openssl/ssl/quic/quic_record_tx.c

/*
 * Copyright 2022 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
 */

#include "internal/quic_record_tx.h"
#include "internal/bio_addr.h"
#include "internal/common.h"
#include "quic_record_shared.h"
#include "../ssl_local.h"

/*
 * TXE
 * ===
 * Encrypted packets awaiting transmission are kept in TX Entries (TXEs), which
 * are queued in linked lists just like TXEs.
 */
typedef struct txe_st TXE;

struct txe_st {
    TXE                *prev, *next;
    size_t              data_len, alloc_len;

    /*
     * Destination and local addresses, as applicable. Both of these are only
     * used if the family is not AF_UNSPEC.
     */
    BIO_ADDR            peer, local;

    /*
     * alloc_len allocated bytes (of which data_len bytes are valid) follow this
     * structure.
     */
};

static ossl_inline unsigned char *txe_data(const TXE *e)
{
    return (unsigned char *)(e + 1);
}

typedef struct txe_list_st {
    TXE *head, *tail;
} TXE_LIST;

static void txe_remove(TXE_LIST *l, TXE *e)
{
    if (e->prev != NULL)
        e->prev->next = e->next;
    if (e->next != NULL)
        e->next->prev = e->prev;

    if (e == l->head)
        l->head = e->next;
    if (e == l->tail)
        l->tail = e->prev;

    e->next = e->prev = NULL;
}

static void txe_insert_tail(TXE_LIST *l, TXE *e)
{
    if (l->tail == NULL) {
        l->head = l->tail = e;
        e->next = e->prev = NULL;
        return;
    }

    l->tail->next = e;
    e->prev = l->tail;
    e->next = NULL;
    l->tail = e;
}

/*
 * QTX
 * ===
 */

/* (Encryption level, direction)-specific state. */
typedef struct ossl_qtx_enc_level_st {
    /* Hash function used for key derivation. */
    EVP_MD                     *md;
    /* Context used for packet body ciphering. */
    EVP_CIPHER_CTX             *cctx;
    /* IV used to construct nonces used for AEAD packet body ciphering. */
    unsigned char               iv[EVP_MAX_IV_LENGTH];
    /* Have we permanently discarded this encryption level? */
    unsigned char               discarded;
    /* QTX_SUITE_* value. */
    uint32_t                    suite_id;
    /* Length of authentication tag. */
    uint32_t                    tag_len;
    /*
     * Cryptographic context used to apply and remove header protection from
     * packet headers.
     */
    QUIC_HDR_PROTECTOR          hpr;
} OSSL_QTX_ENC_LEVEL;

struct ossl_qtx_st {
    OSSL_LIB_CTX               *libctx;
    const char                 *propq;

    /* Per encryption-level state. */
    OSSL_QRL_ENC_LEVEL_SET      el_set;

    /* TX BIO. */
    BIO                        *bio;

    /* TX maximum datagram payload length. */
    size_t                      mdpl;

    /*
     * List of TXEs which are not currently in use. These are moved to the
     * pending list (possibly via tx_cons first) as they are filled.
     */
    TXE_LIST                    free;

    /*
     * List of TXEs which are filled with completed datagrams ready to be
     * transmitted.
     */
    TXE_LIST                    pending;
    size_t                      pending_count; /* items in list */
    size_t                      pending_bytes; /* sum(txe->data_len) in pending */

    /*
     * TXE which is under construction for coalescing purposes, if any.
     * This TXE is neither on the free nor pending list. Once the datagram
     * is completed, it is moved to the pending list.
     */
    TXE                        *cons;
    size_t                      cons_count; /* num packets */
};

