I'd like to upstream the ipv6.patch.

Some distributions downstream supply it for years:

http://pkgs.fedoraproject.org/cgit/screen.git/tree/screen-ipv6.patch
https://sources.debian.net/src/screen/4.2.1-3/debian/patches/48screen-ipv6.patch/
https://build.opensuse.org/package/view_file/openSUSE:Factory/screen/screen-4.0.3-ipv6.patch

Signed-off-by: Alexander Naumov <alexander_naumov@opensuse.org>

7 files changed, 115 insertions, 92 deletions

diff --git a/src/doc/screen.1 b/src/doc/screen.1
index 8a0d51f..abb19ad 100644
--- a/src/doc/screen.1
+++ b/src/doc/screen.1
@@ -409,6 +409,12 @@ several screen sessions running. You can use the \fB-d\fP or
 detached screen sessions. Note that this command doesn't work if
 the session is password protected.
 
+.TP 5
+.B \-4
+Resolve hostnames only to IPv4 addresses.
+.TP 5
+.B \-6
+Resolve hostnames only to IPv6 addresses.
 .SH "DEFAULT KEY BINDINGS"
 .ta 12n 26n
 As mentioned, each
diff --git a/src/extern.h b/src/extern.h
index a3e3ca2..9b564e6 100644
--- a/src/extern.h
+++ b/src/extern.h
@@ -459,8 +459,7 @@ extern void  LayProcessMouseSwitch __P((struct layer *, int));
 
 /* teln.c */
 #ifdef BUILTIN_TELNET
-extern int   TelOpen __P((char **));
-extern int   TelConnect __P((struct win *));
+extern int   TelOpenAndConnect __P((struct win *));
 extern int   TelIsline __P((struct win *p));
 extern void  TelProcessLine __P((char **, int *));
 extern int   DoTelnet __P((char *, int *, int));
diff --git a/src/help.c b/src/help.c
index 8446f34..a2b8614 100644
--- a/src/help.c
+++ b/src/help.c
@@ -66,6 +66,10 @@ char *myname, *message, *arg;
 {
   printf("Use: %s [-opts] [cmd [args]]\n", myname);
   printf(" or: %s -r [host.tty]\n\nOptions:\n", myname);
+#ifdef BUILTIN_TELNET
+  printf("-4            Resolve hostnames only to IPv4 addresses.\n");
+  printf("-6            Resolve hostnames only to IPv6 addresses.\n");
+#endif
   printf("-a            Force all capabilities into each window's termcap.\n");
   printf("-A -[r|R]     Adapt all windows to the new display width & height.\n");
   printf("-c file       Read configuration file instead of '.screenrc'.\n");
diff --git a/src/screen.c b/src/screen.c
index ad798c5..6008039 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -243,13 +243,14 @@ int nethackflag = 0;
 #endif
 int maxwin;
 
-
 struct layer *flayer;
 struct win *fore;
 struct win *windows;
 struct win *console_window;
 
-
+#ifdef BUILTIN_TELNET
+int af;
+#endif
 
 /*
  * Do this last
@@ -507,6 +508,9 @@ char **av;
   nwin = nwin_undef;
   nwin_options = nwin_undef;
   strcpy(screenterm, "screen");
+#ifdef BUILTIN_TELNET
+  af = AF_UNSPEC;
+#endif
 
   logreopen_register(lf_secreopen);
 
@@ -541,6 +545,14 @@ char **av;
 	    {
 	      switch (*ap)
 		{
+#ifdef BUILTIN_TELNET
+		case '4':
+			af = AF_INET;
+			break;
+		case '6':
+			af = AF_INET6;
+			break;
+#endif
 		case 'a':
 		  nwin_options.aflag = 1;
 		  break;
diff --git a/src/teln.c b/src/teln.c
index 1764dbc..0546c35 100644
--- a/src/teln.c
+++ b/src/teln.c
@@ -30,6 +30,7 @@
 #include <sys/socket.h>
 #include <fcntl.h>
 #include <netdb.h>
+#include <stdio.h>
 
 #include "config.h"
 
@@ -42,12 +43,14 @@ extern struct win *fore;
 extern struct layer *flayer;
 extern int visual_bell;
 extern char screenterm[];
+extern int af;
 
 static void TelReply __P((struct win *, char *, int));
 static void TelDocmd __P((struct win *, int, int));
 static void TelDosub __P((struct win *));
 
