FIX: only chown /data/packages in entrypoint

@stephen-dexda pointed out in #341 that our update in #330 changed
the `chown` operation to apply to the entire `/data` directory,
rather than just `/data/packages`. For anyone who was previously
relying on a workflow like mounting a read-only secrets directory
into `/data` to host authentication information, this broke their
workflow.

This fix sets `entrypoint.sh` to only `chown` `/data/packages`, which
should ensure that the permissions issues resolved by #330 (e.g. #309)
remain fixed, while also fixing the issue in #341.

Dockerfile

@@ -51,6 +51,9 @@ COPY --from=builder_dependencies /install /usr/local
 COPY --from=builder_gosu /usr/local/bin/gosu /usr/local/bin/gosu
 COPY entrypoint.sh /entrypoint.sh
 
+# Use a consistent user and group ID so that linux users
+# can create a corresponding system user and set permissions
+# if desired.
 RUN addgroup -S -g 9898 pypiserver \
     && adduser -S -u 9898 -G pypiserver pypiserver \
     && mkdir -p /data/packages \

entrypoint.sh

@@ -1,15 +1,19 @@
-#!/bin/ash
+#!/usr/bin/env bash
 
 set -euo pipefail
 
-chown -R pypiserver:pypiserver /data
+# chown the VOLUME mount set in the dockerfile
+# If you're using an alternative directory for packages,
+# you'll need to ensure that pypiserver has read and
+# write access to that directory
+chown -R pypiserver:pypiserver /data/packages
 
 if [ "$@" = "" ]; then
-    # default CMD
+    # No arguments were provided, use the default.
     echo "Set default option '/data/packages'"
     set -- " /data/packages"
 else
-    # 
+    # Use whatever was provided
     echo "Using custom CMD: $@"
 fi
 exec gosu pypiserver pypi-server -p "$PORT" $@