Add Lua REPL mode and multiline edit function in the mode.

Typing "@repl" after Ctrl-t r, enter Lua REPL mode.
Typing "@exit" in REPL mode will return you to normal mode.

Note:
- the determination of continuation lines is not done automatically, and
  if the end of a line is \, it is determined to be a continuation
  instruction.
- In REPL mode, tio's main loop is blocked. (Ctrl-t q works.)

Example:
>> t = {1,2,3,4,5}
>> for _,v in ipairs(t) do\
>>     print(v,"\r")\
>> end

Implementation improvements:
- Add tty_init() and script_interp_init() in order to only once
  initialization.
- Fix script function to work without device_fd.

src/main.c

@@ -123,6 +123,12 @@ int main(int argc, char *argv[])
         socket_configure();
     }
 
+    /* Script interpreter init */
+    script_interp_init();
+
+    /* Initialize tty module once on program start */
+    tty_init();
+
     /* Spawn input handling into separate thread */
     tty_input_thread_create();
 

src/script.c

@@ -44,7 +44,7 @@
 #define MAX_BUFFER_SIZE 2000 // Maximum size of circular buffer
 #define READ_LINE_SIZE 4096 // read_line buffer length
 
-static int device_fd;
+static int device_fd = 0;
 static lua_State *script_interp = NULL;
 
 // clang-format off
@@ -203,6 +203,11 @@ static int line_set(lua_State *L)
     int cd = lua_tointeger(L, 5);
     int ri = lua_tointeger(L, 6);
 
+    if (device_fd == 0)
+    {
+        return luaL_error(L, "tty device not ready");
+    }
+
     if (dtr != -1)
     {
         line_config[0].mask = TIOCM_DTR;
@@ -252,6 +257,11 @@ static int api_send(lua_State *L)
     int protocol = luaL_checkinteger(L, 2);
     int ret;
 
+    if (device_fd == 0)
+    {
+        return luaL_error(L, "tty device not ready");
+    }
+
     if (file == NULL)
     {
         return 0;
@@ -295,6 +305,11 @@ static int api_write(lua_State *L)
     ssize_t ret;
     int attempts = 100;
 
+    if (device_fd == 0)
+    {
+        return luaL_error(L, "tty device not ready");
+    }
+
     do
     {
         ret = write(device_fd, string, len);
@@ -322,6 +337,11 @@ static int api_twrite(lua_State *L)
     size_t len = 0;
     const char *string = luaL_checklstring(L, 1, &len);
 
+    if (device_fd == 0)
+    {
+        return luaL_error(L, "tty device not ready");
+    }
+
     for (; len > 0; --len, string++)
     {
         forward_to_tty(device_fd, *string);
@@ -339,6 +359,11 @@ static int api_read(lua_State *L)
     int size = luaL_checkinteger(L, 1);
     int timeout = luaL_optinteger(L, 2, -1); // ms, negative value means forever.
 
+    if (device_fd == 0)
+    {
+        return luaL_error(L, "tty device not ready");
+    }
+
     luaL_Buffer buffer;
     luaL_buffinit(L, &buffer);
 
@@ -378,6 +403,11 @@ static int api_readline(lua_State *L)
     luaL_Buffer b;
     char ch;
 
+    if (device_fd == 0)
+    {
+        return luaL_error(L, "tty device not ready");
+    }
+
     luaL_buffinit(L, &b);
     luaL_prepbuffer(&b);
     while (true)
@@ -581,24 +611,36 @@ static lua_State *script_interp_new(void)
     return L;
 }
 
-void script_run(int fd, const char *script_filename)
+void script_device_bind(int fd)
+{
+    device_fd = fd;
+}
+
+void script_device_unbind(void)
+{
+    device_fd = 0;
+}
+
+void script_do_line(const char *script_line)
+{
+    assert(script_line != NULL);
+    assert(script_interp != NULL);
+
+    script_buffer_run(script_interp, script_line);
+}
+
+void script_run(const char *script_filename)
 {
     static bool doopt_by_nul = true;
-    device_fd = fd;
 
     assert(script_filename != NULL);
-
+    assert(script_interp != NULL);
-    if (script_interp == NULL)
-    {
-        if (script_interp_new() == NULL)
-            return;
-    }
 
     if (script_filename[0] == '\0')
     {
         if (doopt_by_nul)
         {
-            script_run_as_specified_by_options(fd);
+            script_run_as_specified_by_options();
         }
         return;
     }
@@ -611,7 +653,7 @@ void script_run(int fd, const char *script_filename)
         }
         else if (strcmp(script_filename, "@doopt") == 0)
         {
-            script_run_as_specified_by_options(fd);
+            script_run_as_specified_by_options();
         }
         else if (strcmp(script_filename, "@nuldo=opt") == 0)
         {
@@ -643,15 +685,9 @@ void script_run(int fd, const char *script_filename)
     }
 }
 
-void script_run_as_specified_by_options(int fd)
+void script_run_as_specified_by_options(void)
 {
-    device_fd = fd;
+    assert(script_interp != NULL);
-
-    if (script_interp == NULL)
-    {
-        if (script_interp_new() == NULL)
-            return;
-    }
 
     if (option.script_filename != NULL)
     {
@@ -682,3 +718,12 @@ const char *script_run_state_to_string(script_run_t state)
             return "Unknown";
     }
 }
+
+void script_interp_init(void)
+{
+    if (script_interp_new() == NULL)
+    {
+        tio_error_printf("Could not start script interpreter.");
+        exit(EXIT_FAILURE);
+    }
+}

src/script.h

@@ -29,6 +29,10 @@ typedef enum
     SCRIPT_RUN_END,
 } script_run_t;
 