-#define TEL_DEFPORT	23
+// why TEL_DEFPORT has "
+#define TEL_DEFPORT     "23"
 #define TEL_CONNECTING	(-2)
 
 #define TC_IAC          255
@@ -105,86 +108,81 @@ char *data;
 }
 
 int
-TelOpen(args)
-char **args;
-{
-  int fd;
-  int on = 1;
+TelOpenAndConnect(struct win *p) {
+	int fd, on = 1;
+	char buf[256];
 
-  if ((fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1)
-    {
-      Msg(errno, "TelOpen: socket");
-      return -1;
-    }
-  if (setsockopt(fd, SOL_SOCKET, SO_OOBINLINE, (char *)&on, sizeof(on)))
-    Msg(errno, "TelOpen: setsockopt SO_OOBINLINE");
-  return fd;
-}
+	struct addrinfo hints, *res0, *res;
 
-int
-TelConnect(p)
-struct win *p;
-{
-  int port = TEL_DEFPORT;
-  struct hostent *hp;
-  char **args;
-  char buf[256];
+	if (!(p->w_cmdargs[1])) {
+		Msg(0, "Usage: screen //telnet host [port]");
+		return -1;
+	}
 
-  args = p->w_cmdargs + 1;
+	memset(&hints, 0, sizeof(hints));
+	hints.ai_family = af;
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_protocol = IPPROTO_TCP;
 
-  if (!*args)
-    {
-      Msg(0, "Usage: screen //telnet host [port]");
-      return -1;
-    }
-  if (args[1])
-    port = atoi(args[1]);
-  p->w_telsa.sin_family = AF_INET;
-  if((p->w_telsa.sin_addr.s_addr = inet_addr(*args)) == -1)
-    {
-      if ((hp = gethostbyname(*args)) == NULL)
-        {
-	  Msg(0, "unknown host: %s", *args);
-	  return -1;
-        }
-      if (hp->h_length != sizeof(p->w_telsa.sin_addr.s_addr) || hp->h_addrtype != AF_INET)
-	{
-	  Msg(0, "Bad address type for %s", hp->h_name);
-	  return -1;
-	}
-      bcopy((char *)hp->h_addr,(char *)&p->w_telsa.sin_addr.s_addr, hp->h_length);
-      p->w_telsa.sin_family = hp->h_addrtype;
-    }
-  p->w_telsa.sin_port = htons(port);
-  if (port != TEL_DEFPORT)
-    sprintf(buf, "Trying %s %d...", inet_ntoa(p->w_telsa.sin_addr), port);
-  else
-    sprintf(buf, "Trying %s...", inet_ntoa(p->w_telsa.sin_addr));
-  WriteString(p, buf, strlen(buf));
-  if (connect(p->w_ptyfd, (struct sockaddr *)&p->w_telsa, sizeof(p->w_telsa)))
-    {
-      if (errno == EINPROGRESS)
-        {
-	  p->w_telstate = TEL_CONNECTING;
-	  p->w_telconnev.fd = p->w_ptyfd;
-	  p->w_telconnev.handler = tel_connev_fn;
-	  p->w_telconnev.data = (char *)p;
-	  p->w_telconnev.type = EV_WRITE;
-	  p->w_telconnev.pri = 1;
-	  debug("telnet connect in progress...\n");
-	  evenq(&p->w_telconnev);
+	if(getaddrinfo(p->w_cmdargs[1], p->w_cmdargs[2] ? p->w_cmdargs[2] : TEL_DEFPORT, &hints, &res0)) {
+		Msg(0, "unknown host: %s", p->w_cmdargs[1]);
+		return -1;
 	}
-      else
-        {
-	  Msg(errno, "TelOpen: connect");
-	  return -1;
+
+	for(res = res0; res; res = res->ai_next) {
+		if((fd = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) == -1) {
+			if(res->ai_next)
+				continue;
+			else {
+				Msg(errno, "TelOpenAndConnect: socket");
+				freeaddrinfo(res0);
+				return -1;
+			}
+		}
+
+		if (setsockopt(fd, SOL_SOCKET, SO_OOBINLINE, (char *)&on, sizeof(on)))
+			Msg(errno, "TelOpenAndConnect: setsockopt SO_OOBINLINE");
+
+		if (p->w_cmdargs[2] && strcmp(p->w_cmdargs[2], TEL_DEFPORT))
+			snprintf(buf, 256, "Trying %s %s...", p->w_cmdargs[1], p->w_cmdargs[2]);
+		else
+			snprintf(buf, 256, "Trying %s...", p->w_cmdargs[1]);
+
+		WriteString(p, buf, strlen(buf));
+		if (connect(fd, res->ai_addr, res->ai_addrlen)) {
+			if (errno == EINPROGRESS) {
+				p->w_telstate = TEL_CONNECTING;
+				p->w_telconnev.fd = fd;
+				p->w_telconnev.handler = tel_connev_fn;
+				p->w_telconnev.data = (char *)p;
+				p->w_telconnev.type = EV_WRITE;
+				p->w_telconnev.pri = 1;
+				debug("telnet connect in progress...\n");
+				evenq(&p->w_telconnev);
+			}
+			else {
+				close(fd);
+				if(res->ai_next)
+					continue;
+				else {
+					Msg(errno, "TelOpenAndConnect: connect");
+					freeaddrinfo(res0);
+					return -1;
+				}
+			}
+		}
+		else
+			WriteString(p, "connected.\r\n", 12);
+
+		if (!(p->w_cmdargs[2] && strcmp(p->w_cmdargs[2], TEL_DEFPORT)))
+			TelReply(p, (char *)tn_init, sizeof(tn_init));
+
+		p->w_ptyfd = fd;
+		memcpy(&p->w_telsa, &res->ai_addr, sizeof(res->ai_addr));
+		freeaddrinfo(res0);
+		return 0;
 	}
-    }
-  else
-    WriteString(p, "connected.\r\n", 12);
-  if (port == TEL_DEFPORT)
-    TelReply(p, (char *)tn_init, sizeof(tn_init));
-  return 0;
+	return -1;
 }
 
