include/internal/quic_ackm.h

/*
 * Copyright 2022-2025 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_ACKM_H
#define OSSL_QUIC_ACKM_H

#include "internal/quic_statm.h"
#include "internal/quic_cc.h"
#include "internal/quic_types.h"
#include "internal/quic_wire.h"
#include "internal/quic_predef.h"
#include "internal/time.h"
#include "internal/list.h"

#ifndef OPENSSL_NO_QUIC

OSSL_ACKM *ossl_ackm_new(OSSL_TIME (*now)(void *arg),
    void *now_arg,
    OSSL_STATM *statm,
    const OSSL_CC_METHOD *cc_method,
    OSSL_CC_DATA *cc_data, int is_server);
void ossl_ackm_free(OSSL_ACKM *ackm);

void ossl_ackm_set_loss_detection_deadline_callback(OSSL_ACKM *ackm,
    void (*fn)(OSSL_TIME deadline,
        void *arg),
    void *arg);

void ossl_ackm_set_ack_deadline_callback(OSSL_ACKM *ackm,
    void (*fn)(OSSL_TIME deadline,
        int pkt_space,
        void *arg),
    void *arg);

/*
 * Configures the RX-side maximum ACK delay. This is the maximum amount of time
 * the peer is allowed to delay sending an ACK frame after receiving an
 * ACK-eliciting packet. The peer communicates this value via a transport
 * parameter and it must be provided to the ACKM.
 */
void ossl_ackm_set_rx_max_ack_delay(OSSL_ACKM *ackm, OSSL_TIME rx_max_ack_delay);

/*
 * Configures the TX-side maximum ACK delay. This is the maximum amount of time
 * we are allowed to delay sending an ACK frame after receiving an ACK-eliciting
 * packet. Note that this cannot be changed after a connection is established as
 * it must be accurately reported in the transport parameters we send to our
 * peer.
 */
void ossl_ackm_set_tx_max_ack_delay(OSSL_ACKM *ackm, OSSL_TIME tx_max_ack_delay);

typedef struct ossl_ackm_tx_pkt_st OSSL_ACKM_TX_PKT;
struct ossl_ackm_tx_pkt_st {
    /* The packet number of the transmitted packet. */
    QUIC_PN pkt_num;

    /* The number of bytes in the packet which was sent. */
    size_t num_bytes;

    /* The time at which the packet was sent. */
    OSSL_TIME time;

    /*
     * If the packet being described by this structure contains an ACK frame,
     * this must be set to the largest PN ACK'd by that frame.
     *
     * Otherwise, it should be set to QUIC_PN_INVALID.
     *
     * This is necessary to bound the number of PNs we have to keep track of on
     * the RX side (RFC 9000 s. 13.2.4). It allows older PN tracking information
     * on the RX side to be discarded.
     */
    QUIC_PN largest_acked;

    /*
     * One of the QUIC_PN_SPACE_* values. This qualifies the pkt_num field
     * into a packet number space.
     */
    unsigned int pkt_space : 2;

    /*
     * 1 if the packet is in flight. A packet is considered 'in flight' if it is
     * counted for purposes of congestion control and 'bytes in flight' counts.
     * Most packets are considered in flight. The only circumstance where a
     * numbered packet is not considered in flight is if it contains only ACK
     * frames (not even PADDING frames), as these frames can bypass CC.
     */
    unsigned int is_inflight : 1;

    /*
     * 1 if the packet has one or more ACK-eliciting frames.
     * Note that if this is set, is_inflight must be set.
     */
    unsigned int is_ack_eliciting : 1;

    /* 1 if the packet is a PTO probe. */
    unsigned int is_pto_probe : 1;

    /* 1 if the packet is an MTU probe. */
    unsigned int is_mtu_probe : 1;

