allow OSC-52 clipboards on all terminal emulators

* The XTerm version is still checked if we detect running under XTerm.
* Actually, the XTerm implementation is broken for Unicode clipboard contents.
* Kitty supports OSC-52, but you __must__ enable read-clipboard.
  With read-clipboard-ask, there will be a timeout.
  But we cannot read without a timeout since otherwise we would hang indefinitely
  if the escape sequence turns out to not work.
* For urxvt, I have hacked an existing extension:
  https://gist.github.com/rhaberkorn/d7406420b69841ebbcab97548e38b37d
* st currently supports only setting the clipboard, but not querying it.

5 files changed, 50 insertions, 27 deletions

diff --git a/doc/sciteco.7.template b/doc/sciteco.7.template
index 193d029..a476091 100644
--- a/doc/sciteco.7.template
+++ b/doc/sciteco.7.template
@@ -1525,16 +1525,27 @@ The existence of a clipboard register can thus be checked
 in macros to determine whether getting and modifying that
 particular clipboard is supported natively.
 .br
-.SCITECO_TOPIC xterm
+.SCITECO_TOPIC OSC-52 xterm
 \*(ST does \fBnot\fP generally support clipboards on ncurses,
-but has special support when used with a sufficiently recent version
-of \fBxterm\fP(1).
-Since the operability of XTerm clipboards cannot be tested
+but has special support for OSC-52 escape sequences, as were
+introduced by sufficiently recent versions of
+.BR xterm (1)
+and have since been adopted by several other terminal emulators.
+Since the operability of OSC-52 clipboards cannot be tested
 automatically, users will have to set the flag 256 of the
-\fBED\fP flags if and only if their XTerm is configured for allowing
+\fBED\fP flags if and only if their terminal emulator is properly
+configured.
+.BR xterm (1)
+for instance must be configured for allowing
 the \fISetSelection\fP and \fIGetSelection\fP window operations.
-\*(ST will still check whether XTerm is actually used in
-a particular session.
+If running under
+.BR xterm (1),
+\*(ST will still check whether the XTerm version is sufficient.
+.SCITECO_TOPIC Kitty
+Other terminal emulators like Kitty may ask for permission to read the
+clipboard (\fBread-clipboard-ask\fP).
+This is not supported by \*(ST and must be disabled
+(use \fBread-clipboard\fP instead).
 .SCITECO_TOPIC xclip
 If native clipboard support is unavailable, users may
 still fall back to using external tools like \fBxclip\fP(1)
diff --git a/sample.teco_ini b/sample.teco_ini
index 869bfb9..2935d95 100644
--- a/sample.teco_ini
+++ b/sample.teco_ini
@@ -56,7 +56,7 @@ EMQ[$SCITECOPATH]/session.tes
 ! Enable default function key macros !
 EMQ[$SCITECOPATH]/fnkeys.tes
 
-! Uncomment if XTerm allows clipboard operations !
+! Uncomment if terminal supports OSC-52 clipboards !
 ! 0,256ED !
 
 ! Uncomment to enable Unicode icons in the Curses UI !
diff --git a/src/core-commands.c b/src/core-commands.c
index 300ffef..abe5604 100644
--- a/src/core-commands.c
+++ b/src/core-commands.c
@@ -2061,10 +2061,9 @@ teco_state_ecommand_close(teco_machine_main_t *ctx, GError **error)
  *   - 128: Enable/Disable enforcement of UNIX98
  *     \(lq/bin/sh\(rq emulation for operating system command
  *     executions
- *   - 256: Enable/Disable \fBxterm\fP(1) clipboard support.
- *     Should only be enabled if XTerm allows the
- *     \fIGetSelection\fP and \fISetSelection\fP window
- *     operations.
+ *   - 256: Enable/Disable OSC-52 clipboard support.
+ *     Must only be enabled if the terminal emulator is configured
+ *     properly.
  *   - 512: Enable/Disable Unicode icons in the Curses UI.
  *     This requires a capable font, like the ones provided
  *     by the \(lqNerd Fonts\(rq project.
diff --git a/src/interface-curses/interface.c b/src/interface-curses/interface.c
index 370fc27..039577f 100644
--- a/src/interface-curses/interface.c
+++ b/src/interface-curses/interface.c
@@ -560,7 +560,7 @@ teco_interface_init_screen(void)
 	g_assert(teco_interface.screen_tty != NULL);
 
