Method delegateToService

packages/cli/src/util/dev/server.ts:1551–1662

(
    req: http.IncomingMessage,
    res: http.ServerResponse,
    requestId: string,
    matchedRoute: RouteWithSrc & { destination: ServiceDestination },
    vercelConfig: VercelConfig,
    requestTransforms?: Transform[],
    responseTransforms?: Transform[]
  )

  }

  private async delegateToService(
    req: http.IncomingMessage,
    res: http.ServerResponse,
    requestId: string,
    matchedRoute: RouteWithSrc & { destination: ServiceDestination },
    vercelConfig: VercelConfig,
    requestTransforms?: Transform[],
    responseTransforms?: Transform[]
  ): Promise<void> {
    const { debug } = output;
    const { service: serviceName, path: destPath } = matchedRoute.destination;

    const origin = this.orchestrator?.getServiceOrigin(serviceName);
    if (!origin) {
      output.error(
        `Cannot route to service ${cmd(serviceName)}: it is not running.`
      );
      await this.sendError(
        req,
        res,
        requestId,
        'FUNCTION_INVOCATION_FAILED',
        502
      );
      return;
    }

    // Resolve lookup path for the service's route table
    const parsed = url.parse(req.url || '/');
    const originalPathname = parsed.pathname || '/';

    let lookupPath = originalPathname;
    if (typeof destPath === 'string' && matchedRoute.src) {
      const keys: string[] = [];
      const matcher = PCRE(
        `%${matchedRoute.src}%${this.isCaseSensitive() ? '' : 'i'}`,
        keys
      );
      const match =
        matcher.exec(originalPathname) ||
        matcher.exec(originalPathname.substring(1));
      lookupPath = match
        ? resolveRouteParameters(destPath, match, keys)
        : destPath;
    }

    const serviceRoutes = this.getServiceRouteTable(serviceName);
    const proxyHeaders = this.getProxyHeaders(req, requestId, false);

    const requestTransformsToApply: Transform[] = [
      ...(requestTransforms ?? []),
    ];
    let responseTransformsToApply = responseTransforms;

    if (serviceRoutes.length > 0) {
      const serviceResult = await devRouter(
        `${lookupPath}${parsed.search || ''}`,
        req.method,