    /* Callback called if frames in this packet are lost. arg is cb_arg. */
    void (*on_lost)(void *arg);
    /* Callback called if frames in this packet are acked. arg is cb_arg. */
    void (*on_acked)(void *arg);
    /*
     * Callback called if frames in this packet are neither acked nor lost. arg
     * is cb_arg.
     */
    void (*on_discarded)(void *arg);
    void *cb_arg;

    /*
     * (Internal use fields; must be zero-initialized.)
     *
     * Keep a TX history list, anext is used to manifest
     * a singly-linked list of newly-acknowledged packets, and lnext is used to
     * manifest a singly-linked list of newly lost packets.
     */
    OSSL_LIST_MEMBER(tx_history, OSSL_ACKM_TX_PKT);

    struct ossl_ackm_tx_pkt_st *anext;
    struct ossl_ackm_tx_pkt_st *lnext;
};

int ossl_ackm_on_tx_packet(OSSL_ACKM *ackm, OSSL_ACKM_TX_PKT *pkt);
int ossl_ackm_on_rx_datagram(OSSL_ACKM *ackm, size_t num_bytes);

#define OSSL_ACKM_ECN_NONE 0
#define OSSL_ACKM_ECN_ECT1 1
#define OSSL_ACKM_ECN_ECT0 2
#define OSSL_ACKM_ECN_ECNCE 3

typedef struct ossl_ackm_rx_pkt_st {
    /* The packet number of the received packet. */
    QUIC_PN pkt_num;

    /* The time at which the packet was received. */
    OSSL_TIME time;

    /*
     * One of the QUIC_PN_SPACE_* values. This qualifies the pkt_num field
     * into a packet number space.
     */
    unsigned int pkt_space : 2;

    /* 1 if the packet has one or more ACK-eliciting frames. */
    unsigned int is_ack_eliciting : 1;

    /*
     * One of the OSSL_ACKM_ECN_* values. This is the ECN labelling applied to
     * the received packet. If unknown, use OSSL_ACKM_ECN_NONE.
     */
    unsigned int ecn : 2;
} OSSL_ACKM_RX_PKT;

int ossl_ackm_on_rx_packet(OSSL_ACKM *ackm, const OSSL_ACKM_RX_PKT *pkt);

int ossl_ackm_on_rx_ack_frame(OSSL_ACKM *ackm, const OSSL_QUIC_FRAME_ACK *ack,
    int pkt_space, OSSL_TIME rx_time);

/*
 * Discards a PN space. This must be called for a PN space before freeing the
 * ACKM if you want in-flight packets to have their discarded callbacks called.
 * This should never be called in ordinary QUIC usage for the Application Data
 * PN space, but it may be called for the Application Data PN space prior to
 * freeing the ACKM to simplify teardown implementations.
 */
int ossl_ackm_on_pkt_space_discarded(OSSL_ACKM *ackm, int pkt_space);

int ossl_ackm_on_handshake_confirmed(OSSL_ACKM *ackm);
int ossl_ackm_on_timeout(OSSL_ACKM *ackm);

OSSL_TIME ossl_ackm_get_loss_detection_deadline(OSSL_ACKM *ackm);

/*
 * Generates an ACK frame, regardless of whether the ACK manager thinks
 * one should currently be sent.
 *
 * This clears the flag returned by ossl_ackm_is_ack_desired and the deadline
 * returned by ossl_ackm_get_ack_deadline.
 */
const OSSL_QUIC_FRAME_ACK *ossl_ackm_get_ack_frame(OSSL_ACKM *ackm,
    int pkt_space);

/*
 * Returns the deadline after which an ACK frame should be generated by calling
 * ossl_ackm_get_ack_frame, or OSSL_TIME_INFINITY if no deadline is currently
 * applicable. If the deadline has already passed, this function may return that
 * deadline, or may return OSSL_TIME_ZERO.
 */
OSSL_TIME ossl_ackm_get_ack_deadline(OSSL_ACKM *ackm, int pkt_space);

