringify` when converting the `data` property
* to a JSON string. */
space?: string | number;
}
export interface ServerSentEventTargetOptions {
/** Additional headers to send to the client during startup. These headers
* will overwrite any of the default headers if the key is duplicated. */
headers?: Headers;
/** Keep client connections alive by sending a comment event to the client
* at a specified interval. If `true`, then it polls every 30000 milliseconds
* (30 seconds). If set to a number, then it polls that number of
* milliseconds. The feature is disabled if set to `false`. It defaults to
* `false`. */
keepAlive?: boolean | number;
}
class CloseEvent extends Event {
constructor(eventInit: EventInit) {
super("close", eventInit);
}
}
/** An event which contains information which will be sent to the remote
* connection and be made available in an `EventSource` as an event. A server
* creates new events and dispatches them on the target which will then be
* sent to a client.
*
* See more about Server-sent events on [MDN](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events)
*
* ### Example
*
* ```ts
* import { Application, ServerSentEvent } from "https://deno.land/x/oak/mod.ts";
*
* const app = new Application();
*
* app.use((ctx) => {
* const target = ctx.sendEvents();
* const evt = new ServerSentEvent(
* "message",
* { hello: "world" },
* { id: 1 },
* );
* target.dispatchEvent(evt);
* });
* ```
*/
export class ServerSentEvent extends Event {
#data: string;
#id?: number;
#type: string;
/**
* @param type the event type that will be available on the client. The type
* of `"message"` will be handled specifically as a message
* server-side event.
* @param data arbitrary data to send to the client, data this is a string
* will be sent unmodified, otherwise `JSON.parse()` will be used
* to serialize the value
* @param eventInit initialization options for the event
*/
constructor(
type: string,
data: unknown,
eventInit: ServerSentEventInit = {},
) {
super(type, eventInit);
const { replacer, space } = eventInit;
this.#type = type;
try {
this.#data = typeof data === "string"
? data
: JSON.stringify(data, replacer as (string | number)[], space);
} catch (e) {
assert(e instanceof Error);
throw new TypeError(
`data could not be coerced into a serialized string.\n ${e.message}`,
);
}
const { id } = eventInit;
this.#id = id;
}
/** The data associated with the event, which will be sent to the client and
* be made available in the `EventSource`. */
get data(): string {
return this.#data;
}
/** The optional ID associated with the event that will be sent to the client
* and be made available in the `EventSource`. */
get id(): number | undefined {
return this.#id;
}
toString(): string {
const data = `data: ${this.#data.split("\n").join("\ndata: ")}\n`;
return `${this.#type === "__message" ? "" : `event: ${this.#type}\n`}${
this.#id ? `id: ${String(this.#id)}\n` : ""
}${data}\n`;
}
}
const RESPONSE_HEADERS = [
["Connection", "Keep-Alive"],
["Content-Type", "text/event-stream"],
["Cache-Control", "no-cache"],
["Keep-Alive", `timeout=${Number.MAX_SAFE_INTEGER}`],
] as const;
export interface ServerSentEventTarget extends EventTarget {
/** Is set to `true` if events cannot be sent to the remote connection.
* Otherwise it is set to `false`.
*
* *Note*: This flag is lazily set, and might not reflect a closed state until
* another event, comment or message is attempted to be processed. */
readonly closed: boolean;
/** Close the target, refusing to accept any more events. */
close(): Promise<void>;
/** Send a comment to the remote connection. Comments are not exposed to the
* client `EventSource` but are used for diagnostics and helping ensure a
* connection is kept alive.
*
* ```ts
* import { Application } from "https://deno.land/x/oak/mod.ts";
*
* const app = new Application();
*
* app.use((ctx) => {
* const sse = ctx.getSSETarget();
* sse.dispatchComment("this is a comment");
* });
*
* await app.listen();
* ```
*/
dispatchComment(comment: string): boolean;
/** Dispatch a message to the client. This message will contain `data: ` only
* and be available on the client `EventSource` on the `onmessage` or an event
* listener of type `"message"`. */
dispatchMessage(data: unknown): boolean;
/** Dispatch a server sent event to the client. The event `type` will be
* sent as `event: ` to the client which will be raised as a `MessageEvent`
* on the `EventSource` in the client.
*
* Any local event handlers will be dispatched to first, and if the event
* is cancelled, it will not be sent to the client.
*
* ```ts
* import { Application, ServerSentEvent } from "https://deno.land/x/oak/mod.ts";
*
* const app = new Application();
*
* app.use((ctx) => {
* const sse = ctx.getSSETarget();
* const evt = new ServerSentEvent("ping", "hello");
* sse.dispatchEvent(evt);
* });
*
* await app.listen();
* ```
*/
dispatchEvent(event: ServerSentEvent): boolean;
/** Dispatch a server sent event to the client. The event `type` will be
* sent as `event: ` to the client which will be raised as a `MessageEvent`
* on the `EventSource` in the client.
