wsd: net: handle unexpected closed-socket gracefully

Previously, we threw an exception in this case,
which had a couple of unfortunately side-effects.

First, the onDisconnect() handler wasn't called.
This prevented proper reconnection logic in