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[Feature] settle in parallel
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🚅 Deployed to the echo-pr-695 environment in echo
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| // Case 2: Settle failed but model succeeded | ||
| if (!settleResult && modelResult.success) { |
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Case 2 (settle failed but model succeeded) calls handleResolveResponse after settle has already sent a 402 response, which will cause an Express error when trying to send a second response to the same request.
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📝 Patch Details
diff --git a/packages/app/server/src/handlers.ts b/packages/app/server/src/handlers.ts
index 131d35d9..fb53c578 100644
--- a/packages/app/server/src/handlers.ts
+++ b/packages/app/server/src/handlers.ts
@@ -54,11 +54,7 @@ export async function handleX402Request({
provider: provider.getType(),
url: req.url,
});
- modelRequestService.handleResolveResponse(
- res,
- isStream,
- data
- );
+ // Note: settle already sent a 402 response, so we should not attempt to send another response
return;
}
Analysis
Double response error in handleX402Request Case 2
What fails: In handleX402Request() (packages/app/server/src/handlers.ts, lines 46-62), when settle fails but the model request succeeds (Case 2), the code calls modelRequestService.handleResolveResponse() after settle has already sent a 402 response via buildX402Response(), causing Express to throw "Error: Can't set headers after they are sent to the client".
How to reproduce:
- Send an X402 request where payment settlement fails (e.g., invalid payment authorization)
- Simultaneously, the model request succeeds
- The settle handler calls
buildX402Response(req, res, maxCost)which sendsres.status(402).json(resBody) - Case 2 then attempts to call
modelRequestService.handleResolveResponse(res, isStream, data)which calls eitherres.json(data)(non-streaming) orres.end()(streaming) - Express throws error because headers were already sent
Result: Error thrown and logged by error handler: "Error: Can't set headers after they are sent to the client". While the 402 response reaches the client (and the error handler checks res.headersSent before attempting another response), this is incorrect behavior - no error should be thrown since the 402 response is the correct outcome.
Expected: When settle fails and sends a 402 response indicating payment is required, no subsequent response should be attempted. The 402 response should be the final response to the client.
Root cause: Express.js specification requires exactly one response per HTTP request. Once response headers are sent, attempting to set additional headers or send another response violates this protocol and throws an error.
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