Adapt react-client to use the real backend API (#1545)

Co-authored-by: Philip Molares <philip.molares@udo.edu>
Co-authored-by: Tilman Vatteroth <git@tilmanvatteroth.de>

src/api/common/api-request-builder/api-request-builder-with-body.ts

@@ -0,0 +1,38 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { ApiRequestBuilder } from './api-request-builder'
+
+/**
+ * Builder to construct and execute a call to the HTTP API that contains a body payload.
+ *
+ * @param RequestBodyType The type of the request body if applicable.
+ */
+export abstract class ApiRequestBuilderWithBody<ResponseType, RequestBodyType> extends ApiRequestBuilder<ResponseType> {
+  /**
+   * Adds a body part to the API request. If this is called multiple times, only the body of the last invocation will be
+   * used during the execution of the request.
+   *
+   * @param bodyData The data to use as request body.
+   * @return The API request instance itself for chaining.
+   */
+  withBody(bodyData: BodyInit): this {
+    this.requestBody = bodyData
+    return this
+  }
+
+  /**
+   * Adds a JSON-encoded body part to the API request. This method will set the content-type header appropriately.
+   *
+   * @param bodyData The data to use as request body. Will get stringified to JSON.
+   * @return The API request instance itself for chaining.
+   * @see {withBody}
+   */
+  withJsonBody(bodyData: RequestBodyType): this {
+    this.withHeader('Content-Type', 'application/json')
+    return this.withBody(JSON.stringify(bodyData))
+  }
+}