Set userid at container startup rather than build time. Update documentation on container invocation and usage with SSH-X-forwarding.

Dockerfile

@@ -23,11 +23,10 @@ RUN set -x \
 	&& cmake --build BUILD ${PARALLELMFLAGS} \
 	&& cmake --install BUILD \
 	&& cd \
+	&& mv ${BUILD_DIR}/misc/docker_start.sh / \
 	&& rm -rf ${BUILD_DIR}
 
-ARG USER_ID=1000
-RUN set -x \
-	&& useradd -u "$USER_ID" -ms /bin/bash user
+RUN mkdir -p /home/user && chmod 0777 /home/user
 
-ENTRYPOINT ["xca"]
+ENTRYPOINT ["/docker_start.sh"]
 

INSTALL.docker

@@ -12,7 +12,7 @@ Build XCA container
 
 Use the following command to build XCA container:
 
-	docker build --rm --build-arg USER_ID=`id -u` --tag xca .
+	docker build --rm --tag xca .
 
 This will build a container named "xca" using default configuration.
 
@@ -24,8 +24,6 @@ option to add options.
 
 CODENAME              : code name of ubuntu version
                         example: --build-arg CODENAME=jammy
-USER_ID               : id of user "user" inside of container
-                        example: --build-arg USER_ID=`id -u`
 PARALLELMFLAGS        : make flags for parralel build
                         example: --build-arg PARALLELMFLAGS=-j2
 
@@ -34,7 +32,7 @@ Run XCA
 
 Once the container is built, run it using the following command:
 
-	docker run --rm -it --user `id -u` --network=host \
+	docker run --rm -it -e USER_ID=`id -u` --network=host \
 		-e DISPLAY=$DISPLAY -e "QT_X11_NO_MITSHM=1" \
 		xca
 
@@ -44,9 +42,21 @@ Share local directory
 Use docker volumes to share a local directory. This might be useful to store data base files.
 
 	mkdir -p ./some_local_directory
-	docker run --rm -it --user `id -u` --network=host \
+	docker run --rm -it -e USER_ID=`id -u` --network=host \
 		-e DISPLAY=$DISPLAY -e "QT_X11_NO_MITSHM=1" \
 		-v ./some_local_directory:/backup \
 		xca
 
 This makes ./some_local_directory accessible in the container as /backup.
+
+Run over X-Forwarding with SSH
+------------------------------
+
+To run with X-Forwarding over an SSH connection, you can mount .Xauthority. If the application windows doesn't show up, likely you also want to switch to OpenGL done in software:
+
+	docker run --rm -it --network=host \
+		-e DISPLAY=$DISPLAY -e "QT_X11_NO_MITSHM=1" -e LIBGL_ALWAYS_SOFTWARE=1 \
+		-v $HOME/.Xauthority:/home/user/.Xauthority \
+		xca
+
+Note: the environment variable USER_ID doesn't need to be set, since USER_ID is derived from ownership of .Xauthority file.

misc/docker_start.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -e
+
+default_userid=1000
+
+file_path="/home/user/.Xauthority"
+
+if [ -n "$USER_ID" ]; then
+    if [[ "$USER_ID" =~ ^[0-9]+$ ]] && [ "$USER_ID" -gt 0 ]; then
+        echo "using USER_ID from environment: $USER_ID"
+    else
+        echo "USER_ID from environment not numeric, aborting"
+        exit 1    
+    fi
+else
+    if [ -e "$filepath" ]; then
+        USER_ID=$(stat -c "%u" "$filepath")
+        echo "using USER_ID from .Xauthority: $USER_ID"
+    else
+        USER_ID=$default_userid
+        echo "using default USER_ID: $USER_ID"
+    fi
+fi
+
+useradd -u "$USER_ID" -M -s /bin/bash user
+
+exec su user -c "xca $*"