patch 8.2.0557: no IPv6 support for channelsv8.2.0557

Problem:    No IPv6 support for channels.
Solution:   Add IPv6 support. (Ozaki Kiichi, closes #5893)

21 files changed, 546 insertions, 192 deletions

diff --git a/.travis.yml b/.travis.yml
index 356702cdfc..2c5f5ff304 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -62,9 +62,7 @@ _anchors:
           sudo update-alternatives --install /usr/bin/lua lua /usr/bin/lua5.3 10
         fi
     before_script:
-      # On travis bionic-amd64 gethostbyname() resolves "localhost" to 127.0.1.1
-      # so that makes various channel tests fail.
-      - sudo sed -i '/^127\.0\.1\.1\s/s/\blocalhost\b//g' /etc/hosts
+      - sudo sysctl -w net.ipv6.conf.lo.disable_ipv6=0
       - sudo bash ci/load-snd-dummy.sh || true
       - sudo usermod -a -G audio $USER
       - do_test() { sg audio "sg $(id -gn) '$*'"; }
diff --git a/runtime/doc/channel.txt b/runtime/doc/channel.txt
index 3fa05083cb..42e00c7ae7 100644
--- a/runtime/doc/channel.txt
+++ b/runtime/doc/channel.txt
@@ -120,6 +120,9 @@ Use |ch_status()| to see if the channel could be opened.
 
 {address} has the form "hostname:port".  E.g., "localhost:8765".
 
+When using an IPv6 address, enclose it within square brackets.  E.g.,
+"[2001:db8::1]:8765".
+
 {options} is a dictionary with optional entries:	*channel-open-options*
 
 "mode" can be:						*channel-mode*
@@ -621,6 +624,9 @@ ch_open({address} [, {options}])				*ch_open()*
 		{address} has the form "hostname:port", e.g.,
 		"localhost:8765".
 
+		When using an IPv6 address, enclose it within square brackets.
+		E.g., "[2001:db8::1]:8765".
+
 		If {options} is given it must be a |Dictionary|.
 		See |channel-open-options|.
 
diff --git a/runtime/doc/various.txt b/runtime/doc/various.txt
index b6867bcabd..a88cc81cc1 100644
--- a/runtime/doc/various.txt
+++ b/runtime/doc/various.txt
@@ -375,6 +375,7 @@ m  *+hangul_input*	Hangul input support |hangul|
    *+iconv*		Compiled with the |iconv()| function
    *+iconv/dyn*		Likewise |iconv-dynamic| |/dyn|
 T  *+insert_expand*	|insert_expand| Insert mode completion
+m  *+ipv6*		Support for IPv6 networking |channel|
 m  *+job*		starting and stopping jobs |job|
 S  *+jumplist*		|jumplist|
 B  *+keymap*		|'keymap'|
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 86986482ae..091102e661 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -850,7 +850,7 @@ endif
 
 ifeq ($(CHANNEL),yes)
 OBJ += $(OUTDIR)/channel.o
-LIB += -lwsock32
+LIB += -lwsock32 -lws2_32
 endif
 
 ifeq ($(DIRECTX),yes)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 1d7a3ed112..fa14c9e646 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -469,7 +469,7 @@ CHANNEL_PRO	= proto/channel.pro
 CHANNEL_OBJ	= $(OBJDIR)/channel.obj
 CHANNEL_DEFS	= -DFEAT_JOB_CHANNEL
 
-NETBEANS_LIB	= WSock32.lib
+NETBEANS_LIB	= WSock32.lib Ws2_32.lib
 !endif
 
 # Set which version of the CRT to use
diff --git a/src/auto/configure b/src/auto/configure
index 0a140eed8b..33bf663224 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -7723,8 +7723,7 @@ $as_echo "yes" >&6; }
 fi
 
 if test "$enable_channel" = "yes"; then
-
-  if test "x$HAIKU" = "xyes"; then
+    if test "x$HAIKU" = "xyes"; then
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for socket in -lnetwork" >&5
 $as_echo_n "checking for socket in -lnetwork... " >&6; }
 if ${ac_cv_lib_network_socket+:} false; then :
@@ -7818,7 +7817,63 @@ fi
 
