Initial MVP commit

journald/journald.go

@@ -0,0 +1,114 @@
+package journald
+
+import (
+	"context"
+	"fmt"
+	"iter"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/coreos/go-systemd/v22/sdjournal"
+)
+
+func syslogMatchData(syslogIdentifier string) string {
+	builder := strings.Builder{}
+
+	builder.WriteString(sdjournal.SD_JOURNAL_FIELD_SYSLOG_IDENTIFIER)
+	builder.WriteString("=")
+	builder.WriteString(syslogIdentifier)
+
+	return builder.String()
+}
+
+type Journald struct {
+	journal *sdjournal.Journal
+	lock    sync.Mutex
+}
+
+func NewJournald(syslogName string) (*Journald, error) {
+	journal, err := sdjournal.NewJournal()
+	if err != nil {
+		return nil, fmt.Errorf("failed to initialize journal: %w", err)
+	}
+
+	if syslogName != "" {
+		matchData := syslogMatchData(syslogName)
+		err = journal.AddMatch(matchData)
+		if err != nil {
+			return nil, fmt.Errorf("failed to add match %s to journal: %w", matchData, err)
+		}
+	}
+
+	err = journal.SeekTail()
+	if err != nil {
+		return nil, fmt.Errorf("failed to seek to tail: %w", err)
+	}
+
+	_, err = journal.Previous()
+	if err != nil {
+		return nil, fmt.Errorf("failed to go to tail message: %w", err)
+	}
+
+	return &Journald{
+		journal: journal,
+	}, nil
+}
+
+func (j *Journald) Close() error {
+	err := j.journal.Close()
+	if err != nil {
+		return fmt.Errorf("failed to close journal: %w", err)
+	}
+
+	return nil
+}
+
+func (j *Journald) Next() (*sdjournal.JournalEntry, error) {
+	j.lock.Lock()
+	defer j.lock.Unlock()
+
+	entryCount, err := j.journal.Next()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get next journald entry: %w", err)
+	}
+
+	if entryCount == 0 {
+		return nil, nil
+	}
+
+	entry, err := j.journal.GetEntry()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get journald entry: %w", err)
+	}
+
+	return entry, nil
+}
+
+func (j *Journald) Iter(ctx context.Context) iter.Seq2[*sdjournal.JournalEntry, error] {
+	return func(yield func(*sdjournal.JournalEntry, error) bool) {
+		for {
+			j.journal.Wait(time.Second)
+			if ctx.Err() != nil {
+				yield(nil, fmt.Errorf("failed to iterate on journald, context error: %w", ctx.Err()))
+				return
+			}
+
+			entry, err := j.Next()
+			if err != nil {
+				yield(nil, err)
+				return
+			}
+
+			// no more entries at the moment
+			if entry == nil {
+				continue
+			}
+
+			// we were told to stop
+			if !yield(entry, nil) {
+				return
+			}
+		}
+	}
+}