--- a/src/channel.c
+++ b/src/channel.c
@@ -14,17 +14,106 @@
 
 #if defined(FEAT_CHANNEL) || defined(PROTO)
 
+/*
+ * Change the zero to 1 to enable debugging.
+ * This will write a file "channel_debug.log".
+ */
+#if 0
+# define CHERROR(fmt, arg) cherror(fmt, arg)
+# define CHLOG(idx, send, buf) chlog(idx, send, buf)
+# define CHFILE "channel_debug.log"
+
+static void cherror(char *fmt, char *arg);
+static void chlog(int send, char_u *buf);
+#else
+# define CHERROR(fmt, arg)
+# define CHLOG(idx, send, buf)
+#endif
+
+/* TRUE when netbeans is running with a GUI. */
+#ifdef FEAT_GUI
+# define CH_HAS_GUI (gui.in_use || gui.starting)
+#endif
+
+/* Note: when making changes here also adjust configure.in. */
+#ifdef WIN32
+/* WinSock API is separated from C API, thus we can't use read(), write(),
+ * errno... */
+# define SOCK_ERRNO errno = WSAGetLastError()
+# undef ECONNREFUSED
+# define ECONNREFUSED WSAECONNREFUSED
+# ifdef EINTR
+#  undef EINTR
+# endif
+# define EINTR WSAEINTR
+# define sock_write(sd, buf, len) send(sd, buf, len, 0)
+# define sock_read(sd, buf, len) recv(sd, buf, len, 0)
+# define sock_close(sd) closesocket(sd)
+# define sleep(t) Sleep(t*1000) /* WinAPI Sleep() accepts milliseconds */
+#else
+# include <netdb.h>
+# include <netinet/in.h>
+
+# include <sys/socket.h>
+# ifdef HAVE_LIBGEN_H
+#  include <libgen.h>
+# endif
+# define SOCK_ERRNO
+# define sock_write(sd, buf, len) write(sd, buf, len)
+# define sock_read(sd, buf, len) read(sd, buf, len)
+# define sock_close(sd) close(sd)
+#endif
+
+#ifdef FEAT_GUI_W32
+extern HWND s_hwnd;			/* Gvim's Window handle */
+#endif
+
+struct readqueue
+{
+    char_u		*buffer;
+    struct readqueue	*next;
+    struct readqueue	*prev;
+};
+typedef struct readqueue queue_T;
+
 typedef struct {
-    sock_T  ch_fd;
-    int	    ch_idx;
+    sock_T  ch_fd;	/* the socket, -1 for a closed channel */
+    int	    ch_idx;	/* used by channel_poll_setup() */
+    queue_T ch_head;	/* dummy node, header for circular queue */
+
+    int	    ch_error;	/* When TRUE an error was reported.  Avoids giving
+			 * pages full of error messages when the other side
+			 * has exited, only mention the first error until the
+			 * connection works again. */
+#ifdef FEAT_GUI_X11
+    XtInputId ch_inputHandler;  /* Cookie for input */
+#endif
+#ifdef FEAT_GUI_GTK
+    gint ch_inputHandler;	/* Cookie for input */
+#endif
+#ifdef FEAT_GUI_W32
+    int  ch_inputHandler = -1;	/* simply ret.value of WSAAsyncSelect() */
+#endif
+
+    void (*ch_close_cb)(void);	/* callback invoked when channel is closed */
 } channel_T;
 
+/*
+ * Information about all channels.
+ * There can be gaps for closed channels, they will be reused later.
+ */
 static channel_T *channels = NULL;
 static int channel_count = 0;
 
 /*
+ * TODO: open debug file when desired.
+ */
+FILE *debugfd = NULL;
+
+/*
  * Add a new channel slot, return the index.
- * Returns -1 if out of space.
+ * The channel isn't actually used into ch_fd is set >= 0;
+ * Returns -1 if all channels are in use.
  */
     static int
 add_channel(void)
@@ -39,59 +128,559 @@ add_channel(void)
 		return idx;
     if (channel_count == MAX_OPEN_CHANNELS)
 	return -1;
-    new_channels = (channel_T *)alloc(sizeof(channel_T) * channel_count + 1);
+    new_channels = (channel_T *)alloc(sizeof(channel_T) * (channel_count + 1));
     if (new_channels == NULL)
 	return -1;
     if (channels != NULL)
 	mch_memmove(new_channels, channels, sizeof(channel_T) * channel_count);
     channels = new_channels;
+    (void)vim_memset(&channels[channel_count], 0, sizeof(channel_T));
+
     channels[channel_count].ch_fd = (sock_T)-1;
+#ifdef FEAT_GUI_X11
+    channels[channel_count].ch_inputHandler = (XtInputId)NULL;
+#endif
+#ifdef FEAT_GUI_GTK
+    channels[channel_count].ch_inputHandler = 0;
+#endif
+#ifdef FEAT_GUI_W32
+    channels[channel_count].ch_inputHandler = -1;
+#endif
 
