Function resolveComponentValue

http/unstable_message_signatures.ts:348–400

(
  id: ComponentIdentifier,
  message: Request | Response,
  parsedUrl: { value?: URL },
  relatedRequest?: Request,
  relatedParsedUrl?: { value?: URL },
)

}

function resolveComponentValue(
  id: ComponentIdentifier,
  message: Request | Response,
  parsedUrl: { value?: URL },
  relatedRequest?: Request,
  relatedParsedUrl?: { value?: URL },
): string {
  const params = id.parameters ?? {};

  // Validate incompatible parameter combinations
  if (params.bs && params.sf) {
    throw new TypeError(
      `Cannot combine "bs" and "sf" parameters on component "${id.name}"`,
    );
  }
  if (params.bs && params.key !== undefined) {
    throw new TypeError(
      `Cannot combine "bs" and "key" parameters on component "${id.name}"`,
    );
  }

  if (params.tr) {
    throw new TypeError(
      `Trailer field resolution (";tr") is not supported for component "${id.name}"`,
    );
  }

  // Handle ;req parameter
  if (params.req) {
    if (message instanceof Request) {
      throw new TypeError(
        `Cannot use "req" parameter on component "${id.name}" for a request message`,
      );
    }
    if (!relatedRequest) {
      throw new TypeError(
        `Cannot resolve "req" parameter on component "${id.name}": no related request provided`,
      );
    }
    const { req: _, ...restParams } = params;
    return resolveComponentValue(
      { name: id.name, parameters: restParams },
      relatedRequest,
      relatedParsedUrl ?? {},
    );
  }

  if (id.name.startsWith("@")) {
    return resolveDerivedComponent(id.name, message, params, parsedUrl);
  }

  return resolveFieldComponent(id.name, message, params);
}

const REQUEST_ONLY_DERIVED: ReadonlySet<string> = new Set<DerivedComponent>([
  "@method",