Fix Windows tun read handling

It's too fragile to depend on the 'new_pkt' check, and only do the ReadFile()
call when we allocate a new packet buffer. Keep track of the pending state
directly in the Windows-specific code, instead.

This should fix the fact that it gets out of sync when we get an error.
Such as the ERROR_MORE_DATA errors we get because vpnc-script-win.js
doesn't set the MTU properly yet...

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

mainloop.c

@@ -56,10 +56,8 @@ int tun_mainloop(struct openconnect_info *vpninfo, int *timeout)
 	if (read_fd_monitored(vpninfo, tun)) {
 		while (1) {
 			int len = vpninfo->ip_info.mtu;
-			int new_pkt = 0;
 
 			if (!out_pkt) {
-				new_pkt = 1;
 				out_pkt = malloc(sizeof(struct pkt) + len);
 				if (!out_pkt) {
 					vpn_progress(vpninfo, PRG_ERR, "Allocation failed\n");
@@ -68,7 +66,7 @@ int tun_mainloop(struct openconnect_info *vpninfo, int *timeout)
 				out_pkt->len = len;
 			}
 
-			if (os_read_tun(vpninfo, out_pkt, new_pkt))
+			if (os_read_tun(vpninfo, out_pkt))
 				break;
 
 			vpninfo->stats.tx_pkts++;

openconnect-internal.h

@@ -294,6 +294,7 @@ struct openconnect_info {
 #ifdef _WIN32
 	HANDLE tun_fh;
 	OVERLAPPED tun_rd_overlap, tun_wr_overlap;
+	int tun_rd_pending;
 #else
 	int tun_fd;
 #endif
@@ -453,7 +454,7 @@ int script_config_tun(struct openconnect_info *vpninfo, const char *reason);
 
 /* tun.c / tun-win32.c */
 void os_shutdown_tun(struct openconnect_info *vpninfo);
-int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt, int new_pkt);
+int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt);
 int os_write_tun(struct openconnect_info *vpninfo, struct pkt *pkt);
 intptr_t os_setup_tun(struct openconnect_info *vpninfo);
 

tun-win32.c

@@ -200,33 +200,41 @@ intptr_t os_setup_tun(struct openconnect_info *vpninfo)
 	return search_taps(vpninfo, open_tun, 0);
 }
 
-int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt, int new_pkt)
+int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt)
 {
 	DWORD pkt_size;
 
-	/* For newly-allocated packets we have to trigger the read. */
-	if (new_pkt) {
-		if (!ReadFile(vpninfo->tun_fh, pkt->data, pkt->len, &pkt_size, &vpninfo->tun_rd_overlap)) {
-			DWORD err = GetLastError();
-			if (err != ERROR_IO_PENDING)
-				vpn_progress(vpninfo, PRG_ERR,
-					     _("Failed to read from TAP device: %lx\n"),
-					     err);
-			return -1;
-		}
-	} else {
-		/* IF it isn't a new packet, then there was already a pending read on it. */
-		if (!GetOverlappedResult(vpninfo->tun_fh, &vpninfo->tun_rd_overlap, &pkt_size, FALSE)) {
-			DWORD err = GetLastError();
-
-			if (err != ERROR_IO_INCOMPLETE)
-				vpn_progress(vpninfo, PRG_ERR,
-					     _("Failed to complete read from TAP device: %lx\n"),
-					     err);
-			return -1;
+ reread:
+	if (!vpninfo->tun_rd_pending &&
+	    !ReadFile(vpninfo->tun_fh, pkt->data, pkt->len, &pkt_size,
+		      &vpninfo->tun_rd_overlap)) {
+		DWORD err = GetLastError();
+
+		if (err == ERROR_IO_PENDING)
+			vpninfo->tun_rd_pending = 1;
+		else
+			vpn_progress(vpninfo, PRG_ERR,
+				     _("Failed to read from TAP device: %lx\n"),
+				     err);
+		return -1;
+	} else if (!GetOverlappedResult(vpninfo->tun_fh,
+					&vpninfo->tun_rd_overlap, &pkt_size,
+					FALSE)) {
+		DWORD err = GetLastError();
+
+		if (err != ERROR_IO_INCOMPLETE) {
+			vpninfo->tun_rd_pending = 0;
+			vpn_progress(vpninfo, PRG_ERR,
+				     _("Failed to complete read from TAP device: %lx\n"),
+				     err);
+			goto reread;
 		}
+		return -1;
 	}
 
+	/* Either a straight ReadFile() or a subsequent GetOverlappedResult()
+	   succeeded... */
+	vpninfo->tun_rd_pending = 0;
 	pkt->len = pkt_size;
 	return 0;
 }

tun.c

@@ -376,7 +376,7 @@ int openconnect_setup_tun_script(struct openconnect_info *vpninfo, char *tun_scr
 	return openconnect_setup_tun_fd(vpninfo, fds[0]);
 }
 
-int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt, int new_pkt)
+int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt)
 {
 	int prefix_size = 0;
 	int len;