grpc-gateway - multipart/form-data unmarshaler

.grpc-gateway - multipart form-data unmarshaler.md

marshaler = &runtime.JSONPb{
    MarshalOptions: protojson.MarshalOptions{UseProtoNames: true, EmitUnpopulated: true},
}

grpcMux := runtime.NewServeMux(
    GWMultipartForm(marshaler),
    runtime.WithMarshalerOption(runtime.MIMEWildcard, marshaler),
)

curl -X POST 127.0.0.1:3000/test -F token="my_token" -F audio="@audio.wav"

LICENSE

MIT License

Copyright (c) 2023 Vladislav Fursov (GhostIAm)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

multipart.go

// Copyright (c) 2023 Vladislav Fursov (GhostIAm)
// This code is licensed under MIT license (see LICENSE for details)
// https://gist.github.com/ghostiam/48acd974f2044e25ba43f090316e6f2d

package http

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"mime/multipart"
	"net/url"
	"strings"

	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
	"github.com/grpc-ecosystem/grpc-gateway/v2/utilities"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/reflect/protoreflect"
)

var _ runtime.Marshaler = (*MultipartFormPb)(nil)

type MultipartFormPb struct {
	runtime.Marshaler
}

func GWMultipartForm(marshaler runtime.Marshaler) runtime.ServeMuxOption {
	return runtime.WithMarshalerOption("multipart/form-data", &MultipartFormPb{
		Marshaler: marshaler,
	})
}

func (j *MultipartFormPb) NewDecoder(r io.Reader) runtime.Decoder {
	return runtime.DecoderFunc(func(v any) error {
		msg, ok := v.(proto.Message)
		if !ok {
			return errors.New("not proto message") //nolint:goerr113
		}

		br := bufio.NewReaderSize(r, 1024)
		pb, err := br.Peek(100)
		if err != nil {
			return fmt.Errorf("peek boundary: %w", err)
		}

		if len(pb) < 2 {
			return errors.New("boundary len < 2") //nolint:goerr113
		}

		boundary := bytes.TrimSpace(bytes.Split(pb, []byte("\n"))[0])[2:]

		values := make(url.Values)

		mr := multipart.NewReader(br, string(boundary))
		for {
			var p *multipart.Part
			p, err = mr.NextPart()
			if errors.Is(err, io.EOF) {
				break
			}
			if err != nil {
				return fmt.Errorf("read next part: %w", err)
			}

			formName := p.FormName()

			var fieldDescriptor protoreflect.FieldDescriptor
			fieldDescriptor, err = fieldDescriptorByPath(msg, formName)
			if err != nil {
				return err
			}

			var data []byte
			data, err = io.ReadAll(p)
			if err != nil {
				return fmt.Errorf("read part body: %w", err)
			}

			if fieldDescriptor.Kind() == protoreflect.BytesKind {
				values.Set(formName, base64.StdEncoding.EncodeToString(data))
				continue
			}

			if p.FileName() != "" && fieldDescriptor.Kind() == protoreflect.MessageKind {
				/*
					in proto file:
						message Media {
							string filename = 1;
							string content_type = 2;
							bytes content = 3;
						}
				*/
				values.Set(formName+".filename", p.FileName())
				values.Set(formName+".content_type", p.Header.Get("Content-Type"))
				values.Set(formName+".content", base64.StdEncoding.EncodeToString(data))

				continue
			}

			values.Set(formName, string(data))
		}

		err = runtime.PopulateQueryParameters(msg, values, &utilities.DoubleArray{})
		if err != nil {
			return fmt.Errorf("papulate query params: %w", err)
		}

		return nil
	})
}

func (j *MultipartFormPb) Unmarshal(data []byte, v any) error {
	return j.NewDecoder(bytes.NewReader(data)).Decode(v) //nolint: wrapcheck
}

func fieldDescriptorByPath(msg proto.Message, path string) (protoreflect.FieldDescriptor, error) {
	msgValue := msg.ProtoReflect()
	fieldPath := strings.Split(path, ".")
	var fieldDescriptor protoreflect.FieldDescriptor
	for i, fieldName := range fieldPath {
		msgFields := msgValue.Descriptor().Fields()

		fieldDescriptor = msgFields.ByName(protoreflect.Name(fieldName))
		if fieldDescriptor == nil {
			fieldDescriptor = msgFields.ByJSONName(fieldName)
		}

		// If this is the last element, we're done
		if i == len(fieldPath)-1 {
			break
		}

		// Only singular message fields are allowed
		if fieldDescriptor == nil || fieldDescriptor.Message() == nil || fieldDescriptor.Cardinality() == protoreflect.Repeated {
			//nolint:goerr113
			return nil, fmt.Errorf("invalid path: %q is not a message", path)
		}

		// Get the nested message
		msgValue = msgValue.Mutable(fieldDescriptor).Message()
	}

	if fieldDescriptor == nil {
		//nolint:goerr113
		return nil, fmt.Errorf("invalid path: %q is not a valid field", path)
	}

	return fieldDescriptor, nil
}

test.proto

syntax = "proto3";

message TestRequest {
  string token = 1;
  message Media {
    string filename = 1;
    string content_type = 2;
    bytes content = 3;
  }
  Media audio = 2;
}
message TestResponse {}

service TestService {
  rpc Test (TestRequest) returns (TestResponse) {
    option (google.api.http) = {
      post: "/test"
      body: "*"
    };
  }
}

@agambondan Yes, it works.
I updated the code to my latest version.