[api] Order the wrong wire type assertions on the raw socket

The barrier was a command on the aioesphomeapi connection, which nothing orders against the
raw frames under test; a well formed frame on the raw socket itself now closes each block and
the assertion checks the exact states seen since the marker.

esphome/components/api/api_connection.h

@@ -345,11 +345,7 @@ class APIConnection final : public APIServerConnectionBase {
   /// Returns false as soon as the TCP buffer is full. Marked nodiscard so we
   /// have no silent failures: every caller must handle (or log) a refusal.
   template<typename T> [[nodiscard]] bool send_message(const T &msg) {
-    if constexpr (T::ESTIMATED_SIZE == 0) {
-      return this->send_message_(0, T::MESSAGE_TYPE, &encode_msg_noop, &msg);
-    } else {
-      return this->send_message_(msg.calculate_size(), T::MESSAGE_TYPE, &proto_encode_msg<T>, &msg);
-    }
+    return this->send_message_(T::calc_size_msg(&msg), T::MESSAGE_TYPE, &T::encode_msg, &msg);
   }
 
   /// Clear the shared write buffer and reserve space for the first message.
@@ -405,16 +401,6 @@ class APIConnection final : public APIServerConnectionBase {
   void process_state_subscriptions_();
 #endif
 
-  // Size thunk — converts void* back to concrete type for direct calculate_size() call
-  template<typename T> static uint32_t calc_size(const void *msg) {
-    return static_cast<const T *>(msg)->calculate_size();
-  }
-
-  // Shared no-op encode thunk for empty messages (ESTIMATED_SIZE == 0)
-  static uint8_t *encode_msg_noop(const void *, ProtoWriteBuffer &buf PROTO_ENCODE_DEBUG_PARAM) {
-    return buf.get_pos();
-  }
-
   // Non-template buffer management for send_message
   bool send_message_(uint32_t payload_size, uint16_t message_type, MessageEncodeFn encode_fn, const void *msg);
 
@@ -433,11 +419,7 @@ class APIConnection final : public APIServerConnectionBase {
   // Hot paths (state/info) go through fill_and_encode_entity_state/info instead.
   // batch_message_type_ is already set by dispatch_message_ before reaching here.
   template<typename T> static uint16_t encode_message_to_buffer(T &msg, APIConnection *conn, uint32_t remaining_size) {
-    if constexpr (T::ESTIMATED_SIZE == 0) {
-      return encode_to_buffer_slow(0, &encode_msg_noop, &msg, conn, remaining_size);
-    } else {
-      return encode_to_buffer_slow(msg.calculate_size(), &proto_encode_msg<T>, &msg, conn, remaining_size);
-    }
+    return encode_to_buffer_slow(T::calc_size_msg(&msg), &T::encode_msg, &msg, conn, remaining_size);
   }
 
   // Non-template core — fills state fields and encodes
@@ -449,7 +431,7 @@ class APIConnection final : public APIServerConnectionBase {
   template<typename T>
   static uint16_t fill_and_encode_entity_state(EntityBase *entity, T &msg, APIConnection *conn,
                                                uint32_t remaining_size) {
-    return fill_and_encode_entity_state(entity, msg, &calc_size<T>, &proto_encode_msg<T>, conn, remaining_size);
+    return fill_and_encode_entity_state(entity, msg, &T::calc_size_msg, &T::encode_msg, conn, remaining_size);
   }
 
   // Non-template core — fills info fields, allocates buffers, and encodes
@@ -461,7 +443,7 @@ class APIConnection final : public APIServerConnectionBase {
   template<typename T>
   static uint16_t fill_and_encode_entity_info(EntityBase *entity, T &msg, APIConnection *conn,
                                               uint32_t remaining_size) {
-    return fill_and_encode_entity_info(entity, msg, &calc_size<T>, &proto_encode_msg<T>, conn, remaining_size);
+    return fill_and_encode_entity_info(entity, msg, &T::calc_size_msg, &T::encode_msg, conn, remaining_size);
   }
 
   // Non-template core — fills device_class, then delegates to fill_and_encode_entity_info
@@ -475,8 +457,8 @@ class APIConnection final : public APIServerConnectionBase {
   static uint16_t fill_and_encode_entity_info_with_device_class(EntityBase *entity, T &msg,
                                                                 StringRef &device_class_field, APIConnection *conn,
                                                                 uint32_t remaining_size) {
-    return fill_and_encode_entity_info_with_device_class(entity, msg, device_class_field, &calc_size<T>,
-                                                         &proto_encode_msg<T>, conn, remaining_size);
+    return fill_and_encode_entity_info_with_device_class(entity, msg, device_class_field, &T::calc_size_msg,
+                                                         &T::encode_msg, conn, remaining_size);
   }
 
 #ifdef USE_VOICE_ASSISTANT

esphome/components/api/proto.cpp

@@ -214,73 +214,74 @@ void ProtoDecodableMessage::decode(const uint8_t *buffer, size_t length) {
   const uint8_t *ptr = buffer;
   const uint8_t *end = buffer + length;
 
-  while (ptr < end) {
-    // Parse field header - ptr < end guarantees len >= 1
+  // Single-byte varints dominate, so that case advances the cursor inline.
+  auto read_varint = [&](proto_varint_value_t &value) ESPHOME_ALWAYS_INLINE {
+    if (ptr == end)
+      return false;
+    if (*ptr < 0x80) [[likely]] {
+      value = *ptr++;
+      return true;
+    }
     auto res = ProtoVarInt::parse_non_empty(ptr, end - ptr);
-    if (!res.has_value()) {
+    if (!res.has_value())
+      return false;
+    value = res.value;
+    ptr += res.consumed;
+    return true;
+  };
+
+  while (ptr < end) {
+    proto_varint_value_t tag_value;
+    if (!read_varint(tag_value)) {
       ESP_LOGV(TAG, "Invalid field start at offset %ld", (long) (ptr - buffer));
       return;
     }
 
-    uint32_t tag = static_cast<uint32_t>(res.value);
+    uint32_t tag = static_cast<uint32_t>(tag_value);
     uint32_t field_type = tag & WIRE_TYPE_MASK;
-    uint32_t field_id = tag >> 3;
-    ptr += res.consumed;
+    // Length-delimited fields move this past the length prefix
+    const uint8_t *data = ptr;
+    proto_varint_value_t scalar;
 