-void script_run(int fd, const char *script_filename);
+void script_interp_init(void);
-void script_run_as_specified_by_options(int fd);
+void script_device_bind(int fd);
+void script_device_unbind(void);
+void script_run(const char *script_filename);
+void script_run_as_specified_by_options(void);
+void script_do_line(const char *script_line);
 const char *script_run_state_to_string(script_run_t state);

src/tty.c

@@ -147,6 +147,8 @@ typedef enum
     SUBCOMMAND_MAP,
 } sub_command_t;
 
+#define MLINE_MAX 4096
+
 // clang-format off
 const char random_array[] =
 {
@@ -183,7 +185,7 @@ static char *tty_buffer_write_ptr = tty_buffer;
 static pthread_t thread;
 static int pipefd[2];
 static pthread_mutex_t mutex_input_ready = PTHREAD_MUTEX_INITIALIZER;
-static char line[PATH_MAX];
+static char line[PATH_MAX], mline[MLINE_MAX];
 static size_t listing_device_name_length_max = 0;
 static readline_t *readline_ctx = NULL;
 static readline_t *subcmd_readline_ctx = NULL;
@@ -593,7 +595,9 @@ static void tty_line_poke(int fd, int mask, tty_line_mode_t mode, unsigned int d
 
 static int tio_subcmd_readln(const char *title_prompt)
 {
-    tio_printf_raw("%s\r\n", title_prompt);
+    if (title_prompt && (title_prompt[0] != '\0')) {
+        tio_printf_raw("%s\r\n", title_prompt);
+    }
     readline_prompt_for_input(subcmd_readline_ctx);
 
     /* Read line with line edit and history. */
@@ -660,6 +664,50 @@ static void mappings_print(void)
     // clang-format on
 }
 
+static void handle_script_repl(void)
+{
+    bool local_echo_bkup = option.local_echo;
+    int line_len;
+    int mline_len = 0;
+
+    option.local_echo = true;
+    tio_printf("Enter Lua REPL mode (@exit to exit)");
+
+    strcpy(mline, "");
+    while (true)
+    {
+        tio_subcmd_readln("");
+        if (strcmp(line, "@exit") == 0)
+            break;
+        line_len = strlen(line);
+
+        if (line_len > 0)
+        {
+            if (mline_len + line_len + 1 > MLINE_MAX)
+            {
+                tio_printf("Too long lines. The size should be lesser then %d bytes", MLINE_MAX);
+                strcpy(mline, "");
+                mline_len = 0;
+                continue;
+            }
+
+            strcat(&mline[mline_len], line);
+            mline_len += line_len;
+
+            if (mline_len > 0 && mline[mline_len - 1] == '\\')
+            {
+                mline[mline_len - 1] = '\n';
+                continue;
+            }
+        }
+        script_do_line(mline);
+        strcpy(mline, "");
+        mline_len = 0;
+    }
+
+    option.local_echo = local_echo_bkup;
+}
+
 void handle_command_sequence(char input_char, char *output_char, bool *forward)
 {
     char unused_char;
@@ -1079,8 +1127,15 @@ void handle_command_sequence(char input_char, char *output_char, bool *forward)
                 /* Run script */
                 tio_printf("Run Lua script");
                 tio_subcmd_readln("Enter file name or \"!\" lua commands or \"@\" direction to interpreter: ");
-                clear_line();
+                if (strcmp(line, "@repl") == 0)
-                script_run(device_fd, line);
+                {
+                    handle_script_repl();
+                }
+                else
+                {
+                    clear_line();
+                    script_run(line);
+                }
                 break;
 
             case KEY_SHIFT_R:
@@ -2545,6 +2600,21 @@ void forward_to_tty(int fd, char output_char)
     }
 }
 
+void tty_init(void)
+{
+    // Initialize readline like history
+    readline_ctx = readline_create();
+    subcmd_readline_ctx = readline_create();
+    if (readline_ctx == NULL || subcmd_readline_ctx == NULL)
+    {
+        tio_error_printf("Could not allocate readline buffer.");
+        exit(EXIT_FAILURE);
+    }
+    readline_set_prompt(readline_ctx, "> ");
+    readline_set_prompt(subcmd_readline_ctx, ">> ");
+
+}
+
 int tty_connect(void)
 {
     fd_set rdfs;           /* Read file descriptor set */
@@ -2676,9 +2746,11 @@ int tty_connect(void)
     }
 
     /* Manage script activation */
+    script_device_bind(device_fd);
+
     if (option.script_run != SCRIPT_RUN_NEVER)
     {
-        script_run_as_specified_by_options(device_fd);
+        script_run_as_specified_by_options();
 
         if (option.script_run == SCRIPT_RUN_ONCE)
         {
@@ -2698,17 +2770,6 @@ int tty_connect(void)
         exit(status);
     }
 
-    // Initialize readline like history
-    readline_ctx = readline_create();
-    subcmd_readline_ctx = readline_create();
-    if (readline_ctx == NULL || subcmd_readline_ctx == NULL)
-    {
-        tio_error_printf("Could not allocate readline buffer.");
-        exit(EXIT_FAILURE);
-    }
-    readline_set_prompt(readline_ctx, "> ");
-    readline_set_prompt(subcmd_readline_ctx, ">> ");
-
     /* Input loop */
     while (true)
     {
@@ -3035,6 +3096,7 @@ error_setspeed:
 error_tcsetattr:
 error_tcgetattr:
 error_read:
+    script_device_unbind();
     tty_disconnect();
 error_open:
     return TIO_ERROR;

src/tty.h

@@ -76,6 +76,7 @@ void stdout_configure(void);
 void stdin_configure(void);
 void tty_configure(void);
 void tty_reconfigure(void);
+void tty_init(void);
 int tty_connect(void);
 void tty_wait_for_device(void);
 void list_serial_devices(void);