Expose OS.read_string_from_stdin() to the scripting API (3.x)

[Calinou]

3.x version of #65751. See godotengine/godot-proposals#2322.

This can be used in scripts to read user input in a blocking manner.

This also removes the unused block argument, which is always true.

# Save this script as `example.gd`, then run:
#     godot -s my_script.gd
extends SceneTree

func _initialize():
	var text = ""
	while text != "quit":
		printraw("Insert some text: ")
		text = OS.read_string_from_stdin().strip_edges()
		print("You inserted: %s" % text)
	print("Quitting")
	call_deferred("quit")

---

Note that non-ASCII input doesn't appear to be handled correctly (tested on Linux):

Insert some text: 123 Hello × é
You inserted: 123 Hello
Insert some text: ééé×××x×
You inserted: x

In master, this occurs instead:

Insert some text: 123 Hello × é
You inserted: 123 Hello à é
Insert some text: ééé×××x×
You inserted: éééÃÃÃxÃ

Maybe @bruvzg knows about resolving this encoding issue?

[bruvzg]

Maybe @bruvzg knows about resolving this encoding issue?

Decoding is missing completely, so it's reading it as Latin-1. Fix - #70389

[bruvzg]

Suggested change

	return OS::get_singleton()->get_stdin_string(true);
	return OS::get_singleton()->get_stdin_string(p_block);

But probably the argument should be removed at all (from both CoreBind and OS), it's not useful, setting it to false always return empty string.

[Calinou]

The argument was likely kept in #65751 for forward compatibility (in case non-blocking stdin reading is implemented), but it's not likely to happen in 3.x.

[akien-mga]

I think the argument should be removed here and for 4.0 too. If it's not implemented, there's no point having it. It can be added later if we do implement it.

[akien-mga]

I would also remove the unused parameter from the OS method, not just the binding.

[Calinou]

I've noticed that stdin length is limited to 1024 bytes:

https://github.com/godotengine/godot/blob/cf603aae8b7de7dd91066003b9898a97373eeed8/platform/windows/os_windows.cpp#L3258-L3259

https://github.com/godotengine/godot/blob/cf603aae8b7de7dd91066003b9898a97373eeed8/drivers/unix/os_unix.cpp#L140-L143

The same limitation is also present in master.

Is there a way we could increase this without side effects? If not, I can document it. cc @bruvzg

Edit: This is being addressed by #88863.

[bruvzg]

I've noticed that stdin length is limited to 1024 bytes:

I guess we can call read in a loop and add to String, like

	char buff[1024];
	String ret;
	while (fgets(buf, 1024, stdin) != nullptr) {
		ret += buf;
	}
	return ret;

Also, will need #70389 backported for Unicode support.

[akien-mga]

Thanks!

[Calinou]

I guess we can call read in a loop and add to String, like

	char buff[1024];
	String ret;
	while (fgets(buf, 1024, stdin) != nullptr) {
		ret += buf;
	}
	return ret;

I've tested this locally and it appears to freeze after entering a long string.

The current behavior is that calling OS.read_stdin_from_string() multiple times will do the concatenation for you. Also, if you enter a string before calling OS.read_stdin_from_string(), it will be read immediately without blocking.

Testing project: test_long_stdin.zip