config-schema: add StaticSchemaLoader

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/config-schema/package.json

@@ -22,6 +22,7 @@
   "dependencies": {
     "@backstage/config": "^0.1.4",
     "@backstage/core": "^0.7.3",
+    "@backstage/errors": "^0.1.1",
     "@backstage/theme": "^0.2.5",
     "@material-ui/core": "^4.11.0",
     "@material-ui/icons": "^4.9.1",

plugins/config-schema/src/api/StaticSchemaLoader.ts

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Observable } from '@backstage/core';
+import ObservableImpl from 'zen-observable';
+import { ResponseError } from '@backstage/errors';
+import { Schema } from 'jsonschema';
+import { ConfigSchemaApi, ConfigSchemaResult } from './types';
+
+const DEFAULT_URL = 'config-schema.json';
+
+/**
+ * A ConfigSchemaApi implementation that loads the configuration from a URL.
+ */
+export class StaticSchemaLoader implements ConfigSchemaApi {
+  private readonly url: string;
+
+  constructor({ url = DEFAULT_URL }: { url?: string } = {}) {
+    this.url = url;
+  }
+
+  schema$(): Observable<ConfigSchemaResult> {
+    return new ObservableImpl(subscriber => {
+      this.fetchSchema().then(
+        schema => subscriber.next({ schema }),
+        error => subscriber.error(error),
+      );
+    });
+  }
+
+  private async fetchSchema(): Promise<undefined | Schema> {
+    const res = await fetch(this.url);
+
+    if (!res.ok) {
+      if (res.status === 404) {
+        return undefined;
+      }
+
+      throw ResponseError.fromResponse(res);
+    }
+
+    return await res.json();
+  }
+}

plugins/config-schema/src/api/index.ts

@@ -16,3 +16,4 @@
 
 export { configSchemaApiRef } from './types';
 export type { ConfigSchemaApi } from './types';
+export { StaticSchemaLoader } from './StaticSchemaLoader';

plugins/config-schema/src/index.ts

@@ -13,4 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
+export * from './api';
 export { configSchemaPlugin, ConfigSchemaPage } from './plugin';