Method ProcessRequest

intercept/messages/streaming.go:93–535

ProcessRequest handles a request to /v1/messages. This API has a state-machine behind it, which is described in https://docs.claude.com/en/docs/build-with-claude/streaming#event-types. Each stream uses the following event flow: - `message_start`: contains a Message object with empty content. - A se

(w http.ResponseWriter, r *http.Request)

// results relayed to the SERVER. The response from the server will be handled synchronously, and this loop
// can continue until all injected tool invocations are completed and the response is relayed to the client.
func (i *StreamingInterception) ProcessRequest(w http.ResponseWriter, r *http.Request) (outErr error) {
	if len(i.reqPayload) == 0 {
		return xerrors.New("developer error: request payload is empty")
	}

	ctx, span := i.tracer.Start(r.Context(), "Intercept.ProcessRequest", trace.WithAttributes(tracing.InterceptionAttributesFromContext(r.Context())...))
	defer tracing.EndSpanErr(span, &outErr)

	// Allow us to interrupt watch via cancel.
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()
	r = r.WithContext(ctx) // Rewire context for SSE cancellation.

	logger := i.logger.With(slog.F("model", i.Model()))

	var (
		prompt      string
		promptFound bool
		err         error
	)

	prompt, promptFound, err = i.reqPayload.lastUserPrompt()
	if err != nil {
		logger.Warn(ctx, "failed to determine last user prompt", slog.Error(err))
	}

	// Claude Code uses a "small/fast model" for certain tasks.
	if !i.isSmallFastModel() {
		// Only inject tools into "actual" request.
		i.injectTools()
	}

	streamCtx, streamCancel := context.WithCancelCause(ctx)
	defer streamCancel(xerrors.New("deferred"))

	// TODO(ssncferreira): inject actor headers directly in the client-header
	//   middleware instead of using SDK options.
	var opts []option.RequestOption
	if actor := aibcontext.ActorFromContext(ctx); actor != nil && i.cfg.SendActorHeaders {
		opts = append(opts, intercept.ActorHeadersAsAnthropicOpts(actor)...)
	}

	svc, err := i.newMessagesService(streamCtx, opts...)
	if err != nil {
		err = xerrors.Errorf("create anthropic client: %w", err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return err
	}

	// events will either terminate when shutdown after interaction with upstream completes, or when streamCtx is done.
	events := eventstream.NewEventStream(streamCtx, logger.Named("sse-sender"), i.pingPayload())
	go events.Start(w, r)
	defer func() {
		_ = events.Shutdown(streamCtx) // Catch-all in case it doesn't get shutdown after stream completes.
	}()

	// Accumulate usage across the entire streaming interaction (including tool reinvocations).
	var cumulativeUsage anthropic.Usage