encode.go

/*
Copyright (c) 2013, Samuel Stauffer <samuel@descolada.com>
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.
* Neither the name of the author nor the
  names of its contributors may be used to endorse or promote products
  derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package zetcd

import (
	"encoding/binary"
	"errors"
	"io"
	"net"
	"reflect"
	"runtime"
)

var (
	ErrShortBuffer        = errors.New("short buffer")
	ErrPtrExpected        = errors.New("ptr expected")
	ErrUnhandledFieldType = errors.New("unhandled field type")
)

type decoder interface {
	Decode(buf []byte) (int, error)
}

type encoder interface {
	Encode(buf []byte) (int, error)
}

func decodePacket(buf []byte, st interface{}) (n int, err error) {
	defer func() {
		if r := recover(); r != nil {
			if e, ok := r.(runtime.Error); ok && e.Error() == "runtime error: slice bounds out of range" {
				err = ErrShortBuffer
			} else {
				panic(r)
			}
		}
	}()

	v := reflect.ValueOf(st)
	if v.Kind() != reflect.Ptr || v.IsNil() {
		return 0, ErrPtrExpected
	}
	return decodePacketValue(buf, v)
}

func decodePacketValue(buf []byte, v reflect.Value) (int, error) {
	rv := v
	kind := v.Kind()
	if kind == reflect.Ptr {
		if v.IsNil() {
			v.Set(reflect.New(v.Type().Elem()))
		}
		v = v.Elem()
		kind = v.Kind()
	}

	n := 0
	switch kind {
	default:
		return n, ErrUnhandledFieldType
	case reflect.Struct:
		if de, ok := rv.Interface().(decoder); ok {
			return de.Decode(buf)
		} else if de, ok := v.Interface().(decoder); ok {
			return de.Decode(buf)
		} else {
			for i := 0; i < v.NumField(); i++ {
				field := v.Field(i)
				n2, err := decodePacketValue(buf[n:], field)
				n += n2
				if err != nil {
					return n, err
				}
			}
		}
	case reflect.Bool:
		v.SetBool(buf[n] != 0)
		n++
	case reflect.Int32:
		v.SetInt(int64(binary.BigEndian.Uint32(buf[n : n+4])))
		n += 4
	case reflect.Int64:
		v.SetInt(int64(binary.BigEndian.Uint64(buf[n : n+8])))
		n += 8
	case reflect.String:
		ln := int(binary.BigEndian.Uint32(buf[n : n+4]))
		v.SetString(string(buf[n+4 : n+4+ln]))
		n += 4 + ln
	case reflect.Slice:
		switch v.Type().Elem().Kind() {
		default:
			count := int(binary.BigEndian.Uint32(buf[n : n+4]))
			n += 4
			values := reflect.MakeSlice(v.Type(), count, count)
			v.Set(values)
			for i := 0; i < count; i++ {
				n2, err := decodePacketValue(buf[n:], values.Index(i))
				n += n2
				if err != nil {
					return n, err
				}
			}
		case reflect.Uint8:
			ln := int(int32(binary.BigEndian.Uint32(buf[n : n+4])))
			if ln < 0 {
				n += 4
				v.SetBytes(nil)
			} else {
				bytes := make([]byte, ln)
				copy(bytes, buf[n+4:n+4+ln])
				v.SetBytes(bytes)
				n += 4 + ln
			}
		}
	}
	return n, nil
}

func encodePacket(buf []byte, st interface{}) (n int, err error) {
	defer func() {
		if r := recover(); r != nil {
			if e, ok := r.(runtime.Error); ok && e.Error() == "runtime error: slice bounds out of range" {
				err = ErrShortBuffer
			} else {
				panic(r)
			}
		}
	}()

	v := reflect.ValueOf(st)
	if v.Kind() != reflect.Ptr || v.IsNil() {
		return 0, ErrPtrExpected
	}
	return encodePacketValue(buf, v)
}

