fix: read error response bodies once in the TypeScript client

xdk-gen/src/typescript/generator.rs

@@ -85,6 +85,7 @@ language! {
             render "test_contracts" => "tests/{}/test_contracts.test.ts",
             render "test_pagination" => "tests/{}/test_pagination.test.ts"
         },
+        render "test_client_errors" => "tests/client_errors.test.ts",
         render "jest.config" => "jest.config.cjs"
     ]
 }

xdk-gen/templates/typescript/main_client.j2

@@ -396,13 +396,23 @@ export class Client {
       });
 
       if (!response.ok) {
+        // Read the body exactly once: a fetch Response body is a one-shot
+        // stream, so a failed json() followed by text() would throw
+        // "Body is unusable" and mask the real error.
         let errorData: any;
         try {
-          errorData = await response.json();
+          const errorText = await response.text();
+          try {
+            errorData = JSON.parse(errorText);
+          } catch {
+            errorData = errorText;
+          }
         } catch {
-          errorData = await response.text();
+          // The body could not be read at all (e.g. an aborted stream);
+          // still surface the status line below.
+          errorData = undefined;
         }
-        
+
         throw new ApiError(
           errorData && errorData.message ? errorData.message : `HTTP ${response.status}: ${response.statusText}`,
           response.status,

xdk-gen/templates/typescript/oauth2_auth.j2

@@ -113,8 +113,11 @@ export class OAuth2 {
     });
 
     if (!response.ok) {
-      const errorData = await response.json().catch(() => response.text());
-      throw new Error(`HTTP error! status: ${response.status}, body: ${JSON.stringify(errorData)}`);
+      // Read the body exactly once: a fetch Response body is a one-shot
+      // stream, so json() followed by text() on the same response throws
+      // "Body is unusable" and masks the real error.
+      const errorText = await response.text().catch(() => '');
+      throw new Error(`HTTP error! status: ${response.status}, body: ${errorText}`);
     }
 
     const data = await response.json();
@@ -167,8 +170,11 @@ export class OAuth2 {
     });
 
     if (!response.ok) {
-      const errorData = await response.json().catch(() => response.text());
-      throw new Error(`Failed to refresh token: ${response.status}, body: ${JSON.stringify(errorData)}`);
+      // Read the body exactly once: a fetch Response body is a one-shot
+      // stream, so json() followed by text() on the same response throws
+      // "Body is unusable" and masks the real error.
+      const errorText = await response.text().catch(() => '');
+      throw new Error(`Failed to refresh token: ${response.status}, body: ${errorText}`);
     }
 
     const data = await response.json();

