Make NSString(contentsOf:usedEncoding:) tests work on macOS (#1149)

- Add the NSString-UTF32-{LE,BE}-data.txt tests to the copy resources.

- Skip BOM header when passing data to CFStringCreateWithBytes().

Author: spevans

Foundation.xcodeproj/project.pbxproj

@@ -321,6 +321,8 @@
 		B90C57BC1EEEEA5A005208AE /* TestThread.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E5835F31C20C9B500C81317 /* TestThread.swift */; };
 		B910957A1EEF237800A71930 /* NSString-UTF16-LE-data.txt in Resources */ = {isa = PBXBuildFile; fileRef = B91095781EEF237800A71930 /* NSString-UTF16-LE-data.txt */; };
 		B910957B1EEF237800A71930 /* NSString-UTF16-BE-data.txt in Resources */ = {isa = PBXBuildFile; fileRef = B91095791EEF237800A71930 /* NSString-UTF16-BE-data.txt */; };
+		B933A79E1F3055F700FE6846 /* NSString-UTF32-BE-data.txt in Resources */ = {isa = PBXBuildFile; fileRef = B933A79C1F3055F600FE6846 /* NSString-UTF32-BE-data.txt */; };
+		B933A79F1F3055F700FE6846 /* NSString-UTF32-LE-data.txt in Resources */ = {isa = PBXBuildFile; fileRef = B933A79D1F3055F600FE6846 /* NSString-UTF32-LE-data.txt */; };
 		B9974B961EDF4A22007F15B8 /* TransferState.swift in Sources */ = {isa = PBXBuildFile; fileRef = B9974B8F1EDF4A22007F15B8 /* TransferState.swift */; };
 		B9974B971EDF4A22007F15B8 /* MultiHandle.swift in Sources */ = {isa = PBXBuildFile; fileRef = B9974B901EDF4A22007F15B8 /* MultiHandle.swift */; };
 		B9974B981EDF4A22007F15B8 /* libcurlHelpers.swift in Sources */ = {isa = PBXBuildFile; fileRef = B9974B911EDF4A22007F15B8 /* libcurlHelpers.swift */; };
@@ -785,6 +787,8 @@
 		B167A6641ED7303F0040B09A /* README.md */ = {isa = PBXFileReference; lastKnownFileType = net.daringfireball.markdown; path = README.md; sourceTree = "<group>"; };
 		B91095781EEF237800A71930 /* NSString-UTF16-LE-data.txt */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = "NSString-UTF16-LE-data.txt"; sourceTree = "<group>"; };
 		B91095791EEF237800A71930 /* NSString-UTF16-BE-data.txt */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = "NSString-UTF16-BE-data.txt"; sourceTree = "<group>"; };
+		B933A79C1F3055F600FE6846 /* NSString-UTF32-BE-data.txt */ = {isa = PBXFileReference; lastKnownFileType = text; path = "NSString-UTF32-BE-data.txt"; sourceTree = "<group>"; };
+		B933A79D1F3055F600FE6846 /* NSString-UTF32-LE-data.txt */ = {isa = PBXFileReference; lastKnownFileType = text; path = "NSString-UTF32-LE-data.txt"; sourceTree = "<group>"; };
 		B9974B8F1EDF4A22007F15B8 /* TransferState.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = TransferState.swift; path = http/TransferState.swift; sourceTree = "<group>"; };
 		B9974B901EDF4A22007F15B8 /* MultiHandle.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = MultiHandle.swift; path = http/MultiHandle.swift; sourceTree = "<group>"; };
 		B9974B911EDF4A22007F15B8 /* libcurlHelpers.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; name = libcurlHelpers.swift; path = http/libcurlHelpers.swift; sourceTree = "<group>"; };
@@ -1402,6 +1406,8 @@
 				CE19A88B1C23AA2300B4CB6A /* NSStringTestData.txt */,
 				B91095781EEF237800A71930 /* NSString-UTF16-LE-data.txt */,
 				B91095791EEF237800A71930 /* NSString-UTF16-BE-data.txt */,
+				B933A79C1F3055F600FE6846 /* NSString-UTF32-BE-data.txt */,
+				B933A79D1F3055F600FE6846 /* NSString-UTF32-LE-data.txt */,
 				528776181BF27D9500CB0090 /* Test.plist */,
 				EA66F63B1BF1619600136161 /* NSURLTestData.plist */,
 				E1A3726E1C31EBFB0023AF4D /* NSXMLDocumentTestData.xml */,
@@ -2076,6 +2082,8 @@
 			isa = PBXResourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				B933A79E1F3055F700FE6846 /* NSString-UTF32-BE-data.txt in Resources */,
+				B933A79F1F3055F700FE6846 /* NSString-UTF32-LE-data.txt in Resources */,
 				D3A597F41C34142600295652 /* NSKeyedUnarchiver-NotificationTest.plist in Resources */,
 				528776191BF27D9500CB0090 /* Test.plist in Resources */,
 				EA66F6481BF1619600136161 /* NSURLTestData.plist in Resources */,