-    switch (field_type) {
-      case WIRE_TYPE_VARINT: {  // VarInt
-        res = ProtoVarInt::parse(ptr, end - ptr);
-        if (!res.has_value()) {
-          ESP_LOGV(TAG, "Invalid VarInt at offset %ld", (long) (ptr - buffer));
-          return;
-        }
-        if (!this->decode_varint(field_id, res.value)) {
-          ESP_LOGV(TAG, "Cannot decode VarInt field %" PRIu32 " with value %" PRIu64 "!", field_id,
-                   static_cast<uint64_t>(res.value));
-        }
-        ptr += res.consumed;
-        break;
-      }
-      case WIRE_TYPE_LENGTH_DELIMITED: {  // Length-delimited
-        res = ProtoVarInt::parse(ptr, end - ptr);
-        if (!res.has_value()) {
-          ESP_LOGV(TAG, "Invalid Length Delimited at offset %ld", (long) (ptr - buffer));
-          return;
-        }
-        uint32_t field_length = static_cast<uint32_t>(res.value);
-        ptr += res.consumed;
-        if (field_length > static_cast<size_t>(end - ptr)) {
-          ESP_LOGV(TAG, "Out-of-bounds Length Delimited at offset %ld", (long) (ptr - buffer));
-          return;
-        }
-        if (!this->decode_length(field_id, ProtoLengthDelimited(ptr, field_length))) {
-          ESP_LOGV(TAG, "Cannot decode Length Delimited field %" PRIu32 "!", field_id);
-        }
-        ptr += field_length;
-        break;
-      }
-      case WIRE_TYPE_FIXED32: {  // 32-bit
-        if (end - ptr < 4) {
-          ESP_LOGV(TAG, "Out-of-bounds Fixed32-bit at offset %ld", (long) (ptr - buffer));
-          return;
-        }
-        uint32_t val;
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-        // Protobuf fixed32 is little-endian — direct load on LE platforms
-        memcpy(&val, ptr, 4);
-#else
-        val = encode_uint32(ptr[3], ptr[2], ptr[1], ptr[0]);
-#endif
-        if (!this->decode_32bit(field_id, Proto32Bit(val))) {
-          ESP_LOGV(TAG, "Cannot decode 32-bit field %" PRIu32 " with value %" PRIu32 "!", field_id, val);
-        }
-        ptr += 4;
-        break;
-      }
-      default:
-        ESP_LOGV(TAG, "Invalid field type %" PRIu32 " at offset %ld", field_type, (long) (ptr - buffer));
+    if (field_type == WIRE_TYPE_VARINT) [[likely]] {
+      if (!read_varint(scalar)) {
+        ESP_LOGV(TAG, "Invalid VarInt at offset %ld", (long) (ptr - buffer));
         return;
+      }
+    } else {
+      switch (field_type) {
+        case WIRE_TYPE_LENGTH_DELIMITED: {
+          proto_varint_value_t length_value;
+          if (!read_varint(length_value)) {
+            ESP_LOGV(TAG, "Invalid Length Delimited at offset %ld", (long) (ptr - buffer));
+            return;
+          }
+          uint32_t field_length = static_cast<uint32_t>(length_value);
+          if (field_length > static_cast<size_t>(end - ptr)) {
+            ESP_LOGV(TAG, "Out-of-bounds Length Delimited at offset %ld", (long) (ptr - buffer));
+            return;
+          }
+          data = ptr;
+          scalar = field_length;
+          ptr += field_length;
+          break;
+        }
+        case WIRE_TYPE_FIXED32: {
+          if (end - ptr < 4) {
+            ESP_LOGV(TAG, "Out-of-bounds Fixed32-bit at offset %ld", (long) (ptr - buffer));
+            return;
+          }
+          // Byte loads instead of memcpy: ESP-IDF passes -fno-builtin-memcpy, which made this a call
+          scalar = encode_uint32(ptr[3], ptr[2], ptr[1], ptr[0]);
+          ptr += 4;
+          break;
+        }
+        default:
+          ESP_LOGV(TAG, "Invalid field type %" PRIu32 " at offset %ld", field_type, (long) (ptr - buffer));
+          return;
+      }
     }
+    this->decode_field(tag, data, scalar);
   }
 }
 

esphome/components/api/proto.h

@@ -170,40 +170,43 @@ class ProtoVarInt {
 class ProtoMessage;
 class ProtoSize;
 
-class ProtoLengthDelimited {
+/// Case label for decode_field(): the wire tag of a field, so a field that arrives with another wire
+/// type matches no case.
+constexpr uint32_t proto_tag(uint32_t field_id, uint32_t wire_type) { return (field_id << 3) | wire_type; }
+
+/// One decoded field: the payload pointer and a scalar holding the varint or fixed32 value, or the
+/// length of a length-delimited field. The wire type in the tag says which applies; accessors do not check.
+class ProtoFieldValue {
  public:
-  explicit ProtoLengthDelimited(const uint8_t *value, size_t length) : value_(value), length_(length) {}
-  std::string as_string() const { return std::string(reinterpret_cast<const char *>(this->value_), this->length_); }
+  ProtoFieldValue(const uint8_t *data, proto_varint_value_t scalar) : data_(data), scalar_(scalar) {}
 
-  // Direct access to raw data without string allocation
-  const uint8_t *data() const { return this->value_; }
-  size_t size() const { return this->length_; }
+  proto_varint_value_t as_varint() const { return this->scalar_; }
+  // A bool is sent as 0 or 1, so the low word is enough and saves a second compare with 64 bit varints
+  bool as_bool() const { return static_cast<uint32_t>(this->scalar_) != 0; }
 
-  /// Decode the length-delimited data into a message instance.
+  // Length-delimited accessors
+  const uint8_t *data() const { return this->data_; }
+  size_t size() const { return static_cast<size_t>(this->scalar_); }
+  std::string as_string() const { return std::string(reinterpret_cast<const char *>(this->data_), this->size()); }
+  /// Decode the length-delimited payload into a message instance.
   /// Template preserves concrete type so decode() resolves statically.
-  template<typename T> void decode_to_message(T &msg) const;
+  template<typename T> void decode_to_message(T &msg) const { msg.decode(this->data_, this->size()); }
 
- protected:
-  const uint8_t *const value_;
-  const size_t length_;
-};
-
-class Proto32Bit {
- public:
-  explicit Proto32Bit(uint32_t value) : value_(value) {}
-  uint32_t as_fixed32() const { return this->value_; }
-  int32_t as_sfixed32() const { return static_cast<int32_t>(this->value_); }
+  // Fixed32 accessors
+  uint32_t as_fixed32() const { return static_cast<uint32_t>(this->scalar_); }
+  int32_t as_sfixed32() const { return static_cast<int32_t>(this->as_fixed32()); }
   float as_float() const {
     union {
       uint32_t raw;
       float value;
     } s{};
-    s.raw = this->value_;
+    s.raw = this->as_fixed32();
     return s.value;
   }
 
- protected:
-  const uint32_t value_;
+ private:
+  const uint8_t *data_;
+  proto_varint_value_t scalar_;
 };
 
 // NOTE: Proto64Bit class removed - wire type 1 (64-bit fixed) not supported
@@ -252,7 +255,7 @@ class ProtoWriteBuffer {
    *
    * Following https://protobuf.dev/programming-guides/encoding/#structure
    */
-  void encode_field_raw(uint32_t field_id, uint32_t type) { this->encode_varint_raw((field_id << 3) | type); }
+  void encode_field_raw(uint32_t field_id, uint32_t type) { this->encode_varint_raw(proto_tag(field_id, type)); }
   /// Single-pass encode for repeated submessage elements.
   /// Thin template wrapper; all buffer work is in the non-template core.
   template<typename T> void encode_sub_message(uint32_t field_id, const T &value);
@@ -382,7 +385,7 @@ class ProtoEncode {
   }
   [[nodiscard]] static inline uint8_t *ESPHOME_ALWAYS_INLINE
   encode_field_raw(uint8_t *__restrict__ pos PROTO_ENCODE_DEBUG_PARAM, uint32_t field_id, uint32_t type) {
-    return encode_varint_raw(pos PROTO_ENCODE_DEBUG_ARG, (field_id << 3) | type);
+    return encode_varint_raw(pos PROTO_ENCODE_DEBUG_ARG, proto_tag(field_id, type));
   }
   /// Write a single precomputed tag byte. Tag must be < 128.
   [[nodiscard]] static inline uint8_t *ESPHOME_ALWAYS_INLINE
@@ -692,11 +695,12 @@ class DumpBuffer {
 
 class ProtoMessage {
  public:
-  // Non-virtual defaults for messages with no fields.
-  // Concrete message classes hide these with their own implementations.
-  // All call sites use templates to preserve the concrete type, so virtual
-  // dispatch is not needed. This eliminates per-message vtable entries for
-  // encode/calculate_size, saving ~1.3 KB of flash across all message types.
+  // Non-virtual defaults for messages with no fields; generated classes hide all four. The
+  // static encode_msg/calc_size_msg take const void * so &T::encode_msg needs no thunk.
+  static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) {
+    return buffer.get_pos();
+  }
+  static uint32_t calc_size_msg(const void *self) { return 0; }
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const { return buffer.get_pos(); }
   uint32_t calculate_size() const { return 0; }
 #ifdef HAS_PROTO_MESSAGE_DUMP
@@ -731,10 +735,10 @@ class ProtoDecodableMessage : public ProtoMessage {
 
