simplelog/relp_handler.go

package simplelog

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/url"
	"os"
	"path/filepath"
	"time"

	"github.com/google/uuid"
)

const (
	cacheDir          = "/var/cache/relploggercache"
	diskBufferLimit   = 100         // Write to disk after accumulating 100 failed events
	diskWriteInterval = time.Second // Or write every second, whichever comes first
)

type RELPHandler struct {
	relpServerURL string
	conn          net.Conn
	ch            chan Event
	done          chan struct{}
	failedCh      chan Event
	timer         *time.Timer
}

func NewRELPHandler(relpURL string) (*RELPHandler, error) {
	parsedURL, err := url.Parse(relpURL)
	if err != nil {
		return nil, fmt.Errorf("Error parsing RELP URL: %v", err)
	}
	if parsedURL.Scheme != "tcp" {
		return nil, fmt.Errorf("RELP URL must have the tcp scheme, got %s", parsedURL.Scheme)
	}
	if err := os.MkdirAll(cacheDir, 0755); err != nil {
		return nil, fmt.Errorf("Failed to create cache directory: %v", err)
	}
	return &RELPHandler{
		relpServerURL: parsedURL.Host,
		ch:            make(chan Event, diskBufferLimit),
		done:          make(chan struct{}),
		failedCh:      make(chan Event, diskBufferLimit),
		timer:         time.NewTimer(diskWriteInterval),
	}, nil
}

func (r *RELPHandler) Startup() error {
	var err error
	r.conn, err = net.Dial("tcp", r.relpServerURL)
	if err != nil {
		return fmt.Errorf("Failed to establish TCP connection: %v", err)
	}
	go r.receiveEventsFromChannel()
	go r.processFailedEvents()
	go r.watchDirectoryForFailedEventFiles()
	return nil
}

func (r *RELPHandler) Log(event Event) error {
	select {
	case r.ch <- event:
		return nil // Successfully sent event to channel
	default:
		return fmt.Errorf("failed to log event: channel is full")
	}
}

func (r *RELPHandler) receiveEventsFromChannel() {
	for {
		select {
		case event := <-r.ch:
			if err := r.sendEventToRELPServer(event); err != nil {
				r.failedCh <- event
			}
		case <-r.done:
			return
		}
	}
}

func (r *RELPHandler) processFailedEvents() {
	for {
		select {
		case event := <-r.failedCh:
			if err := r.sendEventToRELPServer(event); err != nil {
				// If still failing, write to disk
				r.writeFailedToDisk(event)
			}
		case <-r.timer.C:
			// Flush all events in failedCh to disk
			for len(r.failedCh) > 0 {
				event := <-r.failedCh
				r.writeFailedToDisk(event)
			}
		case <-r.done:
			return
		}
	}
}

func (r *RELPHandler) sendEventToRELPServer(event Event) error {
	jsonData, _ := json.Marshal(event)
	_, err := r.conn.Write(jsonData)
	if err != nil {
		return err
	}
	// Implement TCP read for the acknowledgment with a timeout
	r.conn.SetReadDeadline(time.Now().Add(2 * time.Second))
	ack := make([]byte, 256)
	n, err := r.conn.Read(ack)
	if err != nil || string(ack[:n]) != "ACK" {
		return err
	}
	return nil
}

func (r *RELPHandler) watchDirectoryForFailedEventFiles() {
	for {
		select {
		case <-r.done:
			return
		default:
			if r.isConnected() {
				files, err := ioutil.ReadDir(cacheDir)
				if err != nil {
					log.Printf("Error reading cache directory: %v", err)
					continue
				}
				for _, file := range files {
					filePath := filepath.Join(cacheDir, file.Name())
					data, err := ioutil.ReadFile(filePath)
					if err != nil {
						log.Printf("Error reading file %s: %v", file.Name(), err)
						continue
					}
					var event Event
					if err := json.Unmarshal(data, &event); err != nil {
						log.Printf("Error unmarshalling event from file %s: %v", file.Name(), err)
						continue
					}
					r.ch <- event
					os.Remove(filePath) // Remove file after processing
				}
			}
			time.Sleep(10 * time.Second) // Check disk every 10 seconds
		}
	}
}

func (r *RELPHandler) isConnected() bool {
	_, err := r.conn.Write([]byte{})
	return err == nil
}

func (r *RELPHandler) Shutdown() error {
	close(r.done)
	return r.conn.Close()
}

func (r *RELPHandler) writeFailedToDisk(event Event) {
	fileName := filepath.Join(cacheDir, uuid.New().String()+".logevent")
	data, _ := json.Marshal(event)
	ioutil.WriteFile(fileName, data, 0644)
}