Foundation/NSString.swift

@@ -1260,25 +1260,33 @@ extension NSString {
     public convenience init(contentsOf url: URL, usedEncoding enc: UnsafeMutablePointer<UInt>?) throws {
         let readResult = try NSData(contentsOf: url, options:[])
 
+        var offset = 0
         let bytePtr = readResult.bytes.bindMemory(to: UInt8.self, capacity:readResult.length)
         if readResult.length >= 4 && bytePtr[0] == 0xFF && bytePtr[1] == 0xFE && bytePtr[2] == 0x00 && bytePtr[3] == 0x00 {
-          enc?.pointee = String.Encoding.utf32LittleEndian.rawValue
+            enc?.pointee = String.Encoding.utf32LittleEndian.rawValue
+            offset = 4
         }
         else if readResult.length >= 2 && bytePtr[0] == 0xFE && bytePtr[1] == 0xFF {
-          enc?.pointee = String.Encoding.utf16BigEndian.rawValue
+            enc?.pointee = String.Encoding.utf16BigEndian.rawValue
+            offset = 2
         }
         else if readResult.length >= 2 && bytePtr[0] == 0xFF && bytePtr[1] == 0xFE {
-          enc?.pointee = String.Encoding.utf16LittleEndian.rawValue
+            enc?.pointee = String.Encoding.utf16LittleEndian.rawValue
+            offset = 2
         }
         else if readResult.length >= 4 && bytePtr[0] == 0x00 && bytePtr[1] == 0x00 && bytePtr[2] == 0xFE && bytePtr[3] == 0xFF {
-          enc?.pointee = String.Encoding.utf32BigEndian.rawValue
+            enc?.pointee = String.Encoding.utf32BigEndian.rawValue
+            offset = 4
         }
         else {
-          //Need to work on more conditions. This should be the default
-          enc?.pointee = String.Encoding.utf8.rawValue
+            //Need to work on more conditions. This should be the default
+            enc?.pointee = String.Encoding.utf8.rawValue
         }
 
-        guard let enc = enc, let cf = CFStringCreateWithBytes(kCFAllocatorDefault, bytePtr, readResult.length, CFStringConvertNSStringEncodingToEncoding(enc.pointee), true) else {
+        // Since the encoding being passed includes the byte order the BOM wont be checked or skipped, so pass offset to
+        // manually skip the BOM header.
+        guard let enc = enc, let cf = CFStringCreateWithBytes(kCFAllocatorDefault, bytePtr + offset, readResult.length - offset,
+                                                              CFStringConvertNSStringEncodingToEncoding(enc.pointee), true) else {
             throw NSError(domain: NSCocoaErrorDomain, code: CocoaError.fileReadInapplicableStringEncoding.rawValue, userInfo: [
                 "NSDebugDescription" : "Unable to create a string using the specified encoding."
                 ])