tweak

esphome/components/web_server/web_server.cpp

@@ -404,10 +404,11 @@ void WebServer::handle_js_request(AsyncWebServerRequest *request) {
 
 // Helper functions to reduce code size by avoiding macro expansion
 static void set_json_id(JsonObject &root, EntityBase *obj, const char *prefix, JsonDetail start_config) {
-  char object_id_buf[OBJECT_ID_MAX_LEN];
-  StringRef object_id = obj->get_object_id_to(object_id_buf);
-  char id_buf[160];  // object_id can be up to 128 chars + prefix + dash + null
-  snprintf(id_buf, sizeof(id_buf), "%s-%s", prefix, object_id.c_str());
+  char id_buf[160];  // prefix + dash + object_id (up to 128) + null
+  size_t len = strlen(prefix);
+  memcpy(id_buf, prefix, len);
+  id_buf[len++] = '-';
+  obj->write_object_id_to(id_buf + len, sizeof(id_buf) - len);
   root[ESPHOME_F("id")] = id_buf;
   if (start_config == DETAIL_ALL) {
     root[ESPHOME_F("name")] = obj->get_name();

esphome/core/entity_base.cpp

@@ -78,18 +78,34 @@ void EntityBase::calc_object_id_() {
   this->object_id_hash_ = fnv1_hash(object_id.c_str());
 }
 
+size_t EntityBase::write_object_id_to(char *buf, size_t buf_size) const {
+  if (!this->is_object_id_dynamic_()) {
+    // Static case: copy from stored c_str
+    const char *src = this->object_id_c_str_ == nullptr ? "" : this->object_id_c_str_;
+    size_t len = strlen(src);
+    if (len >= buf_size)
+      len = buf_size - 1;
+    memcpy(buf, src, len);
+    buf[len] = '\0';
+    return len;
+  }
+  // Dynamic case: format into buffer
+  const std::string &name = App.get_friendly_name();
+  size_t len = std::min(name.size(), buf_size - 1);
+  for (size_t i = 0; i < len; i++) {
+    buf[i] = to_sanitized_char(to_snake_case_char(name[i]));
+  }
+  buf[len] = '\0';
+  return len;
+}
+
 StringRef EntityBase::get_object_id_to(std::span<char, OBJECT_ID_MAX_LEN> buf) const {
   if (!this->is_object_id_dynamic_()) {
     // Static case: return direct reference, buffer unused
     return this->object_id_c_str_ == nullptr ? StringRef() : StringRef(this->object_id_c_str_);
   }
-  // Dynamic case: format into buffer
-  const std::string &name = App.get_friendly_name();
-  size_t len = std::min(name.size(), buf.size() - 1);
-  for (size_t i = 0; i < len; i++) {
-    buf[i] = to_sanitized_char(to_snake_case_char(name[i]));
-  }
-  buf[len] = '\0';
+  // Dynamic case: write to buffer and return StringRef
+  size_t len = this->write_object_id_to(buf.data(), buf.size());
   return StringRef(buf.data(), len);
 }
 

esphome/core/entity_base.h

@@ -47,6 +47,10 @@ class EntityBase {
   /// For dynamic case: formats into buffer and returns StringRef to buffer
   StringRef get_object_id_to(std::span<char, OBJECT_ID_MAX_LEN> buf) const;
 
+  /// Write object_id directly to buffer, returns length written (excluding null)
+  /// Useful for building compound strings without intermediate buffer
+  size_t write_object_id_to(char *buf, size_t buf_size) const;
+
   // Get/set whether this Entity should be hidden outside ESPHome
   bool is_internal() const { return this->flags_.internal; }
   void set_internal(bool internal) { this->flags_.internal = internal; }