/**
 * @file
 * Packet buffer management
 *
 * Packets are built from the pbuf data structure. It supports dynamic
 * memory allocation for packet contents or can reference externally
 * managed packet contents both in RAM and ROM. Quick allocation for
 * incoming packets is provided through pools with fixed sized pbufs.
 *
 * A packet may span over multiple pbufs, chained as a singly linked
 * list. This is called a "pbuf chain".
 *
 * Multiple packets may be queued, also using this singly linked list.
 * This is called a "packet queue".
 * 
 * So, a packet queue consists of one or more pbuf chains, each of
 * which consist of one or more pbufs. CURRENTLY, PACKET QUEUES ARE
 * NOT SUPPORTED!!! Use helper structs to queue multiple packets.
 * 
 * The differences between a pbuf chain and a packet queue are very
 * precise but subtle. 
 *
 * The last pbuf of a packet has a ->tot_len field that equals the
 * ->len field. It can be found by traversing the list. If the last
 * pbuf of a packet has a ->next field other than NULL, more packets
 * are on the queue.
 *
 * Therefore, looping through a pbuf of a single packet, has an
 * loop end condition (tot_len == p->len), NOT (next == NULL).
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

#include "vma/lwip/opt.h"

#include "vma/lwip/stats.h"
#include "vma/lwip/pbuf.h"


#if TCP_QUEUE_OOSEQ
#include "vma/lwip/tcp_impl.h"
#endif

/**
 * Shrink a pbuf chain to a desired length.
 *
 * @param p pbuf to shrink.
 * @param new_len desired new length of pbuf chain
 *
 * Depending on the desired length, the first few pbufs in a chain might
 * be skipped and left unchanged. The new last pbuf in the chain will be
 * resized, and any remaining pbufs will be freed.
 *
 * @note If the pbuf is ROM/REF, only the ->tot_len and ->len fields are adjusted.
 * @note May not be called on a packet queue.
 *
 * @note Despite its name, pbuf_realloc cannot grow the size of a pbuf (chain).
 */
void
pbuf_realloc(struct pbuf *p, u16_t new_len)
{
  struct pbuf *q;
  u16_t rem_len; /* remaining length */
  s32_t grow;

  LWIP_ASSERT("pbuf_realloc: p != NULL", p != NULL);
  LWIP_ASSERT("pbuf_realloc: sane p->type", p->type == PBUF_POOL ||
              p->type == PBUF_ROM ||
              p->type == PBUF_RAM ||
              p->type == PBUF_REF);

  /* desired length larger than current length? */
  if (new_len >= p->tot_len) {
    /* enlarging not yet supported */
    return;
  }

  /* the pbuf chain grows by (new_len - p->tot_len) bytes
   * (which may be negative in case of shrinking) */
  grow = new_len - p->tot_len;

  /* first, step over any pbufs that should remain in the chain */
  rem_len = new_len;
  q = p;
  /* should this pbuf be kept? */
  while (rem_len > q->len) {
    /* decrease remaining length by pbuf length */
    rem_len -= q->len;
    /* decrease total length indicator */
    LWIP_ASSERT("grow < max_u16_t", grow < 0xffff);
    q->tot_len += grow;
    /* proceed to next pbuf in chain */
    q = q->next;
    LWIP_ASSERT("pbuf_realloc: q != NULL", q != NULL);
  }
  /* we have now reached the new last pbuf (in q) */
  /* rem_len == desired length for pbuf q */

  /* shrink allocated memory for PBUF_RAM */
  /* (other types merely adjust their length fields */
  if ((q->type == PBUF_RAM) && (rem_len != q->len)) {
    LWIP_ASSERT("pbuf_realloc: we don't need to be here ",0);
  }
  /* adjust length fields for new last pbuf */
  q->len = rem_len;
  q->tot_len = q->len;

  /* any remaining pbufs in chain? */
  if (q->next != NULL) {
    /* free remaining pbufs in chain */
    pbuf_free(q->next);
  }
  /* q is last packet in chain */
  q->next = NULL;

