log: Remove trailing newlines and escape internal newlines. (#4925)

Fixes #4914.

cmd/shell.go

@@ -138,7 +138,8 @@ type logWriter struct {
 }
 
 func (lw logWriter) Write(p []byte) (n int, err error) {
-	lw.Logger.Info(string(p))
+	// Lines received by logWriter will always have a trailing newline.
+	lw.Logger.Info(strings.Trim(string(p), "\n"))
 	return
 }
 

cmd/shell_test.go

@@ -194,3 +194,12 @@ func TestReadConfigFile(t *testing.T) {
 	test.AssertNotError(t, err, "ReadConfigFile(../test/config/notify-mailer.json) errored")
 	test.AssertEquals(t, c.NotifyMailer.SMTPConfig.Server, "localhost")
 }
+
+func TestLogWriter(t *testing.T) {
+	mock := blog.UseMock()
+	lw := logWriter{mock}
+	_, _ = lw.Write([]byte("hi\n"))
+	lines := mock.GetAllMatching(".*")
+	test.AssertEquals(t, len(lines), 1)
+	test.AssertEquals(t, lines[0], "INFO: hi")
+}

log/log.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"hash/crc32"
+	"io"
 	"log/syslog"
 	"os"
 	"path"
@@ -60,7 +61,7 @@ func New(log *syslog.Writer, stdoutLogLevel int, syslogLogLevel int) (Logger, er
 		return nil, errors.New("Attempted to use a nil System Logger.")
 	}
 	return &impl{
-		&bothWriter{log, stdoutLogLevel, syslogLogLevel, clock.New()},
+		&bothWriter{log, stdoutLogLevel, syslogLogLevel, clock.New(), os.Stdout},
 	}, nil
 }
 
@@ -118,6 +119,7 @@ type bothWriter struct {
 	stdoutLevel int
 	syslogLevel int
 	clk         clock.Clock
+	stdout      io.Writer
 }
 
 func LogLineChecksum(line string) string {
@@ -138,6 +140,9 @@ func (w *bothWriter) logAtLevel(level syslog.Priority, msg string) {
 	const red = "\033[31m\033[1m"
 	const yellow = "\033[33m"
 
+	// Since messages are delimited by newlines, we have to escape any internal or
+	// trailing newlines before generating the checksum or outputting the message.
+	msg = strings.Replace(msg, "\n", "\\n", -1)
 	msg = fmt.Sprintf("%s %s", LogLineChecksum(msg), msg)
 
 	switch syslogAllowed := int(level) <= w.syslogLevel; level {
@@ -175,7 +180,7 @@ func (w *bothWriter) logAtLevel(level syslog.Priority, msg string) {
 	}
 
 	if int(level) <= w.stdoutLevel {
-		if _, err := fmt.Printf("%s%s %s %s%s\n",
+		if _, err := fmt.Fprintf(w.stdout, "%s%s %s %s%s\n",
 			prefix,
 			w.clk.Now().Format("150405"),
 			path.Base(os.Args[0]),

log/log_test.go

@@ -1,6 +1,7 @@
 package log
 
 import (
+	"bytes"
 	"fmt"
 	"log"
 	"log/syslog"
@@ -340,3 +341,11 @@ func TestStdoutFailure(t *testing.T) {
 	// Try to audit log something
 	log.AuditInfo("This should cause a panic, stdout is closed!")
 }
+
+func TestLogAtLevelEscapesNewlines(t *testing.T) {
+	var buf bytes.Buffer
+	w := &bothWriter{nil, 6, 0, clock.New(), &buf}
+	w.logAtLevel(6, "foo\nbar")
+
+	test.Assert(t, strings.Contains(buf.String(), "foo\\nbar"), "failed to escape newline")
+}