First completly working solution

packets.go

@@ -0,0 +1,148 @@
+package main
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"errors"
+	"fmt"
+)
+
+const HeaderSize int = 32 + 1 + 4 + 4
+
+type SessionID [32]byte
+
+type Packet struct {
+	// headerLength uint32
+	sid        SessionID
+	flag       HeaderFlag
+	sync       uint32
+	dataLength uint32
+	data       []byte
+}
+
+func PacketFromBytes(bytes []byte) Packet {
+	sid := SessionID(bytes[0:32])
+	flag := HeaderFlag(bytes[32])
+	sync := binary.LittleEndian.Uint32(bytes[33:37])
+	dataLength := binary.LittleEndian.Uint32(bytes[37:41])
+	pck := Packet{
+		sid:        sid,
+		flag:       flag,
+		sync:       sync,
+		dataLength: dataLength,
+		data:       bytes[41 : 41+dataLength],
+	}
+	return pck
+}
+
+func NewAck(pckToAck *Packet) *Packet {
+	data := make([]byte, 4)
+	binary.LittleEndian.PutUint32(data, pckToAck.sync)
+	return &Packet{
+		sid:        pckToAck.sid,
+		flag:       Ack,
+		sync:       pckToAck.sync + 1,
+		dataLength: uint32(4),
+		data:       data,
+	}
+}
+
+func NewRequest(path string) *Packet {
+	data := []byte(path)
+	buf := make([]byte, 32)
+	_, err := rand.Read(buf)
+	if err != nil {
+		panic(err)
+	}
+
+	return &Packet{
+		sid:        SessionID(buf),
+		flag:       Request,
+		sync:       0,
+		dataLength: uint32(len(data)),
+		data:       data,
+	}
+}
+
+func NewFile(lastPck *Packet, data []byte) *Packet {
+	return &Packet{
+		sid:        lastPck.sid,
+		flag:       File,
+		sync:       lastPck.sync + 1,
+		dataLength: uint32(len(data)),
+		data:       data,
+	}
+}
+
+func NewEnd(lastFilePck *Packet) *Packet {
+	data := make([]byte, 4)
+	binary.LittleEndian.PutUint32(data, lastFilePck.sync)
+	return &Packet{
+		sid:        lastFilePck.sid,
+		flag:       End,
+		sync:       lastFilePck.sync + 1,
+		dataLength: uint32(4),
+		data:       data,
+	}
+}
+
+func NewResend(sync uint32, lastPck *Packet) *Packet {
+	data := make([]byte, 4)
+	binary.LittleEndian.PutUint32(data, sync)
+	return &Packet{
+		sid:        lastPck.sid,
+		flag:       Resend,
+		sync:       lastPck.sync + 1,
+		dataLength: uint32(4),
+		data:       data,
+	}
+}
+
+func NewPte(fileSize uint32, lastPck *Packet) *Packet {
+	data := make([]byte, 4)
+	binary.LittleEndian.PutUint32(data, fileSize)
+	return &Packet{
+		sid:        lastPck.sid,
+		flag:       PTE,
+		sync:       lastPck.sync + 1,
+		dataLength: uint32(4),
+		data:       data,
+	}
+}
+
+func (pck *Packet) GetUint32Payload() (uint32, error) {
+	flag := pck.flag
+	if flag != PTE && flag != Ack && flag != End && flag != Resend {
+		return 0, errors.New(fmt.Sprintf("Can not get Sync from Packet Type with flag: %v", flag))
+	}
+	return binary.LittleEndian.Uint32(pck.data), nil
+}
+
+func (pck *Packet) GetFilePath() (string, error) {
+	if pck.flag != Request {
+		return "", errors.New("Can not get FilePath from Packet that is not Request")
+	}
+	return string(pck.data), nil
+}
+
+func (pck *Packet) ToBytes() []byte {
+	arr := make([]byte, HeaderSize+int(pck.dataLength))
+	copy(arr[0:32], pck.sid[:])
+	arr[32] = byte(pck.flag)
+	binary.LittleEndian.PutUint32(arr[33:37], pck.sync)
+	binary.LittleEndian.PutUint32(arr[37:41], pck.dataLength)
+	copy(arr[41:], pck.data)
+
+	return arr
+}
+
+type HeaderFlag uint8
+
+const (
+	Request HeaderFlag = iota
+	PTE     HeaderFlag = iota
+	Ack     HeaderFlag = iota
+	File    HeaderFlag = iota
+	End     HeaderFlag = iota
+	Resend  HeaderFlag = iota
+)