readConfig,loadLabels: stop using regex

Using a globally initialized regex incurs some overhead during package
initialization, which is noticeable for all other packages importing it.

Besides, there's no need to use regex to perform key=value split.

Rewrite both functions without using regex, and add benchmarks, which
show that the new code is faster:

name          old time/op    new time/op    delta
ReadConfig-4    4.86µs ± 1%    3.46µs ± 2%  -28.82%  (p=0.002 n=6+6)
LoadLabels-4    12.7µs ± 3%     6.8µs ± 1%  -46.24%  (p=0.002 n=6+6)

name          old alloc/op   new alloc/op   delta
ReadConfig-4    5.08kB ± 0%    4.35kB ± 0%  -14.33%  (p=0.002 n=6+6)
LoadLabels-4    6.49kB ± 0%    6.10kB ± 0%   -6.07%  (p=0.000 n=6+5)

name          old allocs/op  new allocs/op  delta
ReadConfig-4      20.0 ± 0%       8.0 ± 0%  -60.00%  (p=0.002 n=6+6)
LoadLabels-4      45.0 ± 0%      45.0 ± 0%     ~     (all equal)

Besides, the init overhead is eliminated:

Before:
init github.com/opencontainers/selinux/go-selinux @2.4 ms, 0.088 ms clock, 5016 bytes, 72 allocs

After:
init github.com/opencontainers/selinux/go-selinux @2.9 ms, 0.001 ms clock, 160 bytes, 8 allocs

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

go-selinux/selinux_linux.go

@@ -12,7 +12,6 @@ import (
 	"os"
 	"path"
 	"path/filepath"
-	"regexp"
 	"strconv"
 	"strings"
 	"sync"
@@ -68,7 +67,6 @@ const (
 )
 
 var (
-	assignRegex       = regexp.MustCompile(`^([^=]+)=(.*)$`)
 	readOnlyFileLabel string
 	state             = selinuxState{
 		mcsList: make(map[string]bool),
@@ -237,7 +235,7 @@ func readConfig(target string) string {
 	scanner := bufio.NewScanner(in)
 
 	for scanner.Scan() {
-		line := strings.TrimSpace(scanner.Text())
+		line := bytes.TrimSpace(scanner.Bytes())
 		if len(line) == 0 {
 			// Skip blank lines
 			continue
@@ -246,11 +244,12 @@ func readConfig(target string) string {
 			// Skip comments
 			continue
 		}
-		if groups := assignRegex.FindStringSubmatch(line); groups != nil {
-			key, val := strings.TrimSpace(groups[1]), strings.TrimSpace(groups[2])
-			if key == target {
-				return strings.Trim(val, "\"")
-			}
+		fields := bytes.SplitN(line, []byte{'='}, 2)
+		if len(fields) != 2 {
+			continue
+		}
+		if bytes.Equal(fields[0], []byte(target)) {
+			return string(bytes.Trim(fields[1], `"`))
 		}
 	}
 	return ""
@@ -920,7 +919,7 @@ func loadLabels() {
 	scanner := bufio.NewScanner(in)
 
 	for scanner.Scan() {
-		line := strings.TrimSpace(scanner.Text())
+		line := bytes.TrimSpace(scanner.Bytes())
 		if len(line) == 0 {
 			// Skip blank lines
 			continue
@@ -929,10 +928,12 @@ func loadLabels() {
 			// Skip comments
 			continue
 		}
-		if groups := assignRegex.FindStringSubmatch(line); groups != nil {
-			key, val := strings.TrimSpace(groups[1]), strings.TrimSpace(groups[2])
-			labels[key] = strings.Trim(val, "\"")
+		fields := bytes.SplitN(line, []byte{'='}, 2)
+		if len(fields) != 2 {
+			continue
 		}
+		key, val := bytes.TrimSpace(fields[0]), bytes.TrimSpace(fields[1])
+		labels[string(key)] = string(bytes.Trim(val, `"`))
 	}
 
 	con, _ := NewContext(labels["file"])

go-selinux/selinux_linux_test.go

@@ -507,3 +507,17 @@ func BenchmarkChcon(b *testing.B) {
 		}
 	}
 }
+
+func BenchmarkReadConfig(b *testing.B) {
+	str := ""
+	for n := 0; n < b.N; n++ {
+		str = readConfig(selinuxTypeTag)
+	}
+	b.Log(str)
+}
+
+func BenchmarkLoadLabels(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		loadLabels()
+	}
+}