res_levis_backend/cmd/server/main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/AFASystems/presence/internal/pkg/model"
	"github.com/gorilla/handlers"
	"github.com/gorilla/mux"
	"github.com/redis/go-redis/v9"
	"github.com/segmentio/kafka-go"
)

func main() {
	HttpServer("0.0.0.0:1902")
}

func HttpServer(addr string) {
	headersOk := handlers.AllowedHeaders([]string{"X-Requested-With"})
	originsOk := handlers.AllowedOrigins([]string{"*"})
	methodsOk := handlers.AllowedMethods([]string{"GET", "HEAD", "POST", "PUT", "DELETE", "OPTIONS"})

	// Kafka writer that relays messages
	writer := kafkaWriter("kafka:9092", "apibeacons")
	defer writer.Close()

	r := mux.NewRouter()

	client := redis.NewClient(&redis.Options{
		Addr:     "kafka:6379",
		Password: "",
	})

	// For now just add beacon DELETE / GET / POST / PUT methods
	r.HandleFunc("/api/beacons/{beacon_id}", beaconsDeleteHandler(writer)).Methods("DELETE")
	r.HandleFunc("/api/beacons", beaconsListHandler(client)).Methods("GET")
	r.HandleFunc("/api/beacons", beaconsAddHandler(writer)).Methods("POST")
	r.HandleFunc("/api/beacons", beaconsAddHandler(writer)).Methods("PUT")
	http.ListenAndServe(addr, handlers.CORS(originsOk, headersOk, methodsOk)(r))
}

// All the functions should do is just relay messages to the decoder through Kafka

func kafkaWriter(kafkaURL, topic string) *kafka.Writer {
	return &kafka.Writer{
		Addr:         kafka.TCP(kafkaURL),
		Topic:        topic,
		Balancer:     &kafka.LeastBytes{},
		BatchSize:    100,
		BatchTimeout: 10 * time.Millisecond,
	}
}

func sendKafkaMessage(writer *kafka.Writer, value *model.ApiUpdate) {
	valueStr, err := json.Marshal(&value)
	if err != nil {
		fmt.Println("error in encoding: ", err)
	}
	msg := kafka.Message{
		Value: valueStr,
	}

	err = writer.WriteMessages(context.Background(), msg)
	if err != nil {
		fmt.Println("Error in sending kafka message: ")
	}
}

func beaconsDeleteHandler(writer *kafka.Writer) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		vars := mux.Vars(r)
		beaconId := vars["beacon_id"]
		apiUpdate := model.ApiUpdate{
			Method: "DELETE",
			ID:     beaconId,
		}

		sendKafkaMessage(writer, &apiUpdate)
		w.Write([]byte("ok"))
	}
}

func beaconsAddHandler(writer *kafka.Writer) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		decoder := json.NewDecoder(r.Body)
		var inBeacon model.Beacon
		err := decoder.Decode(&inBeacon)

		if err != nil {
			http.Error(w, err.Error(), 400)
			return
		}

		if (len(strings.TrimSpace(inBeacon.Name)) == 0) || (len(strings.TrimSpace(inBeacon.Beacon_id)) == 0) {
			http.Error(w, "name and beacon_id cannot be blank", 400)
			return
		}

		apiUpdate := model.ApiUpdate{
			Method: "POST",
			Beacon: inBeacon,
		}

		sendKafkaMessage(writer, &apiUpdate)

		w.Write([]byte("ok"))
	}
}

func beaconsListHandler(client *redis.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		beaconsList, err := client.Get(context.Background(), "beaconsList").Result()
		if err == redis.Nil {
			fmt.Println("no beacons list, starting empty")
			http.Error(w, "list is empty", 500)
		} else if err != nil {
			http.Error(w, "Internal server error", 500)
			panic(err)
		} else {
			w.Write([]byte(beaconsList))
		}
	}
}