Fix #15: Alternate interface to plain readline(), for event loops

This rather big patch adds support for the GNU Readline alternate
interface, for use with event loops:

    void rl_callback_handler_install (const char *prompt, rl_vcpfunc_t *lhandler);
    void rl_callback_read_char       (void);
    void rl_callback_handler_remove  (void);

The code has been tested using the testit and excallback examples.
Both regular editing and searching works as intended.

Also, the problem with lingering artefacts on screen when scrolling
through the history has been fixed.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

include/editline.h

@@ -51,6 +51,7 @@ typedef int  rl_hook_func_t(void);
 typedef int  rl_getc_func_t(void);
 typedef void rl_voidfunc_t(void);
 typedef void rl_vintfunc_t(int);
+typedef void rl_vcpfunc_t(char *);
 
 /* Display 8-bit chars "as-is" or as `M-x'? Toggle with M-m. (Default:0 - "as-is") */
 extern int rl_meta_chars;
@@ -107,6 +108,11 @@ extern int   write_history      (const char *filename);
 extern rl_complete_func_t    *rl_set_complete_func    (rl_complete_func_t *func);
 extern rl_list_possib_func_t *rl_set_list_possib_func (rl_list_possib_func_t *func);
 
+/* Alternate interface to plain readline(), for event loops */
+extern void rl_callback_handler_install (const char *prompt, rl_vcpfunc_t *lhandler);
+extern void rl_callback_read_char       (void);
+extern void rl_callback_handler_remove  (void);
+
 #ifdef __cplusplus
 }
 #endif

src/editline.c

@@ -110,6 +110,10 @@ static char       *backspace = "\b";
 static char       *old_search = NULL;
 static int        tty_cols = SCREEN_COLS;
 static int        tty_rows = SCREEN_ROWS;
+static int        Searching = 0;
+static const char *(*search_move)(void);
+static const char *old_prompt = NULL;
+static rl_vcpfunc_t *line_handler = NULL;
 
 int               el_no_echo = 0; /* e.g., under Emacs */
 int               el_no_hist = 0;
@@ -125,7 +129,7 @@ FILE             *rl_instream = NULL;  /* The stdio stream from which input is r
 FILE             *rl_outstream = NULL; /* The stdio stream to which output is flushed. Defaults to stdout if NULL */
 
 /* Declarations. */
-static char     *editinput(void);
+static char     *editinput(int complete);
 #ifdef CONFIG_USE_TERMCAP
 extern char     *tgetstr(const char *, char **);
 extern int      tgetent(char *, const char *);
@@ -559,19 +563,16 @@ static const char *prev_hist(void)
 
 static el_status_t do_insert_hist(const char *p)
 {
-    el_status_t ret;
-
     if (p == NULL)
         return el_ring_bell();
 
+    clear_line();
+
     rl_point = 0;
     reposition();
     rl_end = 0;
 
-    ret = insert_string(p);
-    ceol();
-
-    return ret;
+    return insert_string(p);
 }
 
 static el_status_t do_hist(const char *(*move)(void))
@@ -669,13 +670,28 @@ static const char *search_hist(const char *search, const char *(*move)(void))
     return NULL;
 }
 
+static el_status_t h_search_end(const char *p)
+{
+    rl_prompt = old_prompt;
+    Searching = 0;
+
+    if (p == NULL && el_intr_pending > 0) {
+        el_intr_pending = 0;
+        clear_line();
+        return redisplay();
+    }
+
+    p = search_hist(p, search_move);
+    if (p == NULL) {
+        el_ring_bell();
+        return redisplay();
+    }
+
+    return do_insert_hist(p);
+}
+
 static el_status_t h_search(void)
 {
-    static int Searching;
-    const char *old_prompt;
-    const char *(*move)(void);
-    const char *p;
-
     if (Searching)
         return el_ring_bell();
     Searching = 1;
@@ -685,27 +701,13 @@ static el_status_t h_search(void)
     rl_prompt = "Search: ";
     tty_puts(rl_prompt);
 
-    move = Repeat == NO_ARG ? prev_hist : next_hist;
-    p = editinput();
-
-    rl_prompt = old_prompt;
-    Searching = 0;
-    tty_puts(rl_prompt);
-
-    if (p == NULL && el_intr_pending > 0) {
-        el_intr_pending = 0;
-        clear_line();
-        return redisplay();
+    search_move = Repeat == NO_ARG ? prev_hist : next_hist;
+    if (line_handler) {
+	editinput(0);
+	return CSstay;
     }
 