 int
diff --git a/src/window.c b/src/window.c
index f39f419..53cffcd 100644
--- a/src/window.c
+++ b/src/window.c
@@ -614,6 +614,13 @@ struct NewWindow *newwin;
   n = pp - wtab;
   debug1("Makewin creating %d\n", n);
 
+#ifdef BUILTIN_TELNET
+	if(!strcmp(nwin.args[0], "//telnet")) {
+		type = W_TYPE_TELNET;
+		TtyName = "telnet";
+	}
+  else
+#endif
   if ((f = OpenDevice(nwin.args, nwin.lflag, &type, &TtyName)) < 0)
     return -1;
   if (type == W_TYPE_GROUP)
@@ -775,7 +782,7 @@ struct NewWindow *newwin;
 #ifdef BUILTIN_TELNET
   if (type == W_TYPE_TELNET)
     {
-      if (TelConnect(p))
+      if (TelOpenAndConnect(p))
 	{
 	  FreeWindow(p);
 	  return -1;
@@ -895,6 +902,13 @@ struct win *p;
   int lflag, f;
 
   lflag = nwin_default.lflag;
+#ifdef BUILTIN_TELNET
+	if(!strcmp(p->w_cmdargs[0], "//telnet")) {
+		p->w_type = W_TYPE_TELNET;
+		TtyName = "telnet";
+	}
+	else
+#endif
   if ((f = OpenDevice(p->w_cmdargs, lflag, &p->w_type, &TtyName)) < 0)
     return -1;
 
@@ -928,7 +942,7 @@ struct win *p;
 #ifdef BUILTIN_TELNET
   if (p->w_type == W_TYPE_TELNET)
     {
-      if (TelConnect(p))
+      if (TelOpenAndConnect(p))
         return -1;
     }
   else
@@ -1088,16 +1102,6 @@ char **namep;
       *namep = "telnet";
       return 0;
     }
-#ifdef BUILTIN_TELNET
-  if (strcmp(arg, "//telnet") == 0)
-    {
-      f = TelOpen(args + 1);
-      lflag = 0;
-      *typep = W_TYPE_TELNET;
-      *namep = "telnet";
-    }
-  else
-#endif
   if (strncmp(arg, "//", 2) == 0)
     {
       Msg(0, "Invalid argument '%s'", arg);
diff --git a/src/window.h b/src/window.h
index 380d3e9..f14ed04 100644
--- a/src/window.h
+++ b/src/window.h
@@ -271,7 +271,7 @@ struct win
   struct display *w_zdisplay;
 #endif
 #ifdef BUILTIN_TELNET
-  struct sockaddr_in w_telsa;
+  struct sockaddr_storage w_telsa;
   char   w_telbuf[IOSIZE];
   int    w_telbufl;
   char   w_telmopts[256];