85 lines
2.6 KiB
Go
85 lines
2.6 KiB
Go
// Copyright 2015 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package buffer
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import (
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"reflect"
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"unsafe"
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"github.com/jacobsa/fuse/internal/fusekernel"
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)
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// OutMessage provides a mechanism for constructing a single contiguous fuse
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// message from multiple segments, where the first segment is always a
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// fusekernel.OutHeader message.
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//
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// Must be created with NewOutMessage. Exception: the zero value has
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// Bytes() == nil.
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type OutMessage struct {
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slice []byte
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}
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// Create a new buffer whose initial contents are a zeroed fusekernel.OutHeader
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// message, and with room enough to grow by extra bytes.
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func NewOutMessage(extra uintptr) (b OutMessage) {
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const headerSize = unsafe.Sizeof(fusekernel.OutHeader{})
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b.slice = make([]byte, headerSize, headerSize+extra)
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return
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}
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// Return a pointer to the header at the start of the buffer.
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func (b *OutMessage) OutHeader() (h *fusekernel.OutHeader) {
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sh := (*reflect.SliceHeader)(unsafe.Pointer(&b.slice))
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h = (*fusekernel.OutHeader)(unsafe.Pointer(sh.Data))
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return
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}
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// Grow the buffer by the supplied number of bytes, returning a pointer to the
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// start of the new segment. The sum of the arguments given to Grow must not
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// exceed the argument given to New when creating the buffer.
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func (b *OutMessage) Grow(size uintptr) (p unsafe.Pointer) {
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sh := (*reflect.SliceHeader)(unsafe.Pointer(&b.slice))
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p = unsafe.Pointer(sh.Data + uintptr(sh.Len))
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b.slice = b.slice[:len(b.slice)+int(size)]
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return
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}
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// Equivalent to growing by the length of p, then copying p into the new segment.
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func (b *OutMessage) Append(p []byte) {
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sh := reflect.SliceHeader{
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Data: uintptr(b.Grow(uintptr(len(p)))),
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Len: len(p),
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Cap: len(p),
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}
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copy(*(*[]byte)(unsafe.Pointer(&sh)), p)
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}
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// Equivalent to growing by the length of s, then copying s into the new segment.
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func (b *OutMessage) AppendString(s string) {
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sh := reflect.SliceHeader{
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Data: uintptr(b.Grow(uintptr(len(s)))),
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Len: len(s),
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Cap: len(s),
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}
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copy(*(*[]byte)(unsafe.Pointer(&sh)), s)
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}
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// Return a reference to the current contents of the buffer.
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func (b *OutMessage) Bytes() []byte {
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return b.slice
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}
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