github.com/vpnishe/netstack@v1.10.6/tcpip/network/fragmentation/frag_heap.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package fragmentation
    16  
    17  import (
    18  	"container/heap"
    19  	"fmt"
    20  
    21  	"github.com/vpnishe/netstack/tcpip/buffer"
    22  )
    23  
    24  type fragment struct {
    25  	offset uint16
    26  	vv     buffer.VectorisedView
    27  }
    28  
    29  type fragHeap []fragment
    30  
    31  func (h *fragHeap) Len() int {
    32  	return len(*h)
    33  }
    34  
    35  func (h *fragHeap) Less(i, j int) bool {
    36  	return (*h)[i].offset < (*h)[j].offset
    37  }
    38  
    39  func (h *fragHeap) Swap(i, j int) {
    40  	(*h)[i], (*h)[j] = (*h)[j], (*h)[i]
    41  }
    42  
    43  func (h *fragHeap) Push(x interface{}) {
    44  	*h = append(*h, x.(fragment))
    45  }
    46  
    47  func (h *fragHeap) Pop() interface{} {
    48  	old := *h
    49  	n := len(old)
    50  	x := old[n-1]
    51  	*h = old[:n-1]
    52  	return x
    53  }
    54  
    55  // reassamble empties the heap and returns a VectorisedView
    56  // containing a reassambled version of the fragments inside the heap.
    57  func (h *fragHeap) reassemble() (buffer.VectorisedView, error) {
    58  	curr := heap.Pop(h).(fragment)
    59  	views := curr.vv.Views()
    60  	size := curr.vv.Size()
    61  
    62  	if curr.offset != 0 {
    63  		return buffer.VectorisedView{}, fmt.Errorf("offset of the first packet is != 0 (%d)", curr.offset)
    64  	}
    65  
    66  	for h.Len() > 0 {
    67  		curr := heap.Pop(h).(fragment)
    68  		if int(curr.offset) < size {
    69  			curr.vv.TrimFront(size - int(curr.offset))
    70  		} else if int(curr.offset) > size {
    71  			return buffer.VectorisedView{}, fmt.Errorf("packet has a hole, expected offset %d, got %d", size, curr.offset)
    72  		}
    73  		size += curr.vv.Size()
    74  		views = append(views, curr.vv.Views()...)
    75  	}
    76  	return buffer.NewVectorisedView(size, views), nil
    77  }