/* Instantiates a new QTX. */
OSSL_QTX *ossl_qtx_new(const OSSL_QTX_ARGS *args)
{
    OSSL_QTX *qtx;

    qtx = OPENSSL_zalloc(sizeof(OSSL_QTX));
    if (qtx == NULL)
        return 0;

    if (args->bio != NULL && !BIO_up_ref(args->bio)) {
        OPENSSL_free(qtx);
        return 0;
    }

    qtx->libctx             = args->libctx;
    qtx->propq              = args->propq;
    qtx->bio                = args->bio;
    qtx->mdpl               = args->mdpl;
    return qtx;
}

static void qtx_cleanup_txl(TXE_LIST *l)
{
    TXE *e, *enext;
    for (e = l->head; e != NULL; e = enext) {
        enext = e->next;
        OPENSSL_free(e);
    }
    l->head = l->tail = NULL;
}

/* Frees the QTX. */
void ossl_qtx_free(OSSL_QTX *qtx)
{
    uint32_t i;

    /* Free TXE queue data. */
    qtx_cleanup_txl(&qtx->pending);
    qtx_cleanup_txl(&qtx->free);

    /* Drop keying material and crypto resources. */
    for (i = 0; i < QUIC_ENC_LEVEL_NUM; ++i)
        ossl_qrl_enc_level_set_discard(&qtx->el_set, i, 1);

    OPENSSL_free(qtx);
}

int ossl_qtx_provide_secret(OSSL_QTX              *qtx,
                            uint32_t               enc_level,
                            uint32_t               suite_id,
                            EVP_MD                *md,
                            const unsigned char   *secret,
                            size_t                 secret_len)
{
    if (enc_level >= QUIC_ENC_LEVEL_NUM)
        return 0;

    return ossl_qrl_enc_level_set_provide_secret(&qtx->el_set,
                                                 qtx->libctx,
                                                 qtx->propq,
                                                 enc_level,
                                                 suite_id,
                                                 md,
                                                 secret,
                                                 secret_len);
}

int ossl_qtx_discard_enc_level(OSSL_QTX *qtx, uint32_t enc_level)
{
    if (enc_level >= QUIC_ENC_LEVEL_NUM)
        return 0;

    ossl_qrl_enc_level_set_discard(&qtx->el_set, enc_level, 1);
    return 1;
}

/* Allocate a new TXE. */
static TXE *qtx_alloc_txe(size_t alloc_len)
{
    TXE *txe;

    if (alloc_len >= SIZE_MAX - sizeof(TXE))
        return NULL;

    txe = OPENSSL_malloc(sizeof(TXE) + alloc_len);
    if (txe == NULL)
        return NULL;

    txe->prev = txe->next = NULL;
    txe->alloc_len = alloc_len;
    txe->data_len  = 0;
    return txe;
}

/*
 * Ensures there is at least one TXE in the free list, allocating a new entry
 * if necessary. The returned TXE is in the free list; it is not popped.
 *
 * alloc_len is a hint which may be used to determine the TXE size if allocation
 * is necessary. Returns NULL on allocation failure.
 */
static TXE *qtx_ensure_free_txe(OSSL_QTX *qtx, size_t alloc_len)
{
    TXE *txe;

    if (qtx->free.head != NULL)
        return qtx->free.head;

    txe = qtx_alloc_txe(alloc_len);
    if (txe == NULL)
        return NULL;

    txe_insert_tail(&qtx->free, txe);
    return txe;
}

/*
 * Resize the data buffer attached to an TXE to be n bytes in size. The address
 * of the TXE might change; the new address is returned, or NULL on failure, in
 * which case the original TXE remains valid.
 */
static TXE *qtx_resize_txe(OSSL_QTX *qtx, TXE_LIST *txl, TXE *txe, size_t n)
{
    TXE *txe2;

    /* Should never happen. */
    if (txe == NULL)
        return NULL;

    if (n >= SIZE_MAX - sizeof(TXE))
        return NULL;

