Dockerfile.mm2

# Enhanced MirrorMaker 2: apache/kafka:4.0.0 with a patched MirrorSourceTask.
#
# Rather than rebuilding all of Kafka (~30+ min), we recompile only the modified
# source file against the jars from the official image, then drop the new .class
# files into the existing connect-mirror jar. Same package, same classloader,
# so package-private references resolve at runtime.

ARG KAFKA_IMAGE=apache/kafka:4.0.0

FROM ${KAFKA_IMAGE} AS kafka-base

FROM eclipse-temurin:17-jdk AS builder
WORKDIR /work

# Pull the runtime libs so we can compile against them
COPY --from=kafka-base /opt/kafka/libs /kafka-libs

# Only the file we changed (mirrored from the apache/kafka fork at kafka-fork/connect/mirror/...)
COPY mm2-patch/org/apache/kafka/connect/mirror/MirrorSourceTask.java \
     /work/src/org/apache/kafka/connect/mirror/MirrorSourceTask.java

RUN mkdir -p /work/classes && \
    javac -source 17 -target 17 -d /work/classes -cp "/kafka-libs/*" \
        /work/src/org/apache/kafka/connect/mirror/MirrorSourceTask.java

# Find the existing connect-mirror jar (not the -client variant) and overlay our class files
RUN SRC_JAR=$(ls /kafka-libs/connect-mirror-[0-9]*.jar | head -1) && \
    echo "patching: $SRC_JAR" && \
    cp "$SRC_JAR" /work/connect-mirror.jar && \
    cd /work/classes && \
    jar uf /work/connect-mirror.jar org/apache/kafka/connect/mirror/MirrorSourceTask.class && \
    (ls org/apache/kafka/connect/mirror/MirrorSourceTask\$*.class 2>/dev/null | \
        xargs -r jar uf /work/connect-mirror.jar || true)

FROM ${KAFKA_IMAGE}
USER root
COPY --from=builder /work/connect-mirror.jar /tmp/connect-mirror-patched.jar
RUN ORIG=$(ls /opt/kafka/libs/connect-mirror-[0-9]*.jar | head -1) && \
    cp /tmp/connect-mirror-patched.jar "$ORIG" && \
    rm /tmp/connect-mirror-patched.jar
USER appuser