   fi
 
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for gethostbyname in -lnsl" >&5
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether compiling with IPv6 networking is possible" >&5
+$as_echo_n "checking whether compiling with IPv6 networking is possible... " >&6; }
+if ${vim_cv_ipv6_networking+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <fcntl.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+	/* Check bitfields */
+	struct nbbuf {
+	unsigned int  initDone:1;
+	unsigned short signmaplen;
+	};
+
+int
+main ()
+{
+
+		/* Check creating a socket. */
+		struct sockaddr_in server;
+		struct addrinfo *res;
+		(void)socket(AF_INET, SOCK_STREAM, 0);
+		(void)htons(100);
+		(void)getaddrinfo("microsoft.com", NULL, NULL, &res);
+		if (errno == ECONNREFUSED)
+		  (void)connect(1, (struct sockaddr *)&server, sizeof(server));
+		(void)freeaddrinfo(res);
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  vim_cv_ipv6_networking="yes"
+else
+  vim_cv_ipv6_networking="no"
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $vim_cv_ipv6_networking" >&5
+$as_echo "$vim_cv_ipv6_networking" >&6; }
+
+  if test "x$vim_cv_ipv6_networking" = "xyes"; then
+    $as_echo "#define FEAT_IPV6 1" >>confdefs.h
+
+  else
+        { $as_echo "$as_me:${as_lineno-$LINENO}: checking for gethostbyname in -lnsl" >&5
 $as_echo_n "checking for gethostbyname in -lnsl... " >&6; }
 if ${ac_cv_lib_nsl_gethostbyname+:} false; then :
   $as_echo_n "(cached) " >&6
@@ -7863,8 +7918,11 @@ _ACEOF
 
 fi
 
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether compiling with process communication is possible" >&5
-$as_echo_n "checking whether compiling with process communication is possible... " >&6; }
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether compiling with IPv4 networking is possible" >&5
+$as_echo_n "checking whether compiling with IPv4 networking is possible... " >&6; }
+if ${vim_cv_ipv4_networking+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -7900,15 +7958,17 @@ main ()
 }
 _ACEOF
 if ac_fn_c_try_link "$LINENO"; then :
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
+  vim_cv_ipv4_networking="yes"
 else
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }; enable_netbeans="no"; enable_channel="no"
+  vim_cv_ipv4_networking="no"; enable_netbeans="no"; enable_channel="no"
 fi
 rm -f core conftest.err conftest.$ac_objext \
     conftest$ac_exeext conftest.$ac_ext
 fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $vim_cv_ipv4_networking" >&5
+$as_echo "$vim_cv_ipv4_networking" >&6; }
+  fi
+fi
 if test "$enable_netbeans" = "yes"; then
   $as_echo "#define FEAT_NETBEANS_INTG 1" >>confdefs.h
 
diff --git a/src/channel.c b/src/channel.c
index 1dfb28f854..8f15c659bf 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -10,6 +10,13 @@
  * Implements communication through a socket or any file handle.
  */
 
+#ifdef WIN32
+// Must include winsock2.h before windows.h since it conflicts with winsock.h
+// (included in windows.h).
+# include <winsock2.h>
+# include <ws2tcpip.h>
+#endif
+
 #include "vim.h"
 
 #if defined(FEAT_JOB_CHANNEL) || defined(PROTO)
@@ -40,7 +47,7 @@
 #else
 # include <netdb.h>
 # include <netinet/in.h>
-
+# include <arpa/inet.h>
 # include <sys/socket.h>
 # ifdef HAVE_LIBGEN_H
 #  include <libgen.h>
@@ -711,90 +718,38 @@ channel_gui_unregister(channel_T *channel)
 static char *e_cannot_connect = N_("E902: Cannot connect to port");
 
