pam/gdm: Support conversations using JSON data sent to PAM via gdm bi…

…nary protocol

Add an utility function to perform GDM-PAM binary conversations using
the custom JSON protocol.

This function does not much per se, but it allows us to do some proper
testing via the dummy module transaction and so we can test how this
data is passed back and forth the two sides, and stress the C <-> go
structures conversions.

pam/gdm/conversation.go

@@ -0,0 +1,28 @@
+package gdm
+
+import "C"
+
+import (
+	"errors"
+
+	"github.com/msteinert/pam"
+)
+
+func sendToGdm(pamMTx pam.ModuleTransaction, data []byte) ([]byte, error) {
+	binReq, err := NewBinaryJSONProtoRequest(data)
+	if err != nil {
+		return nil, err
+	}
+	defer binReq.Release()
+	res, err := pamMTx.StartConv(binReq)
+	if err != nil {
+		return nil, err
+	}
+
+	binRes, ok := res.(pam.BinaryConvResponse)
+	if !ok {
+		return nil, errors.New("returned value is not in binary form")
+	}
+	defer binRes.Release()
+	return binRes.Decode(decodeJSONProtoMessage)
+}

pam/gdm/conversation_test.go

@@ -0,0 +1,107 @@
+package gdm
+
+import (
+	"testing"
+
+	"github.com/msteinert/pam"
+	"github.com/stretchr/testify/require"
+	"github.com/ubuntu/authd/pam/pam_test"
+)
+
+func TestSendToGdm(t *testing.T) {
+	t.Parallel()
+	t.Cleanup(pam_test.MaybeDoLeakCheck)
+
+	testCases := map[string]struct {
+		value []byte
+
+		wantReturn []byte
+		wantError  error
+	}{
+		"JSON null data can be sent and received": {
+			value: []byte(`null`),
+		},
+
+		"JSON number can be sent and received": {
+			value: []byte(`1.5`),
+		},
+
+		"Single char is sent and received as string": {
+			value: []byte(`"m"`),
+		},
+
+		"JSON null is returned": {
+			value:      []byte(`"give me 🚫"`),
+			wantReturn: []byte("null"),
+		},
+
+		"Utf-8 data is sent and returned": {
+			value:      []byte(`"give me 🍕"`),
+			wantReturn: []byte(`"😋"`),
+		},
+
+		// Error cases
+		"Error on empty data": {
+			value:     []byte{},
+			wantError: ErrInvalidJSON,
+		},
+
+		"Error on nil data": {
+			value:     nil,
+			wantError: ErrInvalidJSON,
+		},
+
+		"Error with empty data returned": {
+			value:      []byte(`"give me 🗑‼"`),
+			wantReturn: []byte{},
+			wantError:  ErrInvalidJSON,
+		},
+
+		"Error with nil data returned": {
+			value:      []byte(`"give me 🚫"`),
+			wantReturn: []byte(nil),
+			wantError:  ErrInvalidJSON,
+		},
+	}
+
+	for name, tc := range testCases {
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			t.Cleanup(pam_test.MaybeDoLeakCheck)
+
+			convFuncCalled := true
+			mt := pam_test.NewModuleTransactionDummy(pam.BinaryPointerConversationFunc(
+				func(ptr pam.BinaryPointer) (pam.BinaryPointer, error) {
+					convFuncCalled = true
+					require.NotNil(t, ptr)
+					req, err := decodeJSONProtoMessage(ptr)
+					require.NoError(t, err)
+					require.Equal(t, tc.value, req)
+					if tc.wantReturn != nil {
+						msg, err := newJSONProtoMessage(tc.wantReturn)
+						return pam.BinaryPointer(msg), err
+					}
+					msg, err := newJSONProtoMessage(req)
+					return pam.BinaryPointer(msg), err
+				}))
+
+			data, err := sendToGdm(mt, tc.value)
+			require.True(t, convFuncCalled)
+
+			if tc.wantError != nil {
+				require.Error(t, tc.wantError, err)
+				return
+			}
+
+			require.NoError(t, err)
+
+			if tc.wantReturn != nil {
+				require.Equal(t, tc.wantReturn, data)
+				return
+			}
+
+			require.Equal(t, tc.value, data)
+		})
+	}
+}