     return channel_count++;
 }
 
-#if defined(FEAT_NETBEANS_INTG) || defined(PROTO)
-static int netbeans_channel = -1;
-
+#if defined(FEAT_GUI) || defined(PROTO)
 /*
- * Add the netbeans socket to the channels.
- * Return the channel index.
+ * Read a command from netbeans.
  */
-    int
-channel_add_netbeans(sock_T fd)
+#ifdef FEAT_GUI_X11
+    static void
+messageFromNetbeans(XtPointer clientData,
+		    int *unused1 UNUSED,
+		    XtInputId *unused2 UNUSED)
 {
-    int idx = add_channel();
+    channel_read((int)(long)clientData);
+}
+#endif
 
-    if (idx >= 0)
-    {
-	channels[idx].ch_fd = fd;
-	netbeans_channel = idx;
-    }
-    return idx;
-}
-
-    void
-channel_remove_netbeans()
+#ifdef FEAT_GUI_GTK
+    static void
+messageFromNetbeans(gpointer clientData,
+		    gint unused1 UNUSED,
+		    GdkInputCondition unused2 UNUSED)
 {
-    channels[netbeans_channel].ch_fd = (sock_T)-1;
-    netbeans_channel = -1;
+    channel_read((int)(long)clientData);
 }
 #endif
 
