chore: bake protoc into the hermetic build docker image

.cloudbuild/library_generation/library_generation.Dockerfile

@@ -15,24 +15,36 @@
 # build from the root of this repo:
 FROM gcr.io/cloud-devrel-public-resources/python
 
+SHELL [ "/bin/bash", "-c" ]
+
 ARG SYNTHTOOL_COMMITTISH=63cc541da2c45fcfca2136c43e638da1fbae174d
 ARG OWLBOT_CLI_COMMITTISH=ac84fa5c423a0069bbce3d2d869c9730c8fdf550
+ARG PROTOC_VERSION=25.3
 ENV HOME=/home
 
 # install OS tools
 RUN apt-get update && apt-get install -y \
 	unzip openjdk-17-jdk rsync maven jq \
 	&& apt-get clean
 
+# copy source code
+COPY library_generation /src
+
+# install protobuf
+WORKDIR /protoc
+RUN ls /src
+RUN source /src/utils/utilities.sh \
+	&& download_protoc "${PROTOC_VERSION}" "linux-x86_64"
+# we indicate protoc is available in the container via env vars
+ENV DOCKER_PROTOC_LOCATION=/protoc
+ENV DOCKER_PROTOC_VERSION="${PROTOC_VERSION}"
+
 # use python 3.11 (the base image has several python versions; here we define the default one)
 RUN rm $(which python3)
 RUN ln -s $(which python3.11) /usr/local/bin/python
 RUN ln -s $(which python3.11) /usr/local/bin/python3
 RUN python -m pip install --upgrade pip
 
-# copy source code
-COPY library_generation /src
-
 # install scripts as a python package
 WORKDIR /src
 RUN python -m pip install -r requirements.txt

library_generation/test/generate_library_unit_tests.sh

@@ -134,6 +134,18 @@ download_protoc_failed_with_invalid_arch_test() {
   assertEquals 1 $((res))
 }
 
+download_protoc_succeed_with_baked_protoc() {
+  # this mimics a docker container scenario.
+  # if the specified version matches the docker env var, then it will be just
+  # copied from the docker protoc location (also specified in an env var).
+  export DOCKER_PROTOC_LOCATION=$(mktmp -d)
+  mkdir "${DOCKER_PROTOC_LOCATION}/protoc-99.99"
+  export DOCKER_PROTOC_VERSION="99.99"
+  download_protoc "99.99" "linux-x86_64"
+  assertFileOrDirectoryExists "protoc-99.99"
+  rm -rf "protoc-99.99"
+}
+
 download_grpc_plugin_succeed_with_valid_version_linux_test() {
   download_grpc_plugin "1.55.1" "linux-x86_64"
   assertFileOrDirectoryExists "protoc-gen-grpc-java-1.55.1-linux-x86_64.exe"

library_generation/utils/utilities.sh

@@ -157,7 +157,20 @@ download_generator_artifact() {
 download_protoc() {
   local protoc_version=$1
   local os_architecture=$2
-  if [ ! -d "protoc-${protoc_version}" ]; then
+
+  protoc_path="${output_folder}/protoc-${protoc_version}/bin"
+  if [[ -f "${protoc_path}/protoc" ]]; then
+    return
+  fi
+
+  if [[ -n "${DOCKER_PROTOC_VERSION}" ]] \
+    && [[ "${DOCKER_PROTOC_VERSION}" == "${protoc_version}" ]]; then
+    # if the specified protoc_version matches the one baked in the docker
+    # container, we just copy it into the output folder
+    cp -r "${DOCKER_PROTOC_LOCATION}"/* "${output_folder}"
+  fi
+
+  if [ ! -d "${protoc_path}" ]; then
     # pull proto files and protoc from protobuf repository as maven central
     # doesn't have proto files
     download_from \
@@ -169,7 +182,6 @@ download_protoc() {
     rm "protoc-${protoc_version}.zip"
   fi
 
-  protoc_path="${output_folder}/protoc-${protoc_version}/bin"
 }
 
 download_grpc_plugin() {

renovate.json

@@ -28,6 +28,17 @@
       "depNameTemplate": "com.google.protobuf:protobuf-java",
       "datasourceTemplate": "maven"
     },
+    {
+      "customType": "regex",
+      "fileMatch": [
+		"^\\.cloudbuild/library_generation/library_generation\\.Dockerfile$"
+      ],
+      "matchStrings": [
+        "ARG PROTOC_VERSION==(?<currentValue>.+?)\\n"
+      ],
+      "depNameTemplate": "com.google.protobuf:protobuf-java",
+      "datasourceTemplate": "maven"
+    },
     {
       "customType": "regex",
       "fileMatch": [