70 lines
2.3 KiB
Go
70 lines
2.3 KiB
Go
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// Copyright 2019 The gVisor Authors.
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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 flipcall
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import (
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"reflect"
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"unsafe"
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)
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// Packets consist of an 8-byte header followed by an arbitrarily-sized
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// datagram. The header consists of:
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//
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// - A 4-byte native-endian connection state.
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//
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// - A 4-byte native-endian datagram length in bytes.
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const (
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sizeofUint32 = unsafe.Sizeof(uint32(0))
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// PacketHeaderBytes is the size of a flipcall packet header in bytes. The
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// maximum datagram size supported by a flipcall connection is equal to the
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// length of the packet window minus PacketHeaderBytes.
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//
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// PacketHeaderBytes is exported to support its use in constant
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// expressions. Non-constant expressions may prefer to use
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// PacketWindowLengthForDataCap().
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PacketHeaderBytes = 2 * sizeofUint32
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)
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func (ep *Endpoint) connState() *uint32 {
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return (*uint32)((unsafe.Pointer)(ep.packet))
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}
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func (ep *Endpoint) dataLen() *uint32 {
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return (*uint32)((unsafe.Pointer)(ep.packet + sizeofUint32))
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}
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// Data returns the datagram part of ep's packet window as a byte slice.
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//
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// Note that the packet window is shared with the potentially-untrusted peer
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// Endpoint, which may concurrently mutate the contents of the packet window.
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// Thus:
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//
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// - Readers must not assume that two reads of the same byte in Data() will
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// return the same result. In other words, readers should read any given byte
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// in Data() at most once.
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//
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// - Writers must not assume that they will read back the same data that they
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// have written. In other words, writers should avoid reading from Data() at
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// all.
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func (ep *Endpoint) Data() []byte {
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var bs []byte
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bsReflect := (*reflect.SliceHeader)((unsafe.Pointer)(&bs))
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bsReflect.Data = ep.packet + PacketHeaderBytes
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bsReflect.Len = int(ep.dataCap)
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bsReflect.Cap = int(ep.dataCap)
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return bs
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}
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