http: add to_reply() in httpd::redirect_exception

This function allows for the creation of an `http::reply`
from a thrown `redirect_exception`, with a url for the `Location`
header and an optional `Retry-After` timeout value.

include/seastar/http/exception.hh

@@ -65,10 +65,22 @@ private:
  */
 class redirect_exception : public base_exception {
 public:
- redirect_exception(const std::string& url, http::reply::status_type status = http::reply::status_type::moved_permanently)
- : base_exception("", status), url(url) {
+ redirect_exception(const std::string& url, http::reply::status_type status = http::reply::status_type::moved_permanently, const std::optional<int>& retry_after = std::nullopt)
+ : base_exception("", status), url(url), retry_after(retry_after) {
  }
+
+ http::reply to_reply() const {
+ http::reply reply{};
+ reply.add_header("Location", url);
+ if (retry_after.has_value()) {
+ reply.add_header("Retry-After", std::to_string(retry_after.value()));
+ }
+ reply.set_status(status()).done("json");
+ return reply;
+ }
+
  std::string url;
+ std::optional<int> retry_after;
 };
 
 /**

src/http/routes.cc

@@ -73,8 +73,8 @@ std::unique_ptr<http::reply> routes::exception_reply(std::exception_ptr eptr) {
  }
  std::rethrow_exception(eptr);
  } catch (const redirect_exception& _e) {
-  rep.reset(new http::reply());
- rep->add_header("Location", _e.url).set_status(_e.status());
+ *rep = _e.to_reply();
+ return rep;
  } catch (const base_exception& e) {
  rep->set_status(e.status(), json_exception(e).to_json());
  } catch (...) {
@@ -94,6 +94,8 @@ future<std::unique_ptr<http::reply> > routes::handle(const sstring& path, std::u
  handler->verify_mandatory_params(*req);
  auto r = handler->handle(path, std::move(req), std::move(rep));
  return r.handle_exception(_general_handler);
+ } catch (const redirect_exception& _e) {
+ *rep = _e.to_reply();
  } catch (...) {
  rep = exception_reply(std::current_exception());
  }