39 lines
1.5 KiB
JavaScript
39 lines
1.5 KiB
JavaScript
// TODO: make this more strict against Symbol.toStringTag
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// Is not very significant though, anything faking Symbol.toStringTag could as well override
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// prototypes, which is not something we protect against
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function isAnyArrayBuffer(x) {
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if (x instanceof ArrayBuffer) return true
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if (globalThis.SharedArrayBuffer && x instanceof SharedArrayBuffer) return true
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if (!x || typeof x.byteLength !== 'number') return false
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const s = Object.prototype.toString.call(x)
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return s === '[object ArrayBuffer]' || s === '[object SharedArrayBuffer]'
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}
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export function fromSource(x) {
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if (x instanceof Uint8Array) return x
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if (ArrayBuffer.isView(x)) return new Uint8Array(x.buffer, x.byteOffset, x.byteLength)
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if (isAnyArrayBuffer(x)) {
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if ('detached' in x) return x.detached === true ? new Uint8Array() : new Uint8Array(x)
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// Old engines without .detached, try-catch
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try {
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return new Uint8Array(x)
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} catch {
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return new Uint8Array()
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}
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}
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throw new TypeError('Argument must be a SharedArrayBuffer, ArrayBuffer or ArrayBufferView')
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}
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// Warning: unlike whatwg-encoding, returns lowercased labels
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// Those are case-insensitive and that's how TextDecoder encoding getter normalizes them
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export function getBOMEncoding(input) {
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const u8 = fromSource(input) // asserts
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if (u8.length >= 3 && u8[0] === 0xef && u8[1] === 0xbb && u8[2] === 0xbf) return 'utf-8'
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if (u8.length < 2) return null
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if (u8[0] === 0xff && u8[1] === 0xfe) return 'utf-16le'
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if (u8[0] === 0xfe && u8[1] === 0xff) return 'utf-16be'
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return null
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}
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