stellar-stellar/src/tcp_reassembly/tcp_reassembly.cpp

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <assert.h>

#include "tcp_reassembly.h"
#include "itree.h"

struct segment
{
    struct tcp_reassembly *assy;
    struct segment *next;
    struct segment *prev;

    uint64_t id;
    uint64_t time;
    uint32_t offset;
    uint32_t len;
    char *payload; // Flexible array member
};

struct segment_list
{
    struct segment *head; // del segment from head
    struct segment *tail; // add segment to tail
};

struct tcp_reassembly
{
    struct tcp_reassembly_options opts;
    struct tcp_reassembly_stat stat;
    struct segment_list list;

    struct itree *itree;
    uint64_t exp_seq;
};

/*
 * The next routines deal with comparing 32 bit unsigned ints
 * and worry about wraparound (automatic with unsigned arithmetic).
 */

static inline bool before(uint32_t seq1, uint32_t seq2)
{
    return (int32_t)(seq1 - seq2) < 0;
}

static inline void segment_list_add(struct segment_list *list, struct segment *seg)
{
    if (list->head == NULL)
    {
        list->head = seg;
    }
    else
    {
        list->tail->next = seg;
        seg->prev = list->tail;
    }
    list->tail = seg;
}

static inline void segment_list_del(struct segment_list *list, struct segment *seg)
{
    if (list->head == seg)
    {
        list->head = seg->next;
    }
    if (list->tail == seg)
    {
        list->tail = seg->prev;
    }
    if (seg->prev)
    {
        seg->prev->next = seg->next;
    }
    if (seg->next)
    {
        seg->next->prev = seg->prev;
    }
}

static inline struct segment *segment_list_get_oldest(struct segment_list *list)
{
    return list->head;
}

static inline struct segment *segment_new(uint32_t len)
{
    return (struct segment *)calloc(1, sizeof(struct segment) + len);
}

static inline void *segment_dup(void *p)
{
    return p;
}

static inline void segment_free(void *p)
{
    struct segment *seg = NULL;
    struct tcp_reassembly *assy = NULL;

    if (p)
    {
        seg = (struct segment *)p;
        assy = seg->assy;
        segment_list_del(&assy->list, seg);

        assy->stat.curr_bytes -= seg->len;
        assy->stat.curr_segments--;

        free(seg);
    }
}

struct tcp_reassembly *tcp_reassembly_new(struct tcp_reassembly_options *opts)
{
    struct tcp_reassembly *assy = NULL;

    assy = (struct tcp_reassembly *)calloc(1, sizeof(struct tcp_reassembly));
    if (assy == NULL)
    {
        return NULL;
    }

    memcpy(&assy->opts, opts, sizeof(struct tcp_reassembly_options));
    if (!assy->opts.enable)
    {
        return assy;
    }

    assy->itree = itree_new(segment_dup, segment_free);
    if (assy->itree == NULL)
    {
        goto error_out;
    }

    return assy;

error_out:
    tcp_reassembly_free(assy);
    return NULL;
}

void tcp_reassembly_free(struct tcp_reassembly *assy)
{
    if (assy)
    {
        if (assy->itree)
        {
            itree_delete(assy->itree);
        }
        free(assy);
    }
}

void tcp_reassembly_init(struct tcp_reassembly *assy, uint32_t syn_seq)
{
    if (!assy->opts.enable)
    {
        return;
    }

    assy->exp_seq = syn_seq + 1;
    TCP_REASSEMBLE_DEBUG("reassembler %p init expect seq %lu", assy, assy->exp_seq);
}

void tcp_reassembly_expire(struct tcp_reassembly *assy, uint64_t now)
{
    if (!assy->opts.enable)
    {
        return;
    }

    uint64_t high;
    interval_t expire;
    struct segment *seg = NULL;

    while ((seg = segment_list_get_oldest(&assy->list)) != NULL)
    {
        if (seg->time + assy->opts.max_timeout > now)
        {
            break;
        }

        high = (uint64_t)seg->offset + (uint64_t)seg->len - 1;
        expire = {
            .low = seg->offset,
            .high = high,
            .data = seg,
        };
        assy->stat.timeout_discard_segments++;
        assy->stat.timeout_discard_bytes += seg->len;
        TCP_REASSEMBLE_DEBUG("reassembler %p expire segment %p [%lu, %lu] (time: %lu, now: %lu)", assy, seg, seg->offset, high, seg->time, now);

