log: Replace glog with a new logging module

glog works fine and has great features, but it does not play along well
with systemd or standard log rotators (as it does the rotation itself).

So this patch replaces glog with a new logging module "log", which by
default logs to stderr, in a systemd-friendly manner.

Logging to files or syslog is still supported.

internal/log/log_test.go

@@ -0,0 +1,104 @@
+package log
+
+import (
+	"io/ioutil"
+	"os"
+	"regexp"
+	"testing"
+)
+
+func mustNewFile(t *testing.T) (string, *Logger) {
+	f, err := ioutil.TempFile("", "log_test-")
+	if err != nil {
+		t.Fatalf("failed to create temp file: %v", err)
+	}
+
+	l, err := NewFile(f.Name())
+	if err != nil {
+		t.Fatalf("failed to open new log file: %v", err)
+	}
+
+	return f.Name(), l
+}
+
+func checkContentsMatch(t *testing.T, name, path, expected string) {
+	content, err := ioutil.ReadFile(path)
+	if err != nil {
+		panic(err)
+	}
+
+	got := string(content)
+	if !regexp.MustCompile(expected).Match(content) {
+		t.Errorf("%s: regexp %q did not match %q",
+			name, expected, got)
+	}
+}
+
+func testLogger(t *testing.T, fname string, l *Logger) {
+	l.LogTime = false
+	l.Infof("message %d", 1)
+	checkContentsMatch(t, "info-no-time", fname,
+		"^_ log_test.go:....   message 1\n")
+
+	os.Truncate(fname, 0)
+	l.Infof("message %d\n", 1)
+	checkContentsMatch(t, "info-with-newline", fname,
+		"^_ log_test.go:....   message 1\n")
+
+	os.Truncate(fname, 0)
+	l.LogTime = true
+	l.Infof("message %d", 1)
+	checkContentsMatch(t, "info-with-time", fname,
+		`^\d{8} ..:..:..\.\d{6} _ log_test.go:....   message 1\n`)
+
+	os.Truncate(fname, 0)
+	l.LogTime = false
+	l.Errorf("error %d", 1)
+	checkContentsMatch(t, "error", fname, `^E log_test.go:....   error 1\n`)
+
+	if l.V(Debug) {
+		t.Fatalf("Debug level enabled by default (level: %v)", l.Level)
+	}
+
+	os.Truncate(fname, 0)
+	l.LogTime = false
+	l.Debugf("debug %d", 1)
+	checkContentsMatch(t, "debug-no-log", fname, `^$`)
+
+	os.Truncate(fname, 0)
+	l.Level = Debug
+	l.Debugf("debug %d", 1)
+	checkContentsMatch(t, "debug", fname, `^\. log_test.go:....   debug 1\n`)
+
+	if !l.V(Debug) {
+		t.Errorf("l.Level = Debug, but V(Debug) = false")
+	}
+
+	os.Truncate(fname, 0)
+	l.Level = Info
+	l.Log(Debug, 0, "log debug %d", 1)
+	l.Log(Info, 0, "log info %d", 1)
+	checkContentsMatch(t, "log", fname,
+		`^_ log_test.go:....   log info 1\n`)
+
+}
+
+func TestBasic(t *testing.T) {
+	fname, l := mustNewFile(t)
+	defer l.Close()
+	defer os.Remove(fname)
+
+	testLogger(t, fname, l)
+}
+
+func TestDefaultFile(t *testing.T) {
+	fname, l := mustNewFile(t)
+	l.Close()
+	defer os.Remove(fname)
+
+	*logFile = fname
+
+	Init()
+
+	testLogger(t, fname, Default)
+}