     static void
-channel_read(int idx)
+channel_gui_register(int idx)
+{
+    channel_T	*channel = &channels[idx];
+
+    if (!CH_HAS_GUI)
+	return;
+
+# ifdef FEAT_GUI_X11
+    /* tell notifier we are interested in being called
+     * when there is input on the editor connection socket
+     */
+    if (channel->ch_inputHandler == (XtInputId)NULL)
+	channel->ch_inputHandler =
+	    XtAppAddInput((XtAppContext)app_context, channel->ch_fd,
+			 (XtPointer)(XtInputReadMask + XtInputExceptMask),
+					messageFromNetbeans, (XtPointer)idx);
+# else
+#  ifdef FEAT_GUI_GTK
+    /*
+     * Tell gdk we are interested in being called when there
+     * is input on the editor connection socket
+     */
+    if (channel->ch_inputHandler == 0)
+	channel->ch_inputHandler =
+	    gdk_input_add((gint)channel->ch_fd, (GdkInputCondition)
+			     ((int)GDK_INPUT_READ + (int)GDK_INPUT_EXCEPTION),
+				    messageFromNetbeans, (gpointer)(long)idx);
+#  else
+#   ifdef FEAT_GUI_W32
+    /*
+     * Tell Windows we are interested in receiving message when there
+     * is input on the editor connection socket.
+     * TODO: change WM_NETBEANS to something related to the channel index.
+     */
+    if (channel->ch_inputHandler == -1)
+	channel->ch_inputHandler =
+	    WSAAsyncSelect(channel->ch_fd, s_hwnd, WM_NETBEANS, FD_READ);
+#   endif
+#  endif
+# endif
+}
+
+/*
+ * Register any of our file descriptors with the GUI event handling system.
+ * Called when the GUI has started.
+ */
+    void
+channel_gui_register_all(void)
+{
+    int i;
+
+    for (i = 0; i < channel_count; ++i)
+	if (channels[i].ch_fd >= 0)
+	    channel_gui_register(i);
+}
+
+    static void
+channel_gui_unregister(int idx)
+{
+    channel_T	*channel = &channels[idx];
+
+# ifdef FEAT_GUI_X11
+    if (channel->ch_inputHandler != (XtInputId)NULL)
+    {
+	XtRemoveInput(channel->ch_inputHandler);
+	channel->ch_inputHandler = (XtInputId)NULL;
+    }
+# else
+#  ifdef FEAT_GUI_GTK
+    if (channel->ch_inputHandler != 0)
+    {
+	gdk_input_remove(channel->ch_inputHandler);
+	channel->ch_inputHandler = 0;
+    }
+#  else
+#   ifdef FEAT_GUI_W32
+    if (channel->ch_inputHandler == 0)
+    {
+	WSAAsyncSelect(nbsock, s_hwnd, 0, 0);
+	channel->ch_inputHandler = -1;
+    }
+#   endif
+#  endif
+# endif
+}
+
+#endif
+
+/*
+ * Open a channel to "hostname":"port".
+ * Returns the channel number for success.
+ * Returns a negative number for failure.
+ */
+    int
+channel_open(char *hostname, int port_in, void (*close_cb)(void))
 {
-# ifdef FEAT_NETBEANS_INTG
-    if (idx == netbeans_channel)
-	netbeans_read();
-    else
-# endif
+    int			sd;
+    struct sockaddr_in	server;
+    struct hostent *	host;
+#ifdef FEAT_GUI_W32
+    u_short		port = port_in;
+#else
+    int			port = port_in;
+#endif
+    int			idx;
+
+#ifdef FEAT_GUI_W32
+    channel_init_winsock();
+#endif
+
+    idx = add_channel();
+    if (idx < 0)
+    {
+	CHERROR("All channels are in use\n", "");
+	EMSG(_("E999: All channels are in use"));
+	return -1;
+    }
+
+    if ((sd = (sock_T)socket(AF_INET, SOCK_STREAM, 0)) == (sock_T)-1)
+    {
+	CHERROR("error in socket() in channel_open()\n", "");
+	PERROR("E999: socket() in channel_open()");
+	return -1;
+    }
+
+    /* 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)
+    {
+	CHERROR("error in gethostbyname() in channel_open()\n", "");
+	PERROR("E999: gethostbyname() in channel_open()");
+	sock_close(sd);
+	return -1;
+    }
+    memcpy((char *)&server.sin_addr, host->h_addr, host->h_length);
+
+    /* Connect to server */
+    if (connect(sd, (struct sockaddr *)&server, sizeof(server)))
     {
-	; /* TODO: read */
+	SOCK_ERRNO;
+	CHERROR("channel_open: Connect failed with errno %d\n", errno);
+	if (errno == ECONNREFUSED)
+	{
+	    sock_close(sd);
+	    if ((sd = (sock_T)socket(AF_INET, SOCK_STREAM, 0)) == (sock_T)-1)
+	    {
+		SOCK_ERRNO;
+		CHERROR("socket() retry in channel_open()\n", "");
+		PERROR("E999: socket() retry in channel_open()");
+		return -1;
+	    }
+	    if (connect(sd, (struct sockaddr *)&server, sizeof(server)))
+	    {
+		int retries = 36;
+		int success = FALSE;
+
+		SOCK_ERRNO;
+		while (retries-- && ((errno == ECONNREFUSED)
+							 || (errno == EINTR)))
+		{
+		    CHERROR("retrying...\n", "");
+		    mch_delay(3000L, TRUE);
+		    ui_breakcheck();
+		    if (got_int)
+		    {
+			errno = EINTR;
+			break;
+		    }
+		    if (connect(sd, (struct sockaddr *)&server,
+							 sizeof(server)) == 0)
+		    {
+			success = TRUE;
+			break;
+		    }
+		    SOCK_ERRNO;
+		}
+		if (!success)
+		{
+		    /* Get here when the server can't be found. */
+		    CHERROR("Cannot connect to port after retry\n", "");
+		    PERROR(_("E999: Cannot connect to port after retry2"));
+		    sock_close(sd);
+		    return -1;
+		}
+	    }
+	}
+	else
+	{
+	    CHERROR("Cannot connect to port\n", "");
+	    PERROR(_("E999: Cannot connect to port"));
+	    sock_close(sd);
+	    return -1;
+	}
+    }
+
+    channels[idx].ch_fd = sd;
+    channels[idx].ch_close_cb = close_cb;
+
+#ifdef FEAT_GUI
+    channel_gui_register(idx);
+#endif
+
+    return idx;
+}
+
+/*
+ * Return TRUE when channel "idx" is open.
+ */
+    int
+channel_is_open(int idx)
+{
+    return channels[idx].ch_fd >= 0;
+}
+
+/*
+ * Close channel "idx".
+ * This does not trigger the close callback.
+ */
+    void
+channel_close(int idx)
+{
+    channel_T		*channel = &channels[idx];
+
+    if (channel->ch_fd >= 0)
+    {
+	sock_close(channel->ch_fd);
+	channel->ch_fd = -1;
+#ifdef FEAT_GUI
+	channel_gui_unregister(idx);
+#endif
     }
 }
 