  protected:
   ~ProtoDecodableMessage() = default;
-  virtual bool decode_varint(uint32_t field_id, proto_varint_value_t value) { return false; }
-  virtual bool decode_length(uint32_t field_id, ProtoLengthDelimited value) { return false; }
-  virtual bool decode_32bit(uint32_t field_id, Proto32Bit value) { return false; }
-  // NOTE: decode_64bit removed - wire type 1 not supported
+  /// Store one decoded field; \p scalar is the varint or fixed32 value, or the length of the
+  /// length-delimited payload at \p data. An unknown field or wrong wire type matches no case and is skipped.
+  /// Three register arguments keep the decode loop free of spills.
+  virtual void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {}
 };
 
 class ProtoSize {
@@ -860,7 +864,7 @@ class ProtoSize {
    * @return The number of bytes needed to encode the field ID and wire type
    */
   static constexpr uint32_t field(uint32_t field_id, uint32_t type) {
-    uint32_t tag = (field_id << 3) | (type & WIRE_TYPE_MASK);
+    uint32_t tag = proto_tag(field_id, type & WIRE_TYPE_MASK);
     return varint(tag);
   }
 
@@ -944,24 +948,14 @@ class ProtoSize {
 
 // Implementation of methods that depend on ProtoSize being fully defined
 
-// Encode thunk — converts void* back to concrete type for direct encode() call
-template<typename T> uint8_t *proto_encode_msg(const void *msg, ProtoWriteBuffer &buf PROTO_ENCODE_DEBUG_PARAM) {
-  return static_cast<const T *>(msg)->encode(buf PROTO_ENCODE_DEBUG_ARG);
-}
-
 // Thin template wrapper; delegates to non-template core in proto.cpp.
 template<typename T> inline void ProtoWriteBuffer::encode_sub_message(uint32_t field_id, const T &value) {
-  this->encode_sub_message(field_id, &value, &proto_encode_msg<T>);
+  this->encode_sub_message(field_id, &value, &T::encode_msg);
 }
 
 // Thin template wrapper; delegates to non-template core.
 template<typename T> inline void ProtoWriteBuffer::encode_optional_sub_message(uint32_t field_id, const T &value) {
-  this->encode_optional_sub_message(field_id, value.calculate_size(), &value, &proto_encode_msg<T>);
-}
-
-// Template decode_to_message - preserves concrete type so decode() resolves statically
-template<typename T> void ProtoLengthDelimited::decode_to_message(T &msg) const {
-  msg.decode(this->value_, this->length_);
+  this->encode_optional_sub_message(field_id, T::calc_size_msg(&value), &value, &T::encode_msg);
 }
 
 template<typename T> const char *proto_enum_to_string(T value);

script/api_protobuf/api_protobuf.py

@@ -28,6 +28,11 @@ class WireType(IntEnum):
     END_GROUP = 4  # groups (deprecated)
     FIXED32 = 5  # fixed32, sfixed32, float
 
+    @property
+    def cpp_name(self) -> str:
+        """The matching constant in proto.h."""
+        return f"WIRE_TYPE_{self.name}"
+
 
 # Generate with
 # protoc --python_out=script/api_protobuf -I esphome/components/api/ api_options.proto
@@ -126,11 +131,6 @@ def camel_to_snake(name: str) -> str:
     return re.sub("([a-z0-9])([A-Z])", r"\1_\2", s1).lower()
 
 
-def force_str(force: bool) -> str:
-    """Convert a boolean force value to string format for C++ code."""
-    return str(force).lower()
-
-
 def _encode_call(func: str, *args: str, force: bool = False) -> str:
     """Emit one ProtoEncode call; every helper takes the cursor and returns it advanced."""
     suffix = "_force" if force else ""
@@ -229,41 +229,23 @@ class TypeInfo(ABC):
     def class_member(self) -> str:
         return f"{self.cpp_type} {self.field_name}{{{self.default_value}}};"
 
-    @property
-    def decode_varint_content(self) -> str:
-        content = self.decode_varint
-        if content is None:
-            return None
-        return f"case {self.number}: this->{self.field_name} = {content}; break;"
+    def decode_case(self, body: str) -> str:
+        """Emit one decode_field() case, keyed on the field's wire tag."""
+        return f"case proto_tag({self.number}, {self.wire_type.cpp_name}):\n" + indent(
+            f"{body}\nbreak;"
+        )
 
-    decode_varint = None
+    # Expression that reads this field from `value`; None when the type is never decoded.
+    decode_expr: str | None = None
+
+    def _decode_store(self, expr: str) -> str:
+        return f"this->{self.field_name} = {expr};"
 
     @property
-    def decode_length_content(self) -> str:
-        content = self.decode_length
-        if content is None:
-            return None
-        return f"case {self.number}: this->{self.field_name} = {content}; break;"
-
-    decode_length = None
-
-    @property
-    def decode_32bit_content(self) -> str:
-        content = self.decode_32bit
-        if content is None:
-            return None
-        return f"case {self.number}: this->{self.field_name} = {content}; break;"
-
-    decode_32bit = None
-
-    @property
-    def decode_64bit_content(self) -> str:
-        content = self.decode_64bit
-        if content is None:
-            return None
-        return f"case {self.number}: this->{self.field_name} = {content}; break;"
-
-    decode_64bit = None
+    def decode_content(self) -> str | None:
+        """The decode_field() case for this field, or None when it is never decoded."""
+        expr = self.decode_expr
+        return None if expr is None else self.decode_case(self._decode_store(expr))
 
     # Mapping from encode_func to raw encode expression template.
     # When a forced field has a single-byte tag, the code generator emits
@@ -339,11 +321,12 @@ class TypeInfo(ABC):
             )
         )
 
-    def _encode_fixed32_with_precomputed_tag(self, value_expr: str) -> str | None:
-        """Single-byte tag fixed32 write, or None for multi-byte tags."""
+    def _encode_fixed32_with_precomputed_tag(self, value: str) -> str | None:
+        """Single-byte tag fixed32 write, or None for other types and multi-byte tags."""
         tag = self.calculate_tag()
-        if tag >= 128:
+        if self.fixed32_value_template is None or tag >= 128:
             return None
+        value_expr = self.fixed32_value_template.format(value=value)
         if self.force:
             return _encode_call("write_tag_and_fixed32", str(tag), value_expr)
         return (
@@ -357,14 +340,14 @@ class TypeInfo(ABC):
         value = f"this->{self.field_name}"
         if result := self._encode_with_precomputed_tag(value):
             return result
-        if self.fixed32_value_template is not None and (
-            result := self._encode_fixed32_with_precomputed_tag(
-                self.fixed32_value_template.format(value=value)
-            )
-        ):
+        if result := self._encode_fixed32_with_precomputed_tag(value):
             return result
         return _encode_call(self.encode_func, str(self.number), value, force=self.force)
 
+    def encode_element(self, number: int, element: str) -> str:
+        """Encode one element of a repeated field; elements are always written."""
+        return _encode_call(self.encode_func, str(number), element, force=True)
+
     encode_func = None
 
     @classmethod
@@ -638,7 +621,6 @@ class DoubleType(FixedSizeTypeMixin, TypeInfo):
     # Unsupported but defined for completeness
     cpp_type = "double"
     default_value = "0.0"
-    decode_64bit = "value.as_double()"
     encode_func = "encode_double"
     wire_type = WireType.FIXED64  # Uses wire type 1 according to protobuf spec
 
@@ -664,7 +646,7 @@ class DoubleType(FixedSizeTypeMixin, TypeInfo):
 class FloatType(FixedSizeTypeMixin, TypeInfo):
     cpp_type = "float"
     default_value = "0.0f"
-    decode_32bit = "value.as_float()"
+    decode_expr = "value.as_float()"
     encode_func = "encode_float"
     wire_type = WireType.FIXED32  # Uses wire type 5
 
