Parse any arbitrary http body with grpc-gateway

body_bytes.go

package body_bytes

import (
	"fmt"
	"io"
	"io/ioutil"
	"reflect"

	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
)

// grpc or grpc-gateway does not have an easy way to read the http body into an
// annotated body field. so we create a custom marshaller overriding only the
// decoder to read the http body into a `bytes` field. based on
//  - https://rogchap.com/2019/10/19/webhook-endpoint-for-grpc-gateway/
//  - https://github.com/grpc-ecosystem/grpc-gateway/issues/652
//
// requires `bytes` type for the body field.
//
// usage:
//  // custom marshaller for reading whole body into a variable
//  runtime.WithMarshalerOption(
//  	body_bytes.RawBytesMIME,
//  	&body_bytes.RawBytesPb{JSONPb: &runtime.JSONPb{}},
//  ),
//
// alternatively, use envoy's grpc json transcoder filter, with which you can
// set `google.api.HttpBody` type for the annotated body field, and skip all
// this.
var (
	RawBytesMIME = "application/raw-bytes"
	RawBytesType = reflect.TypeOf([]byte(nil))
)

type RawBytesPb struct {
	*runtime.JSONPb
}

func (RawBytesPb) NewDecoder(r io.Reader) runtime.Decoder {
	return runtime.DecoderFunc(func(v interface{}) error {
		raw, err := ioutil.ReadAll(r)
		if err != nil {
			return err
		}

		rv := reflect.ValueOf(v)

		if rv.Kind() != reflect.Ptr {
			return fmt.Errorf("%T is not a pointer", v)
		}

		rv = rv.Elem()
		if rv.Type() != RawBytesType {
			return fmt.Errorf("type must be []byte but got %T", v)
		}

		rv.Set(reflect.ValueOf(raw))
		return nil
	})
}

func (*RawBytesPb) ContentType(v interface{}) string {
	return RawBytesMIME
}