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string_writer.ts
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string_writer.ts
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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
import type { Writer, WriterSync } from "../types.d.ts";
const decoder = new TextDecoder();
/**
* Writer utility for buffering string chunks.
*
* @example
* ```ts
* import {
* copyN,
* StringReader,
* StringWriter,
* } from "https://deno.land/std@$STD_VERSION/io/mod.ts";
* import { copy } from "https://deno.land/std@$STD_VERSION/streams/copy.ts";
*
* const w = new StringWriter("base");
* const r = new StringReader("0123456789");
* await copyN(r, w, 4); // copy 4 bytes
*
* // Number of bytes read
* console.log(w.toString()); //base0123
*
* await copy(r, w); // copy all
* console.log(w.toString()); // base0123456789
* ```
*
* **Output:**
*
* ```text
* base0123
* base0123456789
* ```
*/
export class StringWriter implements Writer, WriterSync {
#chunks: Uint8Array[] = [];
#byteLength = 0;
#cache: string | undefined;
constructor(private base: string = "") {
const c = new TextEncoder().encode(base);
this.#chunks.push(c);
this.#byteLength += c.byteLength;
}
write(p: Uint8Array): Promise<number> {
return Promise.resolve(this.writeSync(p));
}
writeSync(p: Uint8Array): number {
this.#chunks.push(new Uint8Array(p));
this.#byteLength += p.byteLength;
this.#cache = undefined;
return p.byteLength;
}
toString(): string {
if (this.#cache) {
return this.#cache;
}
const buf = new Uint8Array(this.#byteLength);
let offs = 0;
for (const chunk of this.#chunks) {
buf.set(chunk, offs);
offs += chunk.byteLength;
}
this.#cache = decoder.decode(buf);
return this.#cache;
}
}