41 lines
2.2 KiB
Markdown
41 lines
2.2 KiB
Markdown
# Determine the Encoding of a HTML Byte Stream
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This package implements the HTML Standard's [encoding sniffing algorithm](https://html.spec.whatwg.org/multipage/syntax.html#encoding-sniffing-algorithm) in all its glory. The most interesting part of this is how it pre-scans the first 1024 bytes in order to search for certain `<meta charset>`-related patterns.
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```js
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const htmlEncodingSniffer = require("html-encoding-sniffer");
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const fs = require("fs");
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const htmlBytes = fs.readFileSync("./html-page.html");
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const sniffedEncoding = htmlEncodingSniffer(htmlBytes);
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```
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The passed bytes are given as a `Uint8Array`; the Node.js `Buffer` subclass of `Uint8Array` will also work, as shown above.
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The returned value will be a canonical [encoding name](https://encoding.spec.whatwg.org/#names-and-labels) (not a label). You might then combine this with the [whatwg-encoding](https://github.com/jsdom/whatwg-encoding) package to decode the result:
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```js
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const whatwgEncoding = require("whatwg-encoding");
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const htmlString = whatwgEncoding.decode(htmlBytes, sniffedEncoding);
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```
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## Options
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You can pass two potential options to `htmlEncodingSniffer`:
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```js
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const sniffedEncoding = htmlEncodingSniffer(htmlBytes, {
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transportLayerEncodingLabel,
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defaultEncoding
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});
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```
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These represent two possible inputs into the [encoding sniffing algorithm](https://html.spec.whatwg.org/multipage/syntax.html#encoding-sniffing-algorithm):
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- `transportLayerEncodingLabel` is an encoding label that is obtained from the "transport layer" (probably a HTTP `Content-Type` header), which overrides everything but a BOM.
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- `defaultEncoding` is the ultimate fallback encoding used if no valid encoding is supplied by the transport layer, and no encoding is sniffed from the bytes. It defaults to `"windows-1252"`, as recommended by the algorithm's table of suggested defaults for "All other locales" (including the `en` locale).
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## Credits
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This package was originally based on the excellent work of [@nicolashenry](https://github.com/nicolashenry), [in jsdom](https://github.com/tmpvar/jsdom/blob/16fd85618f2705d181232f6552125872a37164bc/lib/jsdom/living/helpers/encoding.js). It has since been pulled out into this separate package.
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