maillog: Introduce a special-purpose mail logging package

The default INFO logs are more oriented towards debugging and can be
a bit too verbose when looking for high-level information.

This patch introduces a new "maillog" package, used to log messages of
particular relevance to mail transmission at a higher level.

internal/maillog/maillog.go

@@ -0,0 +1,136 @@
+// Package maillog implements a log specifically for email.
+package maillog
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log/syslog"
+	"net"
+	"sync"
+	"time"
+
+	"github.com/golang/glog"
+
+	"blitiri.com.ar/go/chasquid/internal/trace"
+)
+
+// Global event logs.
+var (
+	authLog = trace.NewEventLog("Authentication", "Incoming SMTP")
+)
+
+// A writer that prepends timing information.
+type timedWriter struct {
+	w io.Writer
+}
+
+func (t timedWriter) Write(b []byte) (int, error) {
+	fmt.Fprintf(t.w, "%s  ", time.Now().Format("2006-01-02 15:04:05.000000"))
+	return t.w.Write(b)
+}
+
+type Logger struct {
+	w    io.Writer
+	once sync.Once
+}
+
+func New(w io.Writer) *Logger {
+	return &Logger{w: timedWriter{w}}
+}
+
+func NewSyslog() (*Logger, error) {
+	w, err := syslog.New(syslog.LOG_INFO|syslog.LOG_MAIL, "chasquid")
+	if err != nil {
+		return nil, err
+	}
+
+	l := &Logger{w: w}
+	return l, nil
+}
+
+func (l *Logger) printf(format string, args ...interface{}) {
+	_, err := fmt.Fprintf(l.w, format, args...)
+	if err != nil {
+		l.once.Do(func() {
+			glog.Errorf("failed to write to maillog: %v", err)
+			glog.Error("(will not report this again)")
+		})
+	}
+}
+
+func (l *Logger) Listening(a string) {
+	l.printf("daemon listening on %s\n", a)
+}
+
+func (l *Logger) Auth(netAddr net.Addr, user string, successful bool) {
+	res := "successful"
+	if !successful {
+		res = "failed"
+	}
+	msg := fmt.Sprintf("%s authentication %s for %s\n", netAddr, res, user)
+	l.printf(msg)
+	authLog.Debugf(msg)
+}
+
+func (l *Logger) Rejected(netAddr net.Addr, from string, to []string, err string) {
+	if from != "" {
+		from = fmt.Sprintf(" from=%s", from)
+	}
+	toStr := ""
+	if len(to) > 0 {
+		toStr = fmt.Sprintf(" to=%v", to)
+	}
+	l.printf("%s rejected%s%s - %v\n", netAddr, from, toStr, err)
+}
+
+func (l *Logger) Queued(netAddr net.Addr, from string, to []string, id string) {
+	l.printf("%s from=%s queued ip=%s to=%v\n", id, from, netAddr, to)
+}
+
+func (l *Logger) SendAttempt(id, from, to string, err error, permanent bool) {
+	if err == nil {
+		l.printf("%s from=%s to=%s sent successfully\n", id, from, to)
+	} else {
+		t := "(temporary)"
+		if permanent {
+			t = "(permanent)"
+		}
+		l.printf("%s from=%s to=%s sent failed %s: %v\n", id, from, to, t, err)
+	}
+}
+
+func (l *Logger) QueueLoop(id string, nextDelay time.Duration) {
+	if nextDelay > 0 {
+		l.printf("%s completed loop, next in %v\n", id, nextDelay)
+	} else {
+		l.printf("%s all done\n", id)
+	}
+}
+
+// The default logger used in the following top-level functions.
+var Default *Logger = New(ioutil.Discard)
+
+func Listening(a string) {
+	Default.Listening(a)
+}
+
+func Auth(netAddr net.Addr, user string, successful bool) {
+	Default.Auth(netAddr, user, successful)
+}
+
+func Rejected(netAddr net.Addr, from string, to []string, err string) {
+	Default.Rejected(netAddr, from, to, err)
+}
+
+func Queued(netAddr net.Addr, from string, to []string, id string) {
+	Default.Queued(netAddr, from, to, id)
+}
+
+func SendAttempt(id, from, to string, err error, permanent bool) {
+	Default.SendAttempt(id, from, to, err, permanent)
+}
+
+func QueueLoop(id string, nextDelay time.Duration) {
+	Default.QueueLoop(id, nextDelay)
+}