    /*
     * NOTE: We do not clear old memory, although it does contain decrypted
     * data.
     */
    txe2 = OPENSSL_realloc(txe, sizeof(TXE) + n);
    if (txe2 == NULL)
        /* original TXE is still in tact unchanged */
        return NULL;

    if (txl != NULL && txe != txe2) {
        if (txl->head == txe)
            txl->head = txe2;
        if (txl->tail == txe)
            txl->tail = txe2;
        if (txe->prev != NULL)
            txe->prev->next = txe2;
        if (txe->next != NULL)
            txe->next->prev = txe2;
    }

    if (qtx->cons == txe)
        qtx->cons = txe2;

    txe2->alloc_len = n;
    return txe2;
}

/*
 * Ensure the data buffer attached to an TXE is at least n bytes in size.
 * Returns NULL on failure.
 */
static TXE *qtx_reserve_txe(OSSL_QTX *qtx, TXE_LIST *txl,
                            TXE *txe, size_t n)
{
    if (txe->alloc_len >= n)
        return txe;

    return qtx_resize_txe(qtx, txl, txe, n);
}

/* Move a TXE from pending to free. */
static void qtx_pending_to_free(OSSL_QTX *qtx)
{
    TXE *txe = qtx->pending.head;

    assert(txe != NULL);
    txe_remove(&qtx->pending, txe);
    --qtx->pending_count;
    qtx->pending_bytes -= txe->data_len;
    txe_insert_tail(&qtx->free, txe);
}

/* Add a TXE not currently in any list to the pending list. */
static void qtx_add_to_pending(OSSL_QTX *qtx, TXE *txe)
{
    txe_insert_tail(&qtx->pending, txe);
    ++qtx->pending_count;
    qtx->pending_bytes += txe->data_len;
}

struct iovec_cur {
    const OSSL_QTX_IOVEC *iovec;
    size_t                num_iovec, idx, byte_off, bytes_remaining;
};

static size_t iovec_total_bytes(const OSSL_QTX_IOVEC *iovec,
                                size_t num_iovec)
{
    size_t i, l = 0;

    for (i = 0; i < num_iovec; ++i)
        l += iovec[i].buf_len;

    return l;
}

static void iovec_cur_init(struct iovec_cur *cur,
                           const OSSL_QTX_IOVEC *iovec,
                           size_t num_iovec)
{
    cur->iovec              = iovec;
    cur->num_iovec          = num_iovec;
    cur->idx                = 0;
    cur->byte_off           = 0;
    cur->bytes_remaining    = iovec_total_bytes(iovec, num_iovec);
}

/*
 * Get an extent of bytes from the iovec cursor. *buf is set to point to the
 * buffer and the number of bytes in length of the buffer is returned. This
 * value may be less than the max_buf_len argument. If no more data is
 * available, returns 0.
 */
static size_t iovec_cur_get_buffer(struct iovec_cur *cur,
                                   const unsigned char **buf,
                                   size_t max_buf_len)
{
    size_t l;

    if (max_buf_len == 0) {
        *buf = NULL;
        return 0;
    }

    for (;;) {
        if (cur->idx >= cur->num_iovec)
            return 0;

        l = cur->iovec[cur->idx].buf_len - cur->byte_off;
        if (l > max_buf_len)
            l = max_buf_len;

        if (l > 0) {
            *buf = cur->iovec[cur->idx].buf + cur->byte_off;
            cur->byte_off += l;
            cur->bytes_remaining -= l;
            return l;
        }

        /*
         * Zero-length iovec entry or we already consumed all of it, try the
         * next iovec.
         */
        ++cur->idx;
        cur->byte_off = 0;
    }
}

/* Determines the size of the AEAD output given the input size. */
static size_t qtx_inflate_payload_len(OSSL_QTX *qtx, uint32_t enc_level,
                                      size_t plaintext_len)
{
    OSSL_QRL_ENC_LEVEL *el
        = ossl_qrl_enc_level_set_get(&qtx->el_set, enc_level, 1);

    assert(el != NULL); /* Already checked by caller. */

    /*
     * We currently only support ciphers with a 1:1 mapping between plaintext
     * and ciphertext size, save for authentication tag.
     */
    return plaintext_len + ossl_qrl_get_suite_cipher_tag_len(el->suite_id);
}

/* Any other error (including packet being too big for MDPL). */
#define QTX_FAIL_GENERIC            (-1)