-    p = search_hist(p, move);
-    clear_line();
-    if (p == NULL) {
-        el_ring_bell();
-        return redisplay();
-    }
-
-    return do_insert_hist(p);
+    return h_search_end(editinput(1));
 }
 
 static el_status_t fd_char(void)
@@ -1017,16 +1019,15 @@ static el_status_t tty_special(int c)
     return CSdispatch;
 }
 
-static char *editinput(void)
+static char *editinput(int complete)
 {
     int c;
 
-    Repeat = NO_ARG;
-    old_point = rl_point = rl_mark = rl_end = 0;
-    rl_line_buffer[0] = '\0';
+    do {
+	c = tty_get();
+	if (c == EOF)
+	    break;
 
-    el_intr_pending = -1;
-    while ((c = tty_get()) != EOF) {
         switch (tty_special(c)) {
 	case CSdone:
 	    return rl_line_buffer;
@@ -1065,7 +1066,7 @@ static char *editinput(void)
 	case CSstay:
 	    break;
         }
-    }
+    } while (complete);
 
     return NULL;
 }
@@ -1257,19 +1258,10 @@ void rl_forced_update_display()
     tty_flush();
 }
 
-char *readline(const char *prompt)
+static int el_prep(const char *prompt)
 {
-    char *line;
-
-    /* Unless called by the user already. */
     rl_initialize();
 
-    if (!isatty(0)) {
-        tty_flush();
-
-        return read_redirected();
-    }
-
     if (!rl_line_buffer) {
         Length = MEM_INC;
 	rl_line_buffer = malloc(sizeof(char) * Length);
@@ -1297,7 +1289,16 @@ char *readline(const char *prompt)
 	tty_puts(rl_prompt);
     }
 
-    line = editinput();
+    Repeat = NO_ARG;
+    old_point = rl_point = rl_mark = rl_end = 0;
+    rl_line_buffer[0] = '\0';
+    el_intr_pending = -1;
+
+    return 0;
+}
+
+static char *el_deprep(char *line)
+{
     if (line) {
         line = strdup(line);
         tty_puts(NEWLINE);
@@ -1305,7 +1306,11 @@ char *readline(const char *prompt)
     }
 
     rl_deprep_term_function();
-    free(Screen);
+    if (Screen) {
+	free(Screen);
+	Screen = NULL;
+    }
+
     free(H.Lines[--H.Size]);
     H.Lines[H.Size] = NULL;
 
@@ -1325,6 +1330,96 @@ char *readline(const char *prompt)
     return line;
 }
 
+void rl_callback_handler_install(const char *prompt, rl_vcpfunc_t *lhandler)
+{
+    if (!lhandler)
+	return;
+    line_handler = lhandler;
+
+    /*
+     * Any error from el_prep() is handled by the lhandler callbck as
+     * soon as the user calls rl_callback_read_char().
+     */
+    el_prep(prompt);
+    tty_flush();
+}
+
+/*
+ * Reads one character at a time, when a complete line has been received
+ * the lhandler from rl_callback_handler_install() is called with the
+ * line as argument.
+ *
+ * If the callback returns the terminal is prepped for reading a new
+ * line.
+ *
+ * If any error occurs, either in the _install() phase, or while reading
+ * one character, this function restores the terminal and calls lhandler
+ * with a NULL argument.
+ */
+void rl_callback_read_char(void)
+{
+    char *line;
+
+    if (!line_handler) {
+	errno = EINVAL;
+	return;
+    }
+
+    /*
+     * Check if rl_callback_handler_install() failed
+     * This is the only point where we can tell user
+     */
+    if (!Screen || !rl_line_buffer) {
+	errno = ENOMEM;
+	line_handler(el_deprep(NULL));
+	return;
+    }
+
+    line = editinput(0);
+    if (line) {
+	char *l;
+
+	if (Searching) {
+	    h_search_end(line);
+	    tty_flush();
+	    return;
+	}
+
+	l = el_deprep(line);
+	line_handler(l);
+
+	if (el_prep(rl_prompt))
+	    line_handler(NULL);
+    }
+    tty_flush();
+}
+
+void rl_callback_handler_remove(void)
+{
+    if (!line_handler)
+	return;
+
+    el_deprep(NULL);
+    line_handler = NULL;
+}
+
+char *readline(const char *prompt)
+{
+    /* Unless called by the user already. */
+    rl_initialize();
+
+    if (!isatty(el_infd)) {
+        tty_flush();
+
+        return read_redirected();
+    }
+
+    if (el_prep(prompt))
+	return NULL;
+
+    return el_deprep(editinput(1));
+}
+
 /*
  * Even though readline() itself adds history automatically, the user
  * can also add lines.  This is for compatibility with GNU Readline.