103 lines
2.4 KiB
JavaScript
103 lines
2.4 KiB
JavaScript
/**
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* https://encoding.spec.whatwg.org/#utf-8-decoder
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*/
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module.exports = class UTF8Decoder {
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constructor () {
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this.codePoint = 0
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this.bytesSeen = 0
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this.bytesNeeded = 0
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this.lowerBoundary = 0x80
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this.upperBoundary = 0xbf
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}
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get remaining () {
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return this.bytesSeen
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}
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decode (data) {
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// If we have a fast path, just sniff if the last part is a boundary
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if (this.bytesNeeded === 0) {
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let isBoundary = true
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for (let i = Math.max(0, data.byteLength - 4), n = data.byteLength; i < n && isBoundary; i++) {
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isBoundary = data[i] <= 0x7f
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}
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if (isBoundary) return data.toString()
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}
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let result = ''
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for (let i = 0, n = data.byteLength; i < n; i++) {
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const byte = data[i]
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if (this.bytesNeeded === 0) {
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if (byte <= 0x7f) {
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result += String.fromCharCode(byte)
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} else {
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this.bytesSeen = 1
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if (byte >= 0xc2 && byte <= 0xdf) {
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this.bytesNeeded = 2
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this.codePoint = byte & 0x1f
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} else if (byte >= 0xe0 && byte <= 0xef) {
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if (byte === 0xe0) this.lowerBoundary = 0xa0
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else if (byte === 0xed) this.upperBoundary = 0x9f
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this.bytesNeeded = 3
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this.codePoint = byte & 0xf
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} else if (byte >= 0xf0 && byte <= 0xf4) {
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if (byte === 0xf0) this.lowerBoundary = 0x90
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if (byte === 0xf4) this.upperBoundary = 0x8f
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this.bytesNeeded = 4
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this.codePoint = byte & 0x7
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} else {
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result += '\ufffd'
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}
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}
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continue
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}
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if (byte < this.lowerBoundary || byte > this.upperBoundary) {
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this.codePoint = 0
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this.bytesNeeded = 0
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this.bytesSeen = 0
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this.lowerBoundary = 0x80
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this.upperBoundary = 0xbf
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result += '\ufffd'
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continue
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}
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this.lowerBoundary = 0x80
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this.upperBoundary = 0xbf
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this.codePoint = (this.codePoint << 6) | (byte & 0x3f)
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this.bytesSeen++
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if (this.bytesSeen !== this.bytesNeeded) continue
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result += String.fromCodePoint(this.codePoint)
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this.codePoint = 0
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this.bytesNeeded = 0
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this.bytesSeen = 0
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}
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return result
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}
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flush () {
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const result = this.bytesNeeded > 0 ? '\ufffd' : ''
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this.codePoint = 0
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this.bytesNeeded = 0
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this.bytesSeen = 0
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this.lowerBoundary = 0x80
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this.upperBoundary = 0xbf
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return result
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}
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}
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