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proto.go
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proto.go
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// Package proto provides a usage-inspecific wrapper around 9P's data
// serialization and communication scheme.
package proto
import (
"bytes"
"errors"
"io"
"reflect"
"sync"
"github.com/DeedleFake/p9/internal/util"
)
var (
// ErrLargeMessage is returned by various functions if a message is
// larger than the current maximum message size.
ErrLargeMessage = errors.New("message larger than msize")
// ErrClientClosed is returned by attempts to send to a closed
// client.
ErrClientClosed = errors.New("client closed")
)
const (
// NoTag is a special tag that is used when a tag is unimportant.
NoTag uint16 = 0xFFFF
)
var bufPool = sync.Pool{
New: func() interface{} {
return new(bytes.Buffer)
},
}
// Proto represents a protocol. It maps between message type IDs and
// the Go types that those IDs correspond to.
type Proto struct {
rmap map[uint8]reflect.Type
smap map[reflect.Type]uint8
}
// NewProto builds a Proto from the given one-way mapping.
func NewProto(mapping map[uint8]reflect.Type) Proto {
rmap := make(map[uint8]reflect.Type, len(mapping))
smap := make(map[reflect.Type]uint8, len(mapping))
for id, t := range mapping {
if t.Kind() == reflect.Ptr {
t = t.Elem()
}
rmap[id] = t
smap[t] = id
}
return Proto{
rmap: rmap,
smap: smap,
}
}
// TypeFromID returns the Go type that corresponds to the given ID. If
// the ID is not recognized, it returns nil.
func (p Proto) TypeFromID(id uint8) reflect.Type {
return p.rmap[id]
}
// IDFromType returns the message type ID that corresponds to the
// given Go type, and a boolean indicating that the mapping is valid.
func (p Proto) IDFromType(t reflect.Type) (uint8, bool) {
id, ok := p.smap[t]
return id, ok
}
// Receive receives a message from r using the given maximum message
// size. It returns the message, the tag that the message was sent
// with, and an error, if any.
func (p Proto) Receive(r io.Reader, msize uint32) (msg interface{}, tag uint16, err error) {
var size uint32
err = Read(r, &size)
if err != nil {
return nil, NoTag, util.Errorf("receive: %w", err)
}
if (msize > 0) && (size > msize) {
return nil, NoTag, util.Errorf("receive: %w", ErrLargeMessage)
}
lr := &util.LimitedReader{
R: r,
N: size,
E: ErrLargeMessage,
}
var msgType uint8
err = Read(lr, &msgType)
if err != nil {
return nil, NoTag, util.Errorf("receive: failed to read message type: %w", err)
}
t := p.TypeFromID(msgType)
if t == nil {
if err != nil {
return nil, NoTag, err
}
return nil, NoTag, util.Errorf("receive: invalid message type: %v", msgType)
}
tag = NoTag
err = Read(lr, &tag)
if err != nil {
return nil, tag, util.Errorf("receive: failed to read tag: %w", err)
}
m := reflect.New(t)
err = Read(lr, m.Interface())
if err != nil {
return nil, tag, util.Errorf("receive %v: %w", m.Type().Elem(), err)
}
return m.Interface(), tag, err
}
// Send writes a message to w with the given tag. It returns any
// errors that occur.
//
// Encoded messages are buffered locally before sending to ensure that
// pieces of a message don't get mixed with another one.
func (p Proto) Send(w io.Writer, tag uint16, msg interface{}) (err error) {
buf := bufPool.Get().(*bytes.Buffer)
defer func() {
if err == nil {
_, err = io.Copy(w, buf)
if err != nil {
err = util.Errorf("send: %w", err)
}
}
buf.Reset()
bufPool.Put(buf)
}()
msgType, ok := p.IDFromType(reflect.Indirect(reflect.ValueOf(msg)).Type())
if !ok {
return util.Errorf("send: invalid message type: %T", msg)
}
write := func(v interface{}) {
if err != nil {
return
}
err = Write(buf, v)
if err != nil {
err = util.Errorf("send %T: %w", msg, err)
}
}
n, err := Size(msg)
if err != nil {
return util.Errorf("send %T: %w", msg, err)
}
write(4 + 1 + 2 + n)
write(msgType)
write(tag)
write(msg)
return err
}