        itree_remove(assy->itree, &expire);
    }
}

void tcp_reassembly_insert(struct tcp_reassembly *assy, uint32_t offset, const char *payload, uint32_t len, uint64_t now)
{
    if (!assy->opts.enable)
    {
        return;
    }

    uint64_t low = (uint64_t)offset;
    uint64_t high = (uint64_t)offset + (uint64_t)len - 1; // from uint32_t to uint64_t, so no overflow
    struct segment *seg = NULL;
    interval_t insert;

    assy->stat.insert_segments++;
    assy->stat.insert_bytes += len;

    if (assy->opts.max_segments > 0 && assy->stat.curr_segments >= assy->opts.max_segments)
    {
        assy->stat.overload_bypass_segments++;
        assy->stat.overload_bypass_bytes += len;
        TCP_REASSEMBLE_DEBUG("reassembler %p insert [%lu, %lu] failed, reach max packets %u", assy, low, high, assy->opts.max_segments);
        return;
    }

    if (assy->opts.max_bytes > 0 && assy->stat.curr_bytes >= assy->opts.max_bytes)
    {
        assy->stat.overload_bypass_segments++;
        assy->stat.overload_bypass_bytes += len;
        TCP_REASSEMBLE_DEBUG("reassembler %p insert [%lu, %lu] failed, reach max bytes %u", assy, low, high, assy->opts.max_bytes);
        return;
    }

    if (len == 0 || before(offset + len, assy->exp_seq))
    {
        assy->stat.retrans_bypass_segments++;
        assy->stat.retrans_bypass_bytes += len;
        TCP_REASSEMBLE_DEBUG("reassembler %p insert [%lu, %lu] failed, less the expect seq %lu", assy, low, high, assy->exp_seq);
        return;
    }

    seg = segment_new(len);
    if (seg == NULL)
    {
        return;
    }

    seg->assy = assy;
    seg->id = assy->stat.insert_segments;
    seg->time = now;
    seg->offset = offset;
    seg->len = len;
    seg->payload = (char *)seg + sizeof(struct segment);
    memcpy(seg->payload, payload, len);
    insert = {
        .low = low,
        .high = high,
        .data = seg,
    };
    if (itree_insert(assy->itree, &insert) == 0)
    {
        free(seg);
        return;
    }
    TCP_REASSEMBLE_DEBUG("reassembler %p insert segment %p [%lu, %lu]", assy, seg, insert.low, insert.high);

    segment_list_add(&assy->list, seg);

    assy->stat.curr_segments++;
    assy->stat.curr_bytes += seg->len;
}

const char *tcp_reassembly_peek(struct tcp_reassembly *assy, uint32_t *len)
{
    *len = 0;

    if (!assy->opts.enable)
    {
        return NULL;
    }

    int count = 0;
    interval_t peek;
    uint64_t overlap = 0;
    uint64_t min_id = UINT64_MAX;
    struct segment *seg = NULL;
    ilist_t *list = NULL;
    ilisttrav_t *trav = NULL;
    interval_t *query = NULL;
    interval_t *oldest = NULL;

    peek = {
        .low = assy->exp_seq,
        .high = assy->exp_seq,
    };

    list = itree_findall(assy->itree, &peek);
    if (list == NULL)
    {
        return NULL;
    }

    count = ilist_size(list);
    trav = ilisttrav_new(list);
    for (int i = 0; i < count; i++)
    {
        if (i == 0)
        {
            query = (interval_t *)ilisttrav_first(trav);
        }
        else
        {
            query = (interval_t *)ilisttrav_next(trav);
        }
        seg = (struct segment *)query->data;
        if (seg->id < min_id)
        {
            min_id = seg->id;
            oldest = query;
        }
    }
    ilisttrav_delete(trav);
    ilist_delete(list);

    if (oldest == NULL)
    {
        return NULL;
    }

    seg = (struct segment *)oldest->data;
    if (seg->offset < assy->exp_seq)
    {
        overlap = assy->exp_seq - seg->offset;
        *len = seg->len - overlap;
        TCP_REASSEMBLE_DEBUG("reassembler %p peek [%lu, +∞], found segment %p [%lu, %lu] (left overlap: %lu)", assy, assy->exp_seq, seg, oldest->low, oldest->high, overlap);
        return seg->payload + overlap;
    }
    TCP_REASSEMBLE_DEBUG("reassembler %p peek [%lu, +∞], found segment %p [%lu, %lu]", assy, assy->exp_seq, seg, oldest->low, oldest->high);

