What causes "reasonix: POST %s returned %d: %s" in chenhg5/cc-connect?

Read the response-body snippet embedded in the error — it states the server's own reason

reasonix: POST %s returned %d: %s

Error message

reasonix: POST %s returned %d: %s

What it means

When the reasonix serve endpoint responds with HTTP status >= 400, httpPost reads up to 512 bytes of the response body and returns 'reasonix: POST %s returned %d: %s' including that body for debugging. This turns server-side rejections (bad request, auth, not found, 5xx) into actionable error messages.

Source

Thrown at agent/reasonix/session.go:503

	if err != nil {
		return fmt.Errorf("reasonix: create request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return fmt.Errorf("reasonix: POST %s: %w", path, err)
	}
	defer func() {
		if err := resp.Body.Close(); err != nil {
			slog.Warn("reasonix: POST close body", "path", path, "error", err)
		}
	}()

	if resp.StatusCode >= 400 {
		// Include response body (first 512 bytes) in error for debugging.
		errBody, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		return fmt.Errorf("reasonix: POST %s returned %d: %s", path, resp.StatusCode, strings.TrimSpace(string(errBody)))
	}
	return nil
}

// formatImages builds a comma-separated list of image filenames for inclusion
// in the prompt. Reasons adopts the standard cc-connect file-save pattern so
// the actual image bytes land on disk (via core.SaveFilesToDisk); this list
// gives reasonix serve a human-readable hint about which images were attached.
func formatImages(images []core.ImageAttachment) string {
	names := make([]string, len(images))
	for i, img := range images {
		if img.FileName != "" {
			names[i] = img.FileName
		} else {
			names[i] = fmt.Sprintf("image_%d", i)
		}
	}
	return strings.Join(names, ", ")

View on GitHub (pinned to 4000b2338a)

Solutions

Read the response-body snippet embedded in the error — it states the server's own reason
Check status: 404 → API path/version mismatch, update reasonix serve or cc-connect; 401/403 → fix credentials; 5xx → inspect serve logs
Verify the request payload matches the serve endpoint's expected schema for that path
If a proxy sits in front of serve, check proxy error logs for the upstream failure

Defensive patterns

Strategy: try-catch

Try / catch

// Go
if err := sess.Send(...); err != nil {
    var herr string
    if n, _ := fmt.Sscanf(err.Error(), "reasonix: POST %s returned", &herr); n == 1 || strings.Contains(err.Error(), "returned ") {
        slog.Error("reasonix server rejected request", "detail", err)
    }
}

Prevention

Pin compatible versions of cc-connect adapter and reasonix serve
Keep request payloads within the endpoint's documented limits
Monitor 5xx rates on the serve endpoint
Include response bodies in logs (as this error does) for fast diagnosis

When it happens

Trigger: The serve endpoint replies 400/401/404/500 etc. to a POST issued from newSession, Send, or RespondPermission — e.g. unknown path, invalid session id, malformed payload the server rejects, or the server itself erroring.

Common situations: Version mismatch between cc-connect and the reasonix serve API (endpoint renamed → 404); expired/missing auth token → 401; prompt payload exceeding a server limit → 400/413; serve process crash-looping → 502/503 from a proxy.

Understand the failure class

Background: "API error: {status}" and "HTTP 401/403/404/429/5xx" errors: non-2xx HTTP responses explained — this error's family across 27 libraries.

Related errors

AI-assisted analysis of chenhg5/cc-connect@4000b2338a (2026-09-06). Data as JSON: /api/errors/0d92599fe5390724. Report an issue: GitHub.