Issue #19703 has been reported by YO4 (Yoshinao Muramatsu). ---------------------------------------- Bug #19703: text/binary mode of parent process fd is not properly inherited on windows https://bugs.ruby-lang.org/issues/19703 * Author: YO4 (Yoshinao Muramatsu) * Status: Open * Priority: Normal * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- Windows OS can't inherit parent process fds greater than 2, but C runtime library support this. https://learn.microsoft.com/en-us/cpp/c-runtime-library/spawn-wspawn-functio... So I made test tool below. This tool opens NUL device several times and create child ruby process that dumps fds' translation mode. ``` c // fdinherit.c : test file descprotor inheritance for windows C runtime #include <stdio.h> #include <stdlib.h> #include <process.h> #include <sys/types.h> #include <sys/stat.h> #include <share.h> #include <fcntl.h> #include <io.h> int main(int argc, char* argv[]) { int fh, count = 0; errno_t err; // child process: read fds and check if it includes "\r" and prints // '.' : read as binary // 't' : read as text // 'F' : open error (no fd?) char rb1[] = "print '012'; 3.upto("; char rb2[] = ") { |n|" "print ((IO.for_fd(n, 'rb').read.include?(13.chr) ? '.' : 't') rescue 'F');" "puts if (n % 10) == 9" "}"; char upto[] = "-4294967295"; // fd max number to test if (argc >= 2) count = atoi(argv[1]); if (count < 3) count = 7; // create crlf file (current directory) system("echo;>crlf.txt"); // open fds to inherit // even fds are text mode, odd fds are binary mode for (int i = 3; i <= count; i++) { err = _sopen_s(&fh, "crlf.txt", _O_RDONLY | ((i & 1) ? _O_BINARY : _O_TEXT), _SH_DENYNO, _S_IREAD | _S_IWRITE); if (err > 0) printf("%d %d\n", err, fh); } // on child side, +1'd fd dump will fail (prints 'F') sprintf_s(upto, sizeof(upto), "%d", count + 1); // on windows, arguments are joined into a string. so below has bad manners, but let me take a few corners. _spawnlp(_P_WAIT, "ruby.exe", "ruby.exe", "-e", "\"", rb1, upto, rb2, "\"", NULL); _close(fh); } ``` As an example, this would display something like this ```

fdinherit.exe 012.t.t.F fdinherit.exe 16 012.t.t.t. t.t.t.tF

``` 0,1,2 are stdin, stdout, stderr fds of 3,5,7,... are inherited as binary mode fds of 4,6,... are inherited as text mode And I found a few things to point out. When I modify ruby part like "IO.for_fd(n, 'r')" / "IO.for_fd(n, 'rt')" / "IO.for_fd(n)", It get result like ```012tttttF```, so translation mode are interprited wrong. The odd thing is that the conversion mode is interpreted as is when "IO.for_fd(n, 'rb')", which I think is the expected behavior when "IO.for_fd(n, 'r')". This tool and ruby.exe each work with a combination of msvcrt 32/64bit and ucrt64, so the C runtime interface seems stable. My understanding is that MRI does not state that it supports inheritance of fds larger than 3 in windows, but it seems to work partially. Are there any chances for improvement? For those who want to follow up: it seems that fds are not inherited via cmd.exe /c -- https://bugs.ruby-lang.org/