Fix protobuf encoding size mismatch by passing force parameter in encode_string (#9074)

esphome/components/api/proto.h

@@ -216,7 +216,7 @@ class ProtoWriteBuffer {
     this->buffer_->insert(this->buffer_->end(), data, data + len);
   }
   void encode_string(uint32_t field_id, const std::string &value, bool force = false) {
-    this->encode_string(field_id, value.data(), value.size());
+    this->encode_string(field_id, value.data(), value.size(), force);
   }
   void encode_bytes(uint32_t field_id, const uint8_t *data, size_t len, bool force = false) {
     this->encode_string(field_id, reinterpret_cast<const char *>(data), len, force);

tests/integration/fixtures/host_mode_empty_string_options.yaml

@@ -0,0 +1,58 @@
+esphome:
+  name: host-empty-string-test
+
+host:
+
+api:
+  batch_delay: 50ms
+
+select:
+  - platform: template
+    name: "Select Empty First"
+    id: select_empty_first
+    optimistic: true
+    options:
+      - ""  # Empty string at the beginning
+      - "Option A"
+      - "Option B"
+      - "Option C"
+    initial_option: "Option A"
+
+  - platform: template
+    name: "Select Empty Middle"
+    id: select_empty_middle
+    optimistic: true
+    options:
+      - "Option 1"
+      - "Option 2"
+      - ""  # Empty string in the middle
+      - "Option 3"
+      - "Option 4"
+    initial_option: "Option 1"
+
+  - platform: template
+    name: "Select Empty Last"
+    id: select_empty_last
+    optimistic: true
+    options:
+      - "Choice X"
+      - "Choice Y"
+      - "Choice Z"
+      - ""  # Empty string at the end
+    initial_option: "Choice X"
+
+# Add a sensor to ensure we have other entities in the list
+sensor:
+  - platform: template
+    name: "Test Sensor"
+    id: test_sensor
+    lambda: |-
+      return 42.0;
+    update_interval: 60s
+
+binary_sensor:
+  - platform: template
+    name: "Test Binary Sensor"
+    id: test_binary_sensor
+    lambda: |-
+      return true;

tests/integration/test_host_mode_empty_string_options.py

@@ -0,0 +1,110 @@
+"""Integration test for protobuf encoding of empty string options in select entities."""
+
+from __future__ import annotations
+
+import asyncio
+
+from aioesphomeapi import EntityState, SelectInfo
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_host_mode_empty_string_options(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test that select entities with empty string options are correctly encoded in protobuf messages.
+
+    This tests the fix for the bug where the force parameter was not passed in encode_string,
+    causing empty strings in repeated fields to be skipped during encoding but included in
+    size calculation, leading to protobuf decoding errors.
+    """
+    # Write, compile and run the ESPHome device, then connect to API
+    loop = asyncio.get_running_loop()
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        # Verify we can get device info
+        device_info = await client.device_info()
+        assert device_info is not None
+        assert device_info.name == "host-empty-string-test"
+
+        # Get list of entities - this will encode ListEntitiesSelectResponse messages
+        # with empty string options that would trigger the bug
+        entity_info, services = await client.list_entities_services()
+
+        # Find our select entities
+        select_entities = [e for e in entity_info if isinstance(e, SelectInfo)]
+        assert len(select_entities) == 3, (
+            f"Expected 3 select entities, got {len(select_entities)}"
+        )
+
+        # Verify each select entity by name and check their options
+        selects_by_name = {e.name: e for e in select_entities}
+
+        # Check "Select Empty First" - empty string at beginning
+        assert "Select Empty First" in selects_by_name
+        empty_first = selects_by_name["Select Empty First"]
+        assert len(empty_first.options) == 4
+        assert empty_first.options[0] == ""  # Empty string at beginning
+        assert empty_first.options[1] == "Option A"
+        assert empty_first.options[2] == "Option B"
+        assert empty_first.options[3] == "Option C"
+
+        # Check "Select Empty Middle" - empty string in middle
+        assert "Select Empty Middle" in selects_by_name
+        empty_middle = selects_by_name["Select Empty Middle"]
+        assert len(empty_middle.options) == 5
+        assert empty_middle.options[0] == "Option 1"
+        assert empty_middle.options[1] == "Option 2"
+        assert empty_middle.options[2] == ""  # Empty string in middle
+        assert empty_middle.options[3] == "Option 3"
+        assert empty_middle.options[4] == "Option 4"
+
+        # Check "Select Empty Last" - empty string at end
+        assert "Select Empty Last" in selects_by_name
+        empty_last = selects_by_name["Select Empty Last"]
+        assert len(empty_last.options) == 4
+        assert empty_last.options[0] == "Choice X"
+        assert empty_last.options[1] == "Choice Y"
+        assert empty_last.options[2] == "Choice Z"
+        assert empty_last.options[3] == ""  # Empty string at end
+
+        # If we got here without protobuf decoding errors, the fix is working
+        # The bug would have caused "Invalid protobuf message" errors with trailing bytes
+
+        # Also verify we can interact with the select entities
+        # Subscribe to state changes
+        states: dict[int, EntityState] = {}
+        state_change_future: asyncio.Future[None] = loop.create_future()
+
+        def on_state(state: EntityState) -> None:
+            """Track state changes."""
+            states[state.key] = state
+            # When we receive the state change for our select, resolve the future
+            if state.key == empty_first.key and not state_change_future.done():
+                state_change_future.set_result(None)
+
+        client.subscribe_states(on_state)
+
+        # Try setting a select to an empty string option
+        # This further tests that empty strings are handled correctly
+        client.select_command(empty_first.key, "")
+
+        # Wait for state update with timeout
+        try:
+            await asyncio.wait_for(state_change_future, timeout=5.0)
+        except asyncio.TimeoutError:
+            pytest.fail(
+                "Did not receive state update after setting select to empty string"
+            )
+
+        # Verify the state was set to empty string
+        assert empty_first.key in states
+        select_state = states[empty_first.key]
+        assert hasattr(select_state, "state")
+        assert select_state.state == ""
+
+        # The test passes if no protobuf decoding errors occurred
+        # With the bug, we would have gotten "Invalid protobuf message" errors