wgcfg: use string cut instead of string split

Signed-off-by: julianknodt <julianknodt@gmail.com>

wgengine/wgcfg/parser.go

@@ -69,6 +69,14 @@ func parseKeyHex(s string) (*wgkey.Key, error) {
 	return &key, nil
 }
 
+// stringsCut is strings.Cut from proposed https://github.com/golang/go/issues/46336.
+func stringsCut(s, sep string) (before, after string, found bool) {
+	if i := strings.Index(s, sep); i >= 0 {
+		return s[:i], s[i+len(sep):], true
+	}
+	return s, "", false
+}
+
 // FromUAPI generates a Config from r.
 // r should be generated by calling device.IpcGetOperation;
 // it is not compatible with other uapi streams.
@@ -83,12 +91,10 @@ func FromUAPI(r io.Reader) (*Config, error) {
 		if line == "" {
 			continue
 		}
-		parts := strings.Split(line, "=")
-		if len(parts) != 2 {
-			return nil, fmt.Errorf("failed to parse line %q, found %d =-separated parts, want 2", line, len(parts))
+		key, value, ok := stringsCut(line, "=")
+		if !ok {
+			return nil, fmt.Errorf("failed to cut line %q on =", line)
 		}
-		key := parts[0]
-		value := parts[1]
 		valueBytes := scanner.Bytes()[len(key)+1:]
 
 		if key == "public_key" {

wgengine/wgcfg/parser_test.go

@@ -7,6 +7,7 @@ package wgcfg
 import (
 	"bufio"
 	"bytes"
+	"io"
 	"reflect"
 	"runtime"
 	"testing"
@@ -90,10 +91,10 @@ func BenchmarkFromUAPI(b *testing.B) {
 	r := bytes.NewReader(buf.Bytes())
 	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
+		r.Seek(0, io.SeekStart)
 		_, err := FromUAPI(r)
 		if err != nil {
 			b.Errorf("failed from UAPI: %v", err)
 		}
-		r.Seek(0, 0)
 	}
 }