Generator for reading file line by line.

FileLineStream.swift

//  FileLineStream by Clément Cyril - @clmntcrl - http://clmntcrl.io/
//  Copyright 2015 Clément Cyril.

import Foundation

final class FileLineStream: GeneratorType {

    typealias Element = String

    private var fileHandle: NSFileHandle?
    private var buffer: NSMutableData?
    private let bufferCapacity = 4_096
    private var encoding: UInt


    init(path: String, encoding fileEncoding: UInt = NSUTF8StringEncoding) {
        if let fh = NSFileHandle(forReadingAtPath: path),
        b = NSMutableData(capacity: bufferCapacity)  {
            fileHandle = fh
            buffer = b
        }
        encoding = fileEncoding
    }
    deinit {
        fileHandle?.closeFile()
    }

    func next() -> Element? {
        if let fh = fileHandle,
        b = buffer,
        delimiter = "\n".dataUsingEncoding(encoding) {
            var range = b.rangeOfData(delimiter, options: nil, range: NSMakeRange(0, b.length))
            while range.location == NSNotFound {
                var data = fh.readDataOfLength(bufferCapacity)
                if data.length == 0 {
                    if b.length > 0 { // Last line isn't derminated by delimiter
                        return NSString(data: b, encoding: encoding) as String?
                    }
                    return nil
                }
                b.appendData(data)
                range = b.rangeOfData(delimiter, options: nil, range: NSMakeRange(0, b.length))
            }
            let line = NSString(data: b.subdataWithRange(NSMakeRange(0, range.location)), encoding: encoding) as String?
            b.replaceBytesInRange(NSMakeRange(0, range.location + range.length), withBytes: nil, length: 0)
            return line
        }
        return nil
    }
}