Implemented new datasources (modbus,scpi)

internal/datasource/scpi/transport.go

@@ -0,0 +1,107 @@
+package scpi
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+	"strings"
+	"sync"
+	"time"
+)
+
+// transport is the request/response channel to an instrument. The raw-socket
+// implementation below speaks line-oriented SCPI over TCP (the common
+// "SCPI raw" / port 5025 convention). The interface is kept narrow so a VXI-11
+// (ONC-RPC) transport can be added later without touching the data source.
+type transport interface {
+	// query sends cmd and returns the instrument's single-line response.
+	query(cmd string) (string, error)
+	// write sends cmd and does not wait for a response.
+	write(cmd string) error
+	close()
+}
+
+// rawSocket is a line-based SCPI transport over a single TCP connection. The
+// connection is dialled lazily and dropped on any I/O error so the next call
+// reconnects. Calls are serialised by mu because SCPI is request/response.
+type rawSocket struct {
+	addr       string
+	timeout    time.Duration
+	terminator string
+
+	mu   sync.Mutex
+	conn net.Conn
+	br   *bufio.Reader
+}
+
+func newRawSocket(addr string, timeout time.Duration, terminator string) *rawSocket {
+	if timeout <= 0 {
+		timeout = 3 * time.Second
+	}
+	if terminator == "" {
+		terminator = "\n"
+	}
+	return &rawSocket{addr: addr, timeout: timeout, terminator: terminator}
+}
+
+func (s *rawSocket) dialLocked() error {
+	if s.conn != nil {
+		return nil
+	}
+	conn, err := net.DialTimeout("tcp", s.addr, s.timeout)
+	if err != nil {
+		return fmt.Errorf("scpi: dial %s: %w", s.addr, err)
+	}
+	s.conn = conn
+	s.br = bufio.NewReader(conn)
+	return nil
+}
+
+func (s *rawSocket) closeLocked() {
+	if s.conn != nil {
+		_ = s.conn.Close()
+		s.conn = nil
+		s.br = nil
+	}
+}
+
+func (s *rawSocket) close() {
+	s.mu.Lock()
+	s.closeLocked()
+	s.mu.Unlock()
+}
+
+func (s *rawSocket) sendLocked(cmd string) error {
+	_ = s.conn.SetDeadline(time.Now().Add(s.timeout))
+	if _, err := s.conn.Write([]byte(cmd + s.terminator)); err != nil {
+		s.closeLocked()
+		return fmt.Errorf("scpi: write: %w", err)
+	}
+	return nil
+}
+
+func (s *rawSocket) write(cmd string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if err := s.dialLocked(); err != nil {
+		return err
+	}
+	return s.sendLocked(cmd)
+}
+
+func (s *rawSocket) query(cmd string) (string, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if err := s.dialLocked(); err != nil {
+		return "", err
+	}
+	if err := s.sendLocked(cmd); err != nil {
+		return "", err
+	}
+	line, err := s.br.ReadString('\n')
+	if err != nil {
+		s.closeLocked()
+		return "", fmt.Errorf("scpi: read: %w", err)
+	}
+	return strings.TrimRight(line, "\r\n"), nil
+}