Added basic syslog support

log/extended_writer.go

@@ -0,0 +1,19 @@
+package log
+
+import "io"
+
+// SpecializedWriter represents an extended io.Writer class that can perform
+// contextualized writes.
+type SpecializedWriter interface {
+	GetSpecializedWriter(keyvals ...interface{}) io.Writer
+}
+
+// specializedWriter returns a specialized writer for the specified keys or
+// falls back to returning w if no specialized writer is available.
+func specializedWriter(w io.Writer, keyvals ...interface{}) io.Writer {
+	if ew, ok := w.(SpecializedWriter); ok {
+		w = ew.GetSpecializedWriter(keyvals...)
+	}
+
+	return w
+}

log/json_logger.go

@@ -31,7 +31,7 @@ func (l *jsonLogger) Log(keyvals ...interface{}) error {
 		}
 		merge(m, k, v)
 	}
-	return json.NewEncoder(l.Writer).Encode(m)
+	return json.NewEncoder(specializedWriter(l.Writer, keyvals...)).Encode(m)
 }
 
 func merge(dst map[string]interface{}, k, v interface{}) {

log/logfmt_logger.go

@@ -55,7 +55,7 @@ func (l logfmtLogger) Log(keyvals ...interface{}) error {
 	// The Logger interface requires implementations to be safe for concurrent
 	// use by multiple goroutines. For this implementation that means making
 	// only one call to l.w.Write() for each call to Log.
-	if _, err := l.w.Write(enc.buf.Bytes()); err != nil {
+	if _, err := specializedWriter(l.w, keyvals...).Write(enc.buf.Bytes()); err != nil {
 		return err
 	}
 	return nil

log/syslog/syslog.go

@@ -0,0 +1,86 @@
+// +build linux,!appengine darwin freebsd openbsd
+
+package syslog
+
+import (
+	"io"
+	gosyslog "log/syslog"
+
+	"github.com/go-kit/kit/log/level"
+)
+
+type syslogWriter struct {
+	*gosyslog.Writer
+	selector func(keyvals ...interface{}) gosyslog.Priority
+}
+
+type SyslogAdapterOption interface {
+	Apply(*syslogWriter)
+}
+
+func NewSyslogWriter(w *gosyslog.Writer, options ...SyslogAdapterOption) io.Writer {
+	writer := &syslogWriter{
+		Writer:   w,
+		selector: defaultSyslogSelector,
+	}
+
+	for _, option := range options {
+		option.Apply(writer)
+	}
+
+	return *writer
+}
+
+type syslogWriterAdapter struct {
+	f func(string) error
+}
+
+func (a *syslogWriterAdapter) Write(b []byte) (int, error) {
+	return len(b), a.f(string(b))
+}
+
+func (w syslogWriter) GetSpecializedWriter(keyvals ...interface{}) io.Writer {
+	priority := w.selector(keyvals...)
+
+	switch priority {
+	case gosyslog.LOG_DEBUG:
+		return &syslogWriterAdapter{f: w.Debug}
+	case gosyslog.LOG_INFO:
+		return &syslogWriterAdapter{f: w.Info}
+	case gosyslog.LOG_WARNING:
+		return &syslogWriterAdapter{f: w.Warning}
+	case gosyslog.LOG_ERR:
+		return &syslogWriterAdapter{f: w.Err}
+	}
+
+	return w
+}
+
+func defaultSyslogSelector(keyvals ...interface{}) gosyslog.Priority {
+	for i := 1; i < len(keyvals); i += 2 {
+		if v, ok := keyvals[i].(level.Value); ok {
+			switch v {
+			case level.DebugValue():
+				return gosyslog.LOG_DEBUG
+			case level.InfoValue():
+				return gosyslog.LOG_INFO
+			case level.WarnValue():
+				return gosyslog.LOG_WARNING
+			case level.ErrorValue():
+				return gosyslog.LOG_ERR
+			}
+		}
+	}
+
+	return gosyslog.LOG_INFO
+}
+
+// SyslogPrioritySelector is an option that specifies the syslog priority
+// selector.
+type SyslogPrioritySelector struct {
+	PrioritySelector func(keyvals ...interface{}) gosyslog.Priority
+}
+
+func (o SyslogPrioritySelector) Apply(w *syslogWriter) {
+	w.selector = o.PrioritySelector
+}