fix: reject server.user explicitly on windows, add init validation test

Author: rustatian

plugin.go

@@ -5,6 +5,7 @@ import (
 	"log/slog"
 	"os"
 	"os/user"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -58,6 +59,12 @@ func (p *Plugin) Init(cfg Configurer, log NamedLogger) error {
 
 	// resolve the configured run-as user's uid/gid once
 	if p.cfg.User != "" {
+		// process.ExecuteFromUser is a no-op on Windows, and Windows uids (SIDs)
+		// are not numeric — reject the option explicitly instead of failing on Atoi.
+		if runtime.GOOS == "windows" {
+			return errors.E(op, errors.Init, errors.Str("server.user is not supported on windows"))
+		}
+
 		usr, err := user.Lookup(p.cfg.User)
 		if err != nil {
 			return errors.E(op, errors.Init, err)

plugin_test.go

@@ -77,6 +77,25 @@ func TestCommandUnknownUser(t *testing.T) {
 	})
 }
 
+func TestInitUnknownUser(t *testing.T) {
+	log := slog.New(slog.NewTextHandler(os.Stderr, nil))
+	p := &Plugin{
+		preparedEnvs: make([]string, 0),
+		cfg:          &Config{},
+		log:          log,
+	}
+
+	v := viper.New()
+	v.Set("server.command", "php php_test_files/client.php echo pipes")
+	v.Set("server.user", "rr-definitely-missing-user")
+
+	cfg, err := InitMockCfg(v)
+	require.NoError(t, err)
+
+	err = p.Init(cfg, NewTestLogger(log))
+	require.Error(t, err)
+}
+
 func TestCommand1(t *testing.T) {
 	log := slog.New(slog.NewTextHandler(os.Stderr, nil))
 	p := &Plugin{