module-transaction: Add GetUser() method that prompts an user if non-set

We can now finally test this properly both using a mock and through the
interactive module that will do the request for us in various conditions.

module-transaction-mock.go

@@ -0,0 +1,106 @@
+//go:build !go_pam_module
+
+package pam
+
+/*
+#cgo CFLAGS: -Wall -std=c99
+#include <stdint.h>
+#include <stdlib.h>
+*/
+import "C"
+
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"testing"
+	"unsafe"
+)
+
+type mockModuleTransactionExpectations struct {
+	UserPrompt string
+}
+
+type mockModuleTransactionReturnedData struct {
+	User            string
+	InteractiveUser bool
+	Status          Error
+}
+
+type mockModuleTransaction struct {
+	moduleTransaction
+	T                   *testing.T
+	Expectations        mockModuleTransactionExpectations
+	RetData             mockModuleTransactionReturnedData
+	ConversationHandler ConversationHandler
+	allocatedData       []unsafe.Pointer
+}
+
+func newMockModuleTransaction(m *mockModuleTransaction) *mockModuleTransaction {
+	runtime.SetFinalizer(m, func(m *mockModuleTransaction) {
+		for _, ptr := range m.allocatedData {
+			C.free(ptr)
+		}
+	})
+	return m
+}
+
+func (m *mockModuleTransaction) getUser(outUser **C.char, prompt *C.char) C.int {
+	goPrompt := C.GoString(prompt)
+	if goPrompt != m.Expectations.UserPrompt {
+		m.T.Fatalf("unexpected prompt: %s vs %s", goPrompt, m.Expectations.UserPrompt)
+		return C.int(ErrAbort)
+	}
+
+	user := m.RetData.User
+	if m.RetData.InteractiveUser || (m.RetData.User == "" && m.ConversationHandler != nil) {
+		if m.ConversationHandler == nil {
+			m.T.Fatalf("no conversation handler provided")
+		}
+		u, err := m.ConversationHandler.RespondPAM(PromptEchoOn, goPrompt)
+		user = u
+
+		if err != nil {
+			var pamErr Error
+			if errors.As(err, &pamErr) {
+				return C.int(pamErr)
+			}
+			return C.int(ErrAbort)
+		}
+	}
+
+	cUser := C.CString(user)
+	m.allocatedData = append(m.allocatedData, unsafe.Pointer(cUser))
+
+	*outUser = cUser
+	return C.int(m.RetData.Status)
+}
+
+type mockConversationHandler struct {
+	User              string
+	ExpectedMessage   string
+	CheckEmptyMessage bool
+	ExpectedStyle     Style
+	CheckZeroStyle    bool
+}
+
+func (c mockConversationHandler) RespondPAM(s Style, msg string) (string, error) {
+	if (c.ExpectedMessage != "" || c.CheckEmptyMessage) &&
+		msg != c.ExpectedMessage {
+		return "", fmt.Errorf("%w: unexpected prompt: %s vs %s",
+			ErrConv, msg, c.ExpectedMessage)
+	}
+
+	if (c.ExpectedStyle != 0 || c.CheckZeroStyle) &&
+		s != c.ExpectedStyle {
+		return "", fmt.Errorf("%w: unexpected style: %#v vs %#v",
+			ErrConv, s, c.ExpectedStyle)
+	}
+
+	switch s {
+	case PromptEchoOn:
+		return c.User, nil
+	}
+
+	return "", fmt.Errorf("%w: unhandled style: %v", ErrConv, s)
+}