| // Copyright 2018 The gVisor Authors. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package buffer |
| |
| // Prependable is a buffer that grows backwards, that is, more data can be |
| // prepended to it. It is useful when building networking packets, where each |
| // protocol adds its own headers to the front of the higher-level protocol |
| // header and payload; for example, TCP would prepend its header to the payload, |
| // then IP would prepend its own, then ethernet. |
| type Prependable struct { |
| // Buf is the buffer backing the prependable buffer. |
| buf View |
| |
| // usedIdx is the index where the used part of the buffer begins. |
| usedIdx int |
| } |
| |
| // NewPrependable allocates a new prependable buffer with the given size. |
| func NewPrependable(size int) Prependable { |
| return Prependable{buf: NewView(size), usedIdx: size} |
| } |
| |
| // NewPrependableFromView creates an entirely-used Prependable from a View. |
| // |
| // NewPrependableFromView takes ownership of v. Note that since the entire |
| // prependable is used, further attempts to call Prepend will note that size > |
| // p.usedIdx and return nil. |
| func NewPrependableFromView(v View) Prependable { |
| return Prependable{buf: v, usedIdx: 0} |
| } |
| |
| // NewEmptyPrependableFromView creates a new prependable buffer from a View. |
| func NewEmptyPrependableFromView(v View) Prependable { |
| return Prependable{buf: v, usedIdx: len(v)} |
| } |
| |
| // View returns a View of the backing buffer that contains all prepended |
| // data so far. |
| func (p Prependable) View() View { |
| return p.buf[p.usedIdx:] |
| } |
| |
| // UsedLength returns the number of bytes used so far. |
| func (p Prependable) UsedLength() int { |
| return len(p.buf) - p.usedIdx |
| } |
| |
| // AvailableLength returns the number of bytes used so far. |
| func (p Prependable) AvailableLength() int { |
| return p.usedIdx |
| } |
| |
| // TrimBack removes size bytes from the end. |
| func (p *Prependable) TrimBack(size int) { |
| p.buf = p.buf[:len(p.buf)-size] |
| } |
| |
| // Prepend reserves the requested space in front of the buffer, returning a |
| // slice that represents the reserved space. |
| func (p *Prependable) Prepend(size int) []byte { |
| if size > p.usedIdx { |
| return nil |
| } |
| |
| p.usedIdx -= size |
| return p.View()[:size:size] |
| } |
| |
| // DeepCopy copies p and the bytes backing it. |
| func (p Prependable) DeepCopy() Prependable { |
| p.buf = append(View(nil), p.buf...) |
| return p |
| } |