 /*
- * Open a socket channel to "hostname":"port".
- * "waittime" is the time in msec to wait for the connection.
- * When negative wait forever.
- * Returns the channel for success.
- * Returns NULL for failure.
+ * For Unix we need to call connect() again after connect() failed.
+ * On Win32 one time is sufficient.
  */
-    channel_T *
-channel_open(
-	char *hostname,
-	int port_in,
-	int waittime,
-	void (*nb_close_cb)(void))
+    static int
+channel_connect(
+	channel_T *channel,
+	const struct sockaddr *server_addr,
+	int server_addrlen,
+	int *waittime)
 {
-    int			sd = -1;
-    struct sockaddr_in	server;
-    struct hostent	*host;
+    int		sd = -1;
 #ifdef MSWIN
-    u_short		port = port_in;
-    u_long		val = 1;
-#else
-    int			port = port_in;
+    u_long	val = 1;
 #endif
-    channel_T		*channel;
-    int			ret;
-
-#ifdef MSWIN
-    channel_init_winsock();
-#endif
-
-    channel = add_channel();
-    if (channel == NULL)
-    {
-	ch_error(NULL, "Cannot allocate channel.");
-	return NULL;
-    }
-
-    // Get the server internet address and put into addr structure
-    // fill in the socket address structure and connect to server
-    vim_memset((char *)&server, 0, sizeof(server));
-    server.sin_family = AF_INET;
-    server.sin_port = htons(port);
-    if ((host = gethostbyname(hostname)) == NULL)
-    {
-	ch_error(channel, "in gethostbyname() in channel_open()");
-	PERROR(_("E901: gethostbyname() in channel_open()"));
-	channel_free(channel);
-	return NULL;
-    }
-    {
-	char		*p;
 
-	// When using host->h_addr_list[0] directly ubsan warns for it to not
-	// be aligned.  First copy the pointer to avoid that.
-	memcpy(&p, &host->h_addr_list[0], sizeof(p));
-	memcpy((char *)&server.sin_addr, p, host->h_length);
-    }
-
-    // On Mac and Solaris a zero timeout almost never works.  At least wait
-    // one millisecond. Let's do it for all systems, because we don't know why
-    // this is needed.
-    if (waittime == 0)
-	waittime = 1;
-
-    /*
-     * For Unix we need to call connect() again after connect() failed.
-     * On Win32 one time is sufficient.
-     */
     while (TRUE)
     {
 	long	elapsed_msec = 0;
 	int	waitnow;
+	int	ret;
 
 	if (sd >= 0)
 	    sock_close(sd);
-	sd = socket(AF_INET, SOCK_STREAM, 0);
+	sd = socket(server_addr->sa_family, SOCK_STREAM, 0);
 	if (sd == -1)
 	{
-	    ch_error(channel, "in socket() in channel_open().");
-	    PERROR(_("E898: socket() in channel_open()"));
-	    channel_free(channel);
-	    return NULL;
+	    ch_error(channel, "in socket() in channel_connect().");
+	    PERROR(_("E898: socket() in channel_connect()"));
+	    return -1;
 	}
 
-	if (waittime >= 0)
+	if (*waittime >= 0)
 	{
 	    // Make connect() non-blocking.
 	    if (
@@ -807,23 +762,22 @@ channel_open(
 	    {
 		SOCK_ERRNO;
 		ch_error(channel,
-			 "channel_open: Connect failed with errno %d", errno);
+		      "channel_connect: Connect failed with errno %d", errno);
 		sock_close(sd);
-		channel_free(channel);
-		return NULL;
+		return -1;
 	    }
 	}
 
 	// Try connecting to the server.
-	ch_log(channel, "Connecting to %s port %d", hostname, port);
-	ret = connect(sd, (struct sockaddr *)&server, sizeof(server));
+	ch_log(channel, "Connecting...");
 
+	ret = connect(sd, server_addr, server_addrlen);
 	if (ret == 0)
 	    // The connection could be established.
 	    break;
 
 	SOCK_ERRNO;
-	if (waittime < 0 || (errno != EWOULDBLOCK
+	if (*waittime < 0 || (errno != EWOULDBLOCK
 		&& errno != ECONNREFUSED
 #ifdef EINPROGRESS
 		&& errno != EINPROGRESS
@@ -831,22 +785,24 @@ channel_open(
 		))
 	{
 	    ch_error(channel,
-			 "channel_open: Connect failed with errno %d", errno);
+		      "channel_connect: Connect failed with errno %d", errno);
 	    PERROR(_(e_cannot_connect));
 	    sock_close(sd);
-	    channel_free(channel);
-	    return NULL;
+	    return -1;
+	}
+	else if (errno == ECONNREFUSED)
+	{
+	    ch_error(channel, "channel_connect: Connection refused");
+	    sock_close(sd);
+	    return -1;
 	}
 
