perf: skip decoding discarded diagnostic error bodies (#20276)

Co-authored-by: Orca Worker <orca-worker@localhost>

src/main/observability/diagnostic-upload-http.test.ts

@@ -23,6 +23,22 @@ class FakeResponse extends EventEmitter {
 }
 
 describe('diagnostic upload HTTP', () => {
+  it('reports only the status for an error response with an invalid JSON body', async () => {
+    const request = new FakeRequest()
+    const response = new FakeResponse()
+    response.statusCode = 503
+    httpRequestMock.mockImplementationOnce((_options, callback) => {
+      callback(response)
+      return request
+    })
+    const result = postJsonForJson('http://diagnostics.example/upload', {}, 1000)
+    response.emit('data', Buffer.from('private backend details: not JSON'))
+    response.emit('end')
+    await expect(result).rejects.toThrow(/^HTTP 503$/)
+    expect(response.listenerCount('data')).toBe(0)
+    expect(request.listenerCount('error')).toBe(0)
+  })
+
   it('removes request and response listeners after a successful response', async () => {
     const request = new FakeRequest()
     const response = new FakeResponse()

src/main/observability/diagnostic-upload-http.ts

@@ -89,8 +89,8 @@ function postRaw(
     }
     function onResponseEnd(): void {
       const status = res?.statusCode ?? 0
-      const text = Buffer.concat(chunks).toString('utf8')
       if (status >= 200 && status < 300) {
+        const text = Buffer.concat(chunks).toString('utf8')
         try {
           resolveOnce(text.length > 0 ? JSON.parse(text) : {})
         } catch {