Golang writing SMTP Mailbox service side

Package Mainimport ("FMT", "Net" "OS") type Mail struct {clientName string from string to String Data string Recivedata Bool}func main () {listen, err: = Net. LISTENTCP ("TCP", &net. Tcpaddr{net. Parseip ("127.0.0.1"), +, ""}) if err! = Nil {fmt. PRINTLN ("Listener Port failed:", err.) Error ()) return} defer listen. Close () recive (listen)}func recive (Listen *net. TcpListener) {for {conn, err: = Listen. ACCEPTTCP ()//Receive connection defer Conn. Close () if err! = Nil {fmt. PRINTLN ("Client connection exception", err.) Error ())//Client connection exception continue} conn. Write ([]byte ("Gomailsever")) fmt. PRINTLN ("New Client", Conn. Remoteaddr (). String ()) go func () {tmpbuffer: = make ([]byte, 0)//Create pending byte slice readerchannel: = Mak E (Chan []byte, 16)//Create channel communication pipeline _mail: = &mail{} Go Reader (Readerchannel, Conn, _mail)//chan Nel information receiver data: = Make ([]byte, 1024)//Create output buffer tile for {i, err: = conn. Read//reads data from the socket if err! = Nil {fmt. PRINTLN ("Read error occurred", err.) Error ())//Read failure errors occurred return} Tmpbuffer = Depackmail (Append (tmpbuffer, dat A[:I], Readerchannel)//handle byte//fmt with a custom protocol. Println (data, String)}} ()}}func reader (Readerchannel Chan []byte, Conn *net. Tcpconn, _mail *mail) {for {select {case data: = <-readerchannel:fmt.  Println (String (data[0:4))) switch string (Data[0:4]) {case "HELO": _mail.clientname = String (data[4+2:]) Conn. Write ([]byte ("Give Me Mail")) Break Case "Mail": _mail.from = String (data[4+2 :]) Conn. Write ([]byte ("Give I AM Fine")) Break Case "RCPT": _mail.to = String (data[4+2:]) Conn. Write ([]byte ("Give I AM Fine")) Break Case "DATA": Conn. Write ([]byte ("354 Give I AM Fine")) Break Case "QUIT": Conn. Write ([]byte ("221 Byebye")) file, _: = OS. Create ("./mail/3.eml") file. WriteString (_mail.data) file. Close () fmt.                Println (_mail) Break default: _mail.data = _mail.data + string (data) Fmt. Println (String (_mail.data[len (_mail.data)-1:])) If String (_mail.data[len (_mail.data)-1:]) = = "." {FMT. Println ("111") Conn. Write ([]byte ("Give I AM Fine")} Break}}}}func Depackmail (Buffe R []byte, Readerchannel Chan []byte] []byte {length: = Len (buffer) var i int for i = 0; i < length;        {If length < i+4 {//2-bit for tail mark break} var sindex int for dump: = i; Dump < length-1;            dump++ {if buffer[dump] = = Byte (all) && buffer[dump+1] = = Byte (Ten) {Sindex = dump  }} if Sindex <= 0 {break} data: = Buffer[i:sindex] Readerchannel <-data//sent to the pipeline i = Sindex + 2} if i = = length {//All processing complete return empty package returns make ([]byte, 0)} RE Turn buffer[i:]//Not processed finished return remaining packages}