 	// Limit the waittime to 50 msec.  If it doesn't work within this
 	// time we close the socket and try creating it again.
-	waitnow = waittime > 50 ? 50 : waittime;
+	waitnow = *waittime > 50 ? 50 : *waittime;
 
 	// If connect() didn't finish then try using select() to wait for the
 	// connection to be made. For Win32 always use select() to wait.
-#ifndef MSWIN
-	if (errno != ECONNREFUSED)
-#endif
 	{
 	    struct timeval	tv;
 	    fd_set		rfds;
@@ -868,18 +824,17 @@ channel_open(
 	    gettimeofday(&start_tv, NULL);
 #endif
 	    ch_log(channel,
-		    "Waiting for connection (waiting %d msec)...", waitnow);
-	    ret = select((int)sd + 1, &rfds, &wfds, NULL, &tv);
+		      "Waiting for connection (waiting %d msec)...", waitnow);
 
+	    ret = select((int)sd + 1, &rfds, &wfds, NULL, &tv);
 	    if (ret < 0)
 	    {
 		SOCK_ERRNO;
 		ch_error(channel,
-			"channel_open: Connect failed with errno %d", errno);
+		      "channel_connect: Connect failed with errno %d", errno);
 		PERROR(_(e_cannot_connect));
 		sock_close(sd);
-		channel_free(channel);
-		return NULL;
+		return -1;
 	    }
 
 #ifdef MSWIN
@@ -888,9 +843,9 @@ channel_open(
 	    if (FD_ISSET(sd, &wfds))
 		break;
 	    elapsed_msec = waitnow;
-	    if (waittime > 1 && elapsed_msec < waittime)
+	    if (*waittime > 1 && elapsed_msec < *waittime)
 	    {
-		waittime -= elapsed_msec;
+		*waittime -= elapsed_msec;
 		continue;
 	    }
 #else
@@ -914,12 +869,17 @@ channel_open(
 			))
 		{
 		    ch_error(channel,
-			    "channel_open: Connect failed with errno %d",
+			    "channel_connect: Connect failed with errno %d",
 			    so_error);
 		    PERROR(_(e_cannot_connect));
 		    sock_close(sd);
-		    channel_free(channel);
-		    return NULL;
+		    return -1;
+		}
+		else if (errno == ECONNREFUSED)
+		{
+		    ch_error(channel, "channel_connect: Connection refused");
+		    sock_close(sd);
+		    return -1;
 		}
 	    }
 
@@ -929,30 +889,30 @@ channel_open(
 
 	    gettimeofday(&end_tv, NULL);
 	    elapsed_msec = (end_tv.tv_sec - start_tv.tv_sec) * 1000
-			     + (end_tv.tv_usec - start_tv.tv_usec) / 1000;
+				 + (end_tv.tv_usec - start_tv.tv_usec) / 1000;
 #endif
 	}
 
 #ifndef MSWIN
-	if (waittime > 1 && elapsed_msec < waittime)
+	if (*waittime > 1 && elapsed_msec < *waittime)
 	{
 	    // The port isn't ready but we also didn't get an error.
 	    // This happens when the server didn't open the socket
 	    // yet.  Select() may return early, wait until the remaining
 	    // "waitnow"  and try again.
 	    waitnow -= elapsed_msec;
-	    waittime -= elapsed_msec;
+	    *waittime -= elapsed_msec;
 	    if (waitnow > 0)
 	    {
 		mch_delay((long)waitnow, TRUE);
 		ui_breakcheck();
-		waittime -= waitnow;
+		*waittime -= waitnow;
 	    }
 	    if (!got_int)
 	    {
-		if (waittime <= 0)
+		if (*waittime <= 0)
 		    // give it one more try
-		    waittime = 1;
+		    *waittime = 1;
 		continue;
 	    }
 	    // we were interrupted, behave as if timed out
@@ -962,13 +922,10 @@ channel_open(
 	// We timed out.
 	ch_error(channel, "Connection timed out");
 	sock_close(sd);
-	channel_free(channel);
-	return NULL;
+	return -1;
     }
 
