Improve HTTPError to include response text and JSON

packages/generator/src/client.ts

@@ -54,17 +54,34 @@ export class HTTPError extends Error {
   readonly status: number;
   readonly statusText: string;
   readonly response: Response;
-  constructor(response: Response) {
+  readonly responseText: string | null;
+  readonly responseJson: unknown | null;
+  constructor(
+    response: Response,
+    responseText: string | null,
+    responseJson: unknown | null
+  ) {
     super(\`HTTP Error: \${response.status} \${response.statusText}\`);
     this.name = 'HTTPError';
     this.status = response.status;
     this.statusText = response.statusText;
     this.response = response;
+    this.responseText = responseText;
+    this.responseJson = responseJson;
   }
 }
 
-function _checkOk(response: Response): Response {
-  if (!response.ok) throw new HTTPError(response);
+async function _checkOk(response: Response): Promise<Response> {
+  if (!response.ok) {
+    const responseText = await response.text().catch(() => null);
+    let responseJson: unknown | null = null;
+    if (responseText) {
+      try {
+        responseJson = JSON.parse(responseText);
+      } catch {}
+    }
+    throw new HTTPError(response, responseText, responseJson);
+  }
   return response;
 }
 `;