While spawning a child process, sometimes additional pipes rather than stdin, stdout, stderr are used for IPC. So std::process::Command::new should support it like the nodejs child_process.spawn which has the option to do it.

Motivation

• Applications like chrome uses fd 3 and 4 for remote debugging. Tools like puppeteer use the nodejs child_process.spawn function which can do so.
• Pipes are often used for processes to communicate with each other. These processes often communicate using pipes other than stdin, stdout, stderr like the above example.

Design

Here is an example for how it can be

Parent process:

let (read3, write3) = std::io::pipe();
let (read4, write4) = std::io::pipe();

let process = Command::new("prog")
              .stdin(Stdio::null())
              .stdout(Stdio::null())
              .stderr(Stdio::null())
              .pass(&[&read3, &write4])
              .spawn().unwrap();
write3.write("Foo").unwrap();

let mut s = String::new();
read4.read_to_string(&mut s).unwrap();

The pipe() function can return a tuple of PipeReader and PipeWriter

The pass method in std::process::Command can take a slice of &dyn RawFile where RawFile is a trait that specifies

• The raw fd/HANDLE
• The flags associated with it

Child process:

let read3 = std::io::PipeReader::from_fd(3);
let write4 = std::io::PipeWriter::from_fd(4);

let mut s = String::new();
read3.read_to_string(&mut s).unwrap();

write4.write("Bar").unwrap();

Implementation

In my library I had to use pipes for IPC so I did a basic rust implementation here https://github.com/Srinivasa314/alcro/blob/master/src/chrome/pipe.rs

Unix

For unix dup2 can be used

Windows

Eventhough windows uses handles,the MSVC runtime does have a concept of fd's Refer: open_osfhandle get_osfhandle

For windows lpReserved2 of startupinfo in CreateProcess can be used (The method used by libuv: https://github.com/nodejs/node/blob/8ae28ff3ac49cbf83f4fc3445d63b9900f3cdcda/deps/uv/src/win/process-stdio.c#L32)

The struct should be packed and crtflags are as in https://github.com/nodejs/node/blob/8ae28ff3ac49cbf83f4fc3445d63b9900f3cdcda/deps/uv/src/win/process-stdio.c#L57

The child process can get the HANDLE from fd even without needing the CRT using GetStartupInfo

Alternative

Write code using the C API for windows and unix instead of std::process:Command

Prior art

NodeJS has child_process.spawn which has options.stdio so that many other pipes can be created and it is frequently used for interprocess communication between node js applications.