[canbus] Optimize canbus.send memory usage - store static data in flash

esphome/components/canbus/__init__.py

@@ -4,7 +4,7 @@ from esphome import automation
 import esphome.codegen as cg
 import esphome.config_validation as cv
 from esphome.const import CONF_DATA, CONF_ID, CONF_TRIGGER_ID
-from esphome.core import CORE
+from esphome.core import CORE, ID
 
 CODEOWNERS = ["@mvturnho", "@danielschramm"]
 IS_PLATFORM_COMPONENT = True
@@ -176,5 +176,8 @@ async def canbus_action_to_code(config, action_id, template_arg, args):
     else:
         if isinstance(data, bytes):
             data = [int(x) for x in data]
-        cg.add(var.set_data_static(data))
+        # Generate static array in flash to avoid RAM copy
+        arr_id = ID(f"{action_id}_data", is_declaration=True, type=cg.uint8)
+        arr = cg.static_const_array(arr_id, cg.ArrayInitializer(*data))
+        cg.add(var.set_data_static(arr, len(data)))
     return var

esphome/components/canbus/canbus.h

@@ -112,12 +112,16 @@ class Canbus : public Component {
 
 template<typename... Ts> class CanbusSendAction : public Action<Ts...>, public Parented<Canbus> {
  public:
-  void set_data_template(const std::function<std::vector<uint8_t>(Ts...)> func) {
-    this->data_func_ = func;
+  void set_data_template(std::vector<uint8_t> (*func)(Ts...)) {
+    // Stateless lambdas (generated by ESPHome) implicitly convert to function pointers
+    this->data_.func = func;
     this->static_ = false;
   }
-  void set_data_static(const std::vector<uint8_t> &data) {
-    this->data_static_ = data;
+
+  // Store pointer to static data in flash (no RAM copy)
+  void set_data_static(const uint8_t *data, size_t len) {
+    this->data_.static_data.ptr = data;
+    this->data_.static_data.len = len;
     this->static_ = true;
   }
 
@@ -133,21 +137,27 @@ template<typename... Ts> class CanbusSendAction : public Action<Ts...>, public P
     auto can_id = this->can_id_.has_value() ? *this->can_id_ : this->parent_->can_id_;
     auto use_extended_id =
         this->use_extended_id_.has_value() ? *this->use_extended_id_ : this->parent_->use_extended_id_;
+    std::vector<uint8_t> data;
     if (this->static_) {
-      this->parent_->send_data(can_id, use_extended_id, this->remote_transmission_request_, this->data_static_);
+      data.assign(this->data_.static_data.ptr, this->data_.static_data.ptr + this->data_.static_data.len);
     } else {
-      auto val = this->data_func_(x...);
-      this->parent_->send_data(can_id, use_extended_id, this->remote_transmission_request_, val);
+      data = this->data_.func(x...);
     }
+    this->parent_->send_data(can_id, use_extended_id, this->remote_transmission_request_, data);
   }
 
  protected:
   optional<uint32_t> can_id_{};
   optional<bool> use_extended_id_{};
   bool remote_transmission_request_{false};
-  bool static_{false};
-  std::function<std::vector<uint8_t>(Ts...)> data_func_{};
-  std::vector<uint8_t> data_static_{};
+  bool static_{true};  // Default to static mode (most common case)
+  union Data {
+    std::vector<uint8_t> (*func)(Ts...);  // 4 bytes on 32-bit
+    struct {
+      const uint8_t *ptr;  // 4 bytes on 32-bit
+      size_t len;          // 4 bytes on 32-bit
+    } static_data;         // 8 bytes total on 32-bit
+  } data_;                 // Union size = 8 bytes (max of 4 and 8)
 };
 
 class CanbusTrigger : public Trigger<std::vector<uint8_t>, uint32_t, bool>, public Component {

tests/components/canbus/common.yaml

@@ -37,6 +37,15 @@ canbus:
                   break;
               }
 
+number:
+  - platform: template
+    name: "Test Number"
+    id: test_number
+    optimistic: true
+    min_value: 0
+    max_value: 255
+    step: 1
+
 button:
   - platform: template
     name: Canbus Actions
@@ -44,3 +53,7 @@ button:
       - canbus.send: "abc"
       - canbus.send: [0, 1, 2]
       - canbus.send: !lambda return {0, 1, 2};
+      # Test canbus.send with lambda that references a component (function pointer)
+      - canbus.send: !lambda |-
+          uint8_t val = (uint8_t)id(test_number).state;
+          return std::vector<uint8_t>{0xAA, val, 0xBB};