 	teco_interface.screen = newterm(NULL, teco_interface.screen_tty, teco_interface.screen_tty);
-	if (!teco_interface.screen) {
+	if (G_UNLIKELY(!teco_interface.screen)) {
 		g_fprintf(stderr, "Error initializing interactive mode. "
 		                  "$TERM may be incorrect.\n");
 		exit(EXIT_FAILURE);
@@ -1255,9 +1255,17 @@ teco_interface_init_clipboard(void)
 	 * must be enabled.
 	 * There is no way to find out if they are but we must
 	 * not register the clipboard registers if they aren't.
-	 * Therefore, a special XTerm clipboard ED flag an be set by the user.
+	 * Still, XTerm clipboards are broken with Unicode characters.
+	 * Also, there are other terminal emulators supporting OSC-52,
+	 * so the XTerm version is only checked if the terminal identifies as XTerm.
+	 * Also, a special clipboard ED flag must be set by the user.
+	 *
+	 * NOTE: Apparently there is also a terminfo entry Ms, but it's probably
+	 * not worth using it since it won't always be set and even if set, does not
+	 * tell you whether the terminal will actually answer to the escape sequence or not.
 	 */
-	if (!(teco_ed & TECO_ED_XTERM_CLIPBOARD) || teco_xterm_version() < 203)
+	if (!(teco_ed & TECO_ED_OSC52) ||
+	    (teco_xterm_version() >= 0 && teco_xterm_version() < 203))
 		return;
 
 	teco_qreg_table_insert(&teco_qreg_table_globals, teco_qreg_clipboard_new(""));
@@ -1323,6 +1331,8 @@ teco_interface_set_clipboard(const gchar *name, const gchar *str, gsize str_len,
 gboolean
 teco_interface_get_clipboard(const gchar *name, gchar **str, gsize *len, GError **error)
 {
+	gboolean ret = TRUE;
+
 	/*
 	 * Query the clipboard -- XTerm will reply with the
 	 * OSC-52 command that would set the current selection.
@@ -1350,11 +1360,12 @@ teco_interface_get_clipboard(const gchar *name, gchar **str, gsize *len, GError
 	 * Skip "\e]52;x;" (7 characters).
 	 */
 	for (gint i = 0; i < 7; i++) {
-		if (wgetch(teco_interface.input_pad) == ERR) {
+		ret = wgetch(teco_interface.input_pad) != ERR;
+		if (!ret) {
 			/* timeout */
 			g_set_error_literal(error, TECO_ERROR, TECO_ERROR_FAILED,
 			                    "Timed out reading XTerm clipboard");
-			goto error;
+			goto cleanup;
 		}
 	}
 
@@ -1371,15 +1382,21 @@ teco_interface_get_clipboard(const gchar *name, gchar **str, gsize *len, GError
 		gchar buffer[MAX(3, 7)];
 
 		gchar c = (gchar)wgetch(teco_interface.input_pad);
-		if (c == ERR) {
+		ret = c != ERR;
+		if (!ret) {
 			/* timeout */
 			g_string_free(str_base64, TRUE);
 			g_set_error_literal(error, TECO_ERROR, TECO_ERROR_FAILED,
 			                    "Timed out reading XTerm clipboard");
-			goto error;
+			goto cleanup;
 		}
 		if (c == '\a')
 			break;
+		if (c == '\e') {
+			/* OSC escape sequence can also be terminated by "\e\\" */
+			c = (gchar)wgetch(teco_interface.input_pad);
+			break;
+		}
 
 		/*
 		 * This could be simplified using sscanf() and
@@ -1394,20 +1411,16 @@ teco_interface_get_clipboard(const gchar *name, gchar **str, gsize *len, GError
 		g_string_append_len(str_base64, buffer, out_len);
 	}
 
-	cbreak();
-	keypad(teco_interface.input_pad, TRUE);
-
 	if (str)
 		*str = str_base64->str;
 	*len = str_base64->len;
 
 	g_string_free(str_base64, !str);
-	return TRUE;
 
-error:
-	cbreak();
+cleanup:
 	keypad(teco_interface.input_pad, TRUE);
-	return FALSE;
+	nodelay(teco_interface.input_pad, TRUE);
+	return ret;
 }
 
 #else /* !PDCURSES && !CURSES_TTY */
diff --git a/src/sciteco.h b/src/sciteco.h
index 1597439..7fe09d4 100644
--- a/src/sciteco.h
+++ b/src/sciteco.h
@@ -91,7 +91,7 @@ enum {
 	TECO_ED_HOOKS		= (1 << 5),
 	//TECO_ED_MOUSEKEY	= (1 << 6),
 	TECO_ED_SHELLEMU	= (1 << 7),
-	TECO_ED_XTERM_CLIPBOARD	= (1 << 8),
+	TECO_ED_OSC52		= (1 << 8),
 	TECO_ED_ICONS		= (1 << 9)
 };