networking/grpc-gke-nlb-tutorial/reverse-grpc/api/reverse.go

// Copyright 2021 Google LLC
//
// Licensed 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.

//go:generate protoc --go_out=. --go_opt=paths=source_relative --go-grpc_out=. --go-grpc_opt=paths=source_relative reverse.proto

package api

import (
	"context"
	"log"
	"os"

	"google.golang.org/grpc"
	"google.golang.org/grpc/metadata"
)

// Server for the Reverse gRPC API
type Server struct {
	UnimplementedReverseServer
}

// Reverse the content of the request
func (s *Server) Reverse(ctx context.Context, in *ReverseRequest) (*ReverseResponse, error) {
	log.Printf("Handling Reverse request [%v] with context %v", in, ctx)
	hostname, err := os.Hostname()
	if err != nil {
		log.Printf("Unable to get hostname %v", err)
		hostname = ""
	}
	grpc.SendHeader(ctx, metadata.Pairs("hostname", hostname))
	return &ReverseResponse{Content: reverse(in.Content)}, nil
}

func reverse(input string) string {
	runes := []rune(input)
	for i, j := 0, len(runes)-1; i < len(runes)/2; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}