streams/xp_socket: eliminate poll() when MSG_DONTWAIT is available

If there is a zero timeout and MSG_DONTWAIT is available (or the
socket is non-blocking), the poll() call is not necessary, and we can
just call recv() right away.

Before this change:

 poll([{fd=4, events=POLLIN|POLLPRI|POLLERR|POLLHUP}], 1, 0) = 0 (Timeout)
 poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 60000) = 1 ([{fd=4, revents=POLLIN}])
 recvfrom(4, "HTTP/1.1 301 Moved Permanently\r\n"..., 8192, MSG_DONTWAIT, NULL, NULL) = 348
 poll([{fd=4, events=POLLIN|POLLPRI|POLLERR|POLLHUP}], 1, 0) = 1 ([{fd=4, revents=POLLIN}])
 recvfrom(4, "", 1, MSG_PEEK, NULL, NULL) = 0

After this change:

 recvfrom(4, 0x7ffe0cc719a0, 1, MSG_PEEK|MSG_DONTWAIT, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
 poll([{fd=4, events=POLLIN|POLLERR|POLLHUP}], 1, 60000) = 1 ([{fd=4, revents=POLLIN}])
 recvfrom(4, "HTTP/1.1 301 Moved Permanently\r\n"..., 8192, MSG_DONTWAIT, NULL, NULL) = 348
 recvfrom(4, "", 1, MSG_PEEK|MSG_DONTWAIT, NULL, NULL) = 0

The first poll() is replaced by recvfrom(), and the third poll() is
omitted completely.

ext/openssl/xp_ssl: eliminate poll() when MSG_DONTWAIT is available

If there is a zero timeout and MSG_DONTWAIT is available (or the
socket is non-blocking), the poll() call is not necessary, and we can
just call recv() right away.

Closes GH-8092.

NEWS

@@ -28,6 +28,9 @@ PHP                                                                        NEWS
 - ODBC:
   . Fixed handling of single-key connection strings. (Calvin Buckley)
 
+- OpenSSL:
+  . Discard poll calls on socket when no timeout/non blocking/MSG_DONTWAIT. (Max Kellermann)
+
 - PCRE:
   . Implemented FR #77726 (Allow null character in regex patterns). (cmb)
 
@@ -37,6 +40,9 @@ PHP                                                                        NEWS
 - Standard:
   . Deprecated utf8_encode() and utf8_decode(). (Rowan Tommins)
 
+- Streams:
+  . Discard poll calls on socket when no timeout/non blocking/MSG_DONTWAIT. (Max Kellermann)
+
 09 Jun 2022, PHP 8.2.0alpha1
 
 - CLI:

ext/openssl/xp_ssl.c

@@ -46,6 +46,10 @@
 #undef X509_EXTENSIONS
 #endif
 
+#ifndef MSG_DONTWAIT
+# define MSG_DONTWAIT 0
+#endif
+
 /* Flags for determining allowed stream crypto methods */
 #define STREAM_CRYPTO_IS_CLIENT            (1<<0)
 #define STREAM_CRYPTO_METHOD_SSLv2         (1<<1)
@@ -2395,7 +2399,10 @@ static int php_openssl_sockop_set_option(php_stream *stream, int option, int val
 
 				if (sslsock->s.socket == -1) {
 					alive = 0;
-				} else if (php_pollfd_for(sslsock->s.socket, PHP_POLLREADABLE|POLLPRI, &tv) > 0) {
+				} else if ((!sslsock->ssl_active && value == 0 && (MSG_DONTWAIT || !sslsock->s.is_blocked)) ||
+					   php_pollfd_for(sslsock->s.socket, PHP_POLLREADABLE|POLLPRI, &tv) > 0) {
+					/* the poll() call was skipped if the socket is non-blocking (or MSG_DONTWAIT is available) and if the timeout is zero */
+					/* additionally, we don't use this optimization if SSL is active because in that case, we're not using MSG_DONTWAIT */
 					if (sslsock->ssl_active) {
 						int n = SSL_peek(sslsock->ssl_handle, &buf, sizeof(buf));
 						if (n <= 0) {
@@ -2413,7 +2420,7 @@ static int php_openssl_sockop_set_option(php_stream *stream, int option, int val
 									alive = 0;
 							}
 						}
-					} else if (0 == recv(sslsock->s.socket, &buf, sizeof(buf), MSG_PEEK) && php_socket_errno() != EAGAIN) {
+					} else if (0 == recv(sslsock->s.socket, &buf, sizeof(buf), MSG_PEEK|MSG_DONTWAIT) && php_socket_errno() != EAGAIN) {
 						alive = 0;
 					}
 				}

main/streams/xp_socket.c

@@ -337,15 +337,16 @@ static int php_sockop_set_option(php_stream *stream, int option, int value, void
 
 				if (sock->socket == -1) {
 					alive = 0;
-				} else if (php_pollfd_for(sock->socket, PHP_POLLREADABLE|POLLPRI, &tv) > 0) {
+				} else if ((value == 0 && (MSG_DONTWAIT || !sock->is_blocked)) || php_pollfd_for(sock->socket, PHP_POLLREADABLE|POLLPRI, &tv) > 0) {
+					/* the poll() call was skipped if the socket is non-blocking (or MSG_DONTWAIT is available) and if the timeout is zero */
 #ifdef PHP_WIN32
 					int ret;
 #else
 					ssize_t ret;
 #endif
 					int err;
 
-					ret = recv(sock->socket, &buf, sizeof(buf), MSG_PEEK);
+					ret = recv(sock->socket, &buf, sizeof(buf), MSG_PEEK|MSG_DONTWAIT);
 					err = php_socket_errno();
 					if (0 == ret || /* the counterpart did properly shutdown*/
 						(0 > ret && err != EWOULDBLOCK && err != EAGAIN && err != EMSGSIZE)) { /* there was an unrecoverable error */