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108 lines
3.1 KiB
TypeScript
108 lines
3.1 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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/** Options for {@linkcode JsonStringifyStream}. */
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export interface StringifyStreamOptions {
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/**
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* Prefix to be added after stringify.
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*
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* @default {""}
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*/
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readonly prefix?: string;
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/**
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* Suffix to be added after stringify.
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*
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* @default {"\n"}
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*/
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readonly suffix?: string;
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}
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/**
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* Convert each chunk to JSON string.
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*
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* This can be used to stringify {@link https://jsonlines.org/ | JSON lines},
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* {@link https://ndjson.org/ | NDJSON},
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* {@link https://www.rfc-editor.org/rfc/rfc7464.html | JSON Text Sequences},
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* and {@link https://en.wikipedia.org/wiki/JSON_streaming#Concatenated_JSON | Concatenated JSON}.
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*
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* You can optionally specify a prefix and suffix for each chunk. The default prefix is `""` and the default suffix is `"\n"`.
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*
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* @example Basic usage
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*
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* ```ts
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* import { JsonStringifyStream } from "@std/json/stringify-stream";
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* import { assertEquals } from "@std/assert";
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*
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* const stream = ReadableStream.from([{ foo: "bar" }, { baz: 100 }])
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* .pipeThrough(new JsonStringifyStream());
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*
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* assertEquals(await Array.fromAsync(stream), [
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* `{"foo":"bar"}\n`,
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* `{"baz":100}\n`
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* ]);
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* ```
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*
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* @example Stringify stream of JSON text sequences
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*
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* Set `options.prefix` to `\x1E` to stringify
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* {@linkcode https://www.rfc-editor.org/rfc/rfc7464.html | JSON Text Sequences}.
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*
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* ```ts
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* import { JsonStringifyStream } from "@std/json/stringify-stream";
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* import { assertEquals } from "@std/assert";
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*
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* const stream = ReadableStream.from([{ foo: "bar" }, { baz: 100 }])
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* .pipeThrough(new JsonStringifyStream({ prefix: "\x1E", suffix: "\n" }));
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*
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* assertEquals(await Array.fromAsync(stream), [
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* `\x1E{"foo":"bar"}\n`,
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* `\x1E{"baz":100}\n`
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* ]);
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* ```
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*
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* @example Stringify JSON lines from a server
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*
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* ```ts no-eval no-assert
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* import { JsonStringifyStream } from "@std/json/stringify-stream";
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*
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* // A server that streams one line of JSON every second
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* Deno.serve(() => {
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* let intervalId: number | undefined;
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* const readable = new ReadableStream({
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* start(controller) {
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* // Enqueue data once per second
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* intervalId = setInterval(() => {
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* controller.enqueue({ now: new Date() });
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* }, 1000);
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* },
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* cancel() {
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* clearInterval(intervalId);
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* },
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* });
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*
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* const body = readable
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* .pipeThrough(new JsonStringifyStream()) // Convert data to JSON lines
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* .pipeThrough(new TextEncoderStream()); // Convert a string to a Uint8Array
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*
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* return new Response(body);
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* });
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* ```
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*/
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export class JsonStringifyStream extends TransformStream<unknown, string> {
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/**
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* Constructs new instance.
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*
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* @param options Options for the stream.
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*/
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constructor(options?: StringifyStreamOptions) {
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const { prefix = "", suffix = "\n" } = options ?? {};
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super(
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{
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transform(chunk, controller) {
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controller.enqueue(`${prefix}${JSON.stringify(chunk)}${suffix}`);
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},
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},
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);
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}
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}
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