/*
 * Returned where there is insufficient room in the datagram to write the
 * packet.
 */
#define QTX_FAIL_INSUFFICIENT_LEN   (-2)

static int qtx_write_hdr(OSSL_QTX *qtx, const OSSL_QTX_PKT *pkt, TXE *txe,
                         QUIC_PKT_HDR_PTRS *ptrs)
{
    WPACKET wpkt;
    size_t l = 0;

    if (!WPACKET_init_static_len(&wpkt, txe_data(txe) + txe->data_len,
                                 txe->alloc_len - txe->data_len, 0))
        return 0;

    if (!ossl_quic_wire_encode_pkt_hdr(&wpkt, pkt->hdr->src_conn_id.id_len,
                                       pkt->hdr, ptrs)
        || !WPACKET_get_total_written(&wpkt, &l)) {
        WPACKET_finish(&wpkt);
        return 0;
    }

    txe->data_len += l;
    WPACKET_finish(&wpkt);
    return 1;
}

static int qtx_encrypt_into_txe(OSSL_QTX *qtx, struct iovec_cur *cur, TXE *txe,
                                uint32_t enc_level, QUIC_PN pn,
                                const unsigned char *hdr, size_t hdr_len,
                                QUIC_PKT_HDR_PTRS *ptrs)
{
    int l = 0, l2 = 0;
    OSSL_QRL_ENC_LEVEL *el
        = ossl_qrl_enc_level_set_get(&qtx->el_set, enc_level, 1);
    unsigned char nonce[EVP_MAX_IV_LENGTH];
    size_t nonce_len, i;

    /* We should not have been called if we do not have key material. */
    if (!ossl_assert(el != NULL))
        return 0;

    /*
     * Have we already encrypted the maximum number of packets using the current
     * key?
     */
    if (el->op_count >= ossl_qrl_get_suite_max_pkt(el->suite_id))
        return 0;

    /* Construct nonce (nonce=IV ^ PN). */
    nonce_len = EVP_CIPHER_CTX_get_iv_length(el->cctx);
    if (!ossl_assert(nonce_len >= sizeof(QUIC_PN)))
        return 0;

    memcpy(nonce, el->iv, nonce_len);
    for (i = 0; i < sizeof(QUIC_PN); ++i)
        nonce[nonce_len - i - 1] ^= (unsigned char)(pn >> (i * 8));

    /* type and key will already have been setup; feed the IV. */
    if (EVP_CipherInit_ex(el->cctx, NULL, NULL, NULL, nonce, /*enc=*/1) != 1)
        return 0;

    /* Feed AAD data. */
    if (EVP_CipherUpdate(el->cctx, NULL, &l, hdr, hdr_len) != 1)
        return 0;

    /* Encrypt plaintext directly into TXE. */
    for (;;) {
        const unsigned char *src;
        size_t src_len;

        src_len = iovec_cur_get_buffer(cur, &src, SIZE_MAX);
        if (src_len == 0)
            break;

        if (EVP_CipherUpdate(el->cctx, txe_data(txe) + txe->data_len,
                             &l, src, src_len) != 1)
            return 0;

        assert(l > 0 && src_len == (size_t)l);
        txe->data_len += src_len;
    }

    /* Finalise and get tag. */
    if (EVP_CipherFinal_ex(el->cctx, NULL, &l2) != 1)
        return 0;

    if (EVP_CIPHER_CTX_ctrl(el->cctx, EVP_CTRL_AEAD_GET_TAG,
                            el->tag_len, txe_data(txe) + txe->data_len) != 1)
        return 0;

    txe->data_len += el->tag_len;

    /* Apply header protection. */
    if (!ossl_quic_hdr_protector_encrypt(&el->hpr, ptrs))
        return 0;

    ++el->op_count;
    return 1;
}

/*
 * Append a packet to the TXE buffer, serializing and encrypting it in the
 * process.
 */
static int qtx_write(OSSL_QTX *qtx, const OSSL_QTX_PKT *pkt, TXE *txe,
                     uint32_t enc_level)
{
    int ret, needs_encrypt;
    size_t hdr_len, pred_hdr_len, payload_len, pkt_len, space_left;
    size_t min_len, orig_data_len;
    struct iovec_cur cur;
    QUIC_PKT_HDR_PTRS ptrs;
    unsigned char *hdr_start;