@@ -693,7 +675,7 @@ class Int64Type(VarintTypeMixin, TypeInfo):
     cpp_type = "int64_t"
     _varint_max_bits = 64
     default_value = "0"
-    decode_varint = "static_cast<int64_t>(value)"
+    decode_expr = "static_cast<int64_t>(value.as_varint())"
     encode_func = "encode_int64"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -714,7 +696,7 @@ class UInt64Type(VarintTypeMixin, TypeInfo):
     cpp_type = "uint64_t"
     _varint_max_bits = 64
     default_value = "0"
-    decode_varint = "value"
+    decode_expr = "value.as_varint()"
     encode_func = "encode_uint64"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -749,7 +731,7 @@ class Int32Type(VarintTypeMixin, TypeInfo):
     cpp_type = "int32_t"
     _varint_max_bits = 64  # int32 is sign-extended to 64 bits in protobuf
     default_value = "0"
-    decode_varint = "static_cast<int32_t>(value)"
+    decode_expr = "static_cast<int32_t>(value.as_varint())"
     encode_func = "encode_int32"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -769,7 +751,6 @@ class Int32Type(VarintTypeMixin, TypeInfo):
 class Fixed64Type(FixedSizeTypeMixin, TypeInfo):
     cpp_type = "uint64_t"
     default_value = "0"
-    decode_64bit = "value.as_fixed64()"
     encode_func = "encode_fixed64"
     wire_type = WireType.FIXED64  # Uses wire type 1
 
@@ -795,7 +776,7 @@ class Fixed64Type(FixedSizeTypeMixin, TypeInfo):
 class Fixed32Type(FixedSizeTypeMixin, TypeInfo):
     cpp_type = "uint32_t"
     default_value = "0"
-    decode_32bit = "value.as_fixed32()"
+    decode_expr = "value.as_fixed32()"
     encode_func = "encode_fixed32"
     wire_type = WireType.FIXED32  # Uses wire type 5
 
@@ -824,7 +805,7 @@ class BoolType(VarintTypeMixin, TypeInfo):
     _varint_max_bits = 1
     cpp_type = "bool"
     default_value = "false"
-    decode_varint = "value != 0"
+    decode_expr = "value.as_bool()"
     encode_func = "encode_bool"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -844,7 +825,7 @@ class StringType(TypeInfo):
     default_value = ""
     reference_type = "std::string &"
     const_reference_type = "const std::string &"
-    decode_length = "value.as_string()"
+    decode_expr = "value.as_string()"
     encode_func = "encode_string"
     wire_type = WireType.LENGTH_DELIMITED  # Uses wire type 2
 
@@ -959,6 +940,9 @@ class MessageType(TypeInfo):
     def can_use_dump_field(cls) -> bool:
         return False
 
+    def encode_element(self, number: int, element: str) -> str:
+        return _encode_call("encode_sub_message", "buffer", str(number), element)
+
     @property
     def cpp_type(self) -> str:
         return self._field.type_name[1:]
@@ -985,14 +969,6 @@ class MessageType(TypeInfo):
             self.encode_func, "buffer", str(self.number), f"this->{self.field_name}"
         )
 
-    @property
-    def decode_length(self) -> str:
-        # Override to return None for message types because we can't use template-based
-        # decoding when the specific message type isn't known at compile time.
-        # Instead, we use the non-template decode_to_message() method which allows
-        # runtime polymorphism through virtual function calls.
-        return None
-
     @property
     def public_content(self) -> list[str]:
         content = [self.class_member]
@@ -1008,19 +984,14 @@ class MessageType(TypeInfo):
         )
 
     @property
-    def decode_length_content(self) -> str:
-        # Custom decode that doesn't use templates
+    def decode_content(self) -> str:
+        body = f"value.decode_to_message(this->{self.field_name});"
         if self._track_presence:
             # decode_to_message() cannot report failure, so setting the flag
             # afterwards only documents intent; a status-returning decode could
             # gate it for real without touching callers.
-            return (
-                f"case {self.number}:\n"
-                f"      value.decode_to_message(this->{self.field_name});\n"
-                f"      this->has_{self.name} = true;\n"
-                f"      break;"
-            )
-        return f"case {self.number}: value.decode_to_message(this->{self.field_name}); break;"
+            body += f"\nthis->has_{self.name} = true;"
+        return self.decode_case(body)
 
     def dump(self, name: str) -> str:
         return f"{name}.dump_to(out);"
@@ -1059,7 +1030,7 @@ class BytesType(TypeInfo):
     reference_type = "std::string &"
     const_reference_type = "const std::string &"
     encode_func = "encode_bytes"
-    decode_length = "value.as_string()"
+    decode_expr = "value.as_string()"
     wire_type = WireType.LENGTH_DELIMITED  # Uses wire type 2
 
     @property
@@ -1169,11 +1140,6 @@ class PointerToBufferTypeBase(TypeInfo):
         super().__init__(field)
         self.array_size = 0
 
-    @property
-    def decode_length(self) -> str | None:
-        # This is handled in decode_length_content
-        return None
-
     @property
     def wire_type(self) -> WireType:
         """Get the wire type for this field."""
@@ -1215,12 +1181,11 @@ class PointerToBytesBufferType(PointerToBufferTypeBase):
         )
 
     @property
-    def decode_length_content(self) -> str | None:
-        return f"""case {self.number}: {{
-      this->{self.field_name} = value.data();
-      this->{self.field_name}_len = value.size();
-      break;
-    }}"""
+    def decode_content(self) -> str:
+        return self.decode_case(
+            f"this->{self.field_name} = value.data();\n"
+            f"this->{self.field_name}_len = value.size();",
+        )
 
     def dump(self, name: str) -> str:
         return (
@@ -1280,11 +1245,10 @@ class PointerToStringBufferType(PointerToBufferTypeBase):
         )
 
     @property
-    def decode_length_content(self) -> str | None:
-        return f"""case {self.number}: {{
-      this->{self.field_name} = StringRef(reinterpret_cast<const char *>(value.data()), value.size());
-      break;
-    }}"""
+    def decode_content(self) -> str:
+        return self.decode_case(
+            f"this->{self.field_name} = StringRef(value.data(), value.size());",
+        )
 
     def dump(self, name: str) -> str:
         # Not used since we use dump_field, but required by abstract base class
@@ -1353,14 +1317,13 @@ class PackedBufferTypeInfo(TypeInfo):
         ]
 
     @property
-    def decode_length_content(self) -> str:
+    def decode_content(self) -> str:
         """Store pointer to buffer and calculate count of packed varints."""
-        return f"""case {self.number}: {{
-      this->{self.field_name}_data_ = value.data();
-      this->{self.field_name}_length_ = value.size();
-      this->{self.field_name}_count_ = count_packed_varints(value.data(), value.size());
-      break;
-    }}"""
+        return self.decode_case(
+            f"this->{self.field_name}_data_ = value.data();\n"
+            f"this->{self.field_name}_length_ = value.size();\n"
+            f"this->{self.field_name}_count_ = count_packed_varints(value.data(), value.size());",
+        )
 
     @property
     def encode_content(self) -> str:
@@ -1445,17 +1408,11 @@ class FixedArrayBytesType(TypeInfo):
         ]
 