/*
 * Returns 1 if the ACK manager thinks an ACK frame ought to be generated and
 * sent at this time. ossl_ackm_get_ack_frame will always provide an ACK frame
 * whether or not this returns 1, so it is suggested that you call this function
 * first to determine whether you need to generate an ACK frame.
 *
 * The return value of this function can change based on calls to
 * ossl_ackm_on_rx_packet and based on the passage of time (see
 * ossl_ackm_get_ack_deadline).
 */
int ossl_ackm_is_ack_desired(OSSL_ACKM *ackm, int pkt_space);

/*
 * Returns 1 if the given RX PN is 'processable'. A processable PN is one that
 * is not either
 *
 *   - duplicate, meaning that we have already been passed such a PN in a call
 *     to ossl_ackm_on_rx_packet; or
 *
 *   - written off, meaning that the PN is so old we have stopped tracking state
 *     for it (meaning that we cannot tell whether it is a duplicate and cannot
 *     process it safely).
 *
 * This should be called for a packet before attempting to process its contents.
 * Failure to do so may result in processing a duplicated packet in violation of
 * the RFC.
 *
 * The return value of this function transitions from 1 to 0 for a given PN once
 * that PN is passed to ossl_ackm_on_rx_packet, thus this function must be used
 * before calling ossl_ackm_on_rx_packet.
 */
int ossl_ackm_is_rx_pn_processable(OSSL_ACKM *ackm, QUIC_PN pn, int pkt_space);

typedef struct ossl_ackm_probe_info_st {
    /*
     * The following two probe request types are used only for anti-deadlock
     * purposes in relation to the anti-amplification logic, by generating
     * packets to buy ourselves more anti-amplification credit with the server
     * until a client address is verified. Note that like all Initial packets,
     * any Initial probes are padded.
     *
     * Note: The ACKM will only ever increase these by one at a time,
     * as only one probe packet should be generated for these cases.
     */
    uint32_t anti_deadlock_initial, anti_deadlock_handshake;

    /*
     * Send an ACK-eliciting packet for each count here.
     *
     * Note: The ACKM may increase this by either one or two for each probe
     * request, depending on how many probe packets it thinks should be
     * generated.
     */
    uint32_t pto[QUIC_PN_SPACE_NUM];
} OSSL_ACKM_PROBE_INFO;

/*
 * Returns a pointer to a structure counting any pending probe requests which
 * have been generated by the ACKM. The fields in the structure are incremented
 * by one every time the ACKM wants another probe of the given type to be sent.
 * If the ACKM thinks two packets should be generated for a probe, it will
 * increment the field twice.
 *
 * It is permissible for the caller to decrement or zero these fields to keep
 * track of when it has generated a probe as asked. The returned structure
 * has the same lifetime as the ACKM.
 *
 * This function should be called after calling e.g. ossl_ackm_on_timeout
 * to determine if any probe requests have been generated.
 */
OSSL_ACKM_PROBE_INFO *ossl_ackm_get0_probe_request(OSSL_ACKM *ackm);

int ossl_ackm_get_largest_unacked(OSSL_ACKM *ackm, int pkt_space, QUIC_PN *pn);

/*
 * Forces the ACKM to consider a packet with the given PN in the given PN space
 * as having been pseudo-lost. The main reason to use this is during a Retry, to
 * force any resources sent in the first Initial packet to be resent.
 *
 * The lost callback is called for the packet, but the packet is NOT considered
 * lost for congestion control purposes. Thus this is not exactly the same as a
 * true loss situation.
 */
int ossl_ackm_mark_packet_pseudo_lost(OSSL_ACKM *ackm,
    int pkt_space, QUIC_PN pn);

/*
 * Returns the PTO duration as currently calculated. This is a quantity of time.
 * This duration is used in various parts of QUIC besides the ACKM.
 */
OSSL_TIME ossl_ackm_get_pto_duration(OSSL_ACKM *ackm);

/* Returns the largest acked PN in the given PN space. */
QUIC_PN ossl_ackm_get_largest_acked(OSSL_ACKM *ackm, int pkt_space);

#endif

#endif