Added code to detect encoding in UTF32 files for NSString contestOfURL:usedEncoding:

This pull request is in continuation to PR swiftlang#893

Author: Mohit Athwani

Foundation/NSString.swift

@@ -1301,12 +1301,18 @@ extension NSString {
         let readResult = try NSData(contentsOf: url, options:[])
 
         let bytePtr = readResult.bytes.bindMemory(to: UInt8.self, capacity:readResult.length)
-        if readResult.length >= 2 && bytePtr[0] == 254 && bytePtr[1] == 255 {
+        if readResult.length >= 4 && bytePtr[0] == 255 && bytePtr[1] == 254 && bytePtr[2] == 0 && bytePtr[3] == 0 {
+          enc?.pointee = String.Encoding.utf32LittleEndian.rawValue
+        }
+        else if readResult.length >= 2 && bytePtr[0] == 254 && bytePtr[1] == 255 {
           enc?.pointee = String.Encoding.utf16BigEndian.rawValue
         }
         else if readResult.length >= 2 && bytePtr[0] == 255 && bytePtr[1] == 254 {
           enc?.pointee = String.Encoding.utf16LittleEndian.rawValue
         }
+        else if readResult.length >= 4 && bytePtr[0] == 0 && bytePtr[1] == 0 && bytePtr[2] == 254 && bytePtr[3] == 255 {
+          enc?.pointee = String.Encoding.utf32BigEndian.rawValue
+        }
         else {
           //Need to work on more conditions. This should be the default
           enc?.pointee = String.Encoding.utf8.rawValue

TestFoundation/Resources/NSString-UTF32-BE-data.txt

@@ -68,6 +68,8 @@ class TestNSString : XCTestCase {
             ("test_FromContentsOfURL",test_FromContentsOfURL),
             ("test_FromContentsOfURLUsedEncodingUTF16BE", test_FromContentsOfURLUsedEncodingUTF16BE),
             ("test_FromContentsOfURLUsedEncodingUTF16LE", test_FromContentsOfURLUsedEncodingUTF16LE),
+            ("test_FromContentsOfURLUsedEncodingUTF32BE", test_FromContentsOfURLUsedEncodingUTF32BE),
+            ("test_FromContentsOfURLUsedEncodingUTF32LE", test_FromContentsOfURLUsedEncodingUTF32LE),
             ("test_FromContentOfFile",test_FromContentOfFile),
             ("test_swiftStringUTF16", test_swiftStringUTF16),
             // This test takes forever on build servers; it has been seen up to 1852.084 seconds
@@ -334,6 +336,38 @@ class TestNSString : XCTestCase {
       }
     }
 
+    func test_FromContentsOfURLUsedEncodingUTF32BE() {
+      guard let testFileURL = testBundle().url(forResource: "NSString-UTF32-BE-data", withExtension: "txt") else {
+        XCTFail("URL for NSString-UTF32-BE-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 UTF32 BE file", "Wrong result when reading UTF32BE file")
+         XCTAssertEqual(encoding, String.Encoding.utf32BigEndian.rawValue, "Wrong encoding detected from UTF32BE file")
+      } catch {
+          XCTFail("Unable to init NSString from contentOf:usedEncoding:")
+      }
+    }
+
+    func test_FromContentsOfURLUsedEncodingUTF32LE() {
+      guard let testFileURL = testBundle().url(forResource: "NSString-UTF32-LE-data", withExtension: "txt") else {
+        XCTFail("URL for NSString-UTF32-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 UTF32 LE file", "Wrong result when reading UTF32LE file")
+         XCTAssertEqual(encoding, String.Encoding.utf32LittleEndian.rawValue, "Wrong encoding detected from UTF32LE file")
+      } catch {
+          XCTFail("Unable to init NSString from contentOf:usedEncoding:")
+      }
+    }
+
     func test_FromContentOfFile() {
         let testFilePath = testBundle().path(forResource: "NSStringTestData", ofType: "txt")
         XCTAssertNotNil(testFilePath)

TestFoundation/Resources/NSString-UTF32-LE-data.txt

@@ -462,6 +462,8 @@
     'TestFoundation/Resources/NSStringTestData.txt',
     'TestFoundation/Resources/NSString-UTF16-BE-data.txt',
     'TestFoundation/Resources/NSString-UTF16-LE-data.txt',
+    'TestFoundation/Resources/NSString-UTF32-BE-data.txt',
+    'TestFoundation/Resources/NSString-UTF32-LE-data.txt',
     'TestFoundation/Resources/NSXMLDocumentTestData.xml',
     'TestFoundation/Resources/PropertyList-1.0.dtd',
     'TestFoundation/Resources/NSXMLDTDTestData.xml',