15_cel_plugin

CEL Plugin Example

1. Write plugin definition in ProtocolBuffers

The plugin feature allows you to define global functions, methods, and variables.

plugin.proto

2. Run code generator

Run make generate to generate code by protoc-gen-grpc-federation.

3. Write plugin code

cmd/plugin/main.go is the plugin source.

The helper code needed to write the plugin is already generated, so it is used.

The helper is here.

In plugin/plugin_grpc_federation.pb.go, there is a RegisterRegexpPlugin function required for plugin registration and a RegexpPlugin interface required for the plugin. The code for the plugin is as follows.

package main

import (
	pluginpb "example/plugin"
	"regexp"
	"unsafe"
)

var _ pluginpb.RegexpPlugin = new(plugin)

type plugin struct{}

// For example.regexp.compile function.
func (_ *plugin) Example_Regexp_Compile(ctx context.Context, expr string) (*pluginpb.Regexp, error) {
	re, err := regexp.Compile(expr)
	if err != nil {
		return nil, err
	}
	return &pluginpb.Regexp{
		Ptr: uint32(uintptr(unsafe.Pointer(re))),
	}, nil
}

// For example.regexp.Regexp.matchString method.
func (_ *plugin) Example_Regexp_Regexp_MatchString(ctx context.Context, re *pluginpb.Regexp, s string) (bool, error) {
	return (*regexp.Regexp)(unsafe.Pointer(uintptr(re.Ptr))).MatchString(s), nil
}

func main() {
	pluginpb.RegisterRegexpPlugin(new(plugin))
}

4. Compile a plugin to WebAssembly

Run make build/wasm to compile to WebAssembly. ( regexp.wasm is output )

5. Calculates sha256 value for the WebAssembly file

$ sha256sum regexp.wasm
820f86011519c42da0fe9876bc2ca7fbee5df746acf104d9e2b9bba802ddd2b9  regexp.wasm

6. Load plugin ( WebAssembly ) file

Initialize the gRPC server with the path to the wasm file and the sha256 value of the file.

federationServer, err := federation.NewFederationService(federation.FederationServiceConfig{
	CELPlugin: &federation.FederationServiceCELPluginConfig{
		Regexp: federation.FederationServiceCELPluginWasmConfig{
			Path:   "regexp.wasm",
			Sha256: "820f86011519c42da0fe9876bc2ca7fbee5df746acf104d9e2b9bba802ddd2b9",
		},
	},
})

7. Plugin usage

You can evaluate the plugin's API in the same way you would evaluate a regular usage (e.g. by feature).

message IsMatchResponse {
  option (grpc.federation.message) = {
    def {
      name: "matched"
      by: "example.regexp.compile($.expr).matchString($.target)"
    }
  };
  bool result = 1 [(grpc.federation.field).by = "matched"];
}