     @property
-    def decode_length_content(self) -> str:
-        o = f"case {self.number}: {{\n"
-        o += "  const std::string &data_str = value.as_string();\n"
-        o += f"  this->{self.field_name}_len = data_str.size();\n"
-        o += f"  if (this->{self.field_name}_len > {self.array_size}) {{\n"
-        o += f"    this->{self.field_name}_len = {self.array_size};\n"
-        o += "  }\n"
-        o += f"  memcpy(this->{self.field_name}, data_str.data(), this->{self.field_name}_len);\n"
-        o += "  break;\n"
-        o += "}"
-        return o
+    def decode_content(self) -> str:
+        return self.decode_case(
+            f"this->{self.field_name}_len = std::min<size_t>(value.size(), {self.array_size});\n"
+            f"memcpy(this->{self.field_name}, value.data(), this->{self.field_name}_len);",
+        )
 
     @property
     def encode_content(self) -> str:
@@ -1518,7 +1475,7 @@ class UInt32Type(VarintTypeMixin, TypeInfo):
     cpp_type = "uint32_t"
     _varint_max_bits = 32
     default_value = "0"
-    decode_varint = "value"
+    decode_expr = "value.as_varint()"
     encode_func = "encode_uint32"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -1541,13 +1498,21 @@ class UInt32Type(VarintTypeMixin, TypeInfo):
 class EnumType(VarintTypeMixin, TypeInfo):
     _varint_max_bits = 32
 
+    def encode_element(self, number: int, element: str) -> str:
+        return _encode_call(
+            self.encode_func,
+            str(number),
+            f"static_cast<uint32_t>({element})",
+            force=True,
+        )
+
     @property
     def cpp_type(self) -> str:
         return f"enums::{self._field.type_name[1:]}"
 
     @property
-    def decode_varint(self) -> str:
-        return f"static_cast<{self.cpp_type}>(value)"
+    def decode_expr(self) -> str:
+        return f"static_cast<{self.cpp_type}>(value.as_varint())"
 
     default_value = ""
     wire_type = WireType.VARINT  # Uses wire type 0
@@ -1594,7 +1559,7 @@ class EnumType(VarintTypeMixin, TypeInfo):
 class SFixed32Type(FixedSizeTypeMixin, TypeInfo):
     cpp_type = "int32_t"
     default_value = "0"
-    decode_32bit = "value.as_sfixed32()"
+    decode_expr = "value.as_sfixed32()"
     encode_func = "encode_sfixed32"
     wire_type = WireType.FIXED32  # Uses wire type 5
 
@@ -1620,7 +1585,6 @@ class SFixed32Type(FixedSizeTypeMixin, TypeInfo):
 class SFixed64Type(FixedSizeTypeMixin, TypeInfo):
     cpp_type = "int64_t"
     default_value = "0"
-    decode_64bit = "value.as_sfixed64()"
     encode_func = "encode_sfixed64"
     wire_type = WireType.FIXED64  # Uses wire type 1
 
@@ -1647,7 +1611,7 @@ class SInt32Type(VarintTypeMixin, TypeInfo):
     cpp_type = "int32_t"
     _varint_max_bits = 32  # zigzag encoding keeps it 32-bit
     default_value = "0"
-    decode_varint = "decode_zigzag32(static_cast<uint32_t>(value))"
+    decode_expr = "decode_zigzag32(static_cast<uint32_t>(value.as_varint()))"
     encode_func = "encode_sint32"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -1668,7 +1632,7 @@ class SInt64Type(VarintTypeMixin, TypeInfo):
     cpp_type = "int64_t"
     _varint_max_bits = 64
     default_value = "0"
-    decode_varint = "decode_zigzag64(value)"
+    decode_expr = "decode_zigzag64(value.as_varint())"
     encode_func = "encode_sint64"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -1821,23 +1785,11 @@ class FixedArrayRepeatedType(TypeInfo):
 
     def _encode_element(self, element: str) -> str:
         """Helper to generate encode statement for a single element."""
-        if isinstance(self._ti, EnumType):
-            return _encode_call(
-                self._ti.encode_func,
-                str(self.number),
-                f"static_cast<uint32_t>({element})",
-                force=True,
+        if isinstance(self._ti, MessageType) and _is_inline_encode(self._ti.cpp_type):
+            return _generate_inline_encode_block(
+                self.number, self._ti.cpp_type, element
             )
-        # Repeated message elements use encode_sub_message (force=true is default)
-        if isinstance(self._ti, MessageType):
-            if _is_inline_encode(self._ti.cpp_type):
-                return _generate_inline_encode_block(
-                    self.number, self._ti.cpp_type, element
-                )
-            return _encode_call(
-                "encode_sub_message", "buffer", str(self.number), element
-            )
-        return _encode_call(self._ti.encode_func, str(self.number), element, force=True)
+        return self._ti.encode_element(self.number, element)
 
     @property
     def cpp_type(self) -> str:
@@ -2131,55 +2083,23 @@ class RepeatedTypeInfo(TypeInfo):
         return self._ti.wire_type
 
     @property
-    def decode_varint_content(self) -> str:
-        # Pointer fields don't support decoding
-        if self._use_pointer:
-            return None
-        content = self._ti.decode_varint
-        if content is None:
-            return None
-        return (
-            f"case {self.number}: this->{self.field_name}.push_back({content}); break;"
-        )
+    def decode_expr(self) -> str | None:
+        return self._ti.decode_expr
+
+    def _decode_store(self, expr: str) -> str:
+        return f"this->{self.field_name}.push_back({expr});"
 
     @property
-    def decode_length_content(self) -> str:
+    def decode_content(self) -> str | None:
         # Pointer fields don't support decoding
         if self._use_pointer:
             return None
-        content = self._ti.decode_length
-        if content is None and isinstance(self._ti, MessageType):
-            # Special handling for non-template message decoding
-            return f"case {self.number}: this->{self.field_name}.emplace_back(); value.decode_to_message(this->{self.field_name}.back()); break;"
-        if content is None:
-            return None
-        return (
-            f"case {self.number}: this->{self.field_name}.push_back({content}); break;"
-        )
-
-    @property
-    def decode_32bit_content(self) -> str:
-        # Pointer fields don't support decoding
-        if self._use_pointer:
-            return None
-        content = self._ti.decode_32bit
-        if content is None:
-            return None
-        return (
-            f"case {self.number}: this->{self.field_name}.push_back({content}); break;"
-        )
-
-    @property
-    def decode_64bit_content(self) -> str:
-        # Pointer fields don't support decoding
-        if self._use_pointer:
-            return None
-        content = self._ti.decode_64bit
-        if content is None:
-            return None
-        return (
-            f"case {self.number}: this->{self.field_name}.push_back({content}); break;"
-        )
+        if isinstance(self._ti, MessageType):
+            return self.decode_case(
+                f"this->{self.field_name}.emplace_back();\n"
+                f"value.decode_to_message(this->{self.field_name}.back());"
+            )
+        return super().decode_content
 
     @property
     def _ti_is_bool(self) -> bool:
@@ -2187,20 +2107,7 @@ class RepeatedTypeInfo(TypeInfo):
         return isinstance(self._ti, BoolType)
 
     def _encode_element_call(self, element: str) -> str:
-        """Helper to generate encode call for a single element."""
-        if isinstance(self._ti, EnumType):
-            return _encode_call(
-                self._ti.encode_func,
-                str(self.number),
-                f"static_cast<uint32_t>({element})",
-                force=True,
-            )
-        # Repeated message elements use encode_sub_message (force=true is default)
-        if isinstance(self._ti, MessageType):
-            return _encode_call(
-                "encode_sub_message", "buffer", str(self.number), element
-            )
-        return _encode_call(self._ti.encode_func, str(self.number), element, force=True)
+        return self._ti.encode_element(self.number, element)
 
     @property
     def encode_content(self) -> str:
@@ -2595,10 +2502,7 @@ def build_message_type(
 ) -> tuple[str, str, str]:
     public_content: list[str] = []
     protected_content: list[str] = []
-    decode_varint: list[str] = []
-    decode_length: list[str] = []
-    decode_32bit: list[str] = []
-    decode_64bit: list[str] = []
+    decode: list[str] = []
     encode: list[str] = []
     dump: list[str] = []
     size_calc: list[str] = []
@@ -2727,22 +2631,8 @@ def build_message_type(
             if field.options.HasExtension(pb.field_ifdef):
                 field_ifdef = field.options.Extensions[pb.field_ifdef]
 
