Fixed bug #51800 proc_open on Windows hangs forever

This loop can block for some minutes, theoretically. Practially
however, this is a 99% non issue for a normal use case. This is
required because read() is synchronous. The PHP streams API wants
to fill its internal buffers, therefore it might try to read some
more data than user has demanded. Also, for a case where we want
to read X bytes, but neither enough data nor EOF arrives, read()
will block until it could fill the buffer. If a counterpart station
runs slowly or delivers not all the data at once, read() would
still be waiting. If we quit too early, we possibly could loose
some data from the pipe. Thus it has to emulate the read()
behaviour, but obviously not completely, just to some grade.

Reading big data amount is for sure an issue on any platforms, it
depends on the pipe buffer size, which is controlled by the system.
On Windows, the buffer size seems to be way too small, which causes
buffer congestion and a dead lock. It is essential to read the pipe
descriptors simultaneously and possibly in the same order as the
opposite writes them.

Thus, this will work with smaller buffer data sizes passed through
pipes. As MSDN states, anonymous pipes don't support asynchronous
operations. Neither anonymous pipes do support select() as they are
not SOCKETs but file descriptors. Consequently - bigger data sizes
will need a better solution based on threads. However it is much
more expencive. Maybe a better solution could be exporting a part
of the internal doing as a userspace function which could perform
some kind of lookahead operation on the pipe descriptor.

This is just the first stone, depending on the user feedback we
might go for further improvements in this area.

1 files changed, 28 insertions, 0 deletions

diff --git a/main/streams/plain_wrapper.c b/main/streams/plain_wrapper.c
index a50662b78e..20ec7c2423 100644
--- a/main/streams/plain_wrapper.c
+++ b/main/streams/plain_wrapper.c
@@ -348,6 +348,34 @@ static size_t php_stdiop_read(php_stream *stream, char *buf, size_t count TSRMLS
 	assert(data != NULL);
 
 	if (data->fd >= 0) {
+#ifdef PHP_WIN32
+		php_stdio_stream_data *self = (php_stdio_stream_data*)stream->abstract;
+
+		if (self->is_pipe || self->is_process_pipe) {
+			HANDLE ph = (HANDLE)_get_osfhandle(data->fd);
+			int retry = 0;
+			DWORD avail_read = 0;
+
+			do {
+				/* Look ahead to get the available data amount to read. Do the same
+					as read() does, however not blocking forever. In case it failed,
+					no data will be read (better than block). */
+				if (!PeekNamedPipe(ph, NULL, 0, NULL, &avail_read, NULL)) {
+					break;
+				}
+				/* If there's nothing to read, wait in 100ms periods. */
+				if (0 == avail_read) {
+					usleep(100000);
+				}
+			} while (0 == avail_read && retry++ < 180);
+
+			/* Reduce the required data amount to what is available, otherwise read()
+				will block.*/
+			if (avail_read < count) {
+				count = avail_read;
+			}
+		}
+#endif
 		ret = read(data->fd, buf, count);
 
 		if (ret == (size_t)-1 && errno == EINTR) {