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InputStream.swift
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InputStream.swift
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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import SwiftShims
/// Returns a string read from standard input through the end of the current
/// line or until EOF is reached.
///
/// Standard input is interpreted as `UTF-8`. Invalid bytes are replaced by
/// Unicode [replacement characters][rc].
///
/// [rc]:
/// https://unicode.org/glossary/#replacement_character
///
/// - Parameter strippingNewline: If `true`, newline characters and character
/// combinations are stripped from the result; otherwise, newline characters
/// or character combinations are preserved. The default is `true`.
/// - Returns: The string of characters read from standard input. If EOF has
/// already been reached when `readLine()` is called, the result is `nil`.
public func readLine(strippingNewline: Bool = true) -> String? {
_swift_stdlib_flockfile_stdin()
defer {
_swift_stdlib_funlockfile_stdin()
}
var result = ""
while let character = _readCharacter() {
result.append(character)
if character == "\r", _peekByte() == UInt8(ascii: "\n") {
continue
}
if character.isNewline {
break
}
}
guard !result.isEmpty else {
return nil
}
if strippingNewline, result.last!.isNewline {
_ = result.removeLast()
}
return result
}
//===----------------------------------------------------------------------===//
private let _replacementCharacter: Character = "\u{FFFD}"
private func _readCharacter() -> Character? {
var utf8Bytes = _FixedArray4<UInt8>()
do {
// Leading byte...
guard let byte = _readByte() else {
return nil
}
guard !_isContinuation(byte) else {
return _replacementCharacter
}
utf8Bytes.append(byte)
}
let utf8Count = _utf8ScalarLength(utf8Bytes[0])
switch utf8Count {
case 1:
_internalInvariant(_isASCII(utf8Bytes[0]))
case 2, 3, 4:
for _ in 1 ..< utf8Count {
// Continuation bytes...
guard let byte = _readByte() else {
return _replacementCharacter
}
guard _isContinuation(byte) else {
_ = _pushByte(byte)
return _replacementCharacter
}
utf8Bytes.append(byte)
}
default:
return _replacementCharacter
}
return utf8Bytes.withUnsafeBufferPointer {
_internalInvariant($0.count == utf8Count)
let result = String._fromUTF8Repairing($0).result
return result.count == 1 ? Character(result) : _replacementCharacter
}
}
//===----------------------------------------------------------------------===//
@inline(__always)
private func _readByte() -> UInt8? {
return UInt8(exactly: _swift_stdlib_getc_unlocked_stdin())
}
@inline(__always)
private func _pushByte(_ byte: UInt8) -> Bool {
return UInt8(exactly: _swift_stdlib_ungetc_unlocked_stdin(CInt(byte))) == byte
}
@inline(__always)
private func _peekByte() -> UInt8? {
guard let byte = _readByte(), _pushByte(byte) else {
return nil
}
return byte
}