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106 lines
2.9 KiB
TypeScript
106 lines
2.9 KiB
TypeScript
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
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// This module is browser compatible.
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const NEWLINE_REGEXP = /\r\n|\r|\n/;
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const encoder = new TextEncoder();
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/**
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* Represents a message in the Server-Sent Event (SSE) protocol.
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*
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* @see {@link https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#fields}
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*/
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export interface ServerSentEventMessage {
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/** Ignored by the client. */
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comment?: string;
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/** A string identifying the type of event described. */
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event?: string;
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/** The data field for the message. Split by new lines. */
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data?: string;
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/** The event ID to set the {@linkcode EventSource} object's last event ID value. */
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id?: string | number;
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/** The reconnection time. */
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retry?: number;
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}
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function assertHasNoNewline(value: string, varName: string, errPrefix: string) {
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if (value.match(NEWLINE_REGEXP) !== null) {
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throw new SyntaxError(
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`${errPrefix}: ${varName} cannot contain a newline`,
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);
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}
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}
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/**
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* Converts a server-sent message object into a string for the client.
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*
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* @see {@link https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format}
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*/
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function stringify(message: ServerSentEventMessage): Uint8Array {
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const lines = [];
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if (message.comment) {
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assertHasNoNewline(
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message.comment,
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"`message.comment`",
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"Cannot serialize message",
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);
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lines.push(`:${message.comment}`);
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}
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if (message.event) {
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assertHasNoNewline(
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message.event,
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"`message.event`",
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"Cannot serialize message",
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);
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lines.push(`event:${message.event}`);
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}
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if (message.data) {
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message.data.split(NEWLINE_REGEXP).forEach((line) =>
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lines.push(`data:${line}`)
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);
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}
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if (message.id) {
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assertHasNoNewline(
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message.id.toString(),
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"`message.id`",
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"Cannot serialize message",
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);
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lines.push(`id:${message.id}`);
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}
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if (message.retry) lines.push(`retry:${message.retry}`);
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return encoder.encode(lines.join("\n") + "\n\n");
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}
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/**
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* Transforms server-sent message objects into strings for the client.
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*
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* @see {@link https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events}
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*
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* @example Usage
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* ```ts no-assert
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* import {
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* type ServerSentEventMessage,
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* ServerSentEventStream,
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* } from "@std/http/server-sent-event-stream";
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*
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* const stream = ReadableStream.from<ServerSentEventMessage>([
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* { data: "hello there" }
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* ]).pipeThrough(new ServerSentEventStream());
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* new Response(stream, {
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* headers: {
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* "content-type": "text/event-stream",
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* "cache-control": "no-cache",
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* },
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* });
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* ```
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*/
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export class ServerSentEventStream
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extends TransformStream<ServerSentEventMessage, Uint8Array> {
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constructor() {
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super({
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transform: (message, controller) => {
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controller.enqueue(stringify(message));
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},
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});
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}
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}
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