    /*
     * Determine if the packet needs encryption and the minimum conceivable
     * serialization length.
     */
    if (pkt->hdr->type == QUIC_PKT_TYPE_RETRY
        || pkt->hdr->type == QUIC_PKT_TYPE_VERSION_NEG) {
        needs_encrypt = 0;
        min_len = QUIC_MIN_VALID_PKT_LEN;
    } else {
        needs_encrypt = 1;
        min_len = QUIC_MIN_VALID_PKT_LEN_CRYPTO;
    }

    orig_data_len = txe->data_len;
    space_left = txe->alloc_len - txe->data_len;
    if (space_left < min_len) {
        /* Not even a possibility of it fitting. */
        ret = QTX_FAIL_INSUFFICIENT_LEN;
        goto err;
    }

    /* Walk the iovecs to determine actual input payload length. */
    iovec_cur_init(&cur, pkt->iovec, pkt->num_iovec);

    /* Determine encrypted payload length. */
    payload_len = needs_encrypt ? qtx_inflate_payload_len(qtx, enc_level,
                                                          cur.bytes_remaining)
                                : cur.bytes_remaining;

    /* Determine header length. */
    pkt->hdr->data  = NULL;
    pkt->hdr->len   = payload_len;
    pred_hdr_len = ossl_quic_wire_get_encoded_pkt_hdr_len(pkt->hdr->src_conn_id.id_len,
                                                          pkt->hdr);
    if (pred_hdr_len == 0) {
        ret = QTX_FAIL_GENERIC;
        goto err;
    }

    /* We now definitively know our packet length. */
    pkt_len = pred_hdr_len + payload_len;

    if (pkt_len > space_left) {
        ret = QTX_FAIL_INSUFFICIENT_LEN;
        goto err;
    }

    /* Set some fields in the header we are responsible for. */
    pkt->hdr->key_phase = 0; /* TODO */
    if (!ossl_quic_wire_encode_pkt_hdr_pn(pkt->pn,
                                          pkt->hdr->pn,
                                          pkt->hdr->pn_len)) {
        ret = QTX_FAIL_GENERIC;
        goto err;
    }

    /* Append the header to the TXE. */
    hdr_start = txe_data(txe) + txe->data_len;
    if (!qtx_write_hdr(qtx, pkt, txe, &ptrs)) {
        ret = QTX_FAIL_GENERIC;
        goto err;
    }

    hdr_len = (txe_data(txe) + txe->data_len) - hdr_start;
    assert(hdr_len == pred_hdr_len);

    if (!needs_encrypt) {
        /* Just copy the payload across. */
        const unsigned char *src;
        size_t src_len;

        for (;;) {
            /* Buffer length has already been checked above. */
            src_len = iovec_cur_get_buffer(&cur, &src, SIZE_MAX);
            if (src_len == 0)
                break;

            memcpy(txe_data(txe) + txe->data_len, src, src_len);
            txe->data_len += src_len;
        }
    } else {
        /* Encrypt into TXE. */
        if (!qtx_encrypt_into_txe(qtx, &cur, txe, enc_level, pkt->pn,
                                  hdr_start, hdr_len, &ptrs)) {
            ret = QTX_FAIL_GENERIC;
            goto err;
        }

        assert(txe->data_len - orig_data_len == pkt_len);
    }

    return 1;

err:
    /*
     * Restore original length so we don't leave a half-written packet in the
     * TXE.
     */
    txe->data_len = orig_data_len;
    return ret;
}

static TXE *qtx_ensure_cons(OSSL_QTX *qtx)
{
    TXE *txe = qtx->cons;

    if (txe != NULL)
        return txe;

    txe = qtx_ensure_free_txe(qtx, qtx->mdpl);
    if (txe == NULL)
        return NULL;

    txe_remove(&qtx->free, txe);
    qtx->cons = txe;
    qtx->cons_count = 0;
    txe->data_len = 0;
    return txe;
}

