pipe_out leaks pipe source fd when redirecting both stdout and stderr to same pipe

[dkl]

Hello,

Since commit caa7b2f, pipe_out<1,2>::on_exec_setup() is missing a ::close(source); call as in pipe_out<1,-1>::on_exec_setup() and pipe_out<2,-1>::on_exec_setup(). This leads to the pipe source fd being leaked in the child process, keeping the read end of the pipe open unnecessarily (parent process cannot close it).

An example where the difference is visible:

#include <boost/asio/io_context.hpp>
#include <boost/process/child.hpp>
#include <boost/process/io.hpp>
#include <boost/process/args.hpp>
#include <boost/process/async_pipe.hpp>

struct runner {
	boost::asio::io_context ioctx;
	boost::process::async_pipe stdout_pipe;
	boost::process::child child_process;

	runner()
		: stdout_pipe(ioctx)
		, child_process{
			boost::process::argv({"sh", "-c", "sleep 1; echo test"}),
			(boost::process::std_out & boost::process::std_err) > stdout_pipe,
		}
	{
		stdout_pipe.close();
	}

	void run()
	{
		ioctx.run();
		child_process.wait();
		printf("child exit code %i\n", child_process.exit_code());
	}
};

int main()
{
	runner r;
	r.run();
}

Without the close(source), it prints:

child exit code 0

(unexpected: child process didn't fail even though the parent closes the pipe)

With the close(source), it prints:

child exit code 13

(expected: child process failed due to SIGPIPE when writing to stdout, as expected because the parent closes the pipe)