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-mock.go

@@ -6,6 +6,7 @@ package pam
 #cgo CFLAGS: -Wall -std=c99
 #include <stdint.h>
 #include <stdlib.h>
+#include <security/pam_modules.h>
 */
 import "C"
 
@@ -19,6 +20,7 @@ import (
 
 type mockModuleTransactionExpectations struct {
 	UserPrompt string
+	DataKey    string
 }
 
 type mockModuleTransactionReturnedData struct {
@@ -33,14 +35,19 @@ type mockModuleTransaction struct {
 	Expectations        mockModuleTransactionExpectations
 	RetData             mockModuleTransactionReturnedData
 	ConversationHandler ConversationHandler
+	moduleData          map[string]uintptr
 	allocatedData       []unsafe.Pointer
 }
 
 func newMockModuleTransaction(m *mockModuleTransaction) *mockModuleTransaction {
+	m.moduleData = make(map[string]uintptr)
 	runtime.SetFinalizer(m, func(m *mockModuleTransaction) {
 		for _, ptr := range m.allocatedData {
 			C.free(ptr)
 		}
+		for _, handle := range m.moduleData {
+			_go_pam_data_cleanup(nil, C.uintptr_t(handle), C.PAM_DATA_SILENT)
+		}
 	})
 	return m
 }
@@ -76,6 +83,33 @@ func (m *mockModuleTransaction) getUser(outUser **C.char, prompt *C.char) C.int
 	return C.int(m.RetData.Status)
 }
 
+func (m *mockModuleTransaction) getData(key *C.char, outHandle *C.uintptr_t) C.int {
+	goKey := C.GoString(key)
+	if m.Expectations.DataKey != "" && goKey != m.Expectations.DataKey {
+		m.T.Fatalf("data key mismatch: %#v vs %#v", goKey, m.Expectations.DataKey)
+	}
+	if handle, ok := m.moduleData[goKey]; ok {
+		*outHandle = C.uintptr_t(handle)
+	} else {
+		*outHandle = 0
+	}
+	return C.int(m.RetData.Status)
+}
+
+func (m *mockModuleTransaction) setData(key *C.char, handle C.uintptr_t) C.int {
+	goKey := C.GoString(key)
+	if m.Expectations.DataKey != "" && goKey != m.Expectations.DataKey {
+		m.T.Fatalf("data key mismatch: %#v vs %#v", goKey, m.Expectations.DataKey)
+	}
+	if oldHandle, ok := m.moduleData[goKey]; ok {
+		_go_pam_data_cleanup(nil, C.uintptr_t(oldHandle), C.PAM_DATA_REPLACE)
+	}
+	if handle != 0 {
+		m.moduleData[goKey] = uintptr(handle)
+	}
+	return C.int(m.RetData.Status)
+}
+
 type mockConversationHandler struct {
 	User              string
 	ExpectedMessage   string