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GAPIC Generator

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The GAPIC (Generated API Client) Generator auto-generates client libraries in various programming languages for both grpc-based APIs and Discovery-document-based APIs. Currently, the following programming languages are supported for grpc-based APIs:

For discovery-based APIs, only Java is supported and its output is not stable yet.

The GAPIC Generator also generates packaging files for proto-generated classes and grpc-generated stubs for Java and Python. This feature is not yet documented here in detail - the instructions below will work without it.

Supported platforms

The GAPIC Generator itself doesn't have a platform restriction (because it is purely Java). Since protoc needs to be used as part of the code generation process, the platforms are naturally restricted to what protoc supports.

As of release 3.5.1 of protoc, below are the known platforms that protoc has pre-built binaries for:

More platforms are likely supported when building protoc from C++ source.

Usage

There are two main ways to generate clients:

  1. Build from source and run directly. This is detailed below.
  2. Invoke a code generation pipeline through artman. This takes care of several of the steps below and is not documented here.

Prerequisites for code generation

  1. You need a proto file describing your API. Proto files of existing Google APIs are available at googleapis.
  1. You need a yaml file describing certain service values. This is not yet well-documented, but you can figure out some of the settings by looking at existing files.
  1. An active internet connection. The first time you build gapic-generator, it will download Java dependencies over the network.

Process overview for generating a client library

  1. Generate a descriptor file from the proto (once per API)
  2. Run client config generation (once per API)
  3. Manually tweak the generated client config
  4. Run code generation (once per API x language combination of interest)

Each of these steps are described in more detail below. Note: the instructions assume you are running on a Unix-y system; if you are using Windows, you will need to tweak the steps for yourself.

Set up prerequisites for building from source and running directly

First, make sure you have the Java 8 JDK installed.

Next, you need to install protoc if you don't have it yet: see protocol-compiler-installation. The pre-built binaries are the easiest. There aren't instructions for installation; you just have to download the correct binaries for your platform and put them on your path. Given a platform ${PROTOC_PLATFORM} and a protoc version ${PROTOC_VERSION}:

  1. Download the latest zip file ending in "-${PROTOC_PLATFORM}.zip" from https://github.com/google/protobuf/releases
  2. Unzip the file: unzip protoc-${PROTOC_VERSION}-${PROTOC_PLATFORM}.zip -d protoc-${PROTOC_VERSION}
  3. Copy protoc to a location on your $PATH: cp protoc-${PROTOC_VERSION}/bin/protoc /usr/local/bin

Clone the present repository and build API Client Generator:

git clone https://github.com/googleapis/gapic-generator.git
cd gapic-generator
./gradlew fatJar

The googleapis/gapic-generator directory will hereafter be referenced as ${GAPIC_GENERATOR_DIR}.

Clone the googleapis/googleapis repository (it has some config that is needed):

git clone https://github.com/googleapis/googleapis

The googleapis/googleapis directory will hereafter be referenced as ${GOOGLEAPIS_DIR}.

Generate a descriptor file from the proto

You need to locate/decide on the following before you can generate the descriptor file:

  1. The include directory with the proto files bundled with protoc (from the protoc setup step). Hereafter, this will be referenced as ${PROTOC_INCLUDE_DIR}.
  2. Any directories containing protos that your API depends on. For Google APIs defined in googleapis, this will be ${GOOGLEAPIS_DIR}.
  3. The directory containing your proto. Hereafter, this will be referenced as ${YOUR_PROTO_DIR}.
  4. Your proto file (or files). Hereafter, this will be referenced as ${YOUR_PROTO_FILE}.
  5. The output file name to contain the descriptor file. Hereafter, this will be referenced as ${YOUR_DESCRIPTOR_FILE}.

Run the following command to generate the proto descriptor file:

protoc -I=${PROTOC_INCLUDE_DIR} -I=${GOOGLEAPIS_DIR} -I=${YOUR_PROTO_DIR} \
  --include_imports --include_source_info -o ${YOUR_DESCRIPTOR_FILE} ${YOUR_PROTO_FILE}

Generate proto message classes

(Skip this section for Node.js — it loads proto files into memory at runtime.)

You need to locate/decide on the following before you can generate the proto message classes:

  1. The output directory to contain the proto files. Hereafter, this will be referenced as ${GENERATED_PROTO_DIR}.
  2. The language you are generating for. The possible values for protoc are java, go, php, ruby, python, and csharp. Note: Node.js is not present for the reason listed above. Hereafter, this will be referenced as ${PROTO_OUTPUT_LANG}.

Run the following command to generate the proto message classes:

mkdir -p ${GENERATED_PROTO_DIR}
protoc -I=${PROTOC_INCLUDE_DIR} -I=${GOOGLEAPIS_DIR} -I=${YOUR_PROTO_DIR} \
  --${PROTO_OUTPUT_LANG}_out=${GENERATED_PROTO_DIR} ${YOUR_PROTO_FILE}

Generate grpc stubs

Generating grpc stubs is language-specific.

