Use same uid as host in docker builder container

This makes the host user the owner of any file created by the eks-a
builder container. This is particulary useful for any downloaded go
module and the cache created during build. Without this change, those
folder would be owned by root, which can make following go compilations
fail when run from the host directly.

build/lib/run_target_docker.sh

@@ -72,13 +72,25 @@ if [[ -n "$PLATFORM" ]]; then
 	MAKE_VARS=" BINARY_PLATFORMS=$PLATFORM"
 fi
 
+DOCKER_USER_FLAG=""
+NETRC_DIR="/root"
+if [ "$(uname -s)" = "Linux" ] && [ -n "${USER:-}" ]; then
+	# on a linux host, the uid needs to match the host user otherwise
+	# all the downloaded go modules will be owned by root in the host
+	USER_ID=$(id -u ${USER})
+	USER_GROUP_ID=$(id -g ${USER})
+	DOCKER_USER_FLAG="-u $USER_ID:$USER_GROUP_ID"
+	NETRC_DIR="/home/matchinguser"
+fi
+
+
 if [[ "$SKIP_RUN" == "false" ]]; then
 	build::docker::retry_pull $IMAGE
 
 	NETRC=""
 	if [ -f $HOME/.netrc ]; then
 		DOCKER_RUN_NETRC="${DOCKER_RUN_NETRC:-$HOME/.netrc}"
-		NETRC="--mount type=bind,source=$DOCKER_RUN_NETRC,target=/root/.netrc"
+		NETRC="--mount type=bind,source=$DOCKER_RUN_NETRC,target=$NETRC_DIR/.netrc"
 	else
 		DOCKER_RUN_NETRC=""
 	fi
@@ -91,9 +103,15 @@ if [[ "$SKIP_RUN" == "false" ]]; then
 		-e GOPROXY=${GOPROXY:-} -e GOMODCACHE=/mod-cache -e DOCKER_RUN_BASE_DIRECTORY=$DOCKER_RUN_BASE_DIRECTORY -e DOCKER_RUN_GO_MOD_CACHE=$DOCKER_RUN_GO_MOD_CACHE -e DOCKER_RUN_NETRC=$DOCKER_RUN_NETRC \
 		--entrypoint sleep $IMAGE infinity)
 
-	docker exec -it $CONTAINER_ID git config --global --add safe.directory /eks-anywhere-build-tooling
+	if [ -n "$DOCKER_USER_FLAG" ]; then
+		docker exec -it $CONTAINER_ID groupadd -g 100 users
+		docker exec -it $CONTAINER_ID groupadd --gid "$USER_GROUP_ID" matchinguser
+		docker exec -it $CONTAINER_ID useradd  --no-create-home --uid "$USER_ID" --gid "$USER_GROUP_ID" matchinguser
+		docker exec -it $CONTAINER_ID chown -R matchinguser:matchinguser /home/matchinguser
+	fi
 fi
 
 
-build::common::echo_and_run docker exec -e RELEASE_BRANCH=$RELEASE_BRANCH -it $CONTAINER_ID \
+build::common::echo_and_run docker exec -e RELEASE_BRANCH=$RELEASE_BRANCH $DOCKER_USER_FLAG \
+	-it $CONTAINER_ID \
 	make $TARGET -C /eks-anywhere-build-tooling/projects/$PROJECT $MAKE_VARS