-#if (defined(UNIX) && !defined(HAVE_SELECT)) || defined(PROTO)
+/*
+ * Store "buf[len]" on channel "idx".
+ */
+    void
+channel_save(int idx, char_u *buf, int len)
+{
+    queue_T *node;
+    queue_T *head = &channels[idx].ch_head;
+
+    node = (queue_T *)alloc(sizeof(queue_T));
+    if (node == NULL)
+	return;	    /* out of memory */
+    node->buffer = alloc(len + 1);
+    if (node->buffer == NULL)
+    {
+	vim_free(node);
+	return;	    /* out of memory */
+    }
+    mch_memmove(node->buffer, buf, (size_t)len);
+    node->buffer[len] = NUL;
+
+    if (head->next == NULL)   /* initialize circular queue */
+    {
+	head->next = head;
+	head->prev = head;
+    }
+
+    /* insert node at tail of queue */
+    node->next = head;
+    node->prev = head->prev;
+    head->prev->next = node;
+    head->prev = node;
+
+    if (debugfd != NULL)
+    {
+	fprintf(debugfd, "RECV on %d: ", idx);
+	fwrite(buf, len, 1, debugfd);
+	fprintf(debugfd, "\n");
+    }
+}
+
+/*
+ * Return the first buffer from the channel without removing it.
+ * Returns NULL if there is nothing.
+ */
+    char_u *
+channel_peek(int idx)
+{
+    queue_T *head = &channels[idx].ch_head;
+
+    if (head->next == head || head->next == NULL)
+	return NULL;
+    return head->next->buffer;
+}
+
+/*
+ * Return the first buffer from the channel and remove it.
+ * The caller must free it.
+ * Returns NULL if there is nothing.
+ */
+    char_u *
+channel_get(int idx)
+{
+    queue_T *head = &channels[idx].ch_head;
+    queue_T *node;
+    char_u *p;
+
+    if (head->next == head || head->next == NULL)
+	return NULL;
+    node = head->next;
+    /* dispose of the node but keep the buffer */
+    p = node->buffer;
+    head->next = node->next;
+    node->next->prev = node->prev;
+    vim_free(node);
+    return p;
+}
+
+/*
+ * Collapses the first and second buffer in the channel "idx".
+ * Returns FAIL if that is not possible.
+ */
+    int
+channel_collapse(int idx)
+{
+    queue_T *head = &channels[idx].ch_head;
+    queue_T *node = head->next;
+    char_u  *p;
+
+    if (node == head || node == NULL || node->next == head)
+	return FAIL;
+
+    p = alloc((unsigned)(STRLEN(node->buffer)
+					   + STRLEN(node->next->buffer) + 1));
+    if (p == NULL)
+	return FAIL;	    /* out of memory */
+    STRCPY(p, node->buffer);
+    STRCAT(p, node->next->buffer);
+    vim_free(node->next->buffer);
+    node->next->buffer = p;
+
+    /* dispose of the node and buffer */
+    head->next = node->next;
+    node->next->prev = node->prev;
+    vim_free(node->buffer);
+    vim_free(node);
+    return OK;
+}
+
+/*
+ * Clear the read buffer on channel "idx".
+ */
+    void
+channel_clear(int idx)
+{
+    queue_T *head = &channels[idx].ch_head;
+    queue_T *node = head->next;
+    queue_T *next;
+
+    while (node != NULL && node != head)
+    {
+	next = node->next;
+	vim_free(node->buffer);
+	vim_free(node);
+	if (next == head)
+	{
+	    head->next = head;
+	    head->prev = head;
+	    break;
+	}
+	node = next;
+    }
+}
+
+/* Sent when the channel is found closed when reading. */
+#define DETACH_MSG "\"DETACH\"\n"
+
+/* Buffer size for reading incoming messages. */
+#define MAXMSGSIZE 4096
+
+/*
+ * Read from channel "idx".  The data is put in the read queue.
+ */
+    void
+channel_read(int idx)
+{
+    static char_u	*buf = NULL;
+    int			len = 0;
+    int			readlen = 0;
+#ifdef HAVE_SELECT
+    struct timeval	tval;
+    fd_set		rfds;
+#else
+# ifdef HAVE_POLL
+    struct pollfd	fds;
+# endif
+#endif
+    channel_T		*channel = &channels[idx];
+
+    if (channel->ch_fd < 0)
