extmod/modlwip: Still process remaining incoming data of a closed socket.

It can happen that a socket gets closed while the pbuf is not completely
drained by the application.  It can also happen that a new pbuf comes in
via the recv callback, and then a "peer closed" event comes via the same
callback (pbuf=NULL) before the previous event has been handled.  In both
cases the socket is closed but there is remaining data.  This patch makes
sure such data is passed to the application.

1 files changed, 4 insertions, 6 deletions

diff --git a/extmod/modlwip.c b/extmod/modlwip.c
index 05b6208f2..fccde6a05 100644
--- a/extmod/modlwip.c
+++ b/extmod/modlwip.c
@@ -384,11 +384,6 @@ STATIC mp_uint_t lwip_tcp_send(lwip_socket_obj_t *socket, const byte *buf, mp_ui
 
 // Helper function for recv/recvfrom to handle TCP packets
 STATIC mp_uint_t lwip_tcp_receive(lwip_socket_obj_t *socket, byte *buf, mp_uint_t len, int *_errno) {
-
-    if (socket->state == STATE_PEER_CLOSED) {
-        return 0;
-    }
-
     if (socket->incoming.pbuf == NULL) {
         mp_uint_t start = mp_hal_ticks_ms();
         while (socket->state == STATE_CONNECTED && socket->incoming.pbuf == NULL) {
@@ -399,7 +394,10 @@ STATIC mp_uint_t lwip_tcp_receive(lwip_socket_obj_t *socket, byte *buf, mp_uint_
             poll_sockets();
         }
         if (socket->state == STATE_PEER_CLOSED) {
-            return 0;
+            if (socket->incoming.pbuf == NULL) {
+                // socket closed and no data left in buffer
+                return 0;
+            }
         } else if (socket->state != STATE_CONNECTED) {
             *_errno = -socket->state;
             return -1;