first init

tls_utils.go

@@ -0,0 +1,116 @@
+package modbus
+
+import (
+	"crypto/x509"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"os"
+	"time"
+)
+
+// LoadCertPool loads a certificate store from a file into a CertPool object.
+func LoadCertPool(filePath string) (cp *x509.CertPool, err error) {
+	var buf []byte
+
+	// read the entire cert store, which may contain zero, one
+	// or more certificates
+	buf, err = ioutil.ReadFile(filePath)
+	if err != nil {
+		return
+	}
+
+	if len(buf) == 0 {
+		err = fmt.Errorf("%v: empty file", filePath)
+		return
+	}
+
+	// add these certs to the pool
+	cp = x509.NewCertPool()
+	cp.AppendCertsFromPEM(buf)
+
+	// let the caller know if no usable certificate was found
+	if len(cp.Subjects()) == 0 {
+		err = fmt.Errorf("%v: no certificate found", filePath)
+		return
+	}
+
+	return
+}
+
+// tlsSockWrapper wraps a TLS socket to work around odd error handling in
+// TLSConn on internal connection state corruption.
+// tlsSockWrapper implements the net.Conn interface to allow its
+// use by the modbus TCP transport.
+type tlsSockWrapper struct {
+	sock net.Conn
+}
+
+func newTLSSockWrapper(sock net.Conn) (tsw *tlsSockWrapper) {
+	tsw = &tlsSockWrapper{
+		sock: sock,
+	}
+
+	return
+}
+
+func (tsw *tlsSockWrapper) Read(buf []byte) (rlen int, err error) {
+	rlen, err = tsw.sock.Read(buf)
+
+	return
+}
+
+func (tsw *tlsSockWrapper) Write(buf []byte) (wlen int, err error) {
+	wlen, err = tsw.sock.Write(buf)
+
+	// since write timeouts corrupt the internal state of TLS sockets,
+	// any subsequent read/write operation will fail and return the same write
+	// timeout error (see https://pkg.go.dev/crypto/tls#Conn.SetWriteDeadline).
+	// this isn't all that helpful to clients, which may be tricked into
+	// retrying forever, treating timeout errors as transient.
+	// to avoid this, close the TLS socket after the first write timeout.
+	// this ensures that clients 1) get a timeout error on the first write timeout
+	// and 2) get an ErrNetClosing "use of closed network connection" on subsequent
+	// operations.
+	if err != nil && os.IsTimeout(err) {
+		tsw.sock.Close()
+	}
+
+	return
+}
+
+func (tsw *tlsSockWrapper) Close() (err error) {
+	err = tsw.sock.Close()
+
+	return
+}
+
+func (tsw *tlsSockWrapper) SetDeadline(deadline time.Time) (err error) {
+	err = tsw.sock.SetDeadline(deadline)
+
+	return
+}
+
+func (tsw *tlsSockWrapper) SetReadDeadline(deadline time.Time) (err error) {
+	err = tsw.sock.SetReadDeadline(deadline)
+
+	return
+}
+
+func (tsw *tlsSockWrapper) SetWriteDeadline(deadline time.Time) (err error) {
+	err = tsw.sock.SetWriteDeadline(deadline)
+
+	return
+}
+
+func (tsw *tlsSockWrapper) LocalAddr() (addr net.Addr) {
+	addr = tsw.sock.LocalAddr()
+
+	return
+}
+
+func (tsw *tlsSockWrapper) RemoteAddr() (addr net.Addr) {
+	addr = tsw.sock.RemoteAddr()
+
+	return
+}