229 lines
9.3 KiB
Swift
229 lines
9.3 KiB
Swift
extension PureXML.Parsing {
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/// Decodes a byte stream into characters incrementally. It detects the
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/// encoding from the leading bytes (buffering only those few), strips any
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/// byte-order mark, then yields one Unicode scalar at a time as a Character,
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/// so a byte source is never fully materialized. Invalid sequences yield the
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/// Unicode replacement character rather than failing the stream.
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///
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/// This works at scalar granularity; a multi-scalar grapheme cluster is
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/// surfaced as separate characters, which is harmless for XML tokenization.
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struct StreamingDecoder {
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private let pull: () -> UInt8?
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private var encoding: InputEncoding?
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private var prefix: [UInt8] = []
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private var prefixIndex = 0
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private var finished = false
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private static let replacement: Character = "\u{FFFD}"
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init(pullingBytes pull: @escaping () -> UInt8?) {
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self.pull = pull
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}
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/// Returns the next decoded character, or nil at the end of the stream.
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mutating func next() -> Character? {
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if encoding == nil {
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detect()
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}
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guard !finished, let encoding else {
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return nil
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}
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if let map = PureXML.Parsing.ByteDecoder.singleByteMap(encoding) {
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return nextSingleByte(map)
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}
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return nextWide(encoding)
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}
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/// Dispatches the non-single-byte encodings (the Unicode transformation
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/// formats and the multi-byte CJK encodings).
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private mutating func nextWide(_ encoding: InputEncoding) -> Character? {
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switch encoding {
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case .utf16BigEndian: nextUTF16(bigEndian: true)
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case .utf16LittleEndian: nextUTF16(bigEndian: false)
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case .utf32BigEndian: nextUTF32(bigEndian: true)
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case .utf32LittleEndian: nextUTF32(bigEndian: false)
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case .shiftJIS: nextShiftJIS()
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case .eucJP: nextEUCJP()
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case .eucKR: nextEUCKR()
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case .gbk: nextGBK()
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default: nextUTF8()
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}
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}
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/// Streams one GBK character: ASCII, `0x80` (euro), or a lead+trail.
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private mutating func nextGBK() -> Character? {
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guard let lead = nextByte() else {
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finished = true
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return nil
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}
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if lead <= 0x7F { return Character(Unicode.Scalar(lead)) }
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if lead == 0x80 { return "\u{20AC}" }
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guard (0x81 ... 0xFE).contains(lead) else { return Self.replacement }
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guard let trail = nextByte() else { finished = true
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return Self.replacement
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}
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return PureXML.Parsing.ByteDecoder.GBK.twoByteScalar(lead: lead, trail: trail).map(Character.init) ?? Self.replacement
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}
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/// Streams one EUC-KR character: ASCII, or a lead+trail through CP949.
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private mutating func nextEUCKR() -> Character? {
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guard let lead = nextByte() else {
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finished = true
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return nil
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}
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if lead <= 0x7F { return Character(Unicode.Scalar(lead)) }
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guard (0x81 ... 0xFE).contains(lead) else { return Self.replacement }
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guard let trail = nextByte() else { finished = true
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return Self.replacement
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}
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return PureXML.Parsing.ByteDecoder.EUCKR.twoByteScalar(lead: lead, trail: trail).map(Character.init) ?? Self.replacement
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}
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/// Streams one EUC-JP character: ASCII, `0x8E`+byte (half-width katakana),
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/// `0x8F`+two bytes (JIS X 0212), or a lead+byte through JIS X 0208.
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private mutating func nextEUCJP() -> Character? {
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guard let lead = nextByte() else {
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finished = true
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return nil
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}
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if lead <= 0x7F { return Character(Unicode.Scalar(lead)) }
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if lead == 0x8E {
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guard let byte = nextByte() else { finished = true
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return Self.replacement
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}
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guard (0xA1 ... 0xDF).contains(byte) else { return Self.replacement }
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return Character(Unicode.Scalar(0xFF61 + UInt32(byte) - 0xA1) ?? "\u{FFFD}")
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}
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if lead == 0x8F {
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guard let mid = nextByte(), let trail = nextByte() else { finished = true
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return Self.replacement
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}
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return PureXML.Parsing.ByteDecoder.EUCJP.twoByteScalar(lead: mid, trail: trail, useJis0212: true).map(Character.init) ?? Self.replacement
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}
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guard let trail = nextByte() else { finished = true
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return Self.replacement
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}
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return PureXML.Parsing.ByteDecoder.EUCJP.twoByteScalar(lead: lead, trail: trail, useJis0212: false).map(Character.init) ?? Self.replacement
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}
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/// Streams one Shift-JIS character: a single byte (ASCII or half-width
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/// katakana) or a lead+trail two-byte sequence resolved through JIS X 0208.
