(The code is for Swift 2.2/Xcode 7.3 now. Older versions can be found in the edit history if somebody needs it. An updated version for Swift 3 is provided at the end.)
extension StreamReader : SequenceType { func generate() -> AnyGenerator<String> { return AnyGenerator { return self.nextLine() } } }
Update for Swift 3/Xcode 8 beta 6: Also "modernized" to use guard and the new Data value type:
class StreamReader { let encoding : String.Encoding let chunkSize : Int var fileHandle : FileHandle! let delimData : Data var buffer : Data var atEof : Bool init?(path: String, delimiter: String = "\n", encoding: String.Encoding = .utf8, chunkSize: Int = 4096) { guard let fileHandle = FileHandle(forReadingAtPath: path), let delimData = delimiter.data(using: encoding) else { return nil } self.encoding = encoding self.chunkSize = chunkSize self.fileHandle = fileHandle self.delimData = delimData self.buffer = Data(capacity: chunkSize) self.atEof = false } deinit { self.close() } /// Return next line, or nil on EOF. func nextLine() -> String? { precondition(fileHandle != nil, "Attempt to read from closed file") // Read data chunks from file until a line delimiter is found: while !atEof { if let range = buffer.range(of: delimData) { // Convert complete line (excluding the delimiter) to a string: let line = String(data: buffer.subdata(in: 0..<range.lowerBound), encoding: encoding) // Remove line (and the delimiter) from the buffer: buffer.removeSubrange(0..<range.upperBound) return line } let tmpData = fileHandle.readData(ofLength: chunkSize) if tmpData.count > 0 { buffer.append(tmpData) } else { // EOF or read error. atEof = true if buffer.count > 0 { // Buffer contains last line in file (not terminated by delimiter). let line = String(data: buffer as Data, encoding: encoding) buffer.count = 0 return line } } } return nil } /// Start reading from the beginning of file. func rewind() -> Void { fileHandle.seek(toFileOffset: 0) buffer.count = 0 atEof = false } /// Close the underlying file. No reading must be done after calling this method. func close() -> Void { fileHandle?.closeFile() fileHandle = nil } } extension StreamReader : Sequence { func makeIterator() -> AnyIterator<String> { return AnyIterator { return self.nextLine() } } }
