NDJSON parser

NDJSONParserTests.swift

import Foundation
import XCTest

class NDJSONParserTests: XCTestCase {
    
    let ndJson = "{ \"key\": \"value\" }\n"
    
    func testSimpleNDJSON() {
        let twoLines = ndJson + ndJson
        XCTAssert(parseDataFromString(twoLines).count == 2)
    }
    
    func testEmptyNDJSON() {
        XCTAssert(parseDataFromString("").count == 0)
    }
    
    func testDoubleNewLineNDJSON() {
        let doubleNewLines = ndJson + "\n" + ndJson
        XCTAssert(parseDataFromString(doubleNewLines).count == 2)
    }
    
    func testOneNewLineNDJSON() {
        let doubleNewLines = "\n"
        XCTAssert(parseDataFromString(doubleNewLines).count == 0)
    }
    
    func testLeadingNewLineNDJSON() {
        let leadingNewLine = "\n" + ndJson
        XCTAssert(parseDataFromString(leadingNewLine).count == 1)
    }
    
    func testNoEndingNewLine() {
        let noEndingNewLine = "{ \"key\": \"value\" }"
        XCTAssert(parseDataFromString(noEndingNewLine).count == 1)
    }
    
    func testPerformance() {
        let huge = Array(count: 100000, repeatedValue: ndJson).reduce("", combine: +)
        self.measureBlock {
            self.parseDataFromString(huge)
        }
    }
    
    private func parseDataFromString(string: String) -> [AnyObject] {
        let data = string.dataUsingEncoding(NSUTF8StringEncoding)!
        do {
            return try NDJSONParser.JSONObjectsWithData(data, options: [])
        } catch {
            XCTFail(String(error))
            return []
        }
    }
}

NSJSONParser.swift

import Foundation

class NDJSONParser {
    
    /**
     Simple NDJSON parser implementation. 
     
     String from NDJSON data is converted to JSON array of elements formed with lines. This array is then to be deserialized with Foundation's NSJSONSerialization class.
     Empty lines are disregarded.
     
     - parameter data: A data object containing UTF8 encoded text with NDJSON.
     - parameter opt:  Options for reading the JSON passed to NSJSONSerialization.
     
     - throws: Errors thrown by NSJSONSerialization.
     
     - returns: Array of JSON objects
     */
    class func JSONObjectsWithData(data: NSData, options opt: NSJSONReadingOptions = []) throws -> [AnyObject] {
        let nonEmptyLines = String(data: data, encoding: NSUTF8StringEncoding)!
            .componentsSeparatedByString("\n").filter{ !$0.isEmpty }
        let string =
            "[" + nonEmptyLines.joinWithSeparator(",")
                + "]"
        let data = string.dataUsingEncoding(NSUTF8StringEncoding)!
        return try NSJSONSerialization.JSONObjectWithData(data, options: opt) as! [AnyObject]
    }
}

latest swift syntax for the class func:

 class func JSONObjectsWithData(data: Data, options opt: JSONSerialization.ReadingOptions = []) throws -> [AnyObject] {
    let nonEmptyLines = String(data: data, encoding: String.Encoding.utf8)!
          .components(separatedBy: "\n").filter{ !$0.isEmpty }
    let string =   "[" + nonEmptyLines.joined(separator: ",")  + "]"
    let data = string.data(using: String.Encoding.utf8)!
    return try JSONSerialization.jsonObject(with: data, options: opt) as! [AnyObject]
  }