resolves #164 un-hardcode list of Windows versions

Partially resolves #138 (support for insider base image is still missing)

This commit:
1. Drops the list of valid Windows versions. Instead, ue4-docker now trusts user input and will fail during image download if user enters something nonexistent
2. Drops 1603->ltsc2016, 1809->ltsc2019 and 2009->20H2 renaming. Instead, ue4-docker directly maps host OS release to Windows Server Core image tag
3. However, ue4-docker now uses advanced logic to determine host OS release. It tries to use DisplayName registry key and fallbacks to ReleaseId if DisplayName doesn't exist. This allows to properly detect 20H2 and 21H1 releases.

On the negative side, some checks are lost:
1. It is no longer possible to check that container version is newer that host OS. Though is should still be rejected by Hyper-V
2. ue4-docker no longer prevents user from using suffix that collides with Windows Server Core image tags

ue4docker/build.py

@@ -138,13 +138,8 @@ def build():
 				logger.error('https://unrealcontainers.com/docs/concepts/windows-containers', False)
 				sys.exit(1)
 
-			# Verify that the user is not attempting to build images with a newer kernel version than the host OS
-			if WindowsUtils.isNewerBaseTag(config.hostBasetag, config.basetag):
-				logger.error('Error: cannot build container images with a newer kernel version than that of the host OS!')
-				sys.exit(1)
-
 			# Check if the user is building a different kernel version to the host OS but is still copying DLLs from System32
-			differentKernels = WindowsUtils.isInsiderPreview() or config.basetag != config.hostBasetag
+			differentKernels = config.basetag != config.hostBasetag
 			if config.pullPrerequisites == False and differentKernels == True and config.dlldir == config.defaultDllDir:
 				logger.error('Error: building images with a different kernel version than the host,', False)
 				logger.error('but a custom DLL directory has not specified via the `-dlldir=DIR` arg.', False)

ue4docker/diagnostics/base.py

@@ -60,8 +60,7 @@ def _generateWindowsBuildArgs(self, logger, basetagOverride=None, isolationOverr
 		'''
 
 		# Determine the appropriate container image base tag for the host system release unless the user specified a base tag
-		buildArgs = []
-		defaultBaseTag = WindowsUtils.getReleaseBaseTag(WindowsUtils.getWindowsRelease())
+		defaultBaseTag = WindowsUtils.getWindowsRelease()
 		baseTag = basetagOverride if basetagOverride is not None else defaultBaseTag
 		buildArgs = ['--build-arg', 'BASETAG={}'.format(baseTag)]
 

ue4docker/infrastructure/BuildConfiguration.py

@@ -228,29 +228,20 @@ def _generateWindowsConfig(self):
 		self.dlldir = self.args.dlldir if self.args.dlldir is not None else self.defaultDllDir
 
 		# Determine base tag for the Windows release of the host system
-		self.hostRelease = WindowsUtils.getWindowsRelease()
-		self.hostBasetag = WindowsUtils.getReleaseBaseTag(self.hostRelease)
+		self.hostBasetag = WindowsUtils.getWindowsRelease()
 
 		# Store the tag for the base Windows Server Core image
 		self.basetag = self.args.basetag if self.args.basetag is not None else self.hostBasetag
 		self.baseImage = 'mcr.microsoft.com/windows/servercore:' + self.basetag
 		self.prereqsTag = self.basetag
 
-		# Verify that any user-specified base tag is valid
-		if WindowsUtils.isValidBaseTag(self.basetag) == False:
-			raise RuntimeError('unrecognised Windows Server Core base image tag "{}", supported tags are {}'.format(self.basetag, WindowsUtils.getValidBaseTags()))
-
-		# Verify that any user-specified tag suffix does not collide with our base tags
-		if WindowsUtils.isValidBaseTag(self.suffix) == True:
-			raise RuntimeError('tag suffix cannot be any of the Windows Server Core base image tags: {}'.format(WindowsUtils.getValidBaseTags()))
-
 		# If the user has explicitly specified an isolation mode then use it, otherwise auto-detect
 		if self.args.isolation is not None:
 			self.isolation = self.args.isolation
 		else:
 