+    {
+	CHLOG(idx, FALSE, "channel_read() called while socket is closed\n");
+	return;
+    }
+
+    /* Allocate a buffer to read into. */
+    if (buf == NULL)
+    {
+	buf = alloc(MAXMSGSIZE);
+	if (buf == NULL)
+	    return;	/* out of memory! */
+    }
+
+    /* Keep on reading for as long as there is something to read.
+     * Use select() or poll() to avoid blocking on a message that is exactly
+     * MAXMSGSIZE long. */
+    for (;;)
+    {
+#ifdef HAVE_SELECT
+	FD_ZERO(&rfds);
+	FD_SET(channel->ch_fd, &rfds);
+	tval.tv_sec = 0;
+	tval.tv_usec = 0;
+	if (select(channel->ch_fd + 1, &rfds, NULL, NULL, &tval) <= 0)
+	    break;
+#else
+# ifdef HAVE_POLL
+	fds.fd = channel->ch_fd;
+	fds.events = POLLIN;
+	if (poll(&fds, 1, 0) <= 0)
+	    break;
+# endif
+#endif
+	len = sock_read(channel->ch_fd, buf, MAXMSGSIZE);
+	if (len <= 0)
+	    break;	/* error or nothing more to read */
+
+	/* Store the read message in the queue. */
+	channel_save(idx, buf, len);
+	readlen += len;
+	if (len < MAXMSGSIZE)
+	    break;	/* did read everything that's available */
+    }
+
+    /* Reading a socket disconnection (readlen == 0), or a socket error. */
+    if (readlen <= 0)
+    {
+	/* Queue a "DETACH" netbeans message in the command queue in order to
+	 * terminate the netbeans session later. Do not end the session here
+	 * directly as we may be running in the context of a call to
+	 * netbeans_parse_messages():
+	 *	netbeans_parse_messages
+	 *	    -> autocmd triggered while processing the netbeans cmd
+	 *		-> ui_breakcheck
+	 *		    -> gui event loop or select loop
+	 *			-> channel_read()
+	 */
+	channel_save(idx, (char_u *)DETACH_MSG, (int)STRLEN(DETACH_MSG));
+
+	channel_close(idx);
+	if (channel->ch_close_cb != NULL)
+	    (*channel->ch_close_cb)();
+
+	if (len < 0)
+	{
+	    /* Todo: which channel? */
+	    CHERROR("%s(): cannot from channel\n", "channel_read");
+	    PERROR(_("E999: read from channel"));
+	}
+    }
+
+#if defined(CH_HAS_GUI) && defined(FEAT_GUI_GTK)
+    if (CH_HAS_GUI && gtk_main_level() > 0)
+	gtk_main_quit();
+#endif
+}
+
+/*
+ * Write "buf" (NUL terminated string) to channel "idx".
+ * When "fun" is not NULL an error message might be given.
+ */
+    void
+channel_send(int idx, char_u *buf, char *fun)
+{
+    channel_T	*channel = &channels[idx];
+    int		len = (int)STRLEN(buf);
+
+    if (channel->ch_fd < 0)
+    {
+	if (!channel->ch_error && fun != NULL)
+	{
+	    CHERROR("    %s(): write while not connected\n", fun);
+	    EMSG2("E630: %s(): write while not connected", fun);
+	}
+	channel->ch_error = TRUE;
+    }
+    else if (sock_write(channel->ch_fd, buf, len) != len)
+    {
+	if (!channel->ch_error && fun != NULL)
+	{
+	    CHERROR("    %s(): write failed\n", fun);
+	    EMSG2("E631: %s(): write failed", fun);
+	}
+	channel->ch_error = TRUE;
+    }
+    else
+	channel->ch_error = FALSE;
+}
+
+# if (defined(UNIX) && !defined(HAVE_SELECT)) || defined(PROTO)
 /*
  * Add open channels to the poll struct.
  * Return the adjusted struct index.
@@ -138,9 +727,9 @@ channel_poll_check(int ret_in, void *fds
 
     return ret;
 }
-#endif /* UNIX && !HAVE_SELECT */
+# endif /* UNIX && !HAVE_SELECT */
 
-#if (defined(UNIX) && defined(HAVE_SELECT)) || defined(PROTO)
+# if (defined(UNIX) && defined(HAVE_SELECT)) || defined(PROTO)
 /*
  * The type of "rfds" is hidden to avoid problems with the function proto.
  */
@@ -182,6 +771,6 @@ channel_select_check(int ret_in, void *r
 
     return ret;
 }
-#endif /* UNIX && HAVE_SELECT */
+# endif /* UNIX && HAVE_SELECT */
 
 #endif /* FEAT_CHANNEL */