pam-moduler: Add test that generates a new debug module and verify it works

We mimic what pam_debug.so does by default, by implementing a similar
module fully in go, generated using pam-moduler.

This requires various utilities to generate the module and run the tests
that are in a separate internal modules so that it can be shared between
multiple implementations

cmd/pam-moduler/tests/internal/utils/test-setup.go

@@ -0,0 +1,135 @@
+// Package utils contains the internal test utils
+package utils
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/msteinert/pam/v2"
+)
+
+// TestSetup is an utility type for having a playground for test PAM modules.
+type TestSetup struct {
+	t       *testing.T
+	workDir string
+}
+
+type withWorkDir struct{}
+
+//nolint:revive
+func WithWorkDir() withWorkDir {
+	return withWorkDir{}
+}
+
+// NewTestSetup creates a new TestSetup.
+func NewTestSetup(t *testing.T, args ...interface{}) *TestSetup {
+	t.Helper()
+
+	ts := &TestSetup{t: t}
+	for _, arg := range args {
+		switch argType := arg.(type) {
+		case withWorkDir:
+			ts.ensureWorkDir()
+		default:
+			t.Fatalf("Unknown parameter of type %v", argType)
+		}
+	}
+
+	return ts
+}
+
+// CreateTemporaryDir creates a temporary directory with provided basename.
+func (ts *TestSetup) CreateTemporaryDir(basename string) string {
+	tmpDir, err := os.MkdirTemp(os.TempDir(), basename)
+	if err != nil {
+		ts.t.Fatalf("can't create service path %v", err)
+	}
+
+	ts.t.Cleanup(func() { os.RemoveAll(tmpDir) })
+	return tmpDir
+}
+
+func (ts *TestSetup) ensureWorkDir() string {
+	if ts.workDir != "" {
+		return ts.workDir
+	}
+
+	ts.workDir = ts.CreateTemporaryDir("go-pam-*")
+	return ts.workDir
+}
+
+// WorkDir returns the test setup work directory.
+func (ts TestSetup) WorkDir() string {
+	return ts.workDir
+}
+
+// GenerateModule generates a PAM module for the provided path and name.
+func (ts *TestSetup) GenerateModule(testModulePath string, moduleName string) string {
+	cmd := exec.Command("go", "generate", "-C", testModulePath)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		ts.t.Fatalf("can't build pam module %v: %s", err, out)
+	}
+
+	builtFile := filepath.Join(cmd.Dir, testModulePath, moduleName)
+	modulePath := filepath.Join(ts.ensureWorkDir(), filepath.Base(builtFile))
+	if err = os.Rename(builtFile, modulePath); err != nil {
+		ts.t.Fatalf("can't move module: %v", err)
+		os.Remove(builtFile)
+	}
+
+	return modulePath
+}
+
+func (ts TestSetup) currentFile(skip int) string {
+	_, currentFile, _, ok := runtime.Caller(skip)
+	if !ok {
+		ts.t.Fatalf("can't get current binary path")
+	}
+	return currentFile
+}
+
+// GetCurrentFile returns the current file path.
+func (ts TestSetup) GetCurrentFile() string {
+	// This is a library so we care about the caller location
+	return ts.currentFile(2)
+}
+
+// GetCurrentFileDir returns the current file directory.
+func (ts TestSetup) GetCurrentFileDir() string {
+	return filepath.Dir(ts.currentFile(2))
+}
+
+// GenerateModuleDefault generates a default module.
+func (ts *TestSetup) GenerateModuleDefault(testModulePath string) string {
+	return ts.GenerateModule(testModulePath, "pam_go.so")
+}
+
+// CreateService creates a service file.
+func (ts *TestSetup) CreateService(serviceName string, services []ServiceLine) string {
+	if !pam.CheckPamHasStartConfdir() {
+		ts.t.Skip("PAM has no support for custom service paths")
+		return ""
+	}
+
+	serviceName = strings.ToLower(serviceName)
+	serviceFile := filepath.Join(ts.ensureWorkDir(), serviceName)
+	var contents = []string{}
+
+	for _, s := range services {
+		contents = append(contents, strings.TrimRight(strings.Join([]string{
+			s.Action.String(), s.Control.String(), s.Module, strings.Join(s.Args, " "),
+		}, "\t"), "\t"))
+	}
+
+	if err := os.WriteFile(serviceFile,
+		[]byte(strings.Join(contents, "\n")), 0600); err != nil {
+		ts.t.Fatalf("can't create service file %v: %v", serviceFile, err)
+	}
+
+	return serviceFile
+}