patch 8.1.2080: the terminal API is limited and can't be disabled

Problem:    The terminal API is limited and can't be disabled.
Solution:   Add term_setapi() to set the function prefix. (Ozaki Kiichi,
            closes #2907)

src/terminal.c

@@ -109,6 +109,7 @@ struct terminal_S {
 #define TL_FINISH_OPEN	    'o'	/* ++open */
     char_u	*tl_opencmd;
     char_u	*tl_eof_chars;
+    char_u	*tl_api;	// prefix for terminal API function
 
     char_u	*tl_arg0_cmd;	// To format the status bar
 
@@ -641,6 +642,11 @@ term_start(
 	term->tl_kill = vim_strnsave(opt->jo_term_kill, p - opt->jo_term_kill);
     }
 
+    if (opt->jo_term_api != NULL)
+	term->tl_api = vim_strsave(opt->jo_term_api);
+    else
+	term->tl_api = vim_strsave((char_u *)"Tapi_");
+
     /* System dependent: setup the vterm and maybe start the job in it. */
     if (argv == NULL
 	    && argvar->v_type == VAR_STRING
@@ -708,44 +714,58 @@ ex_terminal(exarg_T *eap)
 	cmd += 2;
 	p = skiptowhite(cmd);
 	ep = vim_strchr(cmd, '=');
-	if (ep != NULL && ep < p)
-	    p = ep;
+	if (ep != NULL)
+	{
+	    if (ep < p)
+		p = ep;
+	    else
+		ep = NULL;
+	}
 
-	if ((int)(p - cmd) == 5 && STRNICMP(cmd, "close", 5) == 0)
+# define OPTARG_HAS(name) ((int)(p - cmd) == sizeof(name) - 1 \
+				 && STRNICMP(cmd, name, sizeof(name) - 1) == 0)
+	if (OPTARG_HAS("close"))
 	    opt.jo_term_finish = 'c';
-	else if ((int)(p - cmd) == 7 && STRNICMP(cmd, "noclose", 7) == 0)
+	else if (OPTARG_HAS("noclose"))
 	    opt.jo_term_finish = 'n';
-	else if ((int)(p - cmd) == 4 && STRNICMP(cmd, "open", 4) == 0)
+	else if (OPTARG_HAS("open"))
 	    opt.jo_term_finish = 'o';
-	else if ((int)(p - cmd) == 6 && STRNICMP(cmd, "curwin", 6) == 0)
+	else if (OPTARG_HAS("curwin"))
 	    opt.jo_curwin = 1;
-	else if ((int)(p - cmd) == 6 && STRNICMP(cmd, "hidden", 6) == 0)
+	else if (OPTARG_HAS("hidden"))
 	    opt.jo_hidden = 1;
-	else if ((int)(p - cmd) == 9 && STRNICMP(cmd, "norestore", 9) == 0)
+	else if (OPTARG_HAS("norestore"))
 	    opt.jo_term_norestore = 1;
-	else if ((int)(p - cmd) == 4 && STRNICMP(cmd, "kill", 4) == 0
-		&& ep != NULL)
+	else if (OPTARG_HAS("kill") && ep != NULL)
 	{
 	    opt.jo_set2 |= JO2_TERM_KILL;
 	    opt.jo_term_kill = ep + 1;
 	    p = skiptowhite(cmd);
 	}
-	else if ((int)(p - cmd) == 4 && STRNICMP(cmd, "rows", 4) == 0
-		&& ep != NULL && isdigit(ep[1]))
+	else if (OPTARG_HAS("api"))
+	{
+	    opt.jo_set2 |= JO2_TERM_API;
+	    if (ep != NULL)
+	    {
+		opt.jo_term_api = ep + 1;
+		p = skiptowhite(cmd);
+	    }
+	    else
+		opt.jo_term_api = NULL;
+	}
+	else if (OPTARG_HAS("rows") && ep != NULL && isdigit(ep[1]))
 	{
 	    opt.jo_set2 |= JO2_TERM_ROWS;
 	    opt.jo_term_rows = atoi((char *)ep + 1);
 	    p = skiptowhite(cmd);
 	}
-	else if ((int)(p - cmd) == 4 && STRNICMP(cmd, "cols", 4) == 0
-		&& ep != NULL && isdigit(ep[1]))
+	else if (OPTARG_HAS("cols") && ep != NULL && isdigit(ep[1]))
 	{
 	    opt.jo_set2 |= JO2_TERM_COLS;
 	    opt.jo_term_cols = atoi((char *)ep + 1);
 	    p = skiptowhite(cmd);
 	}
-	else if ((int)(p - cmd) == 3 && STRNICMP(cmd, "eof", 3) == 0
-								 && ep != NULL)
+	else if (OPTARG_HAS("eof") && ep != NULL)
 	{
 	    char_u *buf = NULL;
 	    char_u *keys;
@@ -785,6 +805,7 @@ ex_terminal(exarg_T *eap)
 	    semsg(_("E181: Invalid attribute: %s"), cmd);
 	    goto theend;
 	}
+# undef OPTARG_HAS
 	cmd = skipwhite(p);
     }
     if (*cmd == NUL)
@@ -933,6 +954,7 @@ free_unused_terminals()
 	free_scrollback(term);
 
