github.com/utrack/clay "application/x-www-form-urlencoded" marshaller

foo.proto

syntax = "proto3";

import "google/api/annotations.proto";

service Foo {
    rpc ParseForm (FormData) returns (FormData) {
        option (google.api.http) = {
            post: "/form"
            body: "*"
        };
    };
}

message FormData {
    string b = 1;
    int32 a = 2;
};

form_marshaller.go

package strings

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

	"github.com/gogo/protobuf/proto"
	"github.com/grpc-ecosystem/grpc-gateway/runtime"
	"github.com/grpc-ecosystem/grpc-gateway/utilities"
	"github.com/pkg/errors"
	"github.com/utrack/clay/v2/transport/httpruntime"
)

const (
	maxFormSize = int64(10 << 20) // 10 MB is a lot of text.
)

type MarshalerFormUrlencoded struct{}

var _ httpruntime.Marshaler = MarshalerFormUrlencoded{}

func (MarshalerFormUrlencoded) ContentType() string {
	return "application/x-www-form-urlencoded"
}

func (m MarshalerFormUrlencoded) Unmarshal(reader io.Reader, dst interface{}) error {
	var msg proto.Message
	var ok bool

	// We need this dirty hack because `dst` contains double pointer to real struct.
	// And we can't extract an interface from a double pointer without some reflection
	v := reflect.ValueOf(dst)
	for {
		if kind := v.Kind(); kind != reflect.Ptr && kind != reflect.Interface {
			break
		}
		vv := v.Interface()
		msg, ok = vv.(proto.Message)
		if ok {
			break
		}
		v = v.Elem()
	}
	if msg == nil {
		return fmt.Errorf("Form unmarshaller supports only `proto.Message` request type, got %T", dst)
	}

	reader = io.LimitReader(reader, maxFormSize+1)
	b, err := ioutil.ReadAll(reader)
	if err != nil {
		return err
	}
	if int64(len(b)) > maxFormSize {
		return errors.New("http: POST too large")
	}
	vs, err := url.ParseQuery(string(b))
	if err != nil {
		return err
	}

	filter := &utilities.DoubleArray{}
	err = runtime.PopulateQueryParameters(msg, vs, filter)
	if err != nil {
		return err
	}
	return nil
}

func (m MarshalerFormUrlencoded) Marshal(w io.Writer, src interface{}) error {
	return errors.New("not implemented")
}

parse_form.go

// Code generated by protoc-gen-goclay, but your can (must) modify it.
// source: strings.proto

package strings

import (
	"context"

	"github.com/utrack/clay/v2/transport/httpruntime"
	desc "<path to pb package>"
)

func init() {
	httpruntime.OverrideMarshaler("application/x-www-form-urlencoded", MarshalerFormUrlencoded{})
}

func (i *Implementation) ParseForm(ctx context.Context, req *desc.FormData) (*desc.FormData, error) {
	return req, nil
}