From 67d518544b13a482013e21a149ea3b895804a74b Mon Sep 17 00:00:00 2001
From: Juliusz Sosinowicz <juliusz@wolfssl.com>
Date: Mon, 1 Aug 2022 15:51:40 +0200
Subject: [PATCH] EmbedReceiveFrom: fix when using a TCP socket

- recvfrom() returns 0 on a closed TCP socket
- TCP sockets set WOLFSSL_CBIO_ERR_ISR on a timeout
---
 src/wolfio.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/wolfio.c b/src/wolfio.c
index 7a958d0ab..20a231ab9 100644
--- a/src/wolfio.c
+++ b/src/wolfio.c
@@ -481,6 +481,20 @@ int EmbedReceiveFrom(WOLFSSL *ssl, char *buf, int sz, void *ctx)
         }
         return recvd;
     }
+    else if (recvd == 0) {
+        int type;
+        XSOCKLENT length = sizeof(int); /* optvalue 'type' is of size int */
+
+        if (getsockopt(sd, SOL_SOCKET, SO_TYPE, &type, &length) == 0 &&
+                type != SOCK_DGRAM) {
+            /* Closed TCP connection */
+            recvd = WOLFSSL_CBIO_ERR_CONN_CLOSE;
+        }
+        else {
+            WOLFSSL_MSG("Ignoring 0-length datagram");
+        }
+        return recvd;
+    }
     else if (dtlsCtx->connected) {
         /* Nothing to do */
     }