Question: embedding node in non-console application

[Let0s]

• Node.js Version: 8.x
• OS: MS Windows 7
• Scope (install, code, runtime, meta, other?): embedding

I try to embed node into non-console application. With console application it works fine. But with non-console application node doesn't evaluate script. debugger output writes next: internal/process/stdio.js:4433: Uncaught Unknown stream file type.
I think it is realted with tty_wrap.guessHandleType(fd) call in lib\internal\process\stdio.js file and GuessHandleType function in tty_wrap.cc file where t variable have UV_UNKNOWN_HANDLE value in my case. And it seems, that there is no any supported input/output in non-console application and node stops script execution.
I need an advice - maybe there is any way to change input/output to what i need or block it?

[Let0s]

Update: if i change source file tty_wrap.cc and will return "FILE" instead of "UNKNOWN" in UV_UNKNOWN_HANDLE case, all works fine. But it is bad solution and I want not to change node source files.

[gireeshpunathil]

Can you see if you can follow what uv_spawn does when child_process.spawn with stdio: ignore option is supplied, and mimic that behavior prior to launching the node dll and see if it meets your requirement?

Also /cc @bnoordhuis for better insights
Also /cc @addaleax who has been leading the embedder's use cases.
Also link #1031

[addaleax]

@Let0s We’ve had bug reports into that direction in the past. Not knowing much about Windows, do you know what value GetFileType() inside uv_guess_handle() returns and to which stream concept, if any, that should match to?

[Let0s]

@gireeshpunathil Thanks for advice.
@addaleax In my case GetFileType() returns 0 and handle value is 0xfffffffe - it looks like handle doesn't exist.
Does it mean, that I should create stdio from my app and node will find it and connect to it automatically?

[gireeshpunathil]

AFAIK, Non-console mode windows apps never opens standard streams. So handles for fds 0,1,2 will all be garbage.

[Let0s]

OK. Thank you, I'll try it.

[addaleax]

It still seems like a valid question to ask what Node.js would do in this case. I think it might make sense to provide dummy stdio streams?

[gireeshpunathil]

@addaleax - yes, agreed on the dummy stdio streams (or at least a valid destination for them so that Node does not crash) and hence my suggestion on uv_spawn with ignore - isn't it aims to achieve the same thing?

[addaleax]

@gireeshpunathil On UNIX systems we get fds 0,1,2 that each refer to /dev/null (reading immediately stops, writing is a no-op). I could imaginge uv_spawn with ignore does something similar on Windows?

[gireeshpunathil]

If I understand correctly, [this sequence] (https://github.com/libuv/libuv/blob/d9d207774ea1f734310982300e55dd64b3f5682b/src/win/process-stdio.c#L290-L293) initializes all the handles with invalid (though not garbage) values, and later fills in the proper values according to user options. We could actually invalidate the host process's handles in this way prior to launching Node and see how does it behave. @Let0s

[Let0s]

@gireeshpunathil in my case (embedding without stdio) uv__stdio_create is not calling. I think it is because node can't find any stdio, and tty_wrap.guessHandleType(fd) returns 'UNKNOWN' and this line stops execution.
About my question: I created pipe in my app, then dynamically call node.dll and it works - node got pipe's handle. But even there uv__stdio_create is not calling.
And i found that uv__stdio_create is used only in uv_spawn function and I know only one way to call it - it is child_process.spawn function call inside already running script.
P.S. I test it all on node v8.x, maybe something was changed in later versions.

[gireeshpunathil]

@Let0s - ok, I did not mean that the routine will be invoked in the regular sequence. Instead, I suggested to follow those steps to make your standard streams to be similar to those, in the embedder itself, prior to the node.dll load. (closing the fds if they are already opened, and assigning their os_handles with INVALID_HANDLE_VALUE

[Let0s]

@gireeshpunathil Maybe I misunderstood you, but I think it is almost impossible. In case with child_process.spawn node creates handles even for 'ignore' option. This comment tells that std(in/out/err) should be initialized, but others can be INVALID_HANDLE_VALUE.
My problem is solved - if I haven't stdio streams in my app, I create them before node initialization.
If you want to solve it globally, as @addaleax said:

It still seems like a valid question to ask what Node.js would do in this case. I think it might make sense to provide dummy stdio streams?

Then I think, Node.js should check (on initialization?) if stdio exists and if it is not exist, Node.js should create dummy stdio streams.