Initial working version

conn.go

@@ -0,0 +1,91 @@
+package journal
+
+import (
+	"net"
+	"sync"
+)
+
+const (
+	// WellKnownSocketPath is where we generally expect to find the systemd
+	// journal daemon's socket.
+	WellKnownSocketPath = "/run/systemd/journal/socket"
+)
+
+// Conn represents an active, open connection to the systemd journal that is
+// ready to write log entries.
+type Conn struct {
+	// Common attributes which are emitted for all messages.
+	Common []Attr
+
+	// ErrHandler is called if there is an error writing to the log. If nil,
+	// the error is silently discarded.
+	ErrHandler func(error)
+
+	s    *net.UnixConn
+	bufs sync.Pool
+}
+
+// Connect to the systemd journal. If the path string is empty, then it uses the
+// well-known socket path.
+func Connect(path string) (*Conn, error) {
+	if path == "" {
+		path = WellKnownSocketPath
+	}
+
+	s, err := net.DialUnix("unixgram", nil, &net.UnixAddr{
+		Name: path,
+		Net:  "unixgram",
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return &Conn{
+		s: s,
+		bufs: sync.Pool{
+			New: func() any {
+				return &net.Buffers{}
+			},
+		},
+	}, nil
+}
+
+var messageAttrKey = AttrKey{key: "MESSAGE"}
+
+// Entry emits a log entry. It will add PRIORITY and MESSAGE key/value pairs
+// as well as any Common attributes.
+//
+// Note: to avoid allocation / garbage, ensure attrs has capacity for an extra
+// 2+len(c.Common) values.
+func (c *Conn) Entry(pri Priority, msg string, attrs []Attr) {
+	err := c.EntryErr(pri, msg, attrs)
+	switch {
+	case err == nil:
+		return
+	case c.ErrHandler == nil:
+		return
+	default:
+		c.ErrHandler(err)
+	}
+}
+
+// EntryErr is like Entry, but will propagate errors to the caller, rather than
+// using the built-in error handler.
+func (c *Conn) EntryErr(pri Priority, msg string, attrs []Attr) error {
+	attrs = append(attrs, pri.Attr(), Attr{
+		Key:   messageAttrKey,
+		Value: []byte(msg),
+	})
+	attrs = append(attrs, c.Common...)
+	return c.WriteAttrs(attrs)
+}
+
+// WriteAttrs is a low-level method which writes a journal entry comprised of
+// only the given set of attributes.
+func (c *Conn) WriteAttrs(attrs []Attr) error {
+	buf := c.bufs.Get().(*net.Buffers)
+	*buf = (*buf)[:0]
+	err := WireWrite(buf, c.s, attrs)
+	c.bufs.Put(buf)
+	return err
+}