-            if ti.decode_varint_content:
-                decode_varint.extend(
-                    wrap_with_ifdef(ti.decode_varint_content, field_ifdef)
-                )
-            if ti.decode_length_content:
-                decode_length.extend(
-                    wrap_with_ifdef(ti.decode_length_content, field_ifdef)
-                )
-            if ti.decode_32bit_content:
-                decode_32bit.extend(
-                    wrap_with_ifdef(ti.decode_32bit_content, field_ifdef)
-                )
-            if ti.decode_64bit_content:
-                decode_64bit.extend(
-                    wrap_with_ifdef(ti.decode_64bit_content, field_ifdef)
-                )
+            if case := ti.decode_content:
+                decode.extend(wrap_with_ifdef(case, field_ifdef))
         if ti.dump_content:
             # Check for field_ifdef option for dump as well
             field_ifdef = None
@@ -2752,49 +2642,15 @@ def build_message_type(
             dump.extend(wrap_with_ifdef(ti.dump_content, field_ifdef))
 
     cpp = ""
-    if decode_varint:
-        o = f"bool {desc.name}::decode_varint(uint32_t field_id, proto_varint_value_t value) {{\n"
-        o += "  switch (field_id) {\n"
-        o += indent("\n".join(decode_varint), "    ") + "\n"
-        o += "    default: return false;\n"
+    if decode:
+        o = f"void {desc.name}::decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {{\n"
+        o += "  const ProtoFieldValue value(data, scalar);\n"
+        o += "  switch (tag) {\n"
+        o += indent("\n".join(decode), "    ") + "\n"
         o += "  }\n"
-        o += "  return true;\n"
         o += "}\n"
         cpp += o
-        prot = "bool decode_varint(uint32_t field_id, proto_varint_value_t value) override;"
-        protected_content.insert(0, prot)
-    if decode_length:
-        o = f"bool {desc.name}::decode_length(uint32_t field_id, ProtoLengthDelimited value) {{\n"
-        o += "  switch (field_id) {\n"
-        o += indent("\n".join(decode_length), "    ") + "\n"
-        o += "    default: return false;\n"
-        o += "  }\n"
-        o += "  return true;\n"
-        o += "}\n"
-        cpp += o
-        prot = "bool decode_length(uint32_t field_id, ProtoLengthDelimited value) override;"
-        protected_content.insert(0, prot)
-    if decode_32bit:
-        o = f"bool {desc.name}::decode_32bit(uint32_t field_id, Proto32Bit value) {{\n"
-        o += "  switch (field_id) {\n"
-        o += indent("\n".join(decode_32bit), "    ") + "\n"
-        o += "    default: return false;\n"
-        o += "  }\n"
-        o += "  return true;\n"
-        o += "}\n"
-        cpp += o
-        prot = "bool decode_32bit(uint32_t field_id, Proto32Bit value) override;"
-        protected_content.insert(0, prot)
-    if decode_64bit:
-        o = f"bool {desc.name}::decode_64bit(uint32_t field_id, Proto64Bit value) {{\n"
-        o += "  switch (field_id) {\n"
-        o += indent("\n".join(decode_64bit), "    ") + "\n"
-        o += "    default: return false;\n"
-        o += "  }\n"
-        o += "  return true;\n"
-        o += "}\n"
-        cpp += o
-        prot = "bool decode_64bit(uint32_t field_id, Proto64Bit value) override;"
+        prot = "void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;"
         protected_content.insert(0, prot)
 
     # Generate custom decode() override for messages with FixedVector fields
@@ -2841,28 +2697,36 @@ def build_message_type(
             )
             for line in encode
         ]
-        o = f"{speed_attr}uint8_t *{desc.name}::encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {{\n"
+        o = f"{speed_attr}uint8_t *{desc.name}::encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) {{\n"
+        o += f"  const auto &msg = *static_cast<const {desc.name} *>(self);\n"
         o += "  uint8_t *__restrict__ pos = buffer.get_pos();\n"
-        o += indent("\n".join(encode_debug)) + "\n"
+        o += indent("\n".join(encode_debug)).replace("this->", "msg.") + "\n"
         o += "  return pos;\n"
         o += "}\n"
         cpp += o
-        prot = (
-            "uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const;"
+        public_content.append(
+            "static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);"
+        )
+        public_content.append(
+            "uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {\n"
+            "  return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);\n"
+            "}"
         )
-        public_content.append(prot)
     # If no fields to encode or message doesn't need encoding, the default implementation in ProtoMessage will be used
 
     # Add calculate_size method only if this message needs encoding and has fields
     if needs_encode and size_calc and not is_inline_only:
-        o = f"{speed_attr}uint32_t {desc.name}::calculate_size() const {{\n"
+        o = f"{speed_attr}uint32_t {desc.name}::calc_size_msg(const void *self) {{\n"
+        o += f"  const auto &msg = *static_cast<const {desc.name} *>(self);\n"
         o += "  uint32_t size = 0;\n"
-        o += indent("\n".join(size_calc)) + "\n"
+        o += indent("\n".join(size_calc)).replace("this->", "msg.") + "\n"
         o += "  return size;\n"
         o += "}\n"
         cpp += o
-        prot = "uint32_t calculate_size() const;"
-        public_content.append(prot)
+        public_content.append("static uint32_t calc_size_msg(const void *self);")
+        public_content.append(
+            "uint32_t calculate_size() const { return calc_size_msg(this); }"
+        )
     # If no fields to calculate size for or message doesn't need encoding, the default implementation in ProtoMessage will be used
 
     # dump_to method declaration in header

tests/benchmarks/components/api/bench_proto_proxy.cpp

@@ -249,7 +249,7 @@ static APIBuffer build_infrared_rf_transmit_wire() {
   std::memcpy(bytes + len, packed, packed_len);
   len += packed_len;
   // field 6: modulation = 1 (non-zero so it's actually emitted and exercises
-  // decode_varint for this field, matching the documented layout above).
+  // decode_field for this field, matching the documented layout above).
   put_byte(0x30);
   put_varint(1);
 

tests/integration/fixtures/api_decode_wire_types.yaml

@@ -0,0 +1,43 @@
+esphome:
+  name: api-decode-wire-types-test
+host:
+api:
+logger:
+  level: DEBUG
+
+switch:
+  - platform: template
+    name: "Wire Switch"
+    optimistic: true
+
+output:
+  - platform: template
+    id: wire_dim
+    type: float
+    write_action:
+      - lambda: ""
+
+light:
+  - platform: monochromatic
+    name: "Wire Light"
+    output: wire_dim
+    default_transition_length: 0s
+    effects:
+      - pulse:
+          name: Pulse
+
+text:
+  - platform: template
+    name: "Wire Text"
+    optimistic: true
+    mode: text
+    min_length: 0
+    max_length: 255
+
+number:
+  - platform: template
+    name: "Wire Number"
+    optimistic: true
+    min_value: -1000
+    max_value: 1000
+    step: 0.5

tests/integration/fixtures/api_empty_message_roundtrip.yaml

@@ -0,0 +1,11 @@
+esphome:
+  name: api-empty-message-test
+host:
+api:
+logger:
+  level: DEBUG
+
+switch:
+  - platform: template
+    name: "Empty Message Switch"
+    optimistic: true

tests/integration/raw_api_client.py

@@ -125,11 +125,12 @@ class RawApiClient:
         await self.read_until_frame(MESSAGE_TYPE_OF[api_pb2.HelloResponse])
 
     async def send_message(self, msg: message.Message) -> None:
+        await self.send_raw(MESSAGE_TYPE_OF[type(msg)], msg.SerializeToString())
+
+    async def send_raw(self, msg_type: int, payload: bytes) -> None:
+        """Send a frame with a hand built payload, for shapes protobuf will not serialize."""
         loop = asyncio.get_running_loop()
-        await loop.sock_sendall(
-            self._sock,
-            encode_frame(MESSAGE_TYPE_OF[type(msg)], msg.SerializeToString()),
-        )
+        await loop.sock_sendall(self._sock, encode_frame(msg_type, payload))
 
     async def read_until_frame(self, msg_type: int, timeout: float = 10.0) -> None:
         """Read until at least one frame of msg_type has been received."""

