Fix #241: avoid copying DLL files that already exist under Windows (#242)

Author: adamrehn

ue4docker/dockerfiles/ue4-build-prerequisites/windows/Dockerfile

@@ -4,9 +4,14 @@ ARG DLLSRCIMAGE
 
 FROM ${DLLSRCIMAGE} as dlls
 
-FROM ${BASEIMAGE} as prerequisites
+FROM ${BASEIMAGE} as deduplication
 SHELL ["cmd", "/S", "/C"]
 
+{% if not disable_labels %}
+# Add a sentinel label so we can easily identify all derived images, including intermediate images
+LABEL com.adamrehn.ue4-docker.sentinel="1"
+{% endif %}
+
 # Gather the system DLLs that we need from the full Windows base image
 COPY --from=dlls `
     C:\Windows\System32\avicap32.dll `
@@ -29,7 +34,16 @@ COPY --from=dlls `
     C:\Windows\System32\opengl32.dll `
     C:\Windows\System32\ResampleDMO.dll `
     C:\Windows\System32\ResourcePolicyClient.dll `
-    C:\Windows\System32\
+    C:\GatheredDLLs\
+
+# Remove any DLL files that already exist in the target base image, to avoid permission errors when attempting to overwrite existing files with a COPY directive
+COPY remove-duplicate-dlls.ps1 C:\remove-duplicate-dlls.ps1
+RUN powershell -ExecutionPolicy Bypass -File C:\remove-duplicate-dlls.ps1
+
+# Copy the DLL files into a clean image
+FROM ${BASEIMAGE} as prerequisites
+SHELL ["cmd", "/S", "/C"]
+COPY --from=deduplication C:\GatheredDlls\ C:\Windows\System32\
 
 {% if not disable_labels %}
 # Add a sentinel label so we can easily identify all derived images, including intermediate images

ue4docker/dockerfiles/ue4-build-prerequisites/windows/remove-duplicate-dlls.ps1

@@ -0,0 +1,11 @@
+$dlls = (Get-ChildItem "C:\GatheredDLLs\*.dll")
+foreach ($dll in $dlls)
+{
+	$filename = $dll.Name
+	$existing = (Get-ChildItem "C:\Windows\System32\${filename}" -ErrorAction SilentlyContinue)
+	if ($existing)
+	{
+		[Console]::Error.WriteLine("${filename} already exists in System32 in the target base image, excluding it from the list of DLL files to copy.")
+		Remove-Item $dll
+	}
+}