Return an error message from x11_setup_display.

The lack of one of those has been a long-standing FIXME for ages.

ssh.h

@@ -921,8 +921,12 @@ int x11_authcmp(void *av, void *bv); /* for putting X11FakeAuth in a tree234 */
  * the supplied authtype parameter configures the preferred
  * authorisation protocol to use at the remote end. The local auth
  * details are looked up by calling platform_get_x11_auth.
+ *
+ * If the returned pointer is NULL, then *error_msg will contain a
+ * dynamically allocated error message string.
  */
-extern struct X11Display *x11_setup_display(const char *display, Conf *);
+extern struct X11Display *x11_setup_display(const char *display, Conf *,
+                                            char **error_msg);
 void x11_free_display(struct X11Display *disp);
 struct X11FakeAuth *x11_invent_fake_auth(tree234 *t, int authtype);
 void x11_free_fake_auth(struct X11FakeAuth *auth);

ssh1connection.c

@@ -649,13 +649,15 @@ static void ssh1_connection_process_queue(PacketProtocolLayer *ppl)
     }
 
     if (conf_get_int(s->conf, CONF_x11_forward)) {
+        char *x11_setup_err;
+
         s->x11disp =
             x11_setup_display(conf_get_str(s->conf, CONF_x11_display),
-                              s->conf);
+                              s->conf, &x11_setup_err);
         if (!s->x11disp) {
-            /* FIXME: return an error message from x11_setup_display */
             ppl_logevent(("X11 forwarding not enabled: unable to"
-                          " initialise X display"));
+                          " initialise X display: %s", x11_setup_err));
+            sfree(x11_setup_err);
         } else {
             s->x11auth = x11_invent_fake_auth
                 (s->x11authtree, conf_get_int(s->conf, CONF_x11_auth));

ssh2connection.c

@@ -1249,12 +1249,14 @@ static void ssh2_connection_process_queue(PacketProtocolLayer *ppl)
 
 	/* Potentially enable X11 forwarding. */
 	if (conf_get_int(s->conf, CONF_x11_forward)) {
+            char *x11_setup_err;
             s->x11disp = x11_setup_display(
-                conf_get_str(s->conf, CONF_x11_display), s->conf);
+                conf_get_str(s->conf, CONF_x11_display),
+                s->conf, &x11_setup_err);
             if (!s->x11disp) {
-                /* FIXME: return an error message from x11_setup_display */
                 ppl_logevent(("X11 forwarding not enabled: unable to"
-                              " initialise X display"));
+                              " initialise X display: %s", x11_setup_err));
+                sfree(x11_setup_err);
             } else {
                 s->x11auth = x11_invent_fake_auth(
                     s->x11authtree, conf_get_int(s->conf, CONF_x11_auth));

unix/uxpgnt.c

@@ -801,12 +801,19 @@ void run_agent(void)
         int greetinglen;
         Socket *s;
         struct X11Connection *conn;
+        char *x11_setup_err;
 
         if (!display) {
             fprintf(stderr, "pageant: no DISPLAY for -X mode\n");
             exit(1);
         }
-        disp = x11_setup_display(display, conf);
+        disp = x11_setup_display(display, conf, &x11_setup_err);
+        if (!disp) {
+            fprintf(stderr, "pageant: unable to connect to X server: %s\n",
+                    x11_setup_err);
+            sfree(x11_setup_err);
+            exit(1);
+        }
 
         conn = snew(struct X11Connection);
         conn->plug.vt = &X11Connection_plugvt;

x11fwd.c

@@ -175,11 +175,14 @@ int x11_authcmp(void *av, void *bv)
     }
 }
 
-struct X11Display *x11_setup_display(const char *display, Conf *conf)
+struct X11Display *x11_setup_display(const char *display, Conf *conf,
+                                     char **error_msg)
 {
     struct X11Display *disp = snew(struct X11Display);
     char *localcopy;
 
+    *error_msg = NULL;
+
     if (!display || !*display) {
 	localcopy = platform_get_x_display();
 	if (!localcopy || !*localcopy) {
@@ -217,9 +220,12 @@ struct X11Display *x11_setup_display(const char *display, Conf *conf)
 
 	colon = host_strrchr(localcopy, ':');
 	if (!colon) {
+            *error_msg = dupprintf("display name '%s' has no ':number'"
+                                   " suffix", localcopy);
+
 	    sfree(disp);
 	    sfree(localcopy);
-	    return NULL;	       /* FIXME: report a specific error? */
+	    return NULL;
 	}
 
 	*colon++ = '\0';
@@ -275,11 +281,14 @@ struct X11Display *x11_setup_display(const char *display, Conf *conf)
                                  NULL, NULL);
     
 	if ((err = sk_addr_error(disp->addr)) != NULL) {
+            *error_msg = dupprintf("unable to resolve host name '%s' in "
+                                   "display name", disp->hostname);
+
 	    sk_addr_free(disp->addr);
 	    sfree(disp->hostname);
 	    sfree(disp->unixsocketpath);
 	    sfree(disp);
-	    return NULL;	       /* FIXME: report an error */
+	    return NULL;
 	}
     }