tests/integration/test_api_decode_wire_types.py

@@ -0,0 +1,142 @@
+"""decode_field() must take fields that match their declared wire type, drop the ones that do
+not, skip unknown fields, and handle two byte tags, varints and length prefixes."""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+import struct
+
+from aioesphomeapi import (
+    EntityState,
+    LightState,
+    NumberState,
+    SwitchState,
+    TextState,
+    api_pb2,
+)
+import pytest
+
+from .raw_api_client import MESSAGE_TYPE_OF, RawApiClient, encode_varint
+from .state_utils import InitialStateHelper, StateWaiter, require_entity
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+SWITCH_COMMAND = MESSAGE_TYPE_OF[api_pb2.SwitchCommandRequest]
+WIRE_VARINT, WIRE_LENGTH, WIRE_FIXED32 = 0, 2, 5
+
+
+def tag(field: int, wire_type: int) -> bytes:
+    return encode_varint((field << 3) | wire_type)
+
+
+@pytest.mark.asyncio
+async def test_api_decode_wire_types(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+    unused_tcp_port: int,
+) -> None:
+    async with (
+        run_compiled(yaml_config),
+        api_client_connected() as client,
+        RawApiClient(unused_tcp_port) as raw,
+    ):
+        entities, _ = await client.list_entities_services()
+        switch = require_entity(entities, "wire_switch")
+        light = require_entity(entities, "wire_light")
+        text = require_entity(entities, "wire_text")
+        number = require_entity(entities, "wire_number")
+        key = tag(1, WIRE_FIXED32) + struct.pack("<I", switch.key)
+        on, off = tag(2, WIRE_VARINT) + b"\x01", tag(2, WIRE_VARINT) + b"\x00"
+
+        switch_states: list[bool] = []
+        waiter = StateWaiter()
+
+        def on_state(state: EntityState) -> None:
+            if isinstance(state, SwitchState) and state.key == switch.key:
+                switch_states.append(state.state)
+            waiter.on_state(state)
+
+        def switch_is(value: bool) -> Callable[[EntityState], bool]:
+            return lambda s: (
+                isinstance(s, SwitchState) and s.key == switch.key and s.state is value
+            )
+
+        def number_is(value: float) -> Callable[[EntityState], bool]:
+            return lambda s: (
+                isinstance(s, NumberState) and s.key == number.key and s.state == value
+            )
+
+        initial = InitialStateHelper(entities)
+        client.subscribe_states(initial.on_state_wrapper(on_state))
+        await initial.wait_for_initial_states()
+        await raw.connect()
+
+        # A well formed command: fixed32 key, varint state
+        await raw.send_raw(SWITCH_COMMAND, key + on)
+        await waiter.expect(switch_is(True))
+        await raw.send_raw(SWITCH_COMMAND, key + off)
+        await waiter.expect(switch_is(False))
+
+        # The same field with the wrong wire type is dropped, and a varint key never matches an
+        # entity; each of these would turn the switch on if the payload were read as a varint
+        seen = len(switch_states)
+        await raw.send_raw(SWITCH_COMMAND, key + tag(2, WIRE_LENGTH) + b"\x01\x01")
+        await raw.send_raw(
+            SWITCH_COMMAND, key + tag(2, WIRE_FIXED32) + b"\x01\x00\x00\x00"
+        )
+        await raw.send_raw(
+            SWITCH_COMMAND, tag(1, WIRE_VARINT) + encode_varint(switch.key) + on
+        )
+        # Ordered on the raw socket itself: this frame cannot be parsed before the bad ones, so
+        # the only switch state since the marker must be the one it produces
+        await raw.send_raw(SWITCH_COMMAND, key + on)
+        await waiter.expect(switch_is(True), label="switch on after wrong wire types")
+        assert switch_states[seen:] == [True]
+        await raw.send_raw(SWITCH_COMMAND, key + off)
+        await waiter.expect(switch_is(False))
+
+        # Truncated bodies stop the decode loop without taking the connection down: a tag with its
+        # continuation bit set and nothing after it, a length prefix past the end of the payload,
+        # and a fixed32 with two of its four bytes
+        seen = len(switch_states)
+        await raw.send_raw(SWITCH_COMMAND, key + b"\x80")
+        await raw.send_raw(SWITCH_COMMAND, key + tag(2, WIRE_LENGTH) + b"\x7f" + b"ab")
+        await raw.send_raw(SWITCH_COMMAND, tag(1, WIRE_FIXED32) + b"\x01\x02")
+        await raw.send_raw(SWITCH_COMMAND, key + on)
+        await waiter.expect(switch_is(True), label="switch on after truncated frames")
+        assert switch_states[seen:] == [True]
+        await raw.send_raw(SWITCH_COMMAND, key + off)
+        await waiter.expect(switch_is(False))
+
+        # A negative number goes through the fixed32 float path of a normal client
+        client.number_command(number.key, -77.5)
+        await waiter.expect(number_is(-77.5))
+
+        # An unknown field ahead of the known ones is skipped; field 200 needs a two byte tag
+        await raw.send_raw(
+            SWITCH_COMMAND, tag(200, WIRE_VARINT) + encode_varint(300) + key + on
+        )
+        await waiter.expect(switch_is(True))
+
+        # Two byte tags (effect fields 18 and 19) and a two byte varint (300 ms transition)
+        client.light_command(
+            light.key, state=True, brightness=0.5, transition_length=0.3, effect="Pulse"
+        )
+        await waiter.expect(
+            lambda s: (
+                isinstance(s, LightState) and s.key == light.key and s.effect == "Pulse"
+            )
+        )
+        client.light_command(light.key, effect="None", state=False)
+        await waiter.expect(
+            lambda s: isinstance(s, LightState) and s.key == light.key and not s.state
+        )
+
+        # A string whose length prefix needs two varint bytes
+        long_text = "w" * 200
+        client.text_command(text.key, long_text)
+        await waiter.expect(
+            lambda s: (
+                isinstance(s, TextState) and s.key == text.key and s.state == long_text
+            )
+        )

tests/integration/test_api_empty_message_roundtrip.py

@@ -0,0 +1,37 @@
+"""Messages without fields go through the shared ProtoMessage entry points on both directions."""
+
+from __future__ import annotations
+
+from aioesphomeapi import api_pb2
+import pytest
+
+from .raw_api_client import MESSAGE_TYPE_OF, RawApiClient
+from .types import RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_api_empty_message_roundtrip(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    unused_tcp_port: int,
+) -> None:
+    async with run_compiled(yaml_config), RawApiClient(unused_tcp_port) as client:
+        await client.connect()
+
+        # Field free request and reply on the plain send path
+        await client.send_message(api_pb2.PingRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.PingResponse])
+
+        # Field free request answered by a message with fields, and a list that ends with
+        # the field free ListEntitiesDoneResponse through the batching path
+        await client.send_message(api_pb2.DeviceInfoRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.DeviceInfoResponse])
+        await client.send_message(api_pb2.ListEntitiesRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.ListEntitiesDoneResponse])
+        assert (
+            client.frame_counts[MESSAGE_TYPE_OF[api_pb2.ListEntitiesSwitchResponse]]
+            == 1
+        )
+
+        await client.send_message(api_pb2.DisconnectRequest())
+        await client.read_until_frame(MESSAGE_TYPE_OF[api_pb2.DisconnectResponse])

