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grpc-gateway-wrapper

The goal of this project is to generates a REST gateway wrapper layer for a grpc server with minimal customization, along with swagger definitions conforming to OpenAPI 2.0.

The gRPC-gateway(https://github.com/grpc-ecosystem/grpc-gateway) is a plugin of the Google protocol buffers compiler protoc. It reads protobuf service definitions and generates a reverse-proxy server which translates a RESTful HTTP API into gRPC.

This repo, the grpc-gateway-wrapper is a python library and executable that builds a go binary that encapsulates the reverse proxy server along with swagger definitions conforming to OpenAPI 2.0.

Installation instructions

Build from source

python setup.py bdist_wheel

Pull from pypi

pip install grpc-gateway-wrapper

Usage

python -m grpc_gateway_wrapper

or:

grpc-gateway-wrapper

(it should be installed on the system path).

This is the main entrypoint script which can generate a working gRPC gateway server that can proxy between an equivalent REST API and a set of gRPC services.

CLI options

╰$ python -m grpc_gateway_wrapper --help

optional arguments:
  -h, --help            show this help message and exit
  --proto_files PROTO_FILES [PROTO_FILES ...], -p PROTO_FILES [PROTO_FILES ...]
                        The proto file to generate from
  --working_dir WORKING_DIR, -w WORKING_DIR
                        Location for intermediate files. If none, random will be generated
  --no_cleanup, -c      Don't clean up working dir
  --output_dir OUTPUT_DIR, -o OUTPUT_DIR
                        Location for output files
  --metadata [METADATA ...], -m [METADATA ...]
                        gRPC metadata name(s) to add to the swagger
  --install_deps, -d    Install go dependencies if they're missing
  --gateway_version GATEWAY_VERSION, -g GATEWAY_VERSION
                        Version of the grpc-gateway tools to install if installing dependencies
  --log_level LOG_LEVEL, -l LOG_LEVEL
                        Log level for informational logging

Prerequisite

  1. go: https://go.dev/doc/install
  2. protoc: https://grpc.io/docs/protoc-installation/

There are additional go dependencies which the library needs which you can directly install by passing the --install_deps argument.

Build a Gateway

To build a gateway for your server, you need to collect the full set of proto files used to create the server interface, including files containing type definitions (the script is not smart enough to find them for you). With that, simply call grpc_gateway_wrapper with the --protos argument. For example:

python -m grpc_gateway_wrapper \
  --proto_files example/sample-messages.proto example/sample-service.proto

gRPC Metadata

Some gRPC APIs rely on the presence of certain metadata entries (e.g. kserve model-mesh requires the mm-model-id or mm-vmodel-id header). These headers are not represented in the proto file, so they're not automatically represented in the swagger API generated by this template. In order to add them, you can use the --metadata argument to grpc_gateway_wrapper. For example:

python -m grpc_gateway_wrapper \
  --proto_files example/sample-messages.proto example/sample-service.proto \
  --metadata foo bar:default_value

Use a Gateway

Once you build the gateway using the commands above, a build directory will be generated with the contents:

build
├── app
└── swagger

The generated binary is the app, along with the swagger directory along side it.

To see the flags that can be passed to the built binary, you can run:

╰$ ./build/app --help

Usage of ./build/app:
  -mtls_client_ca="": CA certificate to use to enable mutual TLS
  -proxy_cert="": Cert to use when making the proxy rpc call
  -proxy_cert_hname="": Hostname override for proxy cert
  -proxy_endpoint="localhost:8004": Endpoint for the server being proxied to
  -proxy_no_cert_val=false: Ignore certificate validation
  -serve_cert="": Public cert to use when serving proxy calls
  -serve_key="": Private key to use when serving proxy calls
  -serve_port=8080: Port to serve the gateway on
  -swagger_path="/swagger": Absolute path to swagger assets

You can run it anywhere (locally, or within a deployment) and simply point it at the running gRPC server:

./build/app \
  --swagger_path $PWD/build/swagger \
  --proxy_endpoint localhost:8004 \
  --serve_port 8080

(TODO - add TLS specific example)

Call a Gateway

Once a gateway is running, you can access it directly using any HTTP client you like (curl, postman, etc...). You can also visit its swagger documentation by hitting the /swagger endpoint (e.g. http://localhost:8080/swagger).

References

This project relies heavily on a few external libraries.

  • grpc-gateway: This project provides the guts of the gateway implementation, as well as the swagger spec generation
  • google api service: In order to avoid forcing annotations into the protobuf files, this project side-loads the REST spec using the google api service definition.