Function ForwardViaBackend

core/services/cloudproxy/backend_forward.go:24–153

ForwardViaBackend loads the cloud-proxy gRPC backend, ships the request via the Forward RPC, and pumps the response back to the client. PII redaction runs request-side (the NER middleware + MITM input path); the response is forwarded unmodified.

(
	c echo.Context,
	cfg *config.ModelConfig,
	body []byte,
	loader *model.ModelLoader,
	appConfig *config.ApplicationConfig,
)

// client. PII redaction runs request-side (the NER middleware + MITM
// input path); the response is forwarded unmodified.
func ForwardViaBackend(
	c echo.Context,
	cfg *config.ModelConfig,
	body []byte,
	loader *model.ModelLoader,
	appConfig *config.ApplicationConfig,
) (resultErr error) {
	// Passthrough forwards bypass core/backend/llm.go and therefore its
	// trace.RecordBackendTrace call — instrument here so passthrough
	// requests show up in the Traces UI alongside translate-mode ones.
	// Named return is unusual for this package but lets the defer capture
	// the final error across the function's many early-return paths
	// without rewriting them.
	var startTime time.Time
	statusCode := 0
	if appConfig.EnableTracing {
		trace.InitBackendTracingIfEnabled(appConfig.TracingMaxItems, appConfig.TracingMaxBodyBytes)
		startTime = time.Now()
	}
	defer func() {
		if !appConfig.EnableTracing {
			return
		}
		errStr := ""
		if resultErr != nil {
			errStr = resultErr.Error()
		}
		data := map[string]any{
			"mode":           cfg.Proxy.Mode,
			"provider":       cfg.Proxy.Provider,
			"upstream":       cfg.Proxy.UpstreamURL,
			"upstream_model": cfg.Proxy.UpstreamModel,
		}
		if statusCode != 0 {
			data["status"] = statusCode
		}
		trace.RecordBackendTrace(trace.BackendTrace{
			Timestamp: startTime,
			Duration:  time.Since(startTime),
			Type:      trace.BackendTraceLLM,
			ModelName: cfg.Name,
			Backend:   cfg.Backend,
			Summary:   trace.TruncateBytes(body, 200),
			Body:      trace.TruncateBytes(body, trace.MaxTraceBodyBytes),
			Error:     errStr,
			Data:      data,
		})
	}()

	if cfg.Proxy.UpstreamURL == "" {
		return echo.NewHTTPError(http.StatusInternalServerError,
			fmt.Sprintf("cloudproxy: proxy.upstream_url empty for model %q", cfg.Name))
	}

	body, err := rewriteModel(body, cfg.Proxy.UpstreamModel)
	if err != nil {
		return echo.NewHTTPError(http.StatusBadRequest, err.Error())
	}