 			# If we are able to use process isolation mode then use it, otherwise fallback to the Docker daemon's default isolation mode
-			differentKernels = WindowsUtils.isInsiderPreview() or self.basetag != self.hostBasetag
+			differentKernels = self.basetag != self.hostBasetag
 			hostSupportsProcess = WindowsUtils.supportsProcessIsolation()
 			dockerSupportsProcess = parse_version(DockerUtils.version()['Version']) >= parse_version('18.09.0')
 			if not differentKernels and hostSupportsProcess and dockerSupportsProcess:

ue4docker/infrastructure/WindowsUtils.py

@@ -7,12 +7,6 @@
 
 class WindowsUtils(object):
 
-	# The latest Windows build version we recognise as a non-Insider build
-	_latestReleaseBuild = 19042
-
-	# The list of Windows Server Core base image tags that we recognise, in ascending version number order
-	_validTags = ['ltsc2016', '1709', '1803', 'ltsc2019', '1903', '1909', '2004', '20H2']
-
 	# The list of Windows Server and Windows 10 host OS releases that are blacklisted due to critical bugs
 	# (See: <https://unrealcontainers.com/docs/concepts/windows-containers>)
 	_blacklistedReleases = ['1903', '1909']
@@ -76,7 +70,13 @@ def getWindowsRelease() -> str:
 		'''
 		Determines the Windows 10 / Windows Server release (1607, 1709, 1803, etc.) of the Windows host system
 		'''
-		return WindowsUtils._getVersionRegKey('ReleaseId')
+		try:
+			# Starting with Windows 20H2 (also known as 2009), Microsoft stopped updating ReleaseId
+			# and instead updates DisplayVersion
+			return WindowsUtils._getVersionRegKey('DisplayVersion')
+		except FileNotFoundError:
+			# Fallback to ReleaseId for pre-20H2 releases that didn't have DisplayVersion
+			return WindowsUtils._getVersionRegKey('ReleaseId')
 
 	@staticmethod
 	def getWindowsBuild() -> int:
@@ -112,56 +112,6 @@ def isWindowsServer() -> bool:
 		# TODO: Replace this with something more reliable
 		return 'Windows Server' in WindowsUtils._getVersionRegKey('ProductName')
 
-	@staticmethod
-	def isInsiderPreview() -> bool:
-		'''
-		Determines if the Windows host system is a Windows Insider preview build
-		'''
-		return WindowsUtils.getWindowsBuild() > WindowsUtils._latestReleaseBuild
-
-	@staticmethod
-	def getReleaseBaseTag(release: str) -> str:
-		'''
-		Retrieves the tag for the Windows Server Core base image matching the specified Windows 10 / Windows Server release
-		'''
-
-		# For Windows Insider preview builds, build the latest release tag
-		if WindowsUtils.isInsiderPreview():
-			return WindowsUtils._validTags[-1]
-
-		# This lookup table is based on the list of valid tags from <https://hub.docker.com/r/microsoft/windowsservercore/>
-		return {
-			'1709': '1709',
-			'1803': '1803',
-			'1809': 'ltsc2019',
-			'1903': '1903',
-			'1909': '1909',
-			'2004': '2004',
-			'2009': '20H2',
-			'20H2': '20H2'
-		}.get(release, 'ltsc2016')
-
-	@staticmethod
-	def getValidBaseTags() -> [str]:
-		'''
-		Returns the list of valid tags for the Windows Server Core base image, in ascending chronological release order
-		'''
-		return WindowsUtils._validTags
-
-	@staticmethod
-	def isValidBaseTag(tag: str) -> bool:
-		'''
-		Determines if the specified tag is a valid Windows Server Core base image tag
-		'''
-		return tag in WindowsUtils._validTags
-
-	@staticmethod
-	def isNewerBaseTag(older: str, newer: str) -> bool:
-		'''
-		Determines if the base tag `newer` is chronologically newer than the base tag `older`
-		'''
-		return WindowsUtils._validTags.index(newer) > WindowsUtils._validTags.index(older)
-
 	@staticmethod
 	def supportsProcessIsolation() -> bool:
 		'''