Ensuring file size is atleasy 2 bytes and added test case for UTF 16 LE

Author: Mohit Athwani

Foundation/NSString.swift

@@ -1301,10 +1301,10 @@ extension NSString {
         let readResult = try NSData(contentsOf: url, options:[])
 
         let bytePtr = readResult.bytes.bindMemory(to: UInt8.self, capacity:readResult.length)
-        if bytePtr[0] == 254 && bytePtr[1] == 255 {
+        if readResult.length >= 2 && bytePtr[0] == 254 && bytePtr[1] == 255 {
           enc?.pointee = String.Encoding.utf16BigEndian.rawValue
         }
-        else if bytePtr[0] == 255 && bytePtr[1] == 254 {
+        else if readResult.length >= 2 && bytePtr[0] == 255 && bytePtr[1] == 254 {
           enc?.pointee = String.Encoding.utf16LittleEndian.rawValue
         }
         else {

TestFoundation/Resources/NSString-UTF16-LE-data.txt

@@ -67,6 +67,7 @@ class TestNSString : XCTestCase {
             ("test_CFStringCreateMutableCopy", test_CFStringCreateMutableCopy),
             ("test_FromContentsOfURL",test_FromContentsOfURL),
             ("test_FromContentsOfURLUsedEncodingUTF16BE", test_FromContentsOfURLUsedEncodingUTF16BE),
+            ("test_FromContentsOfURLUsedEncodingUTF16LE", test_FromContentsOfURLUsedEncodingUTF16LE),
             ("test_FromContentOfFile",test_FromContentOfFile),
             ("test_swiftStringUTF16", test_swiftStringUTF16),
             // This test takes forever on build servers; it has been seen up to 1852.084 seconds
@@ -313,7 +314,23 @@ class TestNSString : XCTestCase {
           XCTAssertEqual(string, "NSString fromURL usedEncoding test with UTF16 BE file", "Wrong result when reading UTF16BE file")
           XCTAssertEqual(encoding, String.Encoding.utf16BigEndian.rawValue, "Wrong encoding detected from UTF16BE file")
       } catch {
-          XCTFail("Unable to init NSString from contentsOf:encoding:")
+          XCTFail("Unable to init NSString from contentsOf:usedEncoding:")
+      }
+    }
+
+    func test_FromContentsOfURLUsedEncodingUTF16LE() {
+      guard let testFileURL = testBundle().url(forResource: "NSString-UTF16-LE-data", withExtension: "txt") else {
+        XCTFail("URL for NSString-UTF16-LE-data.txt is nil")
+        return
+      }
+
+      do {
+          var encoding: UInt = 0
+          let string = try NSString(contentsOf: testFileURL, usedEncoding: &encoding)
+          XCTAssertEqual(string, "NSString fromURL usedEncoding test with UTF16 LE file", "Wrong result when reading UTF16LE file")
+          XCTAssertEqual(encoding, String.Encoding.utf16LittleEndian.rawValue, "Wrong encoding detected from UTF16LE file")
+      } catch {
+          XCTFail("Unable to init NSString from contentOf:usedEncoding:")
       }
     }
 

TestFoundation/TestNSString.swift

@@ -461,6 +461,7 @@
     'TestFoundation/Resources/Test.plist',
     'TestFoundation/Resources/NSStringTestData.txt',
     'TestFoundation/Resources/NSString-UTF16-BE-data.txt',
+    'TestFoundation/Resources/NSString-UTF16-LE-data.txt',
     'TestFoundation/Resources/NSXMLDocumentTestData.xml',
     'TestFoundation/Resources/PropertyList-1.0.dtd',
     'TestFoundation/Resources/NSXMLDTDTestData.xml',