    *len = seg->len;
    return seg->payload;
}

void tcp_reassembly_consume(struct tcp_reassembly *assy, uint32_t len)
{
    if (!assy->opts.enable)
    {
        return;
    }

    if (len == 0)
    {
        return;
    }

    int count;
    uint64_t old_exp_seq;
    uint64_t new_exp_seq;
    interval_t consume;
    ilist_t *list = NULL;
    interval_t *del = NULL;
    ilisttrav_t *trav = NULL;
    struct segment *seg = NULL;

    /*
     * https://www.ietf.org/rfc/rfc0793.txt
     *
     * This space ranges from 0 to 2**32 - 1.
     * Since the space is finite, all arithmetic dealing with sequence
     * numbers must be performed modulo 2**32.  This unsigned arithmetic
     * preserves the relationship of sequence numbers as they cycle from
     * 2**32 - 1 to 0 again.  There are some subtleties to computer modulo
     * arithmetic, so great care should be taken in programming the
     * comparison of such values.  The symbol "=<" means "less than or equal"
     * (modulo 2**32).
     *
     * UINT32_MAX = 4294967295
     * 2^32       = 4294967296
     * 2^32 - 1   = 4294967295
     * seq range: [0, 4294967295]
     * seq range: [0, UINT32_MAX]
     */
    old_exp_seq = assy->exp_seq;
    assy->exp_seq += len;
    if (assy->exp_seq > UINT32_MAX)
    {
        assy->exp_seq = assy->exp_seq % 4294967296;
    }
    new_exp_seq = assy->exp_seq;

    TCP_REASSEMBLE_DEBUG("reassembler %p consume [%lu, %lu], update expect seq %lu -> %lu", assy, old_exp_seq, old_exp_seq + len - 1, old_exp_seq, new_exp_seq);
    consume =
        {
            .low = old_exp_seq,
            .high = old_exp_seq + len - 1,
        };
    list = itree_findall(assy->itree, &consume);
    if (list == NULL)
    {
        return;
    }

    assy->stat.consume_segments++;
    assy->stat.consume_bytes += len;

    count = ilist_size(list);
    trav = ilisttrav_new(list);
    for (int i = 0; i < count; i++)
    {
        if (i == 0)
        {
            del = (interval_t *)ilisttrav_first(trav);
        }
        else
        {
            del = (interval_t *)ilisttrav_next(trav);
        }
        if (del && before(del->high, new_exp_seq))
        {
            seg = (struct segment *)del->data;
            assy->stat.remove_segments++;
            assy->stat.remove_bytes += seg->len;
            TCP_REASSEMBLE_DEBUG("reassembler %p consume [%lu, %lu], delete segment %p [%lu, %lu]", assy, old_exp_seq, old_exp_seq + len - 1, seg, del->low, del->high);
            itree_remove(assy->itree, del);
        }
    }
    ilisttrav_delete(trav);
    ilist_delete(list);
}

struct tcp_reassembly_stat *tcp_reassembly_get_stat(struct tcp_reassembly *assy)
{
    if (!assy->opts.enable)
    {
        return NULL;
    }

    return &assy->stat;
}

void tcp_reassembly_print_stat(struct tcp_reassembly *assy)
{
    if (!assy->opts.enable)
    {
        return;
    }

    TCP_REASSEMBLE_DEBUG("reassembler %p current         : segments %lu, bytes %lu", assy, assy->stat.curr_segments, assy->stat.curr_bytes);
    TCP_REASSEMBLE_DEBUG("reassembler %p insert          : segments %lu, bytes %lu", assy, assy->stat.insert_segments, assy->stat.insert_bytes);
    TCP_REASSEMBLE_DEBUG("reassembler %p remove          : segments %lu, bytes %lu", assy, assy->stat.remove_segments, assy->stat.remove_bytes);
    TCP_REASSEMBLE_DEBUG("reassembler %p consume         : segments %lu, bytes %lu", assy, assy->stat.consume_segments, assy->stat.consume_bytes);
    TCP_REASSEMBLE_DEBUG("reassembler %p retrans  bypass : segments %lu, bytes %lu", assy, assy->stat.retrans_bypass_segments, assy->stat.retrans_bypass_bytes);
    TCP_REASSEMBLE_DEBUG("reassembler %p overload bypass : segments %lu, bytes %lu", assy, assy->stat.overload_bypass_segments, assy->stat.overload_bypass_bytes);
    TCP_REASSEMBLE_DEBUG("reassembler %p timeout discard : segments %lu, bytes %lu", assy, assy->stat.timeout_discard_segments, assy->stat.timeout_discard_bytes);
}