espat: add ResolveUDPAddr and ResolveTCPAddr implementations using AT command for DNS lookup

Signed-off-by: Ron Evans <ron@hybridgroup.com>

espat/commands.go

@@ -85,6 +85,9 @@ const (
 	// Establish TCP connection or register UDP port
 	TCPConnect = "+CIPSTART"
 
+	// DNS Lookup
+	TCPDNSLookup = "+CIPDOMAIN"
+
 	// Send Data
 	TCPSend = "+CIPSEND"
 

espat/net.go

@@ -2,6 +2,7 @@ package espat
 
 import (
 	"strconv"
+	"strings"
 	"time"
 )
 
@@ -156,6 +157,51 @@ func (c *SerialConn) SetWriteDeadline(t time.Time) error {
 	return nil
 }
 
+// ResolveTCPAddr returns an address of TCP end point.
+//
+// The network must be a TCP network name.
+//
+func (d *Device) ResolveTCPAddr(network, address string) (*TCPAddr, error) {
+	// TODO: make sure network is 'tcp'
+	// separate domain from port, if any
+	r := strings.Split(address, ":")
+	ip, err := d.GetDNS(r[0])
+	if err != nil {
+		return nil, err
+	}
+	if len(r) > 1 {
+		port, e := strconv.Atoi(r[1])
+		if e != nil {
+			return nil, e
+		}
+		return &TCPAddr{IP: ip, Port: port}, nil
+	}
+	return &TCPAddr{IP: ip}, nil
+}
+
+// ResolveUDPAddr returns an address of UDP end point.
+//
+// The network must be a UDP network name.
+//
+func (d *Device) ResolveUDPAddr(network, address string) (*UDPAddr, error) {
+	// TODO: make sure network is 'udp'
+	// separate domain from port, if any
+	r := strings.Split(address, ":")
+	ip, err := d.GetDNS(r[0])
+	if err != nil {
+		return nil, err
+	}
+	if len(r) > 1 {
+		port, e := strconv.Atoi(r[1])
+		if e != nil {
+			return nil, e
+		}
+		return &UDPAddr{IP: ip, Port: port}, nil
+	}
+
+	return &UDPAddr{IP: ip}, nil
+}
+
 // The following definitions are here to support a Golang standard package
 // net-compatible interface for IP until TinyGo can compile the net package.
 

espat/tcp.go

@@ -15,11 +15,23 @@ const (
 	TCPTransferModeUnvarnished = 1
 )
 
+// GetDNS returns the IP address for a domain name.
+func (d *Device) GetDNS(domain string) (IP, error) {
+	d.Set(TCPDNSLookup, "\""+domain+"\"")
+	time.Sleep(1000 * time.Millisecond)
+	r := strings.Split(string(d.Response()), ":")
+	if len(r) != 2 {
+		return nil, errors.New("Invalid domain lookup result")
+	}
+	res := strings.Split(r[1], "\r\n")
+	return IP(res[0]), nil
+}
+
 // ConnectTCPSocket creates a new TCP socket connection for the ESP8266/ESP32.
 // Currently only supports single connection mode.
 func (d *Device) ConnectTCPSocket(addr, port string) error {
 	protocol := "TCP"
-	val := "\"" + protocol + "\",\"" + addr + "\"," + port
+	val := "\"" + protocol + "\",\"" + addr + "\"," + port + ",120"
 	d.Set(TCPConnect, val)
 	time.Sleep(1000 * time.Millisecond)
 	r := d.Response()