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Add cancel_after / cancel_at timeout adapters
Lightweight free functions that race an IoAwaitable against a timer. A bidirectional std::stop_source ties the inner op and timeout together — whichever completes first cancels the other. Uses a fire-and-forget coroutine for the timer side, avoiding any timer_service modifications.
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‎include/boost/corosio.hpp‎

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#define BOOST_COROSIO_HPP
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#include <boost/corosio/backend.hpp>
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#include <boost/corosio/cancel.hpp>
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#include <boost/corosio/endpoint.hpp>
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#include <boost/corosio/io_buffer_param.hpp>
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#include <boost/corosio/io_context.hpp>
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#include <boost/corosio/resolver.hpp>
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#include <boost/corosio/resolver_results.hpp>
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#include <boost/corosio/signal_set.hpp>
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#include <boost/corosio/socket_option.hpp>
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#include <boost/corosio/tcp_acceptor.hpp>
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#include <boost/corosio/tcp_server.hpp>
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#include <boost/corosio/tcp_socket.hpp>

‎include/boost/corosio/cancel.hpp‎

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//
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// Copyright (c) 2026 Steve Gerbino
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Official repository: https://github.com/cppalliance/corosio
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//
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#ifndef BOOST_COROSIO_CANCEL_HPP
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#define BOOST_COROSIO_CANCEL_HPP
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#include <boost/corosio/detail/cancel_at_awaitable.hpp>
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#include <boost/corosio/timer.hpp>
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#include <boost/capy/concept/io_awaitable.hpp>
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#include <type_traits>
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#include <utility>
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namespace boost::corosio {
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/** Cancel an operation if it does not complete by a deadline.
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Races @p op against the given timer. If the deadline is reached
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first, the inner operation is cancelled via its stop token and
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completes with an error comparing equal to `capy::cond::canceled`.
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If the inner operation completes first, the timer is cancelled.
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Parent cancellation (from the caller's stop token) is forwarded
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to both the inner operation and the timeout timer.
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The timer's expiry is overwritten by this call. The timer must
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outlive the returned awaitable. Do not issue overlapping waits
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on the same timer.
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@par Completion Conditions
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The returned awaitable resumes when either:
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@li The inner operation completes (successfully or with error).
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@li The deadline expires and the inner operation is cancelled.
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@li The caller's stop token is triggered, cancelling both.
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@par Error Conditions
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@li On timeout or parent cancellation, the inner operation
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completes with an error equal to `capy::cond::canceled`.
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@li All other errors are propagated from the inner operation.
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@par Example
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@code
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timer timeout_timer( ioc );
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auto [ec, n] = co_await cancel_at(
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sock.read_some( buf ), timeout_timer,
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clock::now() + 5s );
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if (ec == capy::cond::canceled)
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// timed out or parent cancelled
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@endcode
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@param op The inner I/O awaitable to wrap.
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@param t The timer to use for the deadline. Must outlive
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the returned awaitable.
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@param deadline The absolute time point at which to cancel.
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@return An awaitable whose result matches @p op's result type.
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@see cancel_after
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*/
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auto cancel_at(
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capy::IoAwaitable auto&& op,
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timer& t,
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timer::time_point deadline)
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{
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return detail::cancel_at_awaitable<
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std::decay_t<decltype(op)>, timer>(
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std::forward<decltype(op)>(op), t, deadline);
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}
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/** Cancel an operation if it does not complete within a duration.
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Equivalent to `cancel_at( op, t, clock::now() + timeout )`.
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The timer's expiry is overwritten by this call. The timer must
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outlive the returned awaitable. Do not issue overlapping waits
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on the same timer.
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@par Completion Conditions
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The returned awaitable resumes when either:
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@li The inner operation completes (successfully or with error).
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@li The timeout elapses and the inner operation is cancelled.
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@li The caller's stop token is triggered, cancelling both.
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@par Error Conditions
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@li On timeout or parent cancellation, the inner operation
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completes with an error equal to `capy::cond::canceled`.
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@li All other errors are propagated from the inner operation.
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@par Example
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@code
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timer timeout_timer( ioc );
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auto [ec, n] = co_await cancel_after(
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sock.read_some( buf ), timeout_timer, 5s );
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if (ec == capy::cond::canceled)
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// timed out
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@endcode
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@param op The inner I/O awaitable to wrap.
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@param t The timer to use for the timeout. Must outlive
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the returned awaitable.
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@param timeout The relative duration after which to cancel.
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@return An awaitable whose result matches @p op's result type.
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@see cancel_at
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*/
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auto cancel_after(
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capy::IoAwaitable auto&& op,
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timer& t,
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timer::duration timeout)
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{
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return cancel_at(
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std::forward<decltype(op)>(op), t,
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timer::clock_type::now() + timeout);
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}
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/** Cancel an operation if it does not complete by a deadline.
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Convenience overload that creates a @ref timer internally.
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Otherwise identical to the explicit-timer overload.
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@par Completion Conditions
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The returned awaitable resumes when either:
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@li The inner operation completes (successfully or with error).
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@li The deadline expires and the inner operation is cancelled.
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@li The caller's stop token is triggered, cancelling both.
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@par Error Conditions
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@li On timeout or parent cancellation, the inner operation
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completes with an error equal to `capy::cond::canceled`.
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@li All other errors are propagated from the inner operation.
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@note Creates a timer per call. Use the explicit-timer overload
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to amortize allocation across multiple timeouts.
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@par Example
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@code
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auto [ec, n] = co_await cancel_at(
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sock.read_some( buf ),
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clock::now() + 5s );
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if (ec == capy::cond::canceled)
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// timed out or parent cancelled
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@endcode
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@param op The inner I/O awaitable to wrap.
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@param deadline The absolute time point at which to cancel.
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@return An awaitable whose result matches @p op's result type.
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@see cancel_after
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*/
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auto cancel_at(
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capy::IoAwaitable auto&& op,
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timer::time_point deadline)
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{
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return detail::cancel_at_awaitable<
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std::decay_t<decltype(op)>, timer, true>(
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std::forward<decltype(op)>(op), deadline);
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}
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/** Cancel an operation if it does not complete within a duration.
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Convenience overload that creates a @ref timer internally.
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Equivalent to `cancel_at( op, clock::now() + timeout )`.
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@par Completion Conditions
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The returned awaitable resumes when either:
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@li The inner operation completes (successfully or with error).
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@li The timeout elapses and the inner operation is cancelled.
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@li The caller's stop token is triggered, cancelling both.
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@par Error Conditions
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@li On timeout or parent cancellation, the inner operation
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completes with an error equal to `capy::cond::canceled`.
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@li All other errors are propagated from the inner operation.
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@note Creates a timer per call. Use the explicit-timer overload
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to amortize allocation across multiple timeouts.
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@par Example
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@code
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auto [ec, n] = co_await cancel_after(
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sock.read_some( buf ), 5s );
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if (ec == capy::cond::canceled)
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// timed out
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@endcode
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@param op The inner I/O awaitable to wrap.
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@param timeout The relative duration after which to cancel.
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@return An awaitable whose result matches @p op's result type.
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@see cancel_at
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*/
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auto cancel_after(
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capy::IoAwaitable auto&& op,
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timer::duration timeout)
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{
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return cancel_at(
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std::forward<decltype(op)>(op),
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timer::clock_type::now() + timeout);
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}
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} // namespace boost::corosio
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#endif

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