module-transaction: Add support for setting/getting module data

Module data is data associated with a module handle that is available
for the whole module loading time so it can be used also during
different operations.

We use cgo handles to preserve the life of the go objects so any value
can be associated with a pam transaction.

module-transaction.go

@@ -2,18 +2,14 @@
 package pam
 
 /*
-#cgo CFLAGS: -Wall -std=c99
-#cgo LDFLAGS: -lpam
-
-#include <security/pam_modules.h>
-#include <stdlib.h>
-#include <stdint.h>
+#include "transaction.h"
 */
 import "C"
 
 import (
 	"errors"
 	"fmt"
+	"runtime/cgo"
 	"unsafe"
 )
 
@@ -26,6 +22,8 @@ type ModuleTransaction interface {
 	GetEnv(name string) string
 	GetEnvList() (map[string]string, error)
 	GetUser(prompt string) (string, error)
+	SetData(key string, data any) error
+	GetData(key string) (any, error)
 }
 
 // ModuleHandlerFunc is a function type used by the ModuleHandler.
@@ -102,6 +100,8 @@ func (m *moduleTransaction) InvokeHandler(handler ModuleHandlerFunc,
 
 type moduleTransactionIface interface {
 	getUser(outUser **C.char, prompt *C.char) C.int
+	setData(key *C.char, handle C.uintptr_t) C.int
+	getData(key *C.char, outHandle *C.uintptr_t) C.int
 }
 
 func (m *moduleTransaction) getUser(outUser **C.char, prompt *C.char) C.int {
@@ -127,3 +127,56 @@ func (m *moduleTransaction) getUserImpl(iface moduleTransactionIface,
 func (m *moduleTransaction) GetUser(prompt string) (string, error) {
 	return m.getUserImpl(m, prompt)
 }
+
+// SetData allows to save any value in the module data that is preserved
+// during the whole time the module is loaded.
+func (m *moduleTransaction) SetData(key string, data any) error {
+	return m.setDataImpl(m, key, data)
+}
+
+func (m *moduleTransaction) setData(key *C.char, handle C.uintptr_t) C.int {
+	return C.set_data(m.handle, key, handle)
+}
+
+// setDataImpl is the implementation for SetData for testing purposes.
+func (m *moduleTransaction) setDataImpl(iface moduleTransactionIface,
+	key string, data any) error {
+	var cKey = C.CString(key)
+	defer C.free(unsafe.Pointer(cKey))
+	var handle cgo.Handle
+	if data != nil {
+		handle = cgo.NewHandle(data)
+	}
+	return m.handlePamStatus(iface.setData(cKey, C.uintptr_t(handle)))
+}
+
+//export _go_pam_data_cleanup
+func _go_pam_data_cleanup(h NativeHandle, handle C.uintptr_t, status C.int) {
+	cgo.Handle(handle).Delete()
+}
+
+// GetData allows to get any value from the module data saved using SetData
+// that is preserved across the whole time the module is loaded.
+func (m *moduleTransaction) GetData(key string) (any, error) {
+	return m.getDataImpl(m, key)
+}
+
+func (m *moduleTransaction) getData(key *C.char, outHandle *C.uintptr_t) C.int {
+	return C.get_data(m.handle, key, outHandle)
+}
+
+// getDataImpl is the implementation for GetData for testing purposes.
+func (m *moduleTransaction) getDataImpl(iface moduleTransactionIface,
+	key string) (any, error) {
+	var cKey = C.CString(key)
+	defer C.free(unsafe.Pointer(cKey))
+	var handle C.uintptr_t
+	if err := m.handlePamStatus(iface.getData(cKey, &handle)); err != nil {
+		return nil, err
+	}
+	if goHandle := cgo.Handle(handle); goHandle != cgo.Handle(0) {
+		return goHandle.Value(), nil
+	}
+
+	return nil, m.handlePamStatus(C.int(ErrNoModuleData))
+}