static int addr_eq(const BIO_ADDR *a, const BIO_ADDR *b)
{
    return ((a == NULL || BIO_ADDR_family(a) == AF_UNSPEC)
            && (b == NULL || BIO_ADDR_family(b) == AF_UNSPEC))
        || (a != NULL && b != NULL && memcmp(a, b, sizeof(*a)) == 0);
}

int ossl_qtx_write_pkt(OSSL_QTX *qtx, const OSSL_QTX_PKT *pkt)
{
    int ret;
    int coalescing = (pkt->flags & OSSL_QTX_PKT_FLAG_COALESCE) != 0;
    int was_coalescing;
    TXE *txe;
    uint32_t enc_level;

    /* Must have EL configured, must have header. */
    if (pkt->hdr == NULL)
        return 0;

    enc_level = ossl_quic_pkt_type_to_enc_level(pkt->hdr->type);

    /* Some packet types must be in a packet all by themselves. */
    if (pkt->hdr->type == QUIC_PKT_TYPE_RETRY
        || pkt->hdr->type == QUIC_PKT_TYPE_VERSION_NEG)
        ossl_qtx_finish_dgram(qtx);
    else if (enc_level >= QUIC_ENC_LEVEL_NUM
               || ossl_qrl_enc_level_set_have_el(&qtx->el_set, enc_level) != 1)
        /* All other packet types are encrypted. */
        return 0;

    was_coalescing = (qtx->cons != NULL && qtx->cons->data_len > 0);
    if (was_coalescing)
        if (!addr_eq(&qtx->cons->peer, pkt->peer)
            || !addr_eq(&qtx->cons->local, pkt->local)) {
            /* Must stop coalescing if addresses have changed */
            ossl_qtx_finish_dgram(qtx);
            was_coalescing = 0;
        }

    for (;;) {
        /*
         * Start a new coalescing session or continue using the existing one and
         * serialize/encrypt the packet. We always encrypt packets as soon as
         * our caller gives them to us, which relieves the caller of any need to
         * keep the plaintext around.
         */
        txe = qtx_ensure_cons(qtx);
        if (txe == NULL)
            return 0; /* allocation failure */

        /*
         * Ensure TXE has at least MDPL bytes allocated. This should only be
         * possible if the MDPL has increased.
         */
        if (!qtx_reserve_txe(qtx, NULL, txe, qtx->mdpl))
            return 0;

        if (!was_coalescing) {
            /* Set addresses in TXE. */
            if (pkt->peer != NULL)
                txe->peer = *pkt->peer;
            else
                BIO_ADDR_clear(&txe->peer);

            if (pkt->local != NULL)
                txe->local = *pkt->local;
            else
                BIO_ADDR_clear(&txe->local);
        }

        ret = qtx_write(qtx, pkt, txe, enc_level);
        if (ret == 1) {
            break;
        } else if (ret == QTX_FAIL_INSUFFICIENT_LEN) {
            if (was_coalescing) {
                /*
                 * We failed due to insufficient length, so end the current
                 * datagram and try again.
                 */
                ossl_qtx_finish_dgram(qtx);
                was_coalescing = 0;
            } else {
                /*
                 * We failed due to insufficient length, but we were not
                 * coalescing/started with an empty datagram, so any future
                 * attempt to write this packet must also fail.
                 */
                return 0;
            }
        } else {
            return 0; /* other error */
        }
    }

    ++qtx->cons_count;

