[core] discard from socket using recv MSG_TRUNC

discard from socket using recv MSG_TRUNC on Linux TCP SOCK_STREAM socket

Currently, lighttpd supports only TCP SOCK_STREAM.  If UDP SOCK_DGRAM
were to be supported in the future, then socket type will need to be
stored so that MSG_TRUNC is used appropriately for the desired effect.

To find out socket type on arbitrary socket fd:
  getsockopt(..., SOL_SOCKET, SO_TYPE, ...)
but better to store it with each listening socket.

src/connections.c

@@ -161,10 +161,11 @@ static void connection_read_for_eos(server *srv, connection *con) {
 	 * it will make the client not see all our output.
 	 */
 	ssize_t len;
-	char buf[4096];
-
+	const int type = con->dst_addr.plain.sa_family;
+	char buf[16384];
 	do {
-		len = read(con->fd, buf, sizeof(buf));
+		len = fdevent_socket_read_discard(con->fd, buf, sizeof(buf),
+						  type, SOCK_STREAM);
 	} while (len > 0 || (len < 0 && errno == EINTR));
 
 	if (len < 0 && errno == EAGAIN) return;

src/fdevent.c

@@ -889,6 +889,28 @@ int fdevent_cycle_logger(const char *logger, int *curfd) {
 }
 
 
+#ifndef MSG_DONTWAIT
+#define MSG_DONTWAIT 0
+#endif
+#ifndef MSG_NOSIGNAL
+#define MSG_NOSIGNAL 0
+#endif
+
+
+ssize_t fdevent_socket_read_discard (int fd, char *buf, size_t sz, int family, int so_type) {
+  #if defined(MSG_TRUNC) && defined(__linux__)
+    if ((family == AF_INET || family == AF_INET6) && so_type == SOCK_STREAM) {
+        ssize_t len = recv(fd, buf, sz, MSG_TRUNC|MSG_DONTWAIT|MSG_NOSIGNAL);
+        if (len >= 0 || errno != EINVAL) return len;
+    }
+  #else
+    UNUSED(family);
+    UNUSED(so_type);
+  #endif
+    return read(fd, buf, sz);
+}
+
+
 #include <sys/ioctl.h>
 #ifdef HAVE_SYS_FILIO_H
 #include <sys/filio.h>  /* FIONREAD (for illumos (OpenIndiana)) */

src/fdevent.h

@@ -78,6 +78,8 @@ void fdevent_close_logger_pipes(void);
 void fdevent_breakagelog_logger_pipe(int fd);
 void fdevent_clr_logger_pipe_pids(void);
 
+ssize_t fdevent_socket_read_discard (int fd, char *buf, size_t sz, int family, int so_type);
+
 int fdevent_ioctl_fionread (int fd, int fdfmt, int *toread);
 
 int fdevent_connect_status(int fd);

src/mod_extforward.c

@@ -1224,7 +1224,7 @@ indicating which element is present :
 #endif
 
 /* returns 0 if needs to poll, <0 upon error or >0 is protocol vers (success) */
-static int hap_PROXY_recv (const int fd, union hap_PROXY_hdr * const hdr)
+static int hap_PROXY_recv (const int fd, union hap_PROXY_hdr * const hdr, const int family, const int so_type)
 {
     static const char v2sig[12] =
         "\x0D\x0A\x0D\x0A\x00\x0D\x0A\x51\x55\x49\x54\x0A";
@@ -1273,10 +1273,22 @@ static int hap_PROXY_recv (const int fd, union hap_PROXY_hdr * const hdr)
 
     /* we need to consume the appropriate amount of data from the socket
      * (overwrites existing contents of hdr with same data) */
+    UNUSED(family);
+    UNUSED(so_type);
     do {
+      #if defined(MSG_TRUNC) && defined(__linux__)
+        if ((family==AF_INET || family==AF_INET6) && so_type == SOCK_STREAM) {
+            ret = recv(fd, hdr, sz, MSG_TRUNC|MSG_DONTWAIT|MSG_NOSIGNAL);
+            if (ret >= 0 || errno != EINVAL) continue;
+        }
+      #endif
         ret = recv(fd, hdr, sz, MSG_DONTWAIT|MSG_NOSIGNAL);
     } while (-1 == ret && errno == EINTR);
     if (ret < 0) return -1;
+    if (ret != (ssize_t)sz) {
+        errno = EIO; /*(partial read; valid but unexpected; not handled)*/
+        return -1;
+    }
     if (1 == ver) hdr->v1.line[sz-2] = '\0'; /*terminate str to ease parsing*/
     return ver;
 }
@@ -1540,7 +1552,8 @@ static int mod_extforward_network_read (server *srv, connection *con,
      * In the future, might add config switch to enable doing this extra work */
 
     union hap_PROXY_hdr hdr;
-    int rc = hap_PROXY_recv(con->fd, &hdr);
+    int rc = hap_PROXY_recv(con->fd, &hdr,
+                            con->dst_addr.plain.sa_family, SOCK_STREAM);
     switch (rc) {
       case  2: rc = mod_extforward_hap_PROXY_v2(con, &hdr); break;
       case  1: rc = mod_extforward_hap_PROXY_v1(con, &hdr); break;