From 9a155ee6a3dd54ea6909c19ee4219e04237f8379 Mon Sep 17 00:00:00 2001
From: JPeer264 <jan.peer@sentry.io>
Date: Wed, 17 Dec 2025 14:20:50 +0100
Subject: [PATCH] fix(cloudflare): Consume body of fetch in the Cloudflare
 transport

---
 packages/cloudflare/src/transport.ts       | 13 +++-
 packages/cloudflare/test/transport.test.ts | 72 ++++++++++++++++++++++
 2 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/packages/cloudflare/src/transport.ts b/packages/cloudflare/src/transport.ts
index 8881e2dd6567..8e0e82aae7e0 100644
--- a/packages/cloudflare/src/transport.ts
+++ b/packages/cloudflare/src/transport.ts
@@ -89,7 +89,18 @@ export function makeCloudflareTransport(options: CloudflareTransportOptions): Tr
     };
 
     return suppressTracing(() => {
-      return (options.fetch ?? fetch)(options.url, requestOptions).then(response => {
+      return (options.fetch ?? fetch)(options.url, requestOptions).then(async response => {
+        // Consume the response body to satisfy Cloudflare Workers' fetch requirements.
+        // The runtime requires all fetch response bodies to be read or explicitly canceled
+        // to prevent connection stalls and potential deadlocks. We read the body as text
+        // even though we don't use the content, as Sentry's response information is in the headers.
+        // See: https://github.com/getsentry/sentry-javascript/issues/18534
+        try {
+          await response.text();
+        } catch {
+          // no-op
+        }
+
         return {
           statusCode: response.status,
           headers: {
diff --git a/packages/cloudflare/test/transport.test.ts b/packages/cloudflare/test/transport.test.ts
index 71b231f542af..fdb9fbc5e30f 100644
--- a/packages/cloudflare/test/transport.test.ts
+++ b/packages/cloudflare/test/transport.test.ts
@@ -106,6 +106,78 @@ describe('Edge Transport', () => {
       ...REQUEST_OPTIONS,
     });
   });
+
+  describe('Response body consumption (issue #18534)', () => {
+    it('consumes the response body to prevent Cloudflare stalled connection warnings', async () => {
+      const textMock = vi.fn(() => Promise.resolve('OK'));
+      const headers = {
+        get: vi.fn(),
+      };
+      mockFetch.mockImplementationOnce(() =>
+        Promise.resolve({
+          headers,
+          status: 200,
+          text: textMock,
+        }),
+      );
+
+      const transport = makeCloudflareTransport(DEFAULT_EDGE_TRANSPORT_OPTIONS);
+
+      await transport.send(ERROR_ENVELOPE);
+      await transport.flush();
+
+      expect(textMock).toHaveBeenCalledTimes(1);
+      expect(headers.get).toHaveBeenCalledTimes(2);
+      expect(headers.get).toHaveBeenCalledWith('X-Sentry-Rate-Limits');
+      expect(headers.get).toHaveBeenCalledWith('Retry-After');
+    });
+
+    it('handles response body consumption errors gracefully', async () => {
+      const textMock = vi.fn(() => Promise.reject(new Error('Body read error')));
+      const headers = {
+        get: vi.fn(),
+      };
+
+      mockFetch.mockImplementationOnce(() =>
+        Promise.resolve({
+          headers,
+          status: 200,
+          text: textMock,
+        }),
+      );
+
+      const transport = makeCloudflareTransport(DEFAULT_EDGE_TRANSPORT_OPTIONS);
+
+      await expect(transport.send(ERROR_ENVELOPE)).resolves.toBeDefined();
+      await expect(transport.flush()).resolves.toBeDefined();
+
+      expect(textMock).toHaveBeenCalledTimes(1);
+      expect(headers.get).toHaveBeenCalledTimes(2);
+      expect(headers.get).toHaveBeenCalledWith('X-Sentry-Rate-Limits');
+      expect(headers.get).toHaveBeenCalledWith('Retry-After');
+    });
+
+    it('handles a potential never existing use case of a non existing text method', async () => {
+      const headers = {
+        get: vi.fn(),
+      };
+
+      mockFetch.mockImplementationOnce(() =>
+        Promise.resolve({
+          headers,
+          status: 200,
+        }),
+      );
+
+      const transport = makeCloudflareTransport(DEFAULT_EDGE_TRANSPORT_OPTIONS);
+
+      await expect(transport.send(ERROR_ENVELOPE)).resolves.toBeDefined();
+      await expect(transport.flush()).resolves.toBeDefined();
+      expect(headers.get).toHaveBeenCalledTimes(2);
+      expect(headers.get).toHaveBeenCalledWith('X-Sentry-Rate-Limits');
+      expect(headers.get).toHaveBeenCalledWith('Retry-After');
+    });
+  });
 });
 
 describe('IsolatedPromiseBuffer', () => {