mp.input: send buffer ids with logs to avoid race conditions

This commit modifies the log methods in mp.input to always send the id
of the latest `input.get()` request with log entries.

Previously, the log methods applied to whichever input request happened
to be open when the log message was received. Even when scripts used
these methods correctly, there was the risk of sending a log to the
wrong log buffer if the active input request changed while the log
message was in transit; a race condition.

Now the id of the latest `input.get()` request is sent alongside the log
messages, preventing data races between scripts while also preventing
those logs from being discarded.

Author: CogentRedTester

DOCS/man/lua.rst

@@ -980,16 +980,18 @@ REPL.
     requests made by other scripts.
 
 ``input.log(message, style, terminal_style)``
-    Add a line to the log buffer. ``style`` can contain additional ASS tags to
-    apply to ``message``, and ``terminal_style`` can contain escape sequences
-    that are used when the console is displayed in the terminal.
+    Add a line to the log buffer of the latest ``input.get()`` request.
+    ``style`` can contain additional ASS tags to apply to ``message``,
+    and ``terminal_style`` can contain escape sequences that are used
+    when the console is displayed in the terminal.
 
 ``input.log_error(message)``
-    Helper to add a line to the log buffer with the same color as the one used
+    Helper to add an error line to the log buffer of the latest ``input.get()``
+    request. The line is styled with the same color as the one used
     for commands that error. Useful when the user submits invalid input.
 
 ``input.set_log(log)``
-    Replace the entire log buffer.
+    Replace the entire log buffer of the latest ``input.get()`` request.
 
     ``log`` is a table of strings, or tables with ``text``, ``style`` and
     ``terminal_style`` keys.

player/javascript/defaults.js

@@ -655,6 +655,7 @@ mp.options = { read_options: read_options };
 *********************************************************************/
 var input_handle_counter = 0;
 var latest_handler_id;
+var latest_log_id;
 
 function register_event_handler(t) {
     var handler_id = "input-event/" + input_handle_counter++;
@@ -686,13 +687,19 @@ function register_event_handler(t) {
     return handler_id;
 }
 
+function input_request(t) {
+    t.has_completions = t.complete !== undefined;
+    t.client_name = mp.script_name;
+    t.handler_id = register_event_handler(t);
+
+    mp.commandv("script-message-to", "console", "get-input", JSON.stringify(t));
+}
+
 mp.input = {
     get: function(t) {
-        t.has_completions = t.complete !== undefined;
-        t.client_name = mp.script_name;
-        t.handler_id = register_event_handler(t);
-
-        mp.commandv("script-message-to", "console", "get-input", JSON.stringify(t));
+        t.id = t.id || mp.script_name + (t.prompt || "");
+        latest_log_id = t.id;
+        return input_request(t);
     },
     terminate: function () {
         mp.commandv("script-message-to", "console", "disable", JSON.stringify({
@@ -701,21 +708,27 @@ mp.input = {
     },
     log: function (message, style, terminal_style) {
         mp.commandv("script-message-to", "console", "log", JSON.stringify({
+                        log_id: latest_log_id,
                         text: message,
                         style: style,
                         terminal_style: terminal_style,
                    }));
     },
     log_error: function (message) {
-        mp.commandv("script-message-to", "console", "log",
-                    JSON.stringify({ text: message, error: true }));
+        mp.commandv("script-message-to", "console", "log", JSON.stringify({
+                        log_id: latest_log_id,
+                        text: message,
+                        error: true,
+                    }));
     },
     set_log: function (log) {
-        mp.commandv("script-message-to", "console", "set-log",
-                    JSON.stringify(log));
+        if (latest_log_id) {
+            mp.commandv("script-message-to", "console", "set-log",
+                        latest_log_id, JSON.stringify(log));
+        }
     }
 }
-mp.input.select = mp.input.get
+mp.input.select = input_request;
 
 /**********************************************************************
  *  various

player/lua/console.lua

@@ -1710,7 +1710,7 @@ mp.register_script_message("get-input", function (args)
     else
         selectable_items = nil
         unbind_mouse()
-        id = args.id or args.client_name .. prompt
+        id = args.id
         log_offset = 0
         completion_buffer = {}
         autoselect_completion = args.autoselect_completion
@@ -1740,8 +1740,13 @@ end)
 
 -- Add a line to the log buffer
 mp.register_script_message("log", function (message)
-    local log_buffer = log_buffers[id]
-    message = utils.parse_json(message)
+    message = utils.parse_json(message or "")
+    if not message or not message.log_id then
+        return
+    end
+
+    local log_buffer = log_buffers[message.log_id]
+    if not log_buffer then return end
 
     log_buffer[#log_buffer + 1] = {
         text = message.text,
@@ -1754,7 +1759,7 @@ mp.register_script_message("log", function (message)
         table.remove(log_buffer, 1)
     end
 
-    if not open then
+    if not open or message.log_id ~= id then
         return
     end
 
@@ -1770,9 +1775,13 @@ mp.register_script_message("log", function (message)
     end
 end)
 
-mp.register_script_message("set-log", function (log)
+mp.register_script_message("set-log", function (log_id, log)
+    if not log_id or not log then
+        return
+    end
+
     log = utils.parse_json(log)
-    log_buffers[id] = {}
+    log_buffers[log_id] = {}
 
     for i = 1, #log do
         if type(log[i]) == "table" then
@@ -1789,7 +1798,9 @@ mp.register_script_message("set-log", function (log)
         end
     end
 
-    render()
+    if log_id == id then
+        render()
+    end
 end)
 
 mp.register_script_message("complete", function (message)

player/lua/input.lua

@@ -20,6 +20,7 @@ local input = {}
 
 local handle_counter = 0
 local latest_handler_id
+local latest_log_id
 
 local function get_non_callbacks(t)
     local non_callbacks = {}
@@ -67,7 +68,7 @@ local function register_event_handler(t)
     return handler_id
 end
 
-function input.get(t)
+local function input_request(t)
     t.has_completions = t.complete ~= nil
     t.client_name = mp.get_script_name()
     t.handler_id = register_event_handler(t)
@@ -76,7 +77,14 @@ function input.get(t)
                 utils.format_json(get_non_callbacks(t)))
 end
 
-input.select = input.get
+function input.get(t)
+    -- input.select does not support log buffers, so cannot override the latest id.
+    t.id = t.id or mp.get_script_name()..(t.prompt or "")
+    latest_log_id = t.id
+    return input_request(t)
+end
+
+input.select = input_request
 
 function input.terminate()
     mp.commandv("script-message-to", "console", "disable", utils.format_json({
@@ -86,19 +94,26 @@ end
 
 function input.log(message, style, terminal_style)
     mp.commandv("script-message-to", "console", "log", utils.format_json({
-                   text = message,
-                   style = style,
-                   terminal_style = terminal_style,
-               }))
+                    log_id = latest_log_id,
+                    text = message,
+                    style = style,
+                    terminal_style = terminal_style,
+                }))
 end
 
 function input.log_error(message)
-    mp.commandv("script-message-to", "console", "log",
-                 utils.format_json({ text = message, error = true }))
+    mp.commandv("script-message-to", "console", "log", utils.format_json({
+                    log_id = latest_log_id,
+                    text = message,
+                    error = true,
+                }))
 end
 
 function input.set_log(log)
-    mp.commandv("script-message-to", "console", "set-log", utils.format_json(log))
+    if latest_log_id then
+        mp.commandv("script-message-to", "console", "set-log",
+            latest_log_id, utils.format_json(log))
+    end
 end
 
 return input