1 files changed, 87 insertions, 0 deletions
diff --git a/sd_daemon/log.go b/sd_daemon/log.go
new file mode 100644
index 0000000..76a735f
--- /dev/null
+++ b/sd_daemon/log.go
@@ -0,0 +1,87 @@
+// Copyright 2015-2016 Luke Shumaker
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:generate make
+
+package sd_daemon
+
+import (
+	"io"
+	"os"
+	"strings"
+	"sync"
+	"fmt"
+	"log/syslog"
+)
+
+// Logger writes "<N>"-prefixed lines to an io.Writer, where N is a
+// syslog priority number.  It implements mostly the same interface as
+// "log/syslog".Writer.
+//
+// You probably don't need any instance of this other than the
+// constant "Log", which uses os.Stderr as the writer.  It is
+// implemented as a struct rather than a set of functions so that it
+// can be passed around as an implementation of an interface.
+type Logger struct{
+	mu  sync.Mutex
+	out io.Writer
+}
+
+func NewLogger(w io.Writer) Logger {
+	return Logger{out: w}
+}
+
+// Log is a Logger that use used very similarly to
+// "log/syslog".Writer, but writes to os.Stderr under the assumption
+// that stderr is forwarded to syslog/journald.
+//
+// You are encouraged to use stderr unless you have a good reason to
+// talk to syslog or journald directly.
+var Log = Logger{out: os.Stderr}
+
+// WriteString writes a message with the specified priority to the
+// log.
+func (l Logger) WriteBytes(level syslog.Priority, msg []byte) (n int, err error) {
+	return l.WriteString(level, string(msg))
+}
+
+// WriteString writes a message with the specified priority to the
+// log.
+func (l Logger) WriteString(level syslog.Priority, msg string) (n int, err error) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	// BUG(lukeshu): Logger uses high-level string functions that
+	// do many small allocations, making it insuitable for in
+	// tight loops; it should use a buffer property to be
+	// essentially zero-allocation.
+	prefix := fmt.Sprintf("<%d>", level)
+	buf := prefix + strings.Replace(strings.TrimSuffix(msg, "\n"), "\n", "\n"+prefix, -1)
+	return io.WriteString(l.out, buf)
+}
+
+type loggerWriter struct {
+	log   Logger
+	level syslog.Priority
+}
+
+func (lw loggerWriter) Write(p []byte) (n int, err error) {
+	return lw.log.WriteBytes(lw.level, p)
+}
+
+// Writer returns an io.Writer that writes messages with the specified
+// priority to the log.
+func (l Logger) Writer(level syslog.Priority) io.Writer {
+	return loggerWriter{log: l, level: level}
+}