FEAT: it's again possible to read dns:// to resolve a hostname

```
>> read dns://
== "Oldes-Aero"
```

It also fixes a bug introduce in rebol#66, that resolving domain name from ip was not possible at all. Now it's again working properly:
```
>> read dns://rebol.com
== 162.216.18.225
>> read dns://162.216.18.225
== "rebol.com"

```

Related to: Oldes/Rebol-issues#1935

Author: Oldes

src/core/p-dns.c

@@ -65,13 +65,22 @@
 		}
 
 		arg = Obj_Value(spec, STD_PORT_SPEC_NET_HOST);
-
-		if (IS_TUPLE(arg) && Scan_Tuple(VAL_BIN(arg), (REBCNT)LEN_BYTES(VAL_BIN(arg)), &tmp)) {
+		if (IS_NONE(arg)) {
+			// case: read dns://
+			sock->data = NULL;
+		}
+		else if (IS_TUPLE(arg)) {
 			SET_FLAG(sock->modes, RST_REVERSE);
-			memcpy(&sock->net.remote_ip, VAL_TUPLE(&tmp), 4);
+			memcpy(&sock->net.remote_ip, VAL_TUPLE(arg), 4);
 		}
 		else if (IS_STRING(arg)) {
-			sock->data = VAL_BIN(arg);
+			if (Scan_Tuple(VAL_BIN(arg), (REBCNT)LEN_BYTES(VAL_BIN(arg)), &tmp)) {
+				SET_FLAG(sock->modes, RST_REVERSE);
+				memcpy(&sock->net.remote_ip, VAL_TUPLE(&tmp), 4);
+			}
+			else {
+				sock->data = VAL_BIN(arg);
+			}
 		}
 		else Trap_Port(RE_INVALID_SPEC, port, -10);
 

src/os/dev-dns.c

@@ -106,11 +106,24 @@ extern HWND Event_Handle;
 #endif
 
 	host = OS_Make(MAXGETHOSTSTRUCT); // be sure to free it
+	sock->net.host_info = host; // stores allocated buffer, deallocated on close or on error
 
 #ifdef HAS_ASYNC_DNS
-	if (!GET_FLAG(sock->modes, RST_REVERSE)) // hostname lookup
-		handle = WSAAsyncGetHostByName(Event_Handle, WM_DNS, sock->data, host, MAXGETHOSTSTRUCT);
-	else
+	// WINDOWS version
+	if (!GET_FLAG(sock->modes, RST_REVERSE)) {// hostname lookup
+		if (sock->data == NULL) {
+			DWORD dwSize = MAXGETHOSTSTRUCT;
+			if (GetComputerNameExA(ComputerNameDnsFullyQualified, host, &dwSize)) {
+				((REBYTE*)host)[dwSize] = 0;
+				sock->data = host;
+				SET_FLAG(sock->modes, RST_REVERSE);
+				SET_FLAG(sock->flags, RRF_DONE);
+				return DR_DONE;
+			}
+			goto error;
+		}
+		handle = WSAAsyncGetHostByName(Event_Handle, WM_DNS, cs_cast(sock->data), host, MAXGETHOSTSTRUCT);
+	} else
 		handle = WSAAsyncGetHostByAddr(Event_Handle, WM_DNS, (char*)&(sock->net.remote_ip), 4, AF_INET, host, MAXGETHOSTSTRUCT);
 
 	if (handle != 0) {
@@ -119,27 +132,34 @@ extern HWND Event_Handle;
 		return DR_PEND; // keep it on pending list
 	}
 #else
+	// POSIX version
 	// Use old-style blocking DNS (mainly for testing purposes):
 	if (GET_FLAG(sock->modes, RST_REVERSE)) {
 		he = gethostbyaddr((char*)&sock->net.remote_ip, 4, AF_INET);
 		if (he) {
-			sock->net.host_info = host; //???
 			sock->data = he->h_name;
 			SET_FLAG(sock->flags, RRF_DONE);
 			return DR_DONE;
 		}
 	}
+	else if (sock->data == NULL) {
+		if(0 == gethostname(host, MAXGETHOSTSTRUCT)) {
+			sock->data = host;
+			SET_FLAG(sock->modes, RST_REVERSE);
+			SET_FLAG(sock->flags, RRF_DONE);
+			return DR_DONE;
+		}
+	}
 	else {
 		he = gethostbyname(sock->data);
 		if (he) {
-			sock->net.host_info = host; // ?? who deallocs?
 			COPY_MEM((char*)&(sock->net.remote_ip), (char *)(*he->h_addr_list), 4); //he->h_length);
 			SET_FLAG(sock->flags, RRF_DONE);
 			return DR_DONE;
 		}
 	}
 #endif
-
+error:
 	OS_Free(host);
 	sock->net.host_info = 0;
 
@@ -178,7 +198,7 @@ extern HWND Event_Handle;
 			if (!req->error) { // success!
 				host = (HOSTENT*)req->net.host_info;
 				if (GET_FLAG(req->modes, RST_REVERSE))
-					req->data = host->h_name;
+					req->data = (REBYTE*)host->h_name;
 				else
 					COPY_MEM((char*)&(req->net.remote_ip), (char *)(*host->h_addr_list), 4); //he->h_length);
 				Signal_Device(req, EVT_READ);

src/tests/units/port-test.r3

@@ -130,4 +130,15 @@ if "true" <> get-env "CONTINUOUS_INTEGRATION" [
 	===end-group===
 ]
 
+
+===start-group=== "DNS"
+;@@ https://github.com/Oldes/Rebol-issues/issues/1935
+	--test-- "read dns://"
+		--assert string? try [probe read dns://] ;- no crash!
+	--test-- "read dns://8.8.8.8"
+		--assert "dns.google" = try [probe read dns://8.8.8.8]
+	--test-- "read dns://google.com"
+		--assert tuple? try [read dns://google.com]
+===end-group===
+
 ~~~end-file~~~