-    ch_log(channel, "Connection made");
-
-    if (waittime >= 0)
+    if (*waittime >= 0)
     {
 #ifdef MSWIN
 	val = 0;
@@ -978,10 +935,151 @@ channel_open(
 #endif
     }
 
+    return sd;
+}
+
+/*
+ * Open a socket channel to "hostname":"port".
+ * "waittime" is the time in msec to wait for the connection.
+ * When negative wait forever.
+ * Returns the channel for success.
+ * Returns NULL for failure.
+ */
+    channel_T *
+channel_open(
+	const char *hostname,
+	int port,
+	int waittime,
+	void (*nb_close_cb)(void))
+{
+    int			sd = -1;
+    channel_T		*channel = NULL;
+#ifdef FEAT_IPV6
+    struct addrinfo	hints;
+    struct addrinfo	*res = NULL;
+    struct addrinfo	*addr = NULL;
+#else
+    struct sockaddr_in	server;
+    struct hostent	*host = NULL;
+#endif
+
+#ifdef MSWIN
+    channel_init_winsock();
+#endif
+
+    channel = add_channel();
+    if (channel == NULL)
+    {
+	ch_error(NULL, "Cannot allocate channel.");
+	return NULL;
+    }
+
+    // Get the server internet address and put into addr structure fill in the
+    // socket address structure and connect to server.
+#ifdef FEAT_IPV6
+    vim_memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_socktype = SOCK_STREAM;
+# ifdef AI_ADDRCONFIG
+    hints.ai_flags = AI_ADDRCONFIG;
+# endif
+    // Set port number manually in order to prevent name resolution services
+    // from being invoked in the environment where AI_NUMERICSERV is not
+    // defined.
+    if (getaddrinfo(hostname, NULL, &hints, &res) != 0)
+    {
+	ch_error(channel, "in getaddrinfo() in channel_open()");
+	PERROR(_("E901: getaddrinfo() in channel_open()"));
+	channel_free(channel);
+	return NULL;
+    }
+
+    for (addr = res; addr != NULL; addr = addr->ai_next)
+    {
+	const char *dst = hostname;
+	const void *src = NULL;
+	char buf[NUMBUFLEN];
+
+	if (addr->ai_family == AF_INET6)
+	{
+	    struct sockaddr_in6 *sai = (struct sockaddr_in6 *)addr->ai_addr;
+
+	    sai->sin6_port = htons(port);
+	    src = &sai->sin6_addr;
+	}
+	else if (addr->ai_family == AF_INET)
+	{
+	    struct sockaddr_in *sai = (struct sockaddr_in *)addr->ai_addr;
+
+	    sai->sin_port = htons(port);
+	    src = &sai->sin_addr;
+	}
+	if (src != NULL)
+	{
+	    dst = inet_ntop(addr->ai_family, src, buf, sizeof(buf));
+	    if (dst != NULL && STRCMP(hostname, dst) != 0)
+		ch_log(channel, "Resolved %s to %s", hostname, dst);
+	}
+
+	ch_log(channel, "Trying to connect to %s port %d", dst, port);
+
+	// On Mac and Solaris a zero timeout almost never works.  At least wait
+	// one millisecond.  Let's do it for all systems, because we don't know
+	// why this is needed.
+	if (waittime == 0)
+	    waittime = 1;
+
+	sd = channel_connect(channel, addr->ai_addr, addr->ai_addrlen,
+								   &waittime);
+	if (sd >= 0)
+	    break;
+    }
+
+    freeaddrinfo(res);
+#else
+    vim_memset((char *)&server, 0, sizeof(server));
+    server.sin_family = AF_INET;
+    server.sin_port = htons(port);
+    if ((host = gethostbyname(hostname)) == NULL)
+    {
+	ch_error(channel, "in gethostbyname() in channel_open()");
+	PERROR(_("E901: gethostbyname() in channel_open()"));
+	channel_free(channel);
+	return NULL;
+    }
+    {
+	char *p;
+
+	// When using host->h_addr_list[0] directly ubsan warns for it to not
+	// be aligned.  First copy the pointer to avoid that.
+	memcpy(&p, &host->h_addr_list[0], sizeof(p));
+	memcpy((char *)&server.sin_addr, p, host->h_length);
+    }
+
+    ch_log(channel, "Trying to connect to %s port %d", hostname, port);
+
+    // On Mac and Solaris a zero timeout almost never works.  At least wait one
+    // millisecond.  Let's do it for all systems, because we don't know why
+    // this is needed.
+    if (waittime == 0)
+	waittime = 1;
+
+    sd = channel_connect(channel, (struct sockaddr *)&server, sizeof(server),
+								   &waittime);
+#endif
+
+    if (sd < 0)
+    {
+	channel_free(channel);
+	return NULL;
+    }
+
+    ch_log(channel, "Connection made");
+
     channel->CH_SOCK_FD = (sock_T)sd;
     channel->ch_nb_close_cb = nb_close_cb;
     channel->ch_hostname = (char *)vim_strsave((char_u *)hostname);
-    channel->ch_port = port_in;
+    channel->ch_port = port;
     channel->ch_to_be_closed |= (1U << PART_SOCK);
 