func encodePacketValue(buf []byte, v reflect.Value) (int, error) {
	rv := v
	for v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface {
		v = v.Elem()
	}

	n := 0
	switch v.Kind() {
	default:
		return n, ErrUnhandledFieldType
	case reflect.Struct:
		if en, ok := rv.Interface().(encoder); ok {
			return en.Encode(buf)
		} else if en, ok := v.Interface().(encoder); ok {
			return en.Encode(buf)
		} else {
			for i := 0; i < v.NumField(); i++ {
				field := v.Field(i)
				n2, err := encodePacketValue(buf[n:], field)
				n += n2
				if err != nil {
					return n, err
				}
			}
		}
	case reflect.Bool:
		if v.Bool() {
			buf[n] = 1
		} else {
			buf[n] = 0
		}
		n++
	case reflect.Int32:
		binary.BigEndian.PutUint32(buf[n:n+4], uint32(v.Int()))
		n += 4
	case reflect.Int64:
		binary.BigEndian.PutUint64(buf[n:n+8], uint64(v.Int()))
		n += 8
	case reflect.String:
		str := v.String()
		binary.BigEndian.PutUint32(buf[n:n+4], uint32(len(str)))
		copy(buf[n+4:n+4+len(str)], []byte(str))
		n += 4 + len(str)
	case reflect.Slice:
		switch v.Type().Elem().Kind() {
		default:
			count := v.Len()
			startN := n
			n += 4
			for i := 0; i < count; i++ {
				n2, err := encodePacketValue(buf[n:], v.Index(i))
				n += n2
				if err != nil {
					return n, err
				}
			}
			binary.BigEndian.PutUint32(buf[startN:startN+4], uint32(count))
		case reflect.Uint8:
			if v.IsNil() {
				binary.BigEndian.PutUint32(buf[n:n+4], uint32(0xffffffff))
				n += 4
			} else {
				bytes := v.Bytes()
				binary.BigEndian.PutUint32(buf[n:n+4], uint32(len(bytes)))
				copy(buf[n+4:n+4+len(bytes)], bytes)
				n += 4 + len(bytes)
			}
		}
	}
	return n, nil
}

func ReadPacket(zk net.Conn, r interface{}) (string, error) {
	buf := make([]byte, 256)
	_, err := io.ReadFull(zk, buf[:4])
	if string(buf[:4]) == flwRUOK {
		return flwRUOK, nil
	}
	if err != nil {
		return "", err
	}
	blen := int(binary.BigEndian.Uint32(buf[:4]))
	if cap(buf) < blen {
		buf = make([]byte, blen)
	}
	_, err = io.ReadFull(zk, buf[:blen])
	if err != nil {
		return "", err
	}
	_, err = decodePacket(buf[:blen], r)
	return "", err
}

func WritePacket(zk net.Conn, r interface{}) error {
	buf := make([]byte, 256)
	n, err := encodePacket(buf[4:], r)
	if err != nil {
		return err
	}
	binary.BigEndian.PutUint32(buf[:4], uint32(n))
	_, err = zk.Write(buf[:n+4])
	return err
}

func (r *MultiRequest) Encode(buf []byte) (int, error) {
	total := 0
	for _, op := range r.Ops {
		op.Header.Done = false
		n, err := encodePacketValue(buf[total:], reflect.ValueOf(op))
		if err != nil {
			return total, err
		}
		total += n
	}
	r.DoneHeader.Done = true
	n, err := encodePacketValue(buf[total:], reflect.ValueOf(r.DoneHeader))
	if err != nil {
		return total, err
	}
	total += n

	return total, nil
}

func (r *MultiRequest) Decode(buf []byte) (int, error) {
	r.Ops = make([]MultiRequestOp, 0)
	r.DoneHeader = MultiHeader{-1, true, -1}
	total := 0
	for {
		header := &MultiHeader{}
		n, err := decodePacketValue(buf[total:], reflect.ValueOf(header))
		if err != nil {
			return total, err
		}
		total += n
		if header.Done {
			r.DoneHeader = *header
			break
		}

