The following Swift code was created by Martin R. (http://stackoverflow.com/users/1187415/martin-r) and it should be used to read files line-by-line as explained in http://stackoverflow.com/questions/24581517/read-a-file-url-line-by-line-in-swift

StreamReader.swift

class StreamReader  {

    let encoding : UInt
    let chunkSize : Int

    var fileHandle : NSFileHandle!
    let buffer : NSMutableData!
    let delimData : NSData!
    var atEof : Bool = false

    init?(path: String, delimiter: String = "\n", encoding : UInt = NSUTF8StringEncoding, chunkSize : Int = 4096) {
        self.chunkSize = chunkSize
        self.encoding = encoding

        if let fileHandle = NSFileHandle(forReadingAtPath: path) {
            self.fileHandle = fileHandle
        } else {
            return nil
        }
        // Create NSData object containing the line delimiter:
        if let delimData = delimiter.dataUsingEncoding(NSUTF8StringEncoding) {
            self.delimData = delimData
        } else {
            return nil
        }
        if let buffer = NSMutableData(capacity: chunkSize) {
            self.buffer = buffer
        } else {
            return nil
        }
    }

    deinit {
        self.close()
    }

    /// Return next line, or nil on EOF.
    func nextLine() -> String? {

        if atEof {
            return nil
        }

        // Read data chunks from file until a line delimiter is found:
        var range = buffer.rangeOfData(delimData, options: nil, range: NSMakeRange(0, buffer.length))
        while range.location == NSNotFound {
            var tmpData = fileHandle.readDataOfLength(chunkSize)
            if tmpData.length == 0 {
                // EOF or read error.
                atEof = true
                if buffer.length > 0 {
                    // Buffer contains last line in file (not terminated by delimiter).
                    let line = NSString(data: buffer, encoding: encoding);
                    buffer.length = 0
                    return line
                }
                // No more lines.
                return nil
            }
            buffer.appendData(tmpData)
            range = buffer.rangeOfData(delimData, options: nil, range: NSMakeRange(0, buffer.length))
        }

        // Convert complete line (excluding the delimiter) to a string:
        let line = NSString(data: buffer.subdataWithRange(NSMakeRange(0, range.location)),
            encoding: encoding)
        // Remove line (and the delimiter) from the buffer:
        buffer.replaceBytesInRange(NSMakeRange(0, range.location + range.length), withBytes: nil, length: 0)

        return line
    }

    /// Start reading from the beginning of file.
    func rewind() -> Void {
        fileHandle.seekToFileOffset(0)
        buffer.length = 0
        atEof = false
    }

    /// Close the underlying file. No reading must be done after calling this method.
    func close() -> Void {
        if fileHandle != nil {
            fileHandle.closeFile()
            fileHandle = nil
        }
    }
}

Usage:

if let aStreamReader = StreamReader(path: "/path/to/file") {
    while let line = aStreamReader.nextLine() {
        println(line)
    }
    // You can close the underlying file explicitly. Otherwise it will be
    // closed when the reader is deallocated.
    aStreamReader.close()
}