    /*
     * Some packet types cannot have another packet come after them.
     */
    if (pkt->hdr->type == QUIC_PKT_TYPE_RETRY
        || pkt->hdr->type == QUIC_PKT_TYPE_VERSION_NEG
        || pkt->hdr->type == QUIC_PKT_TYPE_1RTT)
        coalescing = 0;

    if (!coalescing)
        ossl_qtx_finish_dgram(qtx);

    return 1;
}

/*
 * Finish any incomplete datagrams for transmission which were flagged for
 * coalescing. If there is no current coalescing datagram, this is a no-op.
 */
void ossl_qtx_finish_dgram(OSSL_QTX *qtx)
{
    TXE *txe = qtx->cons;

    if (txe == NULL)
        return;

    if (txe->data_len == 0)
        /*
         * If we did not put anything in the datagram, just move it back to the
         * free list.
         */
        txe_insert_tail(&qtx->free, txe);
    else
        qtx_add_to_pending(qtx, txe);

    qtx->cons       = NULL;
    qtx->cons_count = 0;
}

static void txe_to_msg(TXE *txe, BIO_MSG *msg)
{
    msg->data       = txe_data(txe);
    msg->data_len   = txe->data_len;
    msg->flags      = 0;
    msg->peer
        = BIO_ADDR_family(&txe->peer) != AF_UNSPEC ? &txe->peer : NULL;
    msg->local
        = BIO_ADDR_family(&txe->local) != AF_UNSPEC ? &txe->local : NULL;
}

#define MAX_MSGS_PER_SEND   32

void ossl_qtx_flush_net(OSSL_QTX *qtx)
{
    BIO_MSG msg[MAX_MSGS_PER_SEND];
    size_t i;
    TXE *txe;
    ossl_ssize_t wr;

    if (qtx->bio == NULL)
        return;

    for (;;) {
        for (txe = qtx->pending.head, i = 0;
             txe != NULL && i < OSSL_NELEM(msg);
             txe = txe->next, ++i)
            txe_to_msg(txe, &msg[i]);

        if (!i)
            /* Nothing to send. */
            return;

        wr = BIO_sendmmsg(qtx->bio, msg, sizeof(BIO_MSG), i, 0);
        if (wr <= 0)
            /*
             * We did not get anything, so further calls will probably not
             * succeed either.
             */
            break;

        /*
         * Remove everything which was successfully sent from the pending queue.
         */
        for (i = 0; i < (size_t)wr; ++i)
            qtx_pending_to_free(qtx);
    }
}

int ossl_qtx_pop_net(OSSL_QTX *qtx, BIO_MSG *msg)
{
    TXE *txe = qtx->pending.head;

    if (txe == NULL)
        return 0;

    txe_to_msg(txe, msg);
    qtx_pending_to_free(qtx);
    return 1;
}

int ossl_qtx_set1_bio(OSSL_QTX *qtx, BIO *bio)
{
    if (bio != NULL && !BIO_up_ref(bio))
        return 0;

    BIO_free(qtx->bio);
    qtx->bio = bio;
    return 1;
}

int ossl_qtx_set_mdpl(OSSL_QTX *qtx, size_t mdpl)
{
    qtx->mdpl = mdpl;
    return 1;
}

size_t ossl_qtx_get_queue_len_datagrams(OSSL_QTX *qtx)
{
    return qtx->pending_count;
}

size_t ossl_qtx_get_queue_len_bytes(OSSL_QTX *qtx)
{
    return qtx->pending_bytes;
}

size_t ossl_qtx_get_cur_dgram_len_bytes(OSSL_QTX *qtx)
{
    return qtx->cons != NULL ? qtx->cons->data_len : 0;
}

size_t ossl_qtx_get_unflushed_pkt_count(OSSL_QTX *qtx)
{
    return qtx->cons_count;
}

uint64_t ossl_qtx_get_cur_epoch_pkt_count(OSSL_QTX *qtx, uint32_t enc_level)
{
    OSSL_QRL_ENC_LEVEL *el;

    el = ossl_qrl_enc_level_set_get(&qtx->el_set, enc_level, 1);
    if (el == NULL)
        return UINT64_MAX;

    return el->op_count;
}

uint64_t ossl_qtx_get_max_epoch_pkt_count(OSSL_QTX *qtx, uint32_t enc_level)
{
    OSSL_QRL_ENC_LEVEL *el;

    el = ossl_qrl_enc_level_set_get(&qtx->el_set, enc_level, 1);
    if (el == NULL)
        return UINT64_MAX;

    return ossl_qrl_get_suite_max_pkt(el->suite_id);
}