From 36ebc893f05dad3fcfc5fc13fe09ebe73601d9e5 Mon Sep 17 00:00:00 2001
From: Přemysl Eric Janouch <p@janouch.name>
Date: Mon, 29 Aug 2022 14:10:23 +0200
Subject: WIP: xC: force libedit into asynchronicity

---
 xC.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)

(limited to 'xC.c')

diff --git a/xC.c b/xC.c
index df73492..2f6cf85 100644
--- a/xC.c
+++ b/xC.c
@@ -14778,9 +14778,121 @@ on_editline_return (EditLine *editline, int key)
 	return CC_REFRESH;
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#ifdef EDITLINE_ASYNC
+
+// This is an adjusted version of EL_BUILTIN_GETCFN.
+static int
+app_editline_wgetc (struct app_context *ctx, wchar_t *wch, bool *readable)
+{
+	char buf[MB_LEN_MAX] = {};
+	size_t buf_len = 0;
+	mbstate_t mbs;
+
+	*wch = L'\0';
+	while (ctx->polling)
+	{
+		*readable = false;
+		poller_run (&ctx->poller);
+		if (!*readable)
+			continue;
+
+		ssize_t n_read;
+		if ((n_read = read (STDIN_FILENO, buf + buf_len++, 1)) <= 0)
+			return n_read;
+
+retry:
+		// XXX: This will only really work for non-shifting encodings.
+		memset (&mbs, 0, sizeof mbs);
+		switch (mbrtowc (wch, buf, buf_len, &mbs)) {
+		case (size_t) -1:
+			// Invalid sequence, discard all bytes except any last one.
+			// Not exactly sure what this is supposed to help.
+			if (!--buf_len)
+				continue;
+
+			buf[0] = buf[buf_len];
+			buf_len = 1;
+			goto retry;
+		case (size_t) -2:
+			if (buf_len < sizeof buf)
+				continue;
+
+			errno = EILSEQ;
+			*wch = L'\0';
+			return -1;
+		default:
+			return 1;
+		}
+	}
+	return 0;
+}
+
+static void
+on_editline_tty_readable (const struct pollfd *fd, bool *readable)
+{
+	(void) fd;
+	*readable = true;
+}
+
+static int
+on_editline_wgetc (EditLine *editline, wchar_t *wch)
+{
+	struct app_context *ctx = g_ctx;
+	struct input_el *self = NULL;
+	el_get (editline, EL_CLIENTDATA, &self);
+
+	// We must not touch ourselves at any cost, Editline isn't that reentrant.
+	// TODO: Also defer SIGWINCH, since we keep the foreground process group.
+	self->active = false;
+	ctx->terminal_suspended++;
+	poller_fd_reset (&ctx->tty_event);
+
+	bool readable = false;
+	struct poller_fd tty_event_redirect =
+		poller_fd_make (&ctx->poller, ctx->tty_event.fd);
+	tty_event_redirect.dispatcher = (poller_fd_fn) on_editline_tty_readable;
+	tty_event_redirect.user_data = &readable;
+
+	poller_fd_set (&tty_event_redirect, POLLIN);
+	int result = app_editline_wgetc (ctx, wch, &readable);
+	poller_fd_reset (&tty_event_redirect);
+
+	poller_fd_set (&ctx->tty_event, POLLIN);
+	ctx->terminal_suspended--;
+	self->active = true;
+
+	// TODO: If needed, at the end of input_el_on_tty_readable():
+	//  - buffer_print_backlog (ctx, ctx->current_buffer);
+	//  - update Editline's prompt.
+	// What's hard is detecting when it's needed, because it's a corner case:
+	//  - in general, any time buffer_print_backlog() is called,
+	//  - when log_formatter() doesn't display something for current_buffer,
+	//  - ...
+
+	// TODO: It seems like _buffer_switch() should be deferred,
+	//   at least in case of Editline--it can't wreak much async havoc,
+	//   seeing as it returns right after any command is done.
+	//
+	//   What's worse is that input buffers may need to be removed,
+	//   which would require _buffer_destroy() to take ownership of ::current,
+	//   since we can't destroy /or change/ Editline's current history pointer.
+	return result;
+}
+
+#endif  // EDITLINE_ASYNC
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
 static void
 app_editline_init (struct input_el *self)
 {
+#ifdef EDITLINE_ASYNC
+	// Avoid timeouts while reading in sequences
+	el_wset (self->editline, EL_GETCFN, on_editline_wgetc);
+#endif  // EDITLINE_ASYNC
+
 	// el_set() leaks memory in 20150325 and other versions, we need wchar_t
 	el_wset (self->editline, EL_ADDFN,
 		L"send-line", L"Send line",     on_editline_return);
-- 
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