transaction: Add a transaction base type to define more transaction kinds

A pam handler can be used both by a module and by an Application, go-pam
is meant to be used in the application side right now, but it can be
easily changed to also create modules.

This is the prerequisite work to support this.

transaction.go

@@ -124,12 +124,20 @@ func cbPAMConv(s C.int, msg *C.char, c C.uintptr_t) (*C.char, C.int) {
 	return C.CString(r), success
 }
 
+// transactionBase is a handler for a PAM transaction that can be used to
+// group the operations that can be performed both by the application and the
+// module side
+type transactionBase struct {
+	handle     *C.pam_handle_t
+	lastStatus atomic.Int32
+}
+
 // Transaction is the application's handle for a PAM transaction.
 type Transaction struct {
-	handle     *C.pam_handle_t
+	transactionBase
-	conv       *C.struct_pam_conv
+
-	lastStatus atomic.Int32
+	conv *C.struct_pam_conv
-	c          cgo.Handle
+	c    cgo.Handle
 }
 
 // End cleans up the PAM handle and deletes the callback function.
@@ -146,7 +154,7 @@ func (t *Transaction) End() error {
 }
 
 // Allows to call pam functions managing return status
-func (t *Transaction) handlePamStatus(cStatus C.int) error {
+func (t *transactionBase) handlePamStatus(cStatus C.int) error {
 	t.lastStatus.Store(int32(cStatus))
 	if status := Error(cStatus); status != success {
 		return status
@@ -268,14 +276,14 @@ const (
 )
 
 // SetItem sets a PAM information item.
-func (t *Transaction) SetItem(i Item, item string) error {
+func (t *transactionBase) SetItem(i Item, item string) error {
 	cs := unsafe.Pointer(C.CString(item))
 	defer C.free(cs)
 	return t.handlePamStatus(C.pam_set_item(t.handle, C.int(i), cs))
 }
 
 // GetItem retrieves a PAM information item.
-func (t *Transaction) GetItem(i Item) (string, error) {
+func (t *transactionBase) GetItem(i Item) (string, error) {
 	var s unsafe.Pointer
 	err := t.handlePamStatus(C.pam_get_item(t.handle, C.int(i), &s))
 	if err != nil {
@@ -360,14 +368,14 @@ func (t *Transaction) CloseSession(f Flags) error {
 // NAME=value will set a variable to a value.
 // NAME= will set a variable to an empty value.
 // NAME (without an "=") will delete a variable.
-func (t *Transaction) PutEnv(nameval string) error {
+func (t *transactionBase) PutEnv(nameval string) error {
 	cs := C.CString(nameval)
 	defer C.free(unsafe.Pointer(cs))
 	return t.handlePamStatus(C.pam_putenv(t.handle, cs))
 }
 
 // GetEnv is used to retrieve a PAM environment variable.
-func (t *Transaction) GetEnv(name string) string {
+func (t *transactionBase) GetEnv(name string) string {
 	cs := C.CString(name)
 	defer C.free(unsafe.Pointer(cs))
 	value := C.pam_getenv(t.handle, cs)
@@ -382,7 +390,7 @@ func next(p **C.char) **C.char {
 }
 
 // GetEnvList returns a copy of the PAM environment as a map.
-func (t *Transaction) GetEnvList() (map[string]string, error) {
+func (t *transactionBase) GetEnvList() (map[string]string, error) {
 	env := make(map[string]string)
 	p := C.pam_getenvlist(t.handle)
 	if p == nil {