/
server.go
144 lines (121 loc) · 3.32 KB
/
server.go
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package modbus
import (
"bufio"
"encoding/binary"
"fmt"
"io"
"log"
"net"
"time"
)
// Server is a Modbus server listens on a port and responds on incoming Modbus
// requests.
type Server struct {
l net.Listener
handlers map[uint8]Handler
timeout time.Duration
ErrorLog *log.Logger
}
// NewServer creates a new server on given address.
func NewServer(address string) (*Server, error) {
l, err := net.Listen("tcp", address)
if err != nil {
return nil, fmt.Errorf("failed to start Modbus server: %v", err)
}
return &Server{
l: l,
timeout: 0,
handlers: make(map[uint8]Handler),
}, nil
}
// SetTimeout sets the timeout, which is the maximum duraion a request can take.
func (s *Server) SetTimeout(t time.Duration) {
s.timeout = t
}
// Listen start listening for requests.
func (s *Server) Listen() {
for {
conn, err := s.l.Accept()
if err != nil {
s.logf("golfish: failed to accept incoming connection: %v", err)
continue
}
if d := s.timeout; d != 0 {
if err := conn.SetReadDeadline(time.Now().Add(d)); err != nil {
s.logf("goldfish: failed set timeout %v: %v", conn.RemoteAddr(), err)
if err := conn.Close(); err != nil {
s.logf("goldfish: failed to close connection with %v: %v", conn.RemoteAddr(), err)
}
}
}
go func() {
if err := s.handleConn(conn); err != nil {
s.logf("goldfish: unable to handle request from %v: %v", conn.RemoteAddr(), err)
}
if err := conn.Close(); err != nil {
s.logf("goldfish: failed to close connection with %v: %v", conn.RemoteAddr(), err)
}
}()
}
}
func (s *Server) handleConn(conn io.ReadWriteCloser) error {
r := bufio.NewReader(conn)
for {
buf, err := s.readMessage(r)
if err != nil {
// An EOF error indicates the connection did not send new data. This
// means the connection can be closed, but its not an error in the program.
if err == io.EOF {
return nil
}
return fmt.Errorf("failed to read message from connection: %v", err)
}
var req Request
if err := req.UnmarshalBinary(buf); err != nil {
return fmt.Errorf("failed to parse request: %v", err)
}
if err := s.executeAndRespond(conn, &req); err != nil {
return fmt.Errorf("something went horribly wrong and server has to close connection: %v", err)
}
}
}
func (s *Server) readMessage(r *bufio.Reader) ([]byte, error) {
b, err := r.Peek(6)
if err != nil {
return nil, err
}
length := binary.BigEndian.Uint16(b[4:6])
buf := make([]byte, 6+length)
_, err = r.Read(buf)
if err != nil {
return nil, fmt.Errorf("failed to read request: %v", err)
}
return buf, nil
}
func (s *Server) executeAndRespond(conn io.Writer, req *Request) error {
h, ok := s.handlers[req.FunctionCode]
if ok {
h.ServeModbus(conn, *req)
return nil
}
resp := NewErrorResponse(*req, IllegalFunctionError)
data, err := resp.MarshalBinary()
if err != nil {
return fmt.Errorf("failed to create response: %v", err)
}
if _, err := conn.Write(data); err != nil {
return fmt.Errorf("failed to write response: %v", err)
}
return nil
}
// Handle registers the handler for the given function code.
func (s *Server) Handle(functionCode uint8, h Handler) {
s.handlers[functionCode] = h
}
func (s *Server) logf(format string, args ...interface{}) {
if s.ErrorLog != nil {
s.ErrorLog.Printf(format, args...)
} else {
log.Printf(format, args...)
}
}