1 files changed, 166 insertions, 0 deletions
diff --git a/logging/syslog.go b/logging/syslog.go
new file mode 100644
index 0000000..00e3738
--- /dev/null
+++ b/logging/syslog.go
@@ -0,0 +1,166 @@
+package logging
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+
+	"go.sudomsg.com/kit/net"
+)
+
+type Facility int
+
+const (
+	FacilityKern     Facility = 0  // kernel messages
+	FacilityUser     Facility = 1  // user-level messages
+	FacilityMail     Facility = 2  // mail system
+	FacilityDaemon   Facility = 3  // system daemons
+	FacilityAuth     Facility = 4  // security/authorization messages
+	FacilitySyslog   Facility = 5  // messages generated internally by syslogd
+	FacilityLPR      Facility = 6  // line printer subsystem
+	FacilityNews     Facility = 7  // network news subsystem
+	FacilityUUCP     Facility = 8  // UUCP subsystem
+	FacilityCron     Facility = 9  // clock daemon
+	FacilityAuthPriv Facility = 10 // security/authorization messages (private)
+	FacilityFTP      Facility = 11 // FTP daemon
+	FacilityLocal0   Facility = 16
+	FacilityLocal7   Facility = 23
+)
+
+type SyslogSink struct {
+	Writer       io.Writer
+	Facility     Facility
+	Tag          string
+	Hostname     string
+	Level        slog.Level
+	Encoder      Encoder
+	EmitHostname bool
+	ReplaceAttr  func(groups []string, a slog.Attr) slog.Attr
+	mu           sync.Mutex
+}
+
+var _ Sink = &SyslogSink{}
+
+type SyslogOptions struct {
+	Facility    Facility
+	Tag         string
+	Hostname    string
+	Level       slog.Leveler
+	ReplaceAttr func(groups []string, a slog.Attr) slog.Attr
+}
+
+// DialSyslog creates a Sink connected to a local or remote syslog daemon.
+// raddr: "/dev/log", "localhost:514", etc.
+func DialSyslog(ctx context.Context, network net.NetType, raddr string, enc Encoder, options SyslogOptions) (*SyslogSink, error) {
+	if raddr == "" {
+		network, raddr = resolveLocalEndpoint()
+	}
+
+	conn, err := net.Dial(ctx, network, raddr)
+	if err != nil {
+		return nil, fmt.Errorf("syslog dial failed: %w", err)
+	}
+
+	isLocal := (network == net.NetUnixDatagram || network == net.NetUnix)
+
+	sink := NewSyslogSink(conn, enc, options)
+	sink.EmitHostname = !isLocal
+	return sink, nil
+}
+
+func NewSyslogSink(w io.Writer, enc Encoder, options SyslogOptions) *SyslogSink {
+	if options.Hostname == "" {
+		options.Hostname, _ = os.Hostname()
+	}
+	if options.Hostname == "" {
+		options.Hostname = "localhost"
+	}
+
+	if options.Tag == "" {
+		options.Tag = filepath.Base(os.Args[0])
+	}
+
+	if options.Tag == "" {
+		options.Tag = "kit"
+	}
+
+	if len(options.Tag) > 32 {
+		options.Tag = options.Tag[:32]
+	}
+
+	return &SyslogSink{
+		Writer:      w,
+		Encoder:     enc,
+		Tag:         options.Tag,
+		Facility:    options.Facility,
+		Hostname:    options.Hostname,
+		ReplaceAttr: options.ReplaceAttr,
+	}
+}
+
+func (s *SyslogSink) Enabled(level slog.Level) bool {
+	return s.Level <= level
+}
+
+func (s *SyslogSink) Append(r slog.Record) error {
+	level := slog.Leveler(s.Level)
+	var ts time.Time
+	it := RecordAll(r, func(groups []string, attr slog.Attr) slog.Attr {
+		if s.ReplaceAttr != nil {
+			attr = s.ReplaceAttr(groups, attr)
+		}
+		if len(groups) == 0 {
+			if attr.Key == slog.TimeKey {
+				ts = attr.Value.Time()
+				return slog.Attr{}
+			}
+
+			if attr.Key == slog.LevelKey {
+				level = attr.Value.Any().(slog.Leveler)
+				return slog.Attr{}
+			}
+		}
+		return attr
+	})
+	out, err := s.Encoder(it)
+	if err != nil {
+		return fmt.Errorf("failed to encode: %w", err)
+	}
+
+	pri := int(s.Facility)*8 + mapLevelToSyslog(level.Level())
+
+	// Note: RFC 3164 uses a space for leading zeros in days (e.g., "Jan  2")
+	t := ""
+	if !ts.IsZero() {
+		t = r.Time.Format("Jan _2 15:04:05")
+	}
+	hostname := ""
+	if s.EmitHostname {
+		hostname = s.Hostname
+	}
+	packet := fmt.Sprintf("<%d>%s %s %s: %s", pri, t, hostname, s.Tag, out)
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	_, err = fmt.Fprint(s.Writer, packet)
+	return err
+}
+
+func mapLevelToSyslog(l slog.Level) int {
+	switch {
+	case l >= slog.LevelError:
+		return 3
+	case l >= slog.LevelWarn:
+		return 4
+	case l >= slog.LevelInfo:
+		return 6
+	default:
+		return 7
+	}
+}