quic_reactor.h
/*
* Copyright 2022-2024 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#ifndef OSSL_QUIC_REACTOR_H
# define OSSL_QUIC_REACTOR_H
# include "internal/time.h"
# include "internal/sockets.h"
# include "internal/quic_predef.h"
# include "internal/thread_arch.h"
# include <openssl/bio.h>
# ifndef OPENSSL_NO_QUIC
/*
* Core I/O Reactor Framework
* ==========================
*
* Manages use of async network I/O which the QUIC stack is built on. The core
* mechanic looks like this:
*
* - There is a pollable FD for both the read and write side respectively.
* Readability and writeability of these FDs respectively determines when
* network I/O is available.
*
* - The reactor can export these FDs to the user, as well as flags indicating
* whether the user should listen for readability, writeability, or neither.
*
* - The reactor can export a timeout indication to the user, indicating when
* the reactor should be called (via libssl APIs) regardless of whether
* the network socket has become ready.
*
* The reactor is based around a tick callback which is essentially the mutator
* function. The mutator attempts to do whatever it can, attempting to perform
* network I/O to the extent currently feasible. When done, the mutator returns
* information to the reactor indicating when it should be woken up again:
*
* - Should it be woken up when network RX is possible?
* - Should it be woken up when network TX is possible?
* - Should it be woken up no later than some deadline X?
*
* The intention is that ALL I/O-related SSL_* functions with side effects (e.g.
* SSL_read/SSL_write) consist of three phases:
*
* - Optionally mutate the QUIC machine's state.
* - Optionally tick the QUIC reactor.
* - Optionally mutate the QUIC machine's state.
*
* For example, SSL_write is a mutation (appending to a stream buffer) followed
* by an optional tick (generally expected as we may want to send the data
* immediately, though not strictly needed if transmission is being deferred due
* to Nagle's algorithm, etc.).
*
* SSL_read is also a mutation and in principle does not need to tick the
* reactor, but it generally will anyway to ensure that the reactor is regularly
* ticked by an application which is only reading and not writing.
*
* If the SSL object is being used in blocking mode, SSL_read may need to block
* if no data is available yet, and SSL_write may need to block if buffers
* are full.
*
* The internals of the QUIC I/O engine always use asynchronous I/O. If the
* application desires blocking semantics, we handle this by adding a blocking
* adaptation layer on top of our internal asynchronous I/O API as exposed by
* the reactor interface.
*/
struct quic_tick_result_st {
char net_read_desired;
char net_write_desired;
OSSL_TIME tick_deadline;
};
static ossl_inline ossl_unused void
ossl_quic_tick_result_merge_into(QUIC_TICK_RESULT *r,
const QUIC_TICK_RESULT *src)
{
r->net_read_desired = r->net_read_desired || src->net_read_desired;
r->net_write_desired = r->net_write_desired || src->net_write_desired;
r->tick_deadline = ossl_time_min(r->tick_deadline, src->tick_deadline);
}
struct quic_reactor_st {
/*
* BIO poll descriptors which can be polled. poll_r is a poll descriptor
* which becomes readable when the QUIC state machine can potentially do
* work, and poll_w is a poll descriptor which becomes writable when the
* QUIC state machine can potentially do work. Generally, either of these
* conditions means that SSL_tick() should be called, or another SSL
* function which implicitly calls SSL_tick() (e.g. SSL_read/SSL_write()).
*/
BIO_POLL_DESCRIPTOR poll_r, poll_w;
OSSL_TIME tick_deadline; /* ossl_time_infinite() if none currently applicable */
void (*tick_cb)(QUIC_TICK_RESULT *res, void *arg, uint32_t flags);
void *tick_cb_arg;
/*
* These are true if we would like to know when we can read or write from
* the network respectively.
*/
unsigned int net_read_desired : 1;
unsigned int net_write_desired : 1;
/*
* Are the read and write poll descriptors we are currently configured with
* things we can actually poll?
*/
unsigned int can_poll_r : 1;
unsigned int can_poll_w : 1;
};
void ossl_quic_reactor_init(QUIC_REACTOR *rtor,
void (*tick_cb)(QUIC_TICK_RESULT *res, void *arg,
uint32_t flags),
void *tick_cb_arg,
OSSL_TIME initial_tick_deadline);
void ossl_quic_reactor_set_poll_r(QUIC_REACTOR *rtor,
const BIO_POLL_DESCRIPTOR *r);
void ossl_quic_reactor_set_poll_w(QUIC_REACTOR *rtor,
const BIO_POLL_DESCRIPTOR *w);
const BIO_POLL_DESCRIPTOR *ossl_quic_reactor_get_poll_r(const QUIC_REACTOR *rtor);
const BIO_POLL_DESCRIPTOR *ossl_quic_reactor_get_poll_w(const QUIC_REACTOR *rtor);
int ossl_quic_reactor_can_poll_r(const QUIC_REACTOR *rtor);
int ossl_quic_reactor_can_poll_w(const QUIC_REACTOR *rtor);
int ossl_quic_reactor_can_support_poll_descriptor(const QUIC_REACTOR *rtor,
const BIO_POLL_DESCRIPTOR *d);
int ossl_quic_reactor_net_read_desired(QUIC_REACTOR *rtor);
int ossl_quic_reactor_net_write_desired(QUIC_REACTOR *rtor);
OSSL_TIME ossl_quic_reactor_get_tick_deadline(QUIC_REACTOR *rtor);
/*
* Do whatever work can be done, and as much work as can be done. This involves
* e.g. seeing if we can read anything from the network (if we want to), seeing
* if we can write anything to the network (if we want to), etc.
*
* If the CHANNEL_ONLY flag is set, this indicates that we should only
* touch state which is synchronised by the channel mutex.
*/
#define QUIC_REACTOR_TICK_FLAG_CHANNEL_ONLY (1U << 0)
int ossl_quic_reactor_tick(QUIC_REACTOR *rtor, uint32_t flags);
/*
* Blocking I/O Adaptation Layer
* =============================
*
* The blocking I/O adaptation layer implements blocking I/O on top of our
* asynchronous core.
*
* The core mechanism is block_until_pred(), which does not return until pred()
* returns a value other than 0. The blocker uses OS I/O synchronisation
* primitives (e.g. poll(2)) and ticks the reactor until the predicate is
* satisfied. The blocker is not required to call pred() more than once between
* tick calls.
*
* When pred returns a non-zero value, that value is returned by this function.
* This can be used to allow pred() to indicate error conditions and short
* circuit the blocking process.
*
* A return value of -1 is reserved for network polling errors. Therefore this
* return value should not be used by pred() if ambiguity is not desired. Note
* that the predicate function can always arrange its own output mechanism, for
* example by passing a structure of its own as the argument.
*
* If the SKIP_FIRST_TICK flag is set, the first call to reactor_tick() before
* the first call to pred() is skipped. This is useful if it is known that
* ticking the reactor again will not be useful (e.g. because it has already
* been done).
*
* This function assumes a write lock is held for the entire QUIC_CHANNEL. If
* mutex is non-NULL, it must be a lock currently held for write; it will be
* unlocked during any sleep, and then relocked for write afterwards.
*
* Precondition: mutex is NULL or is held for write (unchecked)
* Postcondition: mutex is NULL or is held for write (unless
* CRYPTO_THREAD_write_lock fails)
*/
#define SKIP_FIRST_TICK (1U << 0)
int ossl_quic_reactor_block_until_pred(QUIC_REACTOR *rtor,
int (*pred)(void *arg), void *pred_arg,
uint32_t flags,
CRYPTO_MUTEX *mutex);
# endif
#endif
