subprocess-win: update to mp_subprocess2

This fixes the "run" and "subprocess" commands on Windows, including
youtube-dl support.

Unix-like FD inheritance is emulated on Windows by using an undocumented
data structure[1] that gets passed to the newly created process in
STARTUPINFO.lpReserved2. It consists of two sparse arrays listing the
HANDLE and internal CRT flags corresponding to each FD. This structure
is used and understood primarily by MSVCRT, but there are other runtimes
and frameworks that can write it, like libuv.

The code for creating asynchronous "anonymous" pipes in Windows has been
enhanced and moved into windows_utils.c. This is mainly an artifact of
an unfinished future change to support anonymous IPC clients in Windows.
Right now, it's still only used in subprocess-win.c

[1]: https://www.catch22.net/tuts/undocumented-createprocess

1 files changed, 23 insertions, 5 deletions

diff --git a/osdep/terminal-win.c b/osdep/terminal-win.c
index ad7631f9da..3672f3a763 100644
--- a/osdep/terminal-win.c
+++ b/osdep/terminal-win.c
@@ -360,10 +360,27 @@ static bool is_a_console(HANDLE h)
 
 static void reopen_console_handle(DWORD std, int fd, FILE *stream)
 {
-    if (is_a_console(GetStdHandle(std))) {
-        freopen("CONOUT$", "wt", stream);
-        dup2(fileno(stream), fd);
+    HANDLE handle = GetStdHandle(std);
+    if (is_a_console(handle)) {
+        if (fd == 0) {
+            freopen("CONIN$", "rt", stream);
+        } else {
+            freopen("CONOUT$", "wt", stream);
+        }
         setvbuf(stream, NULL, _IONBF, 0);
+
+        // Set the low-level FD to the new handle value, since mp_subprocess2
+        // callers might rely on low-level FDs being set. Note, with this
+        // method, fileno(stdin) != STDIN_FILENO, but that shouldn't matter.
+        int unbound_fd = -1;
+        if (fd == 0) {
+             unbound_fd = _open_osfhandle((intptr_t)handle, _O_RDONLY);
+        } else {
+             unbound_fd = _open_osfhandle((intptr_t)handle, _O_WRONLY);
+        }
+        // dup2 will duplicate the underlying handle. Don't close unbound_fd,
+        // since that will close the original handle.
+        dup2(unbound_fd, fd);
     }
 }
 
@@ -384,8 +401,9 @@ bool terminal_try_attach(void)
     if (!AttachConsole(ATTACH_PARENT_PROCESS))
         return false;
 
-    // We have a console window. Redirect output streams to that console's
-    // low-level handles, so things that use printf directly work later on.
+    // We have a console window. Redirect input/output streams to that console's
+    // low-level handles, so things that use stdio work later on.
+    reopen_console_handle(STD_INPUT_HANDLE, STDIN_FILENO, stdin);
     reopen_console_handle(STD_OUTPUT_HANDLE, STDOUT_FILENO, stdout);
     reopen_console_handle(STD_ERROR_HANDLE, STDERR_FILENO, stderr);