store mdns values in flash

esphome/components/mdns/__init__.py

@@ -58,11 +58,21 @@ CONFIG_SCHEMA = cv.All(
 )
 
 
-def mdns_txt_record(key: str, value: str):
+def mdns_txt_record_static(key: str, value: str):
+    """Create a TXT record with a static (compile-time) value stored in flash."""
     return cg.StructInitializer(
         MDNSTXTRecord,
         ("key", cg.RawExpression(f"MDNS_STR({cg.safe_exp(key)})")),
-        ("value", value),
+        ("value", cg.RawExpression(f"MDNS_STR({cg.safe_exp(value)})")),
+    )
+
+
+def mdns_txt_record_dynamic(key: str, value_expr: str):
+    """Create a TXT record with a dynamic value (will be evaluated and stored in vector)."""
+    return cg.StructInitializer(
+        MDNSTXTRecord,
+        ("key", cg.RawExpression(f"MDNS_STR({cg.safe_exp(key)})")),
+        ("value", cg.RawExpression(f"MDNS_STR({value_expr})")),
     )
 
 
@@ -107,23 +117,56 @@ async def to_code(config):
     # Ensure at least 1 service (fallback service)
     cg.add_define("MDNS_SERVICE_COUNT", max(1, service_count))
 
+    # Calculate compile-time dynamic TXT value count
+    # Dynamic values are those that cannot be stored in flash at compile time
+    dynamic_txt_count = 0
+    if "api" in CORE.config:
+        # Always: get_mac_address()
+        dynamic_txt_count += 1
+        # Conditional: friendly_name (if not empty, but we conservatively count it)
+        dynamic_txt_count += 1
+        # Conditional: dashboard_import_url
+        if "dashboard_import" in CORE.config:
+            dynamic_txt_count += 1
+    # User-provided templatable TXT values (only lambdas, not static strings)
+    dynamic_txt_count += sum(
+        1
+        for service in config[CONF_SERVICES]
+        for txt_value in service[CONF_TXT].values()
+        if cg.is_template(txt_value)
+    )
+
+    # Ensure at least 1 to avoid zero-size array
+    cg.add_define("MDNS_DYNAMIC_TXT_COUNT", max(1, dynamic_txt_count))
+
     var = cg.new_Pvariable(config[CONF_ID])
     await cg.register_component(var, config)
 
     for service in config[CONF_SERVICES]:
-        txt = [
-            cg.StructInitializer(
-                MDNSTXTRecord,
-                ("key", cg.RawExpression(f"MDNS_STR({cg.safe_exp(txt_key)})")),
-                ("value", await cg.templatable(txt_value, [], cg.std_string)),
-            )
-            for txt_key, txt_value in service[CONF_TXT].items()
-        ]
+        # Build the txt records list for the service
+        txt_records = []
+        for txt_key, txt_value in service[CONF_TXT].items():
+            if cg.is_template(txt_value):
+                # It's a lambda - evaluate and store using helper
+                templated_value = await cg.templatable(txt_value, [], cg.std_string)
+                txt_records.append(
+                    cg.RawExpression(
+                        f"{{MDNS_STR({cg.safe_exp(txt_key)}), MDNS_STR({var}->add_dynamic_txt_value(({templated_value})()))}}"
+                    )
+                )
+            else:
+                # It's a static string - use directly in flash, no need to store in vector
+                txt_records.append(
+                    cg.RawExpression(
+                        f"{{MDNS_STR({cg.safe_exp(txt_key)}), MDNS_STR({cg.safe_exp(txt_value)})}}"
+                    )
+                )
+
         exp = mdns_service(
             service[CONF_SERVICE],
             service[CONF_PROTOCOL],
             await cg.templatable(service[CONF_PORT], [], cg.uint16),
-            txt,
+            txt_records,
         )
 
         cg.add(var.add_extra_service(exp))