 #ifdef FEAT_GUI
@@ -1222,6 +1320,7 @@ channel_open_func(typval_T *argvars)
     char_u	*p;
     char	*rest;
     int		port;
+    int		is_ipv6 = FALSE;
     jobopt_T    opt;
     channel_T	*channel = NULL;
 
@@ -1234,20 +1333,40 @@ channel_open_func(typval_T *argvars)
     }
 
     // parse address
-    p = vim_strchr(address, ':');
-    if (p == NULL)
+    if (*address == '[')
     {
-	semsg(_(e_invarg2), address);
-	return NULL;
+	// ipv6 address
+	is_ipv6 = TRUE;
+	p = vim_strchr(address + 1, ']');
+	if (p == NULL || *++p != ':')
+	{
+	    semsg(_(e_invarg2), address);
+	    return NULL;
+	}
     }
-    *p++ = NUL;
-    port = strtol((char *)p, &rest, 10);
-    if (*address == NUL || port <= 0 || *rest != NUL)
+    else
+    {
+	p = vim_strchr(address, ':');
+	if (p == NULL)
+	{
+	    semsg(_(e_invarg2), address);
+	    return NULL;
+	}
+    }
+    port = strtol((char *)(p + 1), &rest, 10);
+    if (*address == NUL || port <= 0 || port >= 65536 || *rest != NUL)
     {
-	p[-1] = ':';
 	semsg(_(e_invarg2), address);
 	return NULL;
     }
+    if (is_ipv6)
+    {
+	// strip '[' and ']'
+	++address;
+	*(p - 1) = NUL;
+    }
+    else
+	*p = NUL;
 
     // parse options
     clear_job_options(&opt);
diff --git a/src/config.h.in b/src/config.h.in
index deeceb7a94..166724c916 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -438,6 +438,9 @@
 /* Define if we have shl_load() */
 #undef HAVE_SHL_LOAD
 
+/* Define if we can use IPv6 networking. */
+#undef FEAT_IPV6
+
 /* Define if you want to include NetBeans integration. */
 #undef FEAT_NETBEANS_INTG
 
diff --git a/src/configure.ac b/src/configure.ac
index 89ae06f739..47502a99c4 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -2038,17 +2038,50 @@ else
 fi
 
 if test "$enable_channel" = "yes"; then
-  dnl On Solaris we need the socket and nsl library.
-
+  dnl On Solaris we need the socket library, or on Haiku the network library.
   if test "x$HAIKU" = "xyes"; then
 	AC_CHECK_LIB(network, socket)
   else
 	AC_CHECK_LIB(socket, socket)
   fi
 
