Add API interface to request a complete device config as JSON. (#3911)

Co-authored-by: Paulus Schoutsen <paulus@home-assistant.io>

esphome/dashboard/dashboard.py

@@ -29,6 +29,7 @@ import tornado.web
 import tornado.websocket
 
 from esphome import const, platformio_api, util, yaml_util
+from esphome.core import EsphomeError
 from esphome.helpers import mkdir_p, get_bool_env, run_system_command
 from esphome.storage_json import (
     EsphomeStorageJSON,
@@ -927,6 +928,27 @@ class SecretKeysRequestHandler(BaseHandler):
         self.write(json.dumps(secret_keys))
 
 
+class JsonConfigRequestHandler(BaseHandler):
+    @authenticated
+    @bind_config
+    def get(self, configuration=None):
+        filename = settings.rel_path(configuration)
+        if not os.path.isfile(filename):
+            self.send_error(404)
+            return
+
+        try:
+            content = yaml_util.load_yaml(filename, clear_secrets=False)
+            json_content = json.dumps(
+                content, default=lambda o: {"__type": str(type(o)), "repr": repr(o)}
+            )
+            self.set_header("content-type", "application/json")
+            self.write(json_content)
+        except EsphomeError as err:
+            _LOGGER.warning("Error translating file %s to JSON: %s", filename, err)
+            self.send_error(500)
+
+
 def get_base_frontend_path():
     if ENV_DEV not in os.environ:
         import esphome_dashboard
@@ -1031,6 +1053,7 @@ def make_app(debug=get_bool_env(ENV_DEV)):
             (f"{rel}devices", ListDevicesHandler),
             (f"{rel}import", ImportRequestHandler),
             (f"{rel}secret_keys", SecretKeysRequestHandler),
+            (f"{rel}json-config", JsonConfigRequestHandler),
             (f"{rel}rename", EsphomeRenameHandler),
             (f"{rel}prometheus-sd", PrometheusServiceDiscoveryHandler),
         ],