*
* Any local event handlers will be dispatched to first, and if the event
* is cancelled, it will not be sent to the client.
*
* ```ts
* import { Application, ServerSentEvent } from "https://deno.land/x/oak/mod.ts";
*
* const app = new Application();
*
* app.use((ctx) => {
* const sse = ctx.getSSETarget();
* const evt = new ServerSentEvent("ping", "hello");
* sse.dispatchEvent(evt);
* });
*
* await app.listen();
* ```
*/
dispatchEvent(event: CloseEvent | ErrorEvent): boolean;
}
export class SSEStreamTarget extends EventTarget
implements ServerSentEventTarget {
#closed = false;
#context: Context;
#controller?: ReadableStreamDefaultController<Uint8Array>;
// we are ignoring any here, because when exporting to npn/Node.js, the timer
// handle isn't a number.
// deno-lint-ignore no-explicit-any
#keepAliveId?: any;
// deno-lint-ignore no-explicit-any
#error(error: any) {
console.log("error", error);
this.dispatchEvent(new CloseEvent({ cancelable: false }));
const errorEvent = new ErrorEvent("error", { error });
this.dispatchEvent(errorEvent);
this.#context.app.dispatchEvent(errorEvent);
}
#push(payload: string) {
if (!this.#controller) {
this.#error(new Error("The controller has not been set."));
return;
}
if (this.#closed) {
return;
}
this.#controller.enqueue(encoder.encode(payload));
}
get closed(): boolean {
return this.#closed;
}
constructor(
context: Context,
{ headers, keepAlive = false }: ServerSentEventTargetOptions = {},
) {
super();
this.#context = context;
context.response.body = new ReadableStream<Uint8Array>({
start: (controller) => {
this.#controller = controller;
},
cancel: (error) => {
// connections closing are considered "normal" for SSE events and just
// mean the far side has closed.
if (
error instanceof Error && error.message.includes("connection closed")
) {
this.close();
} else {
this.#error(error);
}
},
});
if (headers) {
for (const [key, value] of headers) {
context.response.headers.set(key, value);
}
}
for (const [key, value] of RESPONSE_HEADERS) {
context.response.headers.set(key, value);
}
this.addEventListener("close", () => {
this.#closed = true;
if (this.#keepAliveId != null) {
clearInterval(this.#keepAliveId);
this.#keepAliveId = undefined;
}
if (this.#controller) {
try {
this.#controller.close();
} catch {
// we ignore any errors here, as it is likely that the controller
// is already closed
}
}
});
if (keepAlive) {
const interval = typeof keepAlive === "number"
? keepAlive
: DEFAULT_KEEP_ALIVE_INTERVAL;
this.#keepAliveId = setInterval(() => {
this.dispatchComment("keep-alive comment");
}, interval);
}
}
close(): Promise<void> {
this.dispatchEvent(new CloseEvent({ cancelable: false }));
return Promise.resolve();
}
dispatchComment(comment: string): boolean {
this.#push(`: ${comment.split("\n").join("\n: ")}\n\n`);
return true;
}
// deno-lint-ignore no-explicit-any
dispatchMessage(data: any): boolean {
const event = new ServerSentEvent("__message", data);
return this.dispatchEvent(event);
}
dispatchEvent(event: ServerSentEvent): boolean;
dispatchEvent(event: CloseEvent | ErrorEvent): boolean;
dispatchEvent(event: ServerSentEvent | CloseEvent | ErrorEvent): boolean {
const dispatched = super.dispatchEvent(event);
if (dispatched && event instanceof ServerSentEvent) {
this.#push(String(event));
}
return dispatched;
}
[Symbol.for("Deno.customInspect")](inspect: (value: unknown) => string) {
return `${this.constructor.name} ${
inspect({ "#closed": this.#closed, "#context": this.#context })
}`;
}
[Symbol.for("nodejs.util.inspect.custom")](
depth: number,
// deno-lint-ignore no-explicit-any
options: any,
inspect: (value: unknown, options?: unknown) => string,
) {
if (depth < 0) {
return options.stylize(`[${this.constructor.name}]`, "special");
}
const newOptions = Object.assign({}, options, {
depth: options.depth === null ? null : options.depth - 1,
});
return `${options.stylize(this.constructor.name, "special")} ${
inspect(
{ "#closed": this.#closed, "#context": this.#context },
newOptions,
)
}`;
}
}