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private mutating func nextShiftJIS() -> Character? {
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guard let lead = nextByte() else {
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finished = true
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return nil
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}
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if let single = PureXML.Parsing.ByteDecoder.ShiftJIS.singleByteScalar(lead) { return Character(single) }
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guard PureXML.Parsing.ByteDecoder.ShiftJIS.isLead(lead) else { return Self.replacement }
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guard let trail = nextByte() else {
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finished = true
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return Self.replacement
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}
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guard let scalar = PureXML.Parsing.ByteDecoder.ShiftJIS.twoByteScalar(lead: lead, trail: trail) else { return Self.replacement }
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return Character(scalar)
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}
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private mutating func nextUTF32(bigEndian: Bool) -> Character? {
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var ordered: [UInt32] = []
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for _ in 0 ..< 4 {
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guard let byte = nextByte() else {
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finished = true
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return nil
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}
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ordered.append(UInt32(byte))
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}
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if !bigEndian { ordered.reverse() }
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let value = ordered.reduce(UInt32(0)) { ($0 << 8) | $1 }
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return Character(Unicode.Scalar(value) ?? "\u{FFFD}")
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}
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private mutating func nextSingleByte(_ map: (UInt8) -> Unicode.Scalar) -> Character? {
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guard let byte = nextByte() else {
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finished = true
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return nil
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}
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return Character(map(byte))
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}
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private mutating func detect() {
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while prefix.count < 4, let byte = pull() {
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prefix.append(byte)
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}
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let detected = InputEncoding.detectWithBOM(prefix)
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encoding = detected.encoding
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prefixIndex = detected.bomLength
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}
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private mutating func nextByte() -> UInt8? {
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if prefixIndex < prefix.count {
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let byte = prefix[prefixIndex]
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prefixIndex += 1
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return byte
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}
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return pull()
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}
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private mutating func nextUTF8() -> Character? {
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guard let first = nextByte() else {
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finished = true
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return nil
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}
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if first < 0x80 {
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return Character(Unicode.Scalar(first))
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}
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let length: Int
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var value: UInt32
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if first & 0xE0 == 0xC0 {
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length = 2
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value = UInt32(first & 0x1F)
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} else if first & 0xF0 == 0xE0 {
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length = 3
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value = UInt32(first & 0x0F)
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} else if first & 0xF8 == 0xF0 {
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length = 4
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value = UInt32(first & 0x07)
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} else {
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return Self.replacement
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}
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for _ in 1 ..< length {
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guard let continuation = nextByte(), continuation & 0xC0 == 0x80 else {
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return Self.replacement
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}
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value = (value << 6) | UInt32(continuation & 0x3F)
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}
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guard let scalar = Unicode.Scalar(value) else {
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return Self.replacement
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}
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return Character(scalar)
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}
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private mutating func nextUTF16(bigEndian: Bool) -> Character? {
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guard let unit = nextUnit(bigEndian: bigEndian) else {
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finished = true
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return nil
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}
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if (0xD800 ... 0xDBFF).contains(unit) {
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guard let low = nextUnit(bigEndian: bigEndian), (0xDC00 ... 0xDFFF).contains(low) else {
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return Self.replacement
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}
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let value = 0x10000 + (UInt32(unit - 0xD800) << 10) + UInt32(low - 0xDC00)
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guard let scalar = Unicode.Scalar(value) else {
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return Self.replacement
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}
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return Character(scalar)
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}
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guard let scalar = Unicode.Scalar(unit) else {
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return Self.replacement
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}
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return Character(scalar)
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}
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private mutating func nextUnit(bigEndian: Bool) -> UInt16? {
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guard let high = nextByte(), let low = nextByte() else {
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return nil
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}
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return bigEndian ? (UInt16(high) << 8 | UInt16(low)) : (UInt16(low) << 8 | UInt16(high))
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}
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}
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}
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