Fix ownership issue when using Docker Volumes

Author: miy4

Dockerfile

@@ -2,10 +2,11 @@ FROM docker.io/alpine:3
 
 ENV PLANTUML_VERSION 1.2021.11
 ENV LANG en_US.UTF-8
-RUN apk add --no-cache openjdk8-jre graphviz ttf-droid ttf-droid-nonlatin curl \
+RUN apk add --no-cache openjdk8-jre graphviz ttf-droid ttf-droid-nonlatin curl shadow su-exec \
     && mkdir /app \
     && curl -L https://sourceforge.net/projects/plantuml/files/plantuml.${PLANTUML_VERSION}.jar/download -o /app/plantuml.jar \
     && apk del curl
+COPY entrypoint /
 
-ENTRYPOINT [ "java", "-jar", "/app/plantuml.jar" ]
+ENTRYPOINT [ "/entrypoint" ]
 CMD [ "-h" ]

README.md

@@ -34,6 +34,17 @@ $ run-plantuml [PLANTUML OPTIONS and ARGUMENTS]
 `docker run` and `run-plantuml` accept and pass a set of parameters to PlantUML CLI.  
 See `docker run miy4/plantuml -h` or `run-plantuml -h` output for more details.
 
+### Environment Variables
+
+You can explicitly set the UID and GID of artifacts using the environment variables `PUML_UID` and `PUML_GID`.
+In the following run example, PlantUML generates `sequence_diagram.png` owned by the user with UID 1000 and GID 1000.
+
+``` sh
+$ docker run -e PUML_UID=1000 -e PUML_GID=1000 -v ${PWD}:/work -w /work --rm -t miy4/plantuml -tpng sequence_diagram.uml
+```
+
+If you don't use `PUML_UID` and `PUML_GID`, PlantUML generates the files to have the same UID and GID as the owner of the working directory given by `-w`, `--workdir`.
+
 ## Example
 
 ```sh

entrypoint

@@ -0,0 +1,30 @@
+#!/bin/sh
+
+if [ "$(id -u)" -ne 0 ]; then
+    printf 'Error: You cannot be non-root users\n' 1>&2
+    printf 'Use environment variables PUML_UID and PUML_GID to pass your UID/GID.\n' 1>&2
+    exit 1
+    # or should do nothing in particular?
+    # exec java -jar /app/plantuml.jar "$@"
+fi
+
+# Read UID/GID via environment variables.
+# If they are not available, Fetch UID/GID from the working directory.
+# These values would be the owner UID/GID of PlantUML's artifacts.
+#
+# Note: For Windows filesystems, stat always returns UID=0 and GID=0
+gid=${PUML_GID:-"$(stat -c '%g' .)"}
+uid=${PUML_UID:-"$(stat -c '%u' .)"}
+
+# Do as the root
+if [ "$uid" -eq 0 ] || [ "$gid" -eq 0 ]; then
+    exec java -jar /app/plantuml.jar "$@"
+fi
+
+# Create a new working user
+user='worker'
+groupadd --non-unique --gid "$gid" "$user"
+useradd --non-unique --uid "$uid" --gid "$gid" --create-home "$user"
+
+# Execute a PlantUML process as the worker
+su-exec "$user" java -jar /app/plantuml.jar "$@"