More Docker changes:

* disable in-network updates
* persistent directory for snark downloads
* listen on port 12345 for i2np connections
* restore multi-stage build
* use better ant target
* allow passing -Xmx via the JVM_XMX variable

Many thanks to LoveIsGrief for the suggestions!

Dockerfile

@@ -1,27 +1,29 @@
-FROM jlesage/baseimage:alpine-3.10-glibc
+FROM jlesage/baseimage:alpine-3.10-glibc as builder
+
 ENV APP_HOME="/i2p"
 
 WORKDIR /tmp/build
 COPY . .
 
-# Build package
-RUN add-pkg openjdk8-jre
-RUN add-pkg --virtual build-base gettext tar bzip2 apache-ant openjdk8
-RUN echo "noExe=true" >> build.properties
-RUN ant clean pkg
-RUN del-pkg build-base gettext tar bzip2 apache-ant openjdk8
+RUN add-pkg --virtual build-base gettext tar bzip2 apache-ant openjdk8 \
+    && ant preppkg-linux-only \
+    && del-pkg build-base gettext tar bzip2 apache-ant openjdk8
 
-# "install" files
-RUN mkdir -p ${APP_HOME}
-RUN mv pkg-temp/* ${APP_HOME}
+FROM jlesage/baseimage:alpine-3.10-glibc
+ENV APP_HOME="/i2p"
+
+RUN add-pkg openjdk8-jre
+WORKDIR ${APP_HOME}
+COPY --from=builder /tmp/build/pkg-temp .
 
 # "install" i2p by copying over installed files
 COPY docker/rootfs/ /
 
-# Mount home
+# Mount home and snark
 VOLUME ["${APP_HOME}/.i2p"]
+VOLUME ["/i2psnark"]
 
-EXPOSE 7654 7656 7657 7658 4444 6668 8998 7659 7660 4445
+EXPOSE 7654 7656 7657 7658 4444 6668 8998 7659 7660 4445 12345
 
 # Metadata.
 LABEL \
@@ -30,3 +32,4 @@ LABEL \
       org.label-schema.version="1.0" \
       org.label-schema.vcs-url="https://github.com/i2p/i2p.i2p" \
       org.label-schema.schema-version="1.0"
+