Fetch plugin logs from server (#193)

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

build/pluginctl/logs.go

@@ -0,0 +1,185 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"slices"
+	"strings"
+	"time"
+
+	"github.com/mattermost/mattermost/server/public/model"
+)
+
+const (
+	logsPerPage     = 100 // logsPerPage is the number of log entries to fetch per API call
+	timeStampFormat = "2006-01-02 15:04:05.000 Z07:00"
+)
+
+// logs fetches the latest 500 log entries from Mattermost,
+// and prints only the ones related to the plugin to stdout.
+func logs(ctx context.Context, client *model.Client4, pluginID string) error {
+	err := checkJSONLogsSetting(ctx, client)
+	if err != nil {
+		return err
+	}
+
+	logs, err := fetchLogs(ctx, client, 0, 500, pluginID, time.Unix(0, 0))
+	if err != nil {
+		return fmt.Errorf("failed to fetch log entries: %w", err)
+	}
+
+	err = printLogEntries(logs)
+	if err != nil {
+		return fmt.Errorf("failed to print logs entries: %w", err)
+	}
+
+	return nil
+}
+
+// watchLogs fetches log entries from Mattermost and print them to stdout.
+// It will return without an error when ctx is canceled.
+func watchLogs(ctx context.Context, client *model.Client4, pluginID string) error {
+	err := checkJSONLogsSetting(ctx, client)
+	if err != nil {
+		return err
+	}
+
+	now := time.Now()
+	var oldestEntry string
+
+	ticker := time.NewTicker(1 * time.Second)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case <-ticker.C:
+			var page int
+			for {
+				logs, err := fetchLogs(ctx, client, page, logsPerPage, pluginID, now)
+				if err != nil {
+					return fmt.Errorf("failed to fetch log entries: %w", err)
+				}
+
+				var allNew bool
+				logs, oldestEntry, allNew = checkOldestEntry(logs, oldestEntry)
+
+				err = printLogEntries(logs)
+				if err != nil {
+					return fmt.Errorf("failed to print logs entries: %w", err)
+				}
+
+				if !allNew {
+					// No more logs to fetch
+					break
+				}
+				page++
+			}
+		}
+	}
+}
+
+// checkOldestEntry check a if logs contains new log entries.
+// It returns the filtered slice of log entries, the new oldest entry and whether or not all entries were new.
+func checkOldestEntry(logs []string, oldest string) ([]string, string, bool) {
+	if len(logs) == 0 {
+		return nil, oldest, false
+	}
+
+	newOldestEntry := logs[(len(logs) - 1)]
+
+	i := slices.Index(logs, oldest)
+	switch i {
+	case -1:
+		// Every log entry is new
+		return logs, newOldestEntry, true
+	case len(logs) - 1:
+		// No new log entries
+		return nil, oldest, false
+	default:
+		// Filter out oldest log entry
+		return logs[i+1:], newOldestEntry, false
+	}
+}
+
+// fetchLogs fetches log entries from Mattermost
+// and filters them based on pluginID and timestamp.
+func fetchLogs(ctx context.Context, client *model.Client4, page, perPage int, pluginID string, since time.Time) ([]string, error) {
+	logs, _, err := client.GetLogs(ctx, page, perPage)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get logs from Mattermost: %w", err)
+	}
+
+	logs, err = filterLogEntries(logs, pluginID, since)
+	if err != nil {
+		return nil, fmt.Errorf("failed to filter log entries: %w", err)
+	}
+
+	return logs, nil
+}
+
+// filterLogEntries filters a given slice of log entries by pluginID.
+// It also filters out any entries which timestamps are older then since.
+func filterLogEntries(logs []string, pluginID string, since time.Time) ([]string, error) {
+	type logEntry struct {
+		PluginID  string `json:"plugin_id"`
+		Timestamp string `json:"timestamp"`
+	}
+
+	var ret []string
+
+	for _, e := range logs {
+		var le logEntry
+		err := json.Unmarshal([]byte(e), &le)
+		if err != nil {
+			return nil, fmt.Errorf("failed to unmarshal log entry into JSON: %w", err)
+		}
+		if le.PluginID != pluginID {
+			continue
+		}
+
+		let, err := time.Parse(timeStampFormat, le.Timestamp)
+		if err != nil {
+			return nil, fmt.Errorf("unknown timestamp format: %w", err)
+		}
+		if let.Before(since) {
+			continue
+		}
+
+		// Log entries returned by the API have a newline a prefix.
+		// Remove that to make printing consistent.
+		e = strings.TrimPrefix(e, "\n")
+
+		ret = append(ret, e)
+	}
+
+	return ret, nil
+}
+
+// printLogEntries prints a slice of log entries to stdout.
+func printLogEntries(entries []string) error {
+	for _, e := range entries {
+		_, err := io.WriteString(os.Stdout, e+"\n")
+		if err != nil {
+			return fmt.Errorf("failed to write log entry to stdout: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func checkJSONLogsSetting(ctx context.Context, client *model.Client4) error {
+	cfg, _, err := client.GetConfig(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to fetch config: %w", err)
+	}
+	if cfg.LogSettings.FileJson == nil || !*cfg.LogSettings.FileJson {
+		return errors.New("JSON output for file logs are disabled. Please enable LogSettings.FileJson via the configration in Mattermost.") //nolint:revive,stylecheck
+	}
+
+	return nil
+}