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buffer.go
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buffer.go
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// 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 p9
import (
"encoding/binary"
)
// encoder is used for messages and 9P primitives.
type encoder interface {
// decode decodes from the given buffer. decode may be called more than once
// to reuse the instance. It must clear any previous state.
//
// This may not fail, exhaustion will be recorded in the buffer.
decode(b *buffer)
// encode encodes to the given buffer.
//
// This may not fail.
encode(b *buffer)
}
// order is the byte order used for encoding.
var order = binary.LittleEndian
// buffer is a slice that is consumed.
//
// This is passed to the encoder methods.
type buffer struct {
// data is the underlying data. This may grow during encode.
data []byte
// overflow indicates whether an overflow has occurred.
overflow bool
}
// append appends n bytes to the buffer and returns a slice pointing to the
// newly appended bytes.
func (b *buffer) append(n int) []byte {
b.data = append(b.data, make([]byte, n)...)
return b.data[len(b.data)-n:]
}
// consume consumes n bytes from the buffer.
func (b *buffer) consume(n int) ([]byte, bool) {
if !b.has(n) {
b.markOverrun()
return nil, false
}
rval := b.data[:n]
b.data = b.data[n:]
return rval, true
}
// has returns true if n bytes are available.
func (b *buffer) has(n int) bool {
return len(b.data) >= n
}
// markOverrun immediately marks this buffer as overrun.
//
// This is used by ReadString, since some invalid data implies the rest of the
// buffer is no longer valid either.
func (b *buffer) markOverrun() {
b.overflow = true
}
// isOverrun returns true if this buffer has run past the end.
func (b *buffer) isOverrun() bool {
return b.overflow
}
// Read8 reads a byte from the buffer.
func (b *buffer) Read8() uint8 {
v, ok := b.consume(1)
if !ok {
return 0
}
return uint8(v[0])
}
// Read16 reads a 16-bit value from the buffer.
func (b *buffer) Read16() uint16 {
v, ok := b.consume(2)
if !ok {
return 0
}
return order.Uint16(v)
}
// Read32 reads a 32-bit value from the buffer.
func (b *buffer) Read32() uint32 {
v, ok := b.consume(4)
if !ok {
return 0
}
return order.Uint32(v)
}
// Read64 reads a 64-bit value from the buffer.
func (b *buffer) Read64() uint64 {
v, ok := b.consume(8)
if !ok {
return 0
}
return order.Uint64(v)
}
// ReadQIDType reads a QIDType value.
func (b *buffer) ReadQIDType() QIDType {
return QIDType(b.Read8())
}
// ReadTag reads a Tag value.
func (b *buffer) ReadTag() Tag {
return Tag(b.Read16())
}
// ReadFID reads a FID value.
func (b *buffer) ReadFID() FID {
return FID(b.Read32())
}
// ReadUID reads a UID value.
func (b *buffer) ReadUID() UID {
return UID(b.Read32())
}
// ReadGID reads a GID value.
func (b *buffer) ReadGID() GID {
return GID(b.Read32())
}
// ReadPermissions reads a file mode value and applies the mask for permissions.
func (b *buffer) ReadPermissions() FileMode {
return b.ReadFileMode() & permissionsMask
}
// ReadFileMode reads a file mode value.
func (b *buffer) ReadFileMode() FileMode {
return FileMode(b.Read32())
}
// ReadOpenFlags reads an OpenFlags.
func (b *buffer) ReadOpenFlags() OpenFlags {
return OpenFlags(b.Read32())
}
// ReadSocketType reads a SocketType.
func (b *buffer) ReadSocketType() SocketType {
return SocketType(b.Read32())
}
// ReadMsgType writes a MsgType.
func (b *buffer) ReadMsgType() MsgType {
return MsgType(b.Read8())
}
// ReadString deserializes a string.
func (b *buffer) ReadString() string {
l := b.Read16()
if !b.has(int(l)) {
// Mark the buffer as corrupted.
b.markOverrun()
return ""
}
bs := make([]byte, l)
for i := 0; i < int(l); i++ {
bs[i] = byte(b.Read8())
}
return string(bs)
}
// Write8 writes a byte to the buffer.
func (b *buffer) Write8(v uint8) {
b.append(1)[0] = byte(v)
}
// Write16 writes a 16-bit value to the buffer.
func (b *buffer) Write16(v uint16) {
order.PutUint16(b.append(2), v)
}
// Write32 writes a 32-bit value to the buffer.
func (b *buffer) Write32(v uint32) {
order.PutUint32(b.append(4), v)
}
// Write64 writes a 64-bit value to the buffer.
func (b *buffer) Write64(v uint64) {
order.PutUint64(b.append(8), v)
}
// WriteQIDType writes a QIDType value.
func (b *buffer) WriteQIDType(qidType QIDType) {
b.Write8(uint8(qidType))
}
// WriteTag writes a Tag value.
func (b *buffer) WriteTag(tag Tag) {
b.Write16(uint16(tag))
}
// WriteFID writes a FID value.
func (b *buffer) WriteFID(fid FID) {
b.Write32(uint32(fid))
}
// WriteUID writes a UID value.
func (b *buffer) WriteUID(uid UID) {
b.Write32(uint32(uid))
}
// WriteGID writes a GID value.
func (b *buffer) WriteGID(gid GID) {
b.Write32(uint32(gid))
}
// WritePermissions applies a permissions mask and writes the FileMode.
func (b *buffer) WritePermissions(perm FileMode) {
b.WriteFileMode(perm & permissionsMask)
}
// WriteFileMode writes a FileMode.
func (b *buffer) WriteFileMode(mode FileMode) {
b.Write32(uint32(mode))
}
// WriteOpenFlags writes an OpenFlags.
func (b *buffer) WriteOpenFlags(flags OpenFlags) {
b.Write32(uint32(flags))
}
// WriteSocketType writes a SocketType.
func (b *buffer) WriteSocketType(flags SocketType) {
b.Write32(uint32(flags))
}
// WriteMsgType writes a MsgType.
func (b *buffer) WriteMsgType(t MsgType) {
b.Write8(uint8(t))
}
// WriteString serializes the given string.
func (b *buffer) WriteString(s string) {
b.Write16(uint16(len(s)))
for i := 0; i < len(s); i++ {
b.Write8(byte(s[i]))
}
}