1 files changed, 262 insertions, 0 deletions
diff --git a/pkg/p9/buffer.go b/pkg/p9/buffer.go
new file mode 100644
index 000000000..fc65d2c5f
--- /dev/null
+++ b/pkg/p9/buffer.go
@@ -0,0 +1,262 @@
+// Copyright 2018 Google Inc.
+//
+// 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.
+	//
+	// 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+// buffer is no longer valid either.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())
+}
+
+// ReadConnectFlags reads a ConnectFlags.
+func (b *buffer) ReadConnectFlags() ConnectFlags {
+	return ConnectFlags(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))
+}
+
+// WriteConnectFlags writes a ConnectFlags.
+func (b *buffer) WriteConnectFlags(flags ConnectFlags) {
+	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]))
+	}
+}