Actually do something with the result of readelf in case of invalid FTL binary

Remove the `cat` of the pihole-FTL binary as it could lead to a very difficult to read logs
Add some more helpful output to the build script

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

build.sh

@@ -18,7 +18,8 @@ usage() {
 }
 
 # Set default values
-DOCKER_BUILD_CMD="docker buildx build src/. --tag pihole:local --load --no-cache"
+TAG="pihole:local"
+DOCKER_BUILD_CMD="docker buildx build src/. --tag ${TAG} --load --no-cache"
 FTL_FLAG=false
 
 # Parse command line arguments
@@ -69,8 +70,9 @@ while [[ $# -gt 0 ]]; do
         shift
         ;;
     -t | --tag)
-        TAG="$2"
-        DOCKER_BUILD_CMD=${DOCKER_BUILD_CMD/pihole:local/$TAG}
+        CUSTOM_TAG="$2"
+        DOCKER_BUILD_CMD=${DOCKER_BUILD_CMD/$TAG/$CUSTOM_TAG}
+        TAG=$CUSTOM_TAG
         shift
         shift
         ;;
@@ -88,3 +90,16 @@ done
 # Execute the docker build command
 echo "Executing command: $DOCKER_BUILD_CMD"
 eval $DOCKER_BUILD_CMD
+
+# Check exit code of previous command
+if [ $? -ne 0 ]; then
+    echo ""
+    echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
+    echo "!! ERROR: Docker build failed, please review logs above !!"
+    echo "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
+    exit 1
+else
+    echo ""
+    echo "Successfully built Docker image with tag '$TAG'"
+    docker images $TAG
+fi

src/Dockerfile

@@ -83,11 +83,12 @@ RUN if   [ "$TARGETPLATFORM" = "linux/amd64" ];    then FTLARCH=amd64; \
     && echo "Arch: ${TARGETPLATFORM}, FTLARCH: ${FTLARCH}" \
     && curl -sSL "https://ftl.pi-hole.net/${FTL_BRANCH}/pihole-FTL-${FTLARCH}" -o /usr/bin/pihole-FTL \
     && chmod +x /usr/bin/pihole-FTL \
-    && readelf -h /usr/bin/pihole-FTL || cat /usr/bin/pihole-FTL
+    && readelf -h /usr/bin/pihole-FTL || (echo "Error with downloaded FTL binary" && exit 1)
 
 FROM base AS local-ftl-install
 # pihole-FTL must be built from source and copied to the src directory first!
 COPY --chmod=0755 pihole-FTL /usr/bin/pihole-FTL
+RUN  readelf -h /usr/bin/pihole-FTL || (echo "Error with local FTL binary" && exit 1)
 
 # Use the appropriate FTL Install stage based on the FTL_SOURCE build-arg
 FROM ${FTL_SOURCE}-ftl-install AS final