Make string globals persist-able using fixed size allocations (#5296)

Co-authored-by: Daniel Dunn <dannydunn@eternityforest.com>

esphome/components/globals/__init__.py

@@ -15,8 +15,14 @@ CODEOWNERS = ["@esphome/core"]
 globals_ns = cg.esphome_ns.namespace("globals")
 GlobalsComponent = globals_ns.class_("GlobalsComponent", cg.Component)
 RestoringGlobalsComponent = globals_ns.class_("RestoringGlobalsComponent", cg.Component)
+RestoringGlobalStringComponent = globals_ns.class_(
+    "RestoringGlobalStringComponent", cg.Component
+)
 GlobalVarSetAction = globals_ns.class_("GlobalVarSetAction", automation.Action)
 
+CONF_MAX_RESTORE_DATA_LENGTH = "max_restore_data_length"
+
+
 MULTI_CONF = True
 CONFIG_SCHEMA = cv.Schema(
     {
@@ -24,6 +30,7 @@ CONFIG_SCHEMA = cv.Schema(
         cv.Required(CONF_TYPE): cv.string_strict,
         cv.Optional(CONF_INITIAL_VALUE): cv.string_strict,
         cv.Optional(CONF_RESTORE_VALUE, default=False): cv.boolean,
+        cv.Optional(CONF_MAX_RESTORE_DATA_LENGTH): cv.int_range(0, 254),
     }
 ).extend(cv.COMPONENT_SCHEMA)
 
@@ -32,12 +39,19 @@ CONFIG_SCHEMA = cv.Schema(
 @coroutine_with_priority(-100.0)
 async def to_code(config):
     type_ = cg.RawExpression(config[CONF_TYPE])
-    template_args = cg.TemplateArguments(type_)
     restore = config[CONF_RESTORE_VALUE]
 
+    # Special casing the strings to their own class with a different save/restore mechanism
+    if str(type_) == "std::string" and restore:
+        template_args = cg.TemplateArguments(
+            type_, config.get(CONF_MAX_RESTORE_DATA_LENGTH, 63) + 1
+        )
+        type = RestoringGlobalStringComponent
+    else:
+        template_args = cg.TemplateArguments(type_)
         type = RestoringGlobalsComponent if restore else GlobalsComponent
-    res_type = type.template(template_args)
 
+    res_type = type.template(template_args)
     initial_value = None
     if CONF_INITIAL_VALUE in config:
         initial_value = cg.RawExpression(config[CONF_INITIAL_VALUE])

esphome/components/globals/globals_component.h

@@ -65,6 +65,64 @@ template<typename T> class RestoringGlobalsComponent : public Component {
   ESPPreferenceObject rtc_;
 };
 
+// Use with string or subclasses of strings
+template<typename T, uint8_t SZ> class RestoringGlobalStringComponent : public Component {
+ public:
+  using value_type = T;
+  explicit RestoringGlobalStringComponent() = default;
+  explicit RestoringGlobalStringComponent(T initial_value) { this->value_ = initial_value; }
+  explicit RestoringGlobalStringComponent(
+      std::array<typename std::remove_extent<T>::type, std::extent<T>::value> initial_value) {
+    memcpy(this->value_, initial_value.data(), sizeof(T));
+  }
+
+  T &value() { return this->value_; }
+
+  void setup() override {
+    char temp[SZ];
+    this->rtc_ = global_preferences->make_preference<uint8_t[SZ]>(1944399030U ^ this->name_hash_);
+    bool hasdata = this->rtc_.load(&temp);
+    if (hasdata) {
+      this->value_.assign(temp + 1, temp[0]);
+    }
+    this->prev_value_.assign(this->value_);
+  }
+
+  float get_setup_priority() const override { return setup_priority::HARDWARE; }
+
+  void loop() override { store_value_(); }
+
+  void on_shutdown() override { store_value_(); }
+
+  void set_name_hash(uint32_t name_hash) { this->name_hash_ = name_hash; }
+
+ protected:
+  void store_value_() {
+    int diff = this->value_.compare(this->prev_value_);
+    if (diff != 0) {
+      // Make it into a length prefixed thing
+      unsigned char temp[SZ];
+
+      // If string is bigger than the allocation, do not save it.
+      // We don't need to waste ram setting prev_value either.
+      int size = this->value_.size();
+      // Less than, not less than or equal, SZ includes the length byte.
+      if (size < SZ) {
+        memcpy(temp + 1, this->value_.c_str(), size);
+        // SZ should be pre checked at the schema level, it can't go past the char range.
+        temp[0] = ((unsigned char) size);
+        this->rtc_.save(&temp);
+        this->prev_value_.assign(this->value_);
+      }
+    }
+  }
+
+  T value_{};
+  T prev_value_{};
+  uint32_t name_hash_{};
+  ESPPreferenceObject rtc_;
+};
+
 template<class C, typename... Ts> class GlobalVarSetAction : public Action<Ts...> {
  public:
   explicit GlobalVarSetAction(C *parent) : parent_(parent) {}
@@ -81,6 +139,7 @@ template<class C, typename... Ts> class GlobalVarSetAction : public Action<Ts...
 
 template<typename T> T &id(GlobalsComponent<T> *value) { return value->value(); }
 template<typename T> T &id(RestoringGlobalsComponent<T> *value) { return value->value(); }
+template<typename T, uint8_t SZ> T &id(RestoringGlobalStringComponent<T, SZ> *value) { return value->value(); }
 
 }  // namespace globals
 }  // namespace esphome

esphome/cpp_generator.py

@@ -663,7 +663,11 @@ async def process_lambda(
     :param return_type: The return type of the lambda.
     :return: The generated lambda expression.
     """
-    from esphome.components.globals import GlobalsComponent, RestoringGlobalsComponent
+    from esphome.components.globals import (
+        GlobalsComponent,
+        RestoringGlobalsComponent,
+        RestoringGlobalStringComponent,
+    )
 
     if value is None:
         return
@@ -676,6 +680,7 @@ async def process_lambda(
             and (
                 full_id.type.inherits_from(GlobalsComponent)
                 or full_id.type.inherits_from(RestoringGlobalsComponent)
+                or full_id.type.inherits_from(RestoringGlobalStringComponent)
             )
         ):
             parts[i * 3 + 1] = var.value()

tests/test2.yaml

@@ -5,6 +5,13 @@ esphome:
   board: nodemcu-32s
   build_path: build/test2
 
+globals:
+  - id: my_global_string
+    type: std::string
+    restore_value: yes
+    max_restore_data_length: 70
+    initial_value: '"DefaultValue"'
+
 substitutions:
   devicename: test2