pkg/client/proxy/proxy.go

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package proxy

import (
	"context"
	"net/url"
)

import (
	"github.com/jhump/protoreflect/dynamic"
	"github.com/jhump/protoreflect/dynamic/grpcdynamic"
	"github.com/jhump/protoreflect/grpcreflect"
	"github.com/pkg/errors"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/credentials/insecure"
	"google.golang.org/grpc/metadata"
	rpb "google.golang.org/grpc/reflection/grpc_reflection_v1alpha"
	"google.golang.org/grpc/status"
)

type Proxy struct {
	cc        *grpc.ClientConn
	reflector *Reflector
	stub      grpcdynamic.Stub
}

// NewProxy creates a new client
func NewProxy() *Proxy {
	return &Proxy{}
}

// Connect opens a connection to target.
func (p *Proxy) Connect(ctx context.Context, target *url.URL) error {
	cc, err := grpc.DialContext(ctx, target.String(), grpc.WithTransportCredentials(insecure.NewCredentials()))
	if err != nil {
		return err
	}
	p.cc = cc
	rc := grpcreflect.NewClient(ctx, rpb.NewServerReflectionClient(p.cc))
	p.reflector = NewReflector(rc)
	p.stub = grpcdynamic.NewStub(p.cc)
	return err
}

// Call performs the gRPC call after doing reflection to obtain type information.
func (p *Proxy) Call(ctx context.Context, serviceName, methodName string, message []byte, md *metadata.MD) ([]byte, error) {
	invocation, err := p.reflector.CreateInvocation(ctx, serviceName, methodName, message)
	if err != nil {
		return nil, err
	}

	output, err := p.stub.InvokeRpc(ctx, invocation.MethodDescriptor, invocation.Message, grpc.Header(md))
	if err != nil {
		stat := status.Convert(err)
		if stat.Code() == codes.Unavailable {
			return nil, errors.Wrap(err, "could not connect to backend")
		}

		return nil, errors.Wrap(err, stat.Message())
	}

	outputMessage := dynamic.NewMessage(invocation.MethodDescriptor.GetOutputType())
	err = outputMessage.ConvertFrom(output)
	if err != nil {
		return nil, errors.Wrap(err, "response from backend could not be converted internally")
	}

	m, err := outputMessage.MarshalJSON()
	if err != nil {
		return nil, err
	}
	return m, err
}