-  AC_CHECK_LIB(nsl, gethostbyname)
-  AC_MSG_CHECKING(whether compiling with process communication is possible)
-  AC_TRY_LINK([
+  AC_CACHE_CHECK([whether compiling with IPv6 networking is possible], [vim_cv_ipv6_networking],
+    [AC_TRY_LINK([
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <fcntl.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+	/* Check bitfields */
+	struct nbbuf {
+	unsigned int  initDone:1;
+	unsigned short signmaplen;
+	};
+	    ], [
+		/* Check creating a socket. */
+		struct sockaddr_in server;
+		struct addrinfo *res;
+		(void)socket(AF_INET, SOCK_STREAM, 0);
+		(void)htons(100);
+		(void)getaddrinfo("microsoft.com", NULL, NULL, &res);
+		if (errno == ECONNREFUSED)
+		  (void)connect(1, (struct sockaddr *)&server, sizeof(server));
+		(void)freeaddrinfo(res);
+	    ],
+	[vim_cv_ipv6_networking="yes"],
+	[vim_cv_ipv6_networking="no"])])
+
+  if test "x$vim_cv_ipv6_networking" = "xyes"; then
+    AC_DEFINE(FEAT_IPV6)
+  else
+    dnl On Solaris we need the nsl library.
+    AC_CHECK_LIB(nsl, gethostbyname)
+    AC_CACHE_CHECK([whether compiling with IPv4 networking is possible], [vim_cv_ipv4_networking],
+      [AC_TRY_LINK([
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
@@ -2072,8 +2105,9 @@ if test "$enable_channel" = "yes"; then
 		if (errno == ECONNREFUSED)
 		  (void)connect(1, (struct sockaddr *)&server, sizeof(server));
 	    ],
-	AC_MSG_RESULT(yes),
-	AC_MSG_RESULT(no); enable_netbeans="no"; enable_channel="no")
+	[vim_cv_ipv4_networking="yes"],
+	[vim_cv_ipv4_networking="no"; enable_netbeans="no"; enable_channel="no"])])
+  fi
 fi
 if test "$enable_netbeans" = "yes"; then
   AC_DEFINE(FEAT_NETBEANS_INTG)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 7170c0e1fe..8ce8c8751d 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3943,6 +3943,13 @@ f_has(typval_T *argvars, typval_T *rettv)
 #endif
 		},
 	{"insert_expand", 1},
+	{"ipv6",
+#ifdef FEAT_IPV6
+		1
+#else
+		0
+#endif
+	},
 	{"job",
 #ifdef FEAT_JOB_CHANNEL
 		1
diff --git a/src/proto/channel.pro b/src/proto/channel.pro
index a441a484f4..56a0167b82 100644
--- a/src/proto/channel.pro
+++ b/src/proto/channel.pro
@@ -7,7 +7,7 @@ int channel_unref(channel_T *channel);
 int free_unused_channels_contents(int copyID, int mask);
 void free_unused_channels(int copyID, int mask);
 void channel_gui_register_all(void);
-channel_T *channel_open(char *hostname, int port_in, int waittime, void (*nb_close_cb)(void));
+channel_T *channel_open(const char *hostname, int port, int waittime, void (*nb_close_cb)(void));
 void channel_set_pipes(channel_T *channel, sock_T in, sock_T out, sock_T err);
 void channel_set_job(channel_T *channel, job_T *job, jobopt_T *options);
 void channel_buffer_free(buf_T *buf);
diff --git a/src/testdir/check.vim b/src/testdir/check.vim
index 34bf5b319d..efb273b005 100644
--- a/src/testdir/check.vim
+++ b/src/testdir/check.vim
@@ -142,4 +142,37 @@ func CheckEnglish()
   endif
 endfunc
 
