feat(python): introduce expect argument to client.call

docs/developers/hello_world_feature_TT.md

@@ -154,7 +154,6 @@ if TYPE_CHECKING:
     from .protobuf import MessageType
 
 
-@expect(messages.HelloWorldResponse, field="text", ret_type=str)
 def say_hello(
     client: "TrezorClient",
     name: str,
@@ -166,8 +165,9 @@ def say_hello(
             name=name,
             amount=amount,
             show_display=show_display,
-        )
+        ),
-    )
+        expect=messages.HelloWorldResponse,
+    ).text
 ```
 
 Code above is sending `HelloWorldRequest` into Trezor and is expecting to get `HelloWorldResponse` back (from which it extracts the `text` string as a response).

python/.changelog.d/4464.added.1

@@ -0,0 +1 @@
+Added an `expect` argument to `TrezorClient.call()`, to enforce the returned message type.

python/src/trezorlib/client.py

@@ -14,6 +14,8 @@
 # You should have received a copy of the License along with this library.
 # If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
 
+from __future__ import annotations
+
 import logging
 import os
 import warnings
@@ -24,14 +26,15 @@ from mnemonic import Mnemonic
 from . import exceptions, mapping, messages, models
 from .log import DUMP_BYTES
 from .messages import Capability
+from .protobuf import MessageType
 from .tools import expect, parse_path, session
 
 if TYPE_CHECKING:
-    from .protobuf import MessageType
     from .transport import Transport
     from .ui import TrezorClientUI
 
 UI = TypeVar("UI", bound="TrezorClientUI")
+MT = TypeVar("MT", bound=MessageType)
 
 LOG = logging.getLogger(__name__)
 
@@ -149,12 +152,12 @@ class TrezorClient(Generic[UI]):
     def cancel(self) -> None:
         self._raw_write(messages.Cancel())
 
-    def call_raw(self, msg: "MessageType") -> "MessageType":
+    def call_raw(self, msg: MessageType) -> MessageType:
         __tracebackhide__ = True  # for pytest # pylint: disable=W0612
         self._raw_write(msg)
         return self._raw_read()
 
-    def _raw_write(self, msg: "MessageType") -> None:
+    def _raw_write(self, msg: MessageType) -> None:
         __tracebackhide__ = True  # for pytest # pylint: disable=W0612
         LOG.debug(
             f"sending message: {msg.__class__.__name__}",
@@ -167,7 +170,7 @@ class TrezorClient(Generic[UI]):
         )
         self.transport.write(msg_type, msg_bytes)
 
-    def _raw_read(self) -> "MessageType":
+    def _raw_read(self) -> MessageType:
         __tracebackhide__ = True  # for pytest # pylint: disable=W0612
         msg_type, msg_bytes = self.transport.read()
         LOG.log(
@@ -181,7 +184,7 @@ class TrezorClient(Generic[UI]):
         )
         return msg
 
-    def _callback_pin(self, msg: messages.PinMatrixRequest) -> "MessageType":
+    def _callback_pin(self, msg: messages.PinMatrixRequest) -> MessageType:
         try:
             pin = self.ui.get_pin(msg.type)
         except exceptions.Cancelled:
@@ -204,12 +207,12 @@ class TrezorClient(Generic[UI]):
         else:
             return resp
 
-    def _callback_passphrase(self, msg: messages.PassphraseRequest) -> "MessageType":
+    def _callback_passphrase(self, msg: messages.PassphraseRequest) -> MessageType:
         available_on_device = Capability.PassphraseEntry in self.features.capabilities
 
         def send_passphrase(
             passphrase: Optional[str] = None, on_device: Optional[bool] = None
-        ) -> "MessageType":
+        ) -> MessageType:
             msg = messages.PassphraseAck(passphrase=passphrase, on_device=on_device)
             resp = self.call_raw(msg)
             if isinstance(resp, messages.Deprecated_PassphraseStateRequest):
@@ -244,7 +247,7 @@ class TrezorClient(Generic[UI]):
 
         return send_passphrase(passphrase, on_device=False)
 
-    def _callback_button(self, msg: messages.ButtonRequest) -> "MessageType":
+    def _callback_button(self, msg: messages.ButtonRequest) -> MessageType:
         __tracebackhide__ = True  # for pytest # pylint: disable=W0612
         # do this raw - send ButtonAck first, notify UI later
         self._raw_write(messages.ButtonAck())
@@ -252,7 +255,7 @@ class TrezorClient(Generic[UI]):
         return self._raw_read()
 
     @session
-    def call(self, msg: "MessageType") -> "MessageType":
+    def call(self, msg: MessageType, expect: type[MT] = MessageType) -> MT:
         self.check_firmware_version()
         resp = self.call_raw(msg)
         while True:
@@ -266,6 +269,8 @@ class TrezorClient(Generic[UI]):
                 if resp.code == messages.FailureType.ActionCancelled:
                     raise exceptions.Cancelled
                 raise exceptions.TrezorFailure(resp)
+            elif not isinstance(resp, expect):
+                raise exceptions.UnexpectedMessageError(expect, resp)
             else:
                 return resp
 
@@ -397,7 +402,7 @@ class TrezorClient(Generic[UI]):
         self,
         msg: str,
         button_protection: bool = False,
-    ) -> "MessageType":
+    ) -> MessageType:
         # We would like ping to work on any valid TrezorClient instance, but
         # due to the protection modes, we need to go through self.call, and that will
         # raise an exception if the firmware is too old.

python/src/trezorlib/exceptions.py

@@ -14,10 +14,13 @@
 # You should have received a copy of the License along with this library.
 # If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
 
+from __future__ import annotations
+
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
     from .messages import Failure
+    from .protobuf import MessageType
 
 
 class TrezorException(Exception):
@@ -25,7 +28,7 @@ class TrezorException(Exception):
 
 
 class TrezorFailure(TrezorException):
-    def __init__(self, failure: "Failure") -> None:
+    def __init__(self, failure: Failure) -> None:
         self.failure = failure
         self.code = failure.code
         self.message = failure.message
@@ -55,3 +58,10 @@ class Cancelled(TrezorException):
 
 class OutdatedFirmwareError(TrezorException):
     pass
+
+
+class UnexpectedMessageError(TrezorException):
+    def __init__(self, expected: type[MessageType], actual: MessageType) -> None:
+        self.expected = expected
+        self.actual = actual
+        super().__init__(f"Expected {expected.__name__} but Trezor sent {actual}")