xdk-gen/templates/typescript/test_client_errors.j2

@@ -0,0 +1,177 @@
+/**
+ * AUTO-GENERATED FILE - DO NOT EDIT
+ * This file was automatically generated by the XDK build tool.
+ * Any manual changes will be overwritten on the next generation.
+ *
+ * Auto-generated error-handling tests for Client.request() and the OAuth2
+ * token flows. This module contains tests that validate how non-OK HTTP
+ * responses are surfaced: JSON bodies, plain-text bodies, and empty bodies.
+ *
+ * The tests use real Response objects rather than mocks with independent
+ * json()/text() resolvers, because a fetch Response body is a one-shot
+ * stream: reading it twice throws "Body is unusable". A mock with separate
+ * resolvers would hide exactly the class of bug these tests guard against.
+ *
+ * Generated automatically - do not edit manually.
+ */
+
+import { describe, it, expect, afterEach, jest } from '@jest/globals';
+import { Client, ApiError } from '../src/client.js';
+import { OAuth2 } from '../src/oauth2_auth.js';
+
+/** Calls an async function that must reject, and returns the rejection. */
+const captureRejection = async (fn: () => Promise<unknown>): Promise<any> => {
+  try {
+    await fn();
+  } catch (error) {
+    return error;
+  }
+  throw new Error('expected the call to reject');
+};
+
+describe('Client.request error handling', () => {
+  const client = new Client({
+    baseUrl: 'https://api.example.com',
+    bearerToken: 'test-token',
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  const mockResponse = (response: Response) => {
+    jest
+      .spyOn(client.httpClient, 'request')
+      .mockResolvedValue(response as any);
+  };
+
+  it('surfaces a non-JSON error body as the ApiError data', async () => {
+    mockResponse(
+      new Response('Route not found', { status: 404, statusText: 'Not Found' })
+    );
+
+    const error = await captureRejection(() =>
+      client.request('GET', '/2/example')
+    );
+
+    expect(error).toBeInstanceOf(ApiError);
+    expect(error.status).toBe(404);
+    expect(error.statusText).toBe('Not Found');
+    expect(error.message).toBe('HTTP 404: Not Found');
+    expect(error.data).toBe('Route not found');
+  });
+
+  it('parses a JSON error body into the ApiError data', async () => {
+    const body = {
+      title: 'Too Many Requests',
+      detail: 'Rate limit exceeded',
+      status: 429,
+    };
+    mockResponse(
+      new Response(JSON.stringify(body), {
+        status: 429,
+        statusText: 'Too Many Requests',
+      })
+    );
+
+    const error = await captureRejection(() =>
+      client.request('GET', '/2/example')
+    );
+
+    expect(error).toBeInstanceOf(ApiError);
+    expect(error.status).toBe(429);
+    expect(error.data).toEqual(body);
+  });
+
+  it('uses the message field of a JSON error body as the error message', async () => {
+    mockResponse(
+      new Response(JSON.stringify({ message: 'Invalid cursor' }), {
+        status: 400,
+        statusText: 'Bad Request',
+      })
+    );
+
+    const error = await captureRejection(() =>
+      client.request('GET', '/2/example')
+    );
+
+    expect(error).toBeInstanceOf(ApiError);
+    expect(error.message).toBe('Invalid cursor');
+    expect(error.status).toBe(400);
+  });
+
+  it('still reports the status when the error body is empty', async () => {
+    mockResponse(
+      new Response(null, { status: 500, statusText: 'Internal Server Error' })
+    );
+
+    const error = await captureRejection(() =>
+      client.request('GET', '/2/example')
+    );
+
+    expect(error).toBeInstanceOf(ApiError);
+    expect(error.status).toBe(500);
+    expect(error.message).toBe('HTTP 500: Internal Server Error');
+  });
+});
+
+describe('OAuth2 token flow error handling', () => {
+  const oauth2 = new OAuth2({
+    clientId: 'test-client-id',
+    redirectUri: 'https://example.com/callback',
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  const mockFetch = (response: Response) => {
+    jest
+      .spyOn(globalThis, 'fetch')
+      .mockResolvedValue(response as any);
+  };
+
+  it('surfaces a non-JSON error body from the code exchange', async () => {
+    mockFetch(
+      new Response('Service Unavailable', {
+        status: 503,
+        statusText: 'Service Unavailable',
+      })
+    );
+
+    const error = await captureRejection(() =>
+      oauth2.exchangeCode('test-code')
+    );
+
+    expect(error.message).toBe(
+      'HTTP error! status: 503, body: Service Unavailable'
+    );
+  });
+
+  it('surfaces a non-JSON error body from the token refresh', async () => {
+    mockFetch(
+      new Response('Bad Gateway', { status: 502, statusText: 'Bad Gateway' })
+    );
+
+    const error = await captureRejection(() =>
+      oauth2.refreshToken('test-refresh-token')
+    );
+
+    expect(error.message).toBe(
+      'Failed to refresh token: 502, body: Bad Gateway'
+    );
+  });
+
+  it('surfaces a JSON error body from the code exchange', async () => {
+    const body = JSON.stringify({ error: 'invalid_grant' });
+    mockFetch(
+      new Response(body, { status: 400, statusText: 'Bad Request' })
+    );
+
+    const error = await captureRejection(() =>
+      oauth2.exchangeCode('test-code')
+    );
+
+    expect(error.message).toBe(`HTTP error! status: 400, body: ${body}`);
+  });
+});