[PATCH] mingw: handle writes to non-blocking pipe

[René Scharfe <l.s.r@xxxxxx>]

write() on Windows reports ENOSPC when writing to a non-blocking pipe
whose buffer is full and rejects writes bigger than the buffer outright.
Change the error code to EAGAIN and try a buffer-sized partial write to
comply with POSIX and the expections of our Git-internal callers.

Helped-by: Jeff King <peff@xxxxxxxx>
Signed-off-by: René Scharfe <l.s.r@xxxxxx>
---
 compat/mingw.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/compat/mingw.c b/compat/mingw.c
index b5502997e2..c6f244c0fe 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -689,6 +689,8 @@ int mingw_fflush(FILE *stream)
 	return ret;
 }

+#define PIPE_BUFFER_SIZE (8192)
+
 #undef write
 ssize_t mingw_write(int fd, const void *buf, size_t len)
 {
@@ -702,6 +704,21 @@ ssize_t mingw_write(int fd, const void *buf, size_t len)
 		else
 			errno = EINVAL;
 	}
+	if (result < 0 && errno == ENOSPC) {
+		/* check if fd is a non-blocking pipe */
+		HANDLE h = (HANDLE) _get_osfhandle(fd);
+		DWORD s;
+		if (GetFileType(h) == FILE_TYPE_PIPE &&
+		    GetNamedPipeHandleState(h, &s, NULL, NULL, NULL, NULL, 0) &&
+		    (s & PIPE_NOWAIT)) {
+			DWORD obuflen;
+			if (!GetNamedPipeInfo(h, NULL, &obuflen, NULL, NULL))
+				obuflen = PIPE_BUFFER_SIZE;
+			if (len > obuflen)
+				return mingw_write(fd, buf, obuflen);
+			errno = EAGAIN;
+		}
+	}

 	return result;
 }
@@ -1079,7 +1096,7 @@ int pipe(int filedes[2])
 	HANDLE h[2];

 	/* this creates non-inheritable handles */
-	if (!CreatePipe(&h[0], &h[1], NULL, 8192)) {
+	if (!CreatePipe(&h[0], &h[1], NULL, PIPE_BUFFER_SIZE)) {
 		errno = err_win_to_posix(GetLastError());
 		return -1;
 	}
--
2.37.1.windows.1