Java

Find the path to the grpc plugin (gradle will pull in the dependency if you don't have it already):

./gradlew showGrpcJavaPluginPath

The command will print out the path to the executable. Hereafter, this will be referenced as ${GRPC_JAVA_PLUGIN}.

protoc -I=${PROTOC_INCLUDE_DIR} -I=${GOOGLEAPIS_DIR} -I=${YOUR_PROTO_DIR} \
  --plugin=protoc-gen-grpc=${GRPC_JAVA_PLUGIN} \
  --grpc_out=${GENERATED_PROTO_DIR} ${YOUR_PROTO_FILE}

Other languages

TODO

Generate initial client config

You need to locate/decide on the following before you call config generation:

  1. The service yaml file, hereafter referenced as ${YOUR_SERVICE_YAML}.
  2. The file name of your output client config file. Hereafter, this will be referenced as ${YOUR_CLIENT_CONFIG}

Run the following command to generate the client config:

cd ${GAPIC_GENERATOR_DIR}
java -cp build/libs/gapic-generator-*-fatjar.jar \
  com.google.api.codegen.GeneratorMain GAPIC_CONFIG \
  --descriptor_set=${YOUR_DESCRIPTOR_FILE} --service_yaml=${YOUR_SERVICE_YAML} \
  -o=${YOUR_CLIENT_CONFIG}

You can safely ignore the warning about control-presence.

Manually tweak the generated client config

The generated client config contains FIXME comments with instructions on how to choose values in the client config. The client config should work as is, though; tweaks are only necessary to improve the quality of the generated output.

Create a package metadata config file

You need to locate/decide on the following before you create the package metadata config file:

  1. The output file to contain the packaging config for your client generation. Hereafter, this will be referenced as ${PACKAGING_CONFIG}.
  2. The short name of your API, which typically does not include the major version. For example, Cloud Language v1's short name is language. Hereafter, this will be referenced as ${API_NAME}.
  3. The API major version. The first major version will typically be v1. Hereafter, this will be referenced as ${API_VERSION}.
  4. The organization name of the API. This would typically include the company name. For example, Cloud Language's organization name is google-cloud. This is used for the full artifact name. Hereafter, this will be referenced as ${ORGANIZATION_NAME}.
  5. The proto path, which is the proto's package with dots converted to slashes. For example, Cloud Language v1's proto path is google/cloud/language/v1. Hereafter, this will be referenced as ${PROTO_PATH}.

Add the following lines to the ${PACKAGING_CONFIG} file:

artifact_type: GAPIC
proto_deps:
- google-common-protos
api_name: ${API_NAME}
api_version: ${API_VERSION}
organization_name: ${ORGANIZATION_NAME}
proto_path: ${PROTO_PATH}

Run code generation

You need to locate/decide on the following before you call code generation:

  1. Your target language, which can be one of java, go, php, ruby, nodejs, python, or csharp. Hereafter, this will be referenced as ${LANGUAGE}.
  2. The output directory for your generated client classes. Hereafter, this will be referenced as ${GENERATED_CLIENT_DIR}.
java -cp build/libs/gapic-generator-*-fatjar.jar  \
  com.google.api.codegen.GeneratorMain LEGACY_GAPIC_AND_PACKAGE \
  --descriptor_set=${YOUR_DESCRIPTOR_FILE} --service_yaml=${YOUR_SERVICE_YAML} \
  --gapic_yaml=${YOUR_CLIENT_CONFIG} --language=${LANGUAGE} \
  --package_yaml2=${PACKAGING_CONFIG} --o=${GENERATED_CLIENT_DIR}

The generated client library code will appear in ${GENERATED_CLIENT_DIR}.

You can safely ignore the warning about control-presence.

Special note for java: several files will be dumped into the parent directory of ${GENERATED_CLIENT_DIR}:

(There is an open issue to fix this: https://github.com/googleapis/gapic-generator/issues/1918 )

Perform fixes to get a working library

The fixes here are language-specific.

Java

Copy the proto-generated classes into the client directory tree:

cp -r ${GENERATED_PROTO_DIR}/* ${GENERATED_CLIENT_DIR}/src/main/java

In ${GENERATED_CLIENT_DIR}/build.gradle, there are a couple dependencies that need to be removed if you are bundling your proto-generated classes and grpc stubs in the same package as the client. They have a comment starting with "// Remove this line if you are bundling". Warning: If you regenerate again, you will need to remove the lines from the build.gradle file again. (There is an open issue to fix this: https://github.com/googleapis/gapic-generator/issues/1917 ).

Node

Copy the proto files into the correct subdirectory of ${GENERATED_CLIENT_DIR}. (Exact instructions to be added later.)

Other languages

TODO