		req := op2req(header.Type)
		if req == nil {
			return total, ErrAPIError
		}
		n, err = decodePacketValue(buf[total:], reflect.ValueOf(req))
		if err != nil {
			return total, err
		}
		total += n
		r.Ops = append(r.Ops, MultiRequestOp{*header, req})
	}
	return total, nil
}

func (r *MultiResponse) Encode(buf []byte) (int, error) {
	total := 0
	for _, op := range r.Ops {
		op.Header.Done = false
		n, err := encodePacketValue(buf[total:], reflect.ValueOf(op.Header))
		if err != nil {
			return total, err
		}
		total += n
		n = 0
		switch op.Header.Type {
		case opCreate:
			n, err = encodePacketValue(buf[total:], reflect.ValueOf(op.String))
		case opSetData:
			n, err = encodePacketValue(buf[total:], reflect.ValueOf(op.Stat))
		}
		total += n
		if err != nil {
			return total, err
		}
	}
	r.DoneHeader.Done = true
	n, err := encodePacketValue(buf[total:], reflect.ValueOf(r.DoneHeader))
	if err != nil {
		return total, err
	}
	total += n
	return total, nil
}

func (r *MultiResponse) Decode(buf []byte) (int, error) {
	r.Ops = make([]MultiResponseOp, 0)
	r.DoneHeader = MultiHeader{-1, true, -1}
	total := 0
	for {
		header := &MultiHeader{}
		n, err := decodePacketValue(buf[total:], reflect.ValueOf(header))
		if err != nil {
			return total, err
		}
		total += n
		if header.Done {
			r.DoneHeader = *header
			break
		}

		res := MultiResponseOp{Header: *header}
		var w reflect.Value
		switch header.Type {
		default:
			return total, ErrAPIError
		case opCreate:
			w = reflect.ValueOf(&res.String)
		case opSetData:
			res.Stat = new(Stat)
			w = reflect.ValueOf(res.Stat)
		case opCheck, opDelete:
		}
		if w.IsValid() {
			n, err := decodePacketValue(buf[total:], w)
			if err != nil {
				return total, err
			}
			total += n
		}
		r.Ops = append(r.Ops, res)
	}
	return total, nil
}

func readBuf(zk net.Conn) ([]byte, uint32, error) {
	buf := make([]byte, 256)
	if _, err := io.ReadFull(zk, buf[:4]); err != nil {
		return nil, 0, err
	}
	blen := binary.BigEndian.Uint32(buf[:4])
	if cap(buf) < int(blen) {
		buf = make([]byte, blen)
	}
	if _, err := io.ReadFull(zk, buf[:blen]); err != nil {
		return nil, 0, err
	}
	return buf, blen, nil
}

func readReqOp(zk net.Conn) (Xid, interface{}, error) {
	buf, blen, err := readBuf(zk)
	if err != nil {
		return 0, nil, err
	}
	hdr := &requestHeader{}
	n, herr := decodePacket(buf, hdr)
	if herr != nil {
		return 0, nil, herr
	}
	op := op2req(hdr.Opcode)
	_, oerr := decodePacket(buf[n:blen], op)
	return hdr.Xid, op, oerr

}

func readRespOp(zk net.Conn, xid2resp func(Xid) interface{}) (*ResponseHeader, interface{}, error) {
	buf, blen, err := readBuf(zk)
	if err != nil {
		return nil, nil, err
	}
	hdr := &ResponseHeader{}
	n, herr := decodePacket(buf, hdr)
	if herr != nil {
		return nil, nil, herr
	}

	var resp interface{}
	if hdr.Err != 0 {
		return hdr, nil, nil
	}
	if hdr.Xid == -1 {
		resp = &WatcherEvent{}
	} else {
		resp = xid2resp(hdr.Xid)
	}
	if resp == nil {
		return nil, nil, ErrAPIError
	}
	_, oerr := decodePacket(buf[n:blen], resp)
	return hdr, resp, oerr
}