From 2cac99dafaf7e3972127f3d22bec94ebe6634db8 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Sat, 8 Nov 2025 22:32:47 -0600
Subject: [PATCH] [udp] Optimize udp.write action memory usage - store static
 data in flash

---
 esphome/components/udp/__init__.py  |  7 +++++--
 esphome/components/udp/automation.h | 25 ++++++++++++++++---------
 tests/components/udp/common.yaml    | 19 +++++++++++++++++++
 3 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/esphome/components/udp/__init__.py b/esphome/components/udp/__init__.py
index 6b1e4f8ed8..69abf4b989 100644
--- a/esphome/components/udp/__init__.py
+++ b/esphome/components/udp/__init__.py
@@ -12,7 +12,7 @@ from esphome.components.packet_transport import (
 )
 import esphome.config_validation as cv
 from esphome.const import CONF_DATA, CONF_ID, CONF_PORT, CONF_TRIGGER_ID
-from esphome.core import Lambda
+from esphome.core import ID, Lambda
 from esphome.cpp_generator import ExpressionStatement, MockObj
 
 CODEOWNERS = ["@clydebarrow"]
@@ -158,5 +158,8 @@ async def udp_write_to_code(config, action_id, template_arg, args):
         templ = await cg.templatable(data, args, cg.std_vector.template(cg.uint8))
         cg.add(var.set_data_template(templ))
     else:
-        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
diff --git a/esphome/components/udp/automation.h b/esphome/components/udp/automation.h
index c5e5e2eae8..a3b76fb4ea 100644
--- a/esphome/components/udp/automation.h
+++ b/esphome/components/udp/automation.h
@@ -11,28 +11,35 @@ namespace udp {
 
 template<typename... Ts> class UDPWriteAction : public Action<Ts...>, public Parented<UDPComponent> {
  public:
-  void set_data_template(std::function<std::vector<uint8_t>(Ts...)> func) {
-    this->data_func_ = func;
+  void set_data_template(std::vector<uint8_t> (*func)(Ts...)) {
+    this->data_.func = func;
     this->static_ = false;
   }
-  void set_data_static(const std::vector<uint8_t> &data) {
-    this->data_static_ = data;
+
+  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;
   }
 
   void play(const Ts &...x) override {
     if (this->static_) {
-      this->parent_->send_packet(this->data_static_);
+      this->parent_->send_packet(this->data_.static_data.ptr, this->data_.static_data.len);
     } else {
-      auto val = this->data_func_(x...);
+      auto val = this->data_.func(x...);
       this->parent_->send_packet(val);
     }
   }
 
  protected:
-  bool static_{false};
-  std::function<std::vector<uint8_t>(Ts...)> data_func_{};
-  std::vector<uint8_t> data_static_{};
+  bool static_{true};
+  union Data {
+    std::vector<uint8_t> (*func)(Ts...);
+    struct {
+      const uint8_t *ptr;
+      size_t len;
+    } static_data;
+  } data_;
 };
 
 }  // namespace udp
diff --git a/tests/components/udp/common.yaml b/tests/components/udp/common.yaml
index 96224d0d1f..98546d49ef 100644
--- a/tests/components/udp/common.yaml
+++ b/tests/components/udp/common.yaml
@@ -17,3 +17,22 @@ udp:
         id: my_udp
         data: !lambda |-
           return std::vector<uint8_t>{1,3,4,5,6};
+
+number:
+  - platform: template
+    name: "UDP Number"
+    id: my_number
+    optimistic: true
+    min_value: 0
+    max_value: 100
+    step: 1
+
+button:
+  - platform: template
+    name: "UDP Button"
+    on_press:
+      then:
+        - udp.write:
+            data: [0x01, 0x02, 0x03]
+        - udp.write: !lambda |-
+            return {0x10, 0x20, (uint8_t)id(my_number).state};