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PR-URL: https://github.com/nodejs/node/pull/55507 Reviewed-By: Luigi Pinca <luigipinca@gmail.com> Reviewed-By: Chemi Atlow <chemi@atlow.co.il>
123 lines
3.6 KiB
Markdown
123 lines
3.6 KiB
Markdown
# String decoder
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<!--introduced_in=v0.10.0-->
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> Stability: 2 - Stable
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<!-- source_link=lib/string_decoder.js -->
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The `node:string_decoder` module provides an API for decoding `Buffer` objects
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into strings in a manner that preserves encoded multi-byte UTF-8 and UTF-16
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characters. It can be accessed using:
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```mjs
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import { StringDecoder } from 'node:string_decoder';
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```
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```cjs
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const { StringDecoder } = require('node:string_decoder');
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```
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The following example shows the basic use of the `StringDecoder` class.
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```mjs
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import { StringDecoder } from 'node:string_decoder';
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import { Buffer } from 'node:buffer';
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const decoder = new StringDecoder('utf8');
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const cent = Buffer.from([0xC2, 0xA2]);
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console.log(decoder.write(cent)); // Prints: ¢
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const euro = Buffer.from([0xE2, 0x82, 0xAC]);
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console.log(decoder.write(euro)); // Prints: €
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```
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```cjs
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const { StringDecoder } = require('node:string_decoder');
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const decoder = new StringDecoder('utf8');
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const cent = Buffer.from([0xC2, 0xA2]);
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console.log(decoder.write(cent)); // Prints: ¢
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const euro = Buffer.from([0xE2, 0x82, 0xAC]);
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console.log(decoder.write(euro)); // Prints: €
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```
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When a `Buffer` instance is written to the `StringDecoder` instance, an
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internal buffer is used to ensure that the decoded string does not contain
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any incomplete multibyte characters. These are held in the buffer until the
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next call to `stringDecoder.write()` or until `stringDecoder.end()` is called.
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In the following example, the three UTF-8 encoded bytes of the European Euro
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symbol (`€`) are written over three separate operations:
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```mjs
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import { StringDecoder } from 'node:string_decoder';
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import { Buffer } from 'node:buffer';
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const decoder = new StringDecoder('utf8');
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decoder.write(Buffer.from([0xE2]));
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decoder.write(Buffer.from([0x82]));
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console.log(decoder.end(Buffer.from([0xAC]))); // Prints: €
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```
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```cjs
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const { StringDecoder } = require('node:string_decoder');
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const decoder = new StringDecoder('utf8');
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decoder.write(Buffer.from([0xE2]));
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decoder.write(Buffer.from([0x82]));
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console.log(decoder.end(Buffer.from([0xAC]))); // Prints: €
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```
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## Class: `StringDecoder`
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### `new StringDecoder([encoding])`
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<!-- YAML
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added: v0.1.99
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-->
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* `encoding` {string} The character [encoding][] the `StringDecoder` will use.
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**Default:** `'utf8'`.
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Creates a new `StringDecoder` instance.
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### `stringDecoder.end([buffer])`
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<!-- YAML
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added: v0.9.3
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-->
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* `buffer` {string|Buffer|TypedArray|DataView} The bytes to decode.
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* Returns: {string}
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Returns any remaining input stored in the internal buffer as a string. Bytes
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representing incomplete UTF-8 and UTF-16 characters will be replaced with
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substitution characters appropriate for the character encoding.
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If the `buffer` argument is provided, one final call to `stringDecoder.write()`
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is performed before returning the remaining input.
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After `end()` is called, the `stringDecoder` object can be reused for new input.
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### `stringDecoder.write(buffer)`
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<!-- YAML
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added: v0.1.99
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changes:
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- version: v8.0.0
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pr-url: https://github.com/nodejs/node/pull/9618
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description: Each invalid character is now replaced by a single replacement
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character instead of one for each individual byte.
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-->
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* `buffer` {string|Buffer|TypedArray|DataView} The bytes to decode.
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* Returns: {string}
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Returns a decoded string, ensuring that any incomplete multibyte characters at
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the end of the `Buffer`, or `TypedArray`, or `DataView` are omitted from the
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returned string and stored in an internal buffer for the next call to
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`stringDecoder.write()` or `stringDecoder.end()`.
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[encoding]: buffer.md#buffers-and-character-encodings
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