+" Command to check that loopback device has IPv6 address
+command CheckIPv6 call CheckIPv6()
+func CheckIPv6()
+  if !has('ipv6')
+    throw 'Skipped: cannot use IPv6 networking'
+  endif
+  if !exists('s:ipv6_loopback')
+    let s:ipv6_loopback = s:CheckIPv6Loopback()
+  endif
+  if !s:ipv6_loopback
+    throw 'Skipped: no IPv6 address for loopback device'
+  endif
+endfunc
+
+func s:CheckIPv6Loopback()
+  if has('win32')
+    return system('netsh interface ipv6 show interface') =~? '\<Loopback\>'
+  elseif filereadable('/proc/net/if_inet6')
+    return (match(readfile('/proc/net/if_inet6'), '\slo$') >= 0)
+  elseif executable('ifconfig')
+    for dev in ['lo0', 'lo', 'loop']
+      " NOTE: On SunOS, need specify address family 'inet6' to get IPv6 info.
+      if system('ifconfig ' .. dev .. ' inet6 2>/dev/null') =~? '\<inet6\>'
+            \ || system('ifconfig ' .. dev .. ' 2>/dev/null') =~? '\<inet6\>'
+        return v:true
+      endif
+    endfor
+  else
+    " TODO: How to check it in other platforms?
+  endif
+  return v:false
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 0d603231aa..3e7e5115f4 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -161,8 +161,7 @@ func RunTheTest(test)
     exe 'call ' . a:test
   else
     try
-      let s:test = a:test
-      au VimLeavePre * call EarlyExit(s:test)
+      au VimLeavePre * call EarlyExit(g:testfunc)
       exe 'call ' . a:test
       au! VimLeavePre
     catch /^\cskipped/
@@ -226,11 +225,11 @@ func AfterTheTest(func_name)
   if len(v:errors) > 0
     if match(s:may_fail_list, '^' .. a:func_name) >= 0
       let s:fail_expected += 1
-      call add(s:errors_expected, 'Found errors in ' . s:test . ':')
+      call add(s:errors_expected, 'Found errors in ' . g:testfunc . ':')
       call extend(s:errors_expected, v:errors)
     else
       let s:fail += 1
-      call add(s:errors, 'Found errors in ' . s:test . ':')
+      call add(s:errors, 'Found errors in ' . g:testfunc . ':')
       call extend(s:errors, v:errors)
     endif
     let v:errors = []
@@ -396,31 +395,31 @@ endif
 
 let s:may_fail_list = []
 if $TEST_MAY_FAIL != ''
-  " Split the list at commas and add () to make it match s:test.
+  " Split the list at commas and add () to make it match g:testfunc.
   let s:may_fail_list = split($TEST_MAY_FAIL, ',')->map({i, v -> v .. '()'})
 endif
 
 " Execute the tests in alphabetical order.
-for s:test in sort(s:tests)
+for g:testfunc in sort(s:tests)
   " Silence, please!
   set belloff=all
   let prev_error = ''
   let total_errors = []
   let g:run_nr = 1
 
-  " A test can set test_is_flaky to retry running the test.
-  let test_is_flaky = 0
+  " A test can set g:test_is_flaky to retry running the test.
+  let g:test_is_flaky = 0
 
-  call RunTheTest(s:test)
+  call RunTheTest(g:testfunc)
 
   " Repeat a flaky test.  Give up when:
   " - it fails again with the same message
   " - it fails five times (with a different message)
   if len(v:errors) > 0
-        \ && (index(s:flaky_tests, s:test) >= 0
-        \      || test_is_flaky)
+        \ && (index(s:flaky_tests, g:testfunc) >= 0
+        \      || g:test_is_flaky)
     while 1
-      call add(s:messages, 'Found errors in ' . s:test . ':')
+      call add(s:messages, 'Found errors in ' . g:testfunc . ':')
       call extend(s:messages, v:errors)
 
       call add(total_errors, 'Run ' . g:run_nr . ':')
@@ -443,7 +442,7 @@ for s:test in sort(s:tests)
       let v:errors = []
       let g:run_nr += 1
 
-      call RunTheTest(s:test)
+      call RunTheTest(g:testfunc)
 
       if len(v:errors) == 0
         " Test passed on rerun.
@@ -452,7 +451,7 @@ for s:test in sort(s:tests)
     endwhile
   endif
 
-  call AfterTheTest(s:test)
+  call AfterTheTest(g:testfunc)
 endfor
 
 call FinishTesting()
diff --git a/src/testdir/test_cdo.vim b/src/testdir/test_cdo.vim
index 8a6b746718..51800a5e6b 100644
--- a/src/testdir/test_cdo.vim
+++ b/src/testdir/test_cdo.vim
@@ -4,7 +4,7 @@ source check.vim
 CheckFeature quickfix
 
 " Create the files used by the tests
-function SetUp()
+func SetUp()
   call writefile(["Line1", "Line2", "Line3"], 'Xtestfile1')
   call writefile(["Line1", "Line2", "Line3"], 'Xtestfile2')
   call writefile(["Line1", "Line2", "Line3"], 'Xtestfile3')
diff -