 	term_free_vterm(term);
+	vim_free(term->tl_api);
 	vim_free(term->tl_title);
 #ifdef FEAT_SESSION
 	vim_free(term->tl_command);
@@ -3769,6 +3791,15 @@ handle_drop_command(listitem_T *item)
     vim_free(tofree);
 }
 
+/*
+ * Return TRUE if "func" starts with "pat" and "pat" isn't empty.
+ */
+    static int
+is_permitted_term_api(char_u *func, char_u *pat)
+{
+    return pat != NULL && *pat != NUL && STRNICMP(func, pat, STRLEN(pat)) == 0;
+}
+
 /*
  * Handles a function call from the job running in a terminal.
  * "item" is the function name, "item->li_next" has the arguments.
@@ -3788,9 +3819,9 @@ handle_call_command(term_T *term, channel_T *channel, listitem_T *item)
     }
     func = tv_get_string(&item->li_tv);
 
-    if (STRNCMP(func, "Tapi_", 5) != 0)
+    if (!is_permitted_term_api(func, term->tl_api))
     {
-	ch_log(channel, "Invalid function name: %s", func);
+	ch_log(channel, "Unpermitted function: %s", func);
 	return;
     }
 
@@ -5545,6 +5576,27 @@ f_term_setansicolors(typval_T *argvars, typval_T *rettv UNUSED)
 }
 #endif
 
+/*
+ * "term_setapi(buf, api)" function
+ */
+    void
+f_term_setapi(typval_T *argvars, typval_T *rettv UNUSED)
+{
+    buf_T	*buf = term_get_buf(argvars, "term_setapi()");
+    term_T	*term;
+    char_u	*api;
+
+    if (buf == NULL)
+	return;
+    term = buf->b_term;
+    vim_free(term->tl_api);
+    api = tv_get_string_chk(&argvars[1]);
+    if (api != NULL)
+	term->tl_api = vim_strsave(api);
+    else
+	term->tl_api = NULL;
+}
+
 /*
  * "term_setrestore(buf, command)" function
  */
@@ -5608,7 +5660,7 @@ f_term_start(typval_T *argvars, typval_T *rettv)
 		    + JO2_TERM_COLS + JO2_TERM_ROWS + JO2_VERTICAL + JO2_CURWIN
 		    + JO2_CWD + JO2_ENV + JO2_EOF_CHARS
 		    + JO2_NORESTORE + JO2_TERM_KILL
-		    + JO2_ANSI_COLORS + JO2_TTY_TYPE) == FAIL)
+		    + JO2_ANSI_COLORS + JO2_TTY_TYPE + JO2_TERM_API) == FAIL)
 	return;
 
     buf = term_start(&argvars[0], NULL, &opt, 0);