fetch-event-stream
Version:
A tiny (736b) utility for Server Sent Event (SSE) streaming via `fetch` and Web Streams API
68 lines (67 loc) • 2.14 kB
JavaScript
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
const NEWLINE_REGEXP = /\r\n|\r|\n/;
const encoder = new TextEncoder();
function assertHasNoNewline(value, varName) {
if (value.match(NEWLINE_REGEXP) !== null) {
throw new RangeError(`${varName} cannot contain a newline`);
}
}
/**
* Converts a server-sent message object into a string for the client.
*
* @see {@link https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format}
*/
function stringify(message) {
const lines = [];
if (message.comment) {
assertHasNoNewline(message.comment, "`message.comment`");
lines.push(`:${message.comment}`);
}
if (message.event) {
assertHasNoNewline(message.event, "`message.event`");
lines.push(`event:${message.event}`);
}
if (message.data) {
message.data.split(NEWLINE_REGEXP).forEach((line) => lines.push(`data:${line}`));
}
if (message.id) {
assertHasNoNewline(message.id.toString(), "`message.id`");
lines.push(`id:${message.id}`);
}
if (message.retry)
lines.push(`retry:${message.retry}`);
return encoder.encode(lines.join("\n") + "\n\n");
}
/**
* Transforms server-sent message objects into strings for the client.
*
* @see {@link https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events}
*
* @example
* ```ts
* import {
* type ServerSentEventMessage,
* ServerSentEventStream,
* } from "@std/http/server-sent-event-stream";
*
* const stream = ReadableStream.from<ServerSentEventMessage>([
* { data: "hello there" }
* ]).pipeThrough(new ServerSentEventStream());
* new Response(stream, {
* headers: {
* "content-type": "text/event-stream",
* "cache-control": "no-cache",
* },
* });
* ```
*/
export class ServerSentEventStream extends TransformStream {
constructor() {
super({
transform: (message, controller) => {
controller.enqueue(stringify(message));
},
});
}
}