}

/**
 * Adjusts the payload pointer to hide or reveal headers in the payload.
 *
 * Adjusts the ->payload pointer so that space for a header
 * (dis)appears in the pbuf payload.
 *
 * The ->payload, ->tot_len and ->len fields are adjusted.
 *
 * @param p pbuf to change the header size.
 * @param header_size_increment Number of bytes to increment header size which
 * increases the size of the pbuf. New space is on the front.
 * (Using a negative value decreases the header size.)
 * If hdr_size_inc is 0, this function does nothing and returns succesful.
 *
 * PBUF_ROM and PBUF_REF type buffers cannot have their sizes increased, so
 * the call will fail. A check is made that the increase in header size does
 * not move the payload pointer in front of the start of the buffer.
 * @return non-zero on failure, zero on success.
 *
 */
u8_t
pbuf_header(struct pbuf *p, s16_t header_size_increment)
{
  u16_t type;
  void *payload;
  u16_t increment_magnitude;

  LWIP_ASSERT("p != NULL", p != NULL);
  if ((header_size_increment == 0) || (p == NULL)) {
    return 0;
  }
 
  if (header_size_increment < 0){
    increment_magnitude = -header_size_increment;
    /* Check that we aren't going to move off the end of the pbuf */
    LWIP_ERROR("increment_magnitude <= p->len", (increment_magnitude <= p->len), return 1;);
  } else {
    increment_magnitude = header_size_increment;
  }

  type = p->type;
  /* remember current payload pointer */
  payload = p->payload;

  /* pbuf types containing payloads? */
  if (type == PBUF_RAM || type == PBUF_POOL) {
    /* set new payload pointer */
    p->payload = (u8_t *)p->payload - header_size_increment;
  /* pbuf types refering to external payloads? */
  } else if (type == PBUF_REF || type == PBUF_ROM) {
    /* hide a header in the payload? */
    if ((header_size_increment < 0) && (increment_magnitude > p->len))
      return 1;
    /* AlexV: we need to check that the header EXPANTION is legal for PBUF_REF & PBUF_ROM pbufs! */
    p->payload = (u8_t *)p->payload - header_size_increment;
  } else {
    /* Unknown type */
    LWIP_ASSERT("bad pbuf type", 0);
    return 1;
  }
  /* modify pbuf length fields */
  p->len += header_size_increment;
  p->tot_len += header_size_increment;

  LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_header: old %p new %p (%"S16_F")\n",
    (void *)payload, (void *)p->payload, header_size_increment));
  (void)payload; /* Fix warning -Wunused-but-set-variable */

  return 0;
}

/**
 * Dereference a pbuf chain or queue and deallocate any no-longer-used
 * pbufs at the head of this chain or queue.
 *
 * Decrements the pbuf reference count. If it reaches zero, the pbuf is
 * deallocated.
 *
 * For a pbuf chain, this is repeated for each pbuf in the chain,
 * up to the first pbuf which has a non-zero reference count after
 * decrementing. So, when all reference counts are one, the whole
 * chain is free'd.
 *
 * @param p The pbuf (chain) to be dereferenced.
 *
 * @return the number of pbufs that were de-allocated
 * from the head of the chain.
 *
 * @note MUST NOT be called on a packet queue (Not verified to work yet).
 * @note the reference counter of a pbuf equals the number of pointers
 * that refer to the pbuf (or into the pbuf).
 *
 * @internal examples:
 *
 * Assuming existing chains a->b->c with the following reference
 * counts, calling pbuf_free(a) results in:
 * 
 * 1->2->3 becomes ...1->3
 * 3->3->3 becomes 2->3->3
 * 1->1->2 becomes ......1
 * 2->1->1 becomes 1->1->1
 * 1->1->1 becomes .......
 *
 */
u8_t
pbuf_free(struct pbuf *p)
{
  u16_t type;
  struct pbuf *q;
  u8_t count;

  if (p == NULL) {
    LWIP_ASSERT("p != NULL", p != NULL);
    /* if assertions are disabled, proceed with debug output */
    LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
      ("pbuf_free(p == NULL) was called.\n"));
    return 0;
  }
  LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free(%p)\n", (void *)p));

  LWIP_ASSERT("pbuf_free: sane type",
    p->type == PBUF_RAM || p->type == PBUF_ROM ||
    p->type == PBUF_REF || p->type == PBUF_POOL);

  count = 0;
  /* de-allocate all consecutive pbufs from the head of the chain that
   * obtain a zero reference count after decrementing*/
  while (p != NULL) {
    u16_t ref;
    /* all pbufs in a chain are referenced at least once */
    LWIP_ASSERT("pbuf_free: p->ref > 0", p->ref > 0);
    /* decrease reference count (number of pointers to pbuf) */
    ref = --(p->ref);
    /* this pbuf is no longer referenced to? */
    if (ref == 0) {
      /* remember next pbuf in chain for next iteration */
      q = p->next;
      LWIP_DEBUGF( PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free: deallocating %p\n", (void *)p));
      type = p->type;
      /* is this a custom pbuf? */
      if ((p->flags & PBUF_FLAG_IS_CUSTOM) != 0) {
        struct pbuf_custom *pc = (struct pbuf_custom*)p;
        LWIP_ASSERT("pc->custom_free_function != NULL", pc->custom_free_function != NULL);
        pc->custom_free_function(p);
      }
      count++;
      /* proceed to next pbuf */
      p = q;
    /* p->ref > 0, this pbuf is still referenced to */
    /* (and so the remaining pbufs in chain as well) */
    } else {
      LWIP_DEBUGF( PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free: %p has ref %"U16_F", ending here.\n", (void *)p, ref));
      /* stop walking through the chain */
      p = NULL;
    }
  }

  (void)type;
  /* return number of de-allocated pbufs */
  return count;
}

/**
 * Count number of pbufs in a chain
 *
 * @param p first pbuf of chain
 * @return the number of pbufs in a chain
 */

u8_t
pbuf_clen(struct pbuf *p)
{
  u8_t len;

  len = 0;
  while (p != NULL) {
    ++len;
    p = p->next;
  }
  return len;
}

/**
 * Increment the reference count of the pbuf.
 *
 * @param p pbuf to increase reference counter of
 *
 */
void
pbuf_ref(struct pbuf *p)
{
  /* pbuf given? */
  if (p != NULL) {
    ++(p->ref);
  }
}

/**
 * Concatenate two pbufs (each may be a pbuf chain) and take over
 * the caller's reference of the tail pbuf.
 * 
 * @note The caller MAY NOT reference the tail pbuf afterwards.
 * Use pbuf_chain() for that purpose in the original lwip project.
 * 
 * @see pbuf_chain()
 */

void
pbuf_cat(struct pbuf *h, struct pbuf *t)
{
  struct pbuf *p;

  LWIP_ERROR_ABORT("(h != NULL) && (t != NULL) (programmer violates API)",
             ((h != NULL) && (t != NULL)), return;);

  /* proceed to last pbuf of chain */
  for (p = h; p->next != NULL; p = p->next) {
    /* add total length of second chain to all totals of first chain */
    p->tot_len += t->tot_len;
  }
  /* { p is last pbuf of first h chain, p->next == NULL } */
  LWIP_ASSERT("p->tot_len == p->len (of last pbuf in chain)", p->tot_len == p->len);
  LWIP_ASSERT("p->next == NULL", p->next == NULL);
  /* add total length of second chain to last pbuf total of first chain */
  p->tot_len += t->tot_len;
  /* chain last pbuf of head (p) with first of tail (t) */
  p->next = t;
  /* p->next now references t, but the caller will drop its reference to t,
   * so netto there is no change to the reference count of t.
   */
}

// windows scale needs large pbuf
/**
 * This method modifies a 'pbuf chain', so that its total length is
 * smaller than 64K. The remainder of the original pbuf chain is stored
 * in *rest.
 * This function never creates new pbufs, but splits an existing chain
 * in two parts. The tot_len of the modified packet queue will likely be
 * smaller than 64K.
 * 'packet queues' are not supported by this function.
 */
void pbuf_split_64k(struct pbuf *p, struct pbuf **rest)
{
	if (p == NULL ||
			p->tot_len < 0xffff) {
		// pbuf is smaller than 64K
		*rest = NULL;
	} else {
		u32_t tot_len_front = 0;
		struct pbuf *i = NULL;

		*rest = p;
		while (*rest != NULL &&
				tot_len_front + (*rest)->len <= 0xffff) {
			tot_len_front += (*rest)->len;
			i = *rest;
			*rest = (*rest)->next;
		}
		/* i now points to last packet of the first segment. Set next
		 * pointer to NULL */
		i->next = NULL;

		/* Update the tot_len field in the first part */
		for (i = p; i && i->next != *rest && *rest; i = i->next) {
			i->tot_len -= (*rest)->tot_len;
		}

		/* tot_len field in rest does not need modifications */
		/* reference counters do not need modifications */
	}
}