tests/unit_tests/components/api/test_api_proto.py

@@ -194,17 +194,17 @@ def test_superseded_device_info_fields_still_declared_in_header() -> None:
 
 def test_superseded_device_info_fields_still_encoded_and_sized() -> None:
     """Each superseded field must still be touched by DeviceInfoResponse's
-    generated encode() and calculate_size(), i.e. it is still put on the wire.
+    generated encode_msg() and calc_size_msg(), i.e. it is still put on the wire.
     """
-    encode_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::encode")
-    size_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::calculate_size")
+    encode_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::encode_msg")
+    size_body = _extract_function_body(CPP_TEXT, "DeviceInfoResponse::calc_size_msg")
     for field_name in SUPERSEDED_FIELDS:
-        assert f"this->{field_name}" in encode_body, (
-            f"DeviceInfoResponse::encode() no longer references {field_name}. "
+        assert f"msg.{field_name}" in encode_body, (
+            f"DeviceInfoResponse::encode_msg() no longer references {field_name}. "
             f"{DEPRECATED_FIELD_TRAP}"
         )
-        assert f"this->{field_name}" in size_body, (
-            f"DeviceInfoResponse::calculate_size() no longer references "
+        assert f"msg.{field_name}" in size_body, (
+            f"DeviceInfoResponse::calc_size_msg() no longer references "
             f"{field_name}. {DEPRECATED_FIELD_TRAP}"
         )
 

tests/unit_tests/components/api/test_api_protobuf_generator.py

@@ -18,7 +18,9 @@ sys.path.insert(0, str(Path(__file__).parents[4] / "script" / "api_protobuf"))
 import aioesphomeapi.api_options_pb2 as pb  # noqa: E402
 from api_protobuf import (  # noqa: E402
     MAX_MESSAGE_ID,
+    SOURCE_CLIENT,
     _make_ifdef_line,
+    build_message_type,
     create_field_type_info,
     get_varint64_ifdef,
     validate_message_id,
@@ -36,12 +38,15 @@ def _file_with_messages(
     file_desc = descriptor_pb2.FileDescriptorProto(name="test.proto")
     for name, field_type, deprecated in messages:
         msg = file_desc.message_type.add(name=name)
-        field = msg.field.add(name="value", number=1, type=field_type)
+        field = msg.field.add()
+        field.CopyFrom(_field(field_type))
         field.options.deprecated = deprecated
     return file_desc
 
 
 UINT64 = descriptor_pb2.FieldDescriptorProto.TYPE_UINT64
+MESSAGE = descriptor_pb2.FieldDescriptorProto.TYPE_MESSAGE
+DOUBLE = descriptor_pb2.FieldDescriptorProto.TYPE_DOUBLE
 INT64 = descriptor_pb2.FieldDescriptorProto.TYPE_INT64
 SINT64 = descriptor_pb2.FieldDescriptorProto.TYPE_SINT64
 UINT32 = descriptor_pb2.FieldDescriptorProto.TYPE_UINT32
@@ -182,3 +187,106 @@ def test_multi_byte_tag_fixed32_falls_back_to_the_generic_helper(
     content = _encode_field(field_type, number=16)
     assert "write_tag_and_fixed32" not in content, content
     assert content.startswith("pos = ProtoEncode::encode_"), content
+
+
+def _decode_case(field_type: int, number: int, *, repeated: bool = False) -> str:
+    """Return the decode_field() case the generator emits for one decoded field."""
+    field = _field(field_type, number, repeated=repeated)
+    if field_type == MESSAGE:
+        field.type_name = ".Sub"
+    return create_field_type_info(
+        field, needs_decode=True, needs_encode=False
+    ).decode_content
+
+
+@pytest.mark.parametrize(
+    ("field_type", "number", "wire_type", "accessor"),
+    [
+        (UINT32, 2, "WIRE_TYPE_VARINT", "value.as_varint()"),
+        (BOOL, 3, "WIRE_TYPE_VARINT", "value.as_bool()"),
+        (STRING, 1, "WIRE_TYPE_LENGTH_DELIMITED", "value.data()"),
+        (FLOAT, 4, "WIRE_TYPE_FIXED32", "value.as_float()"),
+        (FIXED32, 5, "WIRE_TYPE_FIXED32", "value.as_fixed32()"),
+    ],
+)
+def test_decode_cases_carry_field_number_and_wire_type(
+    field_type: int, number: int, wire_type: str, accessor: str
+) -> None:
+    """Each decoded field yields one case keyed on its number and declared wire type."""
+    case = _decode_case(field_type, number)
+    lines = case.splitlines()
+    assert lines[0] == f"case proto_tag({number}, {wire_type}):", case
+    assert accessor in lines[1], case
+    assert lines[-1].strip() == "break;", case
+
+
+@pytest.mark.parametrize(
+    ("field_type", "repeated", "wire_type", "store"),
+    [
+        (UINT32, True, "WIRE_TYPE_VARINT", "this->value.push_back(value.as_varint());"),
+        (
+            STRING,
+            True,
+            "WIRE_TYPE_LENGTH_DELIMITED",
+            "this->value.push_back(value.as_string());",
+        ),
+        (
+            MESSAGE,
+            False,
+            "WIRE_TYPE_LENGTH_DELIMITED",
+            "value.decode_to_message(this->value);",
+        ),
+        (
+            MESSAGE,
+            True,
+            "WIRE_TYPE_LENGTH_DELIMITED",
+            "value.decode_to_message(this->value.back());",
+        ),
+    ],
+)
+def test_repeated_and_message_fields_decode_through_the_same_case_shape(
+    field_type: int, repeated: bool, wire_type: str, store: str
+) -> None:
+    """Repeated and sub message fields land in the one switch with their own store."""
+    case = _decode_case(field_type, 7, repeated=repeated)
+    lines = case.splitlines()
+    assert lines[0] == f"case proto_tag(7, {wire_type}):", case
+    assert store in case, case
+    if field_type == MESSAGE and repeated:
+        assert "this->value.emplace_back();" in case, case
+    assert lines[-1].strip() == "break;", case
+
+
+def test_a_fixed64_field_fails_at_generation_time() -> None:
+    """The decode loop has no 64 bit wire type path, so such a field must never reach it silently."""
+    desc = descriptor_pb2.DescriptorProto(name="Wide")
+    desc.field.add(name="ratio", number=1, type=DOUBLE)
+    with pytest.raises(
+        ValueError, match="64-bit type 'double' .*ratio.* not supported"
+    ):
+        build_message_type(desc, {}, {"Wide": SOURCE_CLIENT})
+
+
+def test_message_gets_a_single_decode_field_override() -> None:
+    """All wire types of a decoded message land in one decode_field() switch."""
+    desc = descriptor_pb2.DescriptorProto(name="Mixed")
+    desc.field.add(name="name", number=1, type=STRING)
+    desc.field.add(name="count", number=2, type=UINT32)
+    desc.field.add(name="level", number=3, type=FLOAT)
+    header, cpp, _ = build_message_type(desc, {}, {"Mixed": SOURCE_CLIENT})
+    decl = "void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;"
+    assert header.count(decl) == 1
+    assert (
+        cpp.count(
+            "void Mixed::decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {"
+        )
+        == 1
+    )
+    assert "switch (tag) {" in cpp
+    assert "const ProtoFieldValue value(data, scalar);" in cpp
+    for number, wire_type in (
+        (1, "WIRE_TYPE_LENGTH_DELIMITED"),
+        (2, "WIRE_TYPE_VARINT"),
+        (3, "WIRE_TYPE_FIXED32"),
+    ):
+        assert f"case proto_tag({number}, {wire_type}):" in cpp, cpp