meowlib/lokiwriter.go

package meowlib

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net/http"
	"time"
)

type LokiWriter struct {
	url        string
	labels     map[string]string
	httpClient *http.Client
}

type LokiPayload struct {
	Streams []LokiStream `json:"streams"`
}

type LokiStream struct {
	Stream map[string]string `json:"stream"`
	Values [][]string        `json:"values"`
}

func NewLokiWriter(url string, labels map[string]string) *LokiWriter {
	return &LokiWriter{
		url:        url,
		labels:     labels,
		httpClient: &http.Client{},
	}
}

func (w *LokiWriter) Write(p []byte) (n int, err error) {
	// Use zerolog to parse the log level
	var event map[string]interface{}
	if err := json.Unmarshal(p, &event); err != nil {
		return 0, fmt.Errorf("failed to unmarshal log event: %w", err)
	}

	level := ""
	if l, ok := event["level"].(string); ok {
		level = l
	}

	message := ""
	if m, ok := event["message"].(string); ok {
		message = m
	}

	// Add log level to labels
	labels := make(map[string]string)
	for k, v := range w.labels {
		labels[k] = v
	}
	labels["level"] = level

	// Format the timestamp in nanoseconds
	timestamp := fmt.Sprintf("%d000000", time.Now().UnixNano()/int64(time.Millisecond))

	stream := LokiStream{
		Stream: labels,
		Values: [][]string{
			{timestamp, message},
		},
	}

	payload := LokiPayload{
		Streams: []LokiStream{stream},
	}

	payloadBytes, err := json.Marshal(payload)
	if err != nil {
		return 0, fmt.Errorf("failed to marshal payload: %w", err)
	}

	//fmt.Printf("Sending payload to Loki: %s\n", string(payloadBytes))

	req, err := http.NewRequest("POST", w.url, bytes.NewReader(payloadBytes))
	if err != nil {
		return 0, fmt.Errorf("failed to create HTTP request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := w.httpClient.Do(req)
	if err != nil {
		return 0, fmt.Errorf("failed to send log to Loki: %w", err)
	}
	defer resp.Body.Close()

	//fmt.Printf("Loki response status: %d\n", resp.StatusCode)
	if resp.StatusCode != http.StatusNoContent {
		return 0, fmt.Errorf("received non-204 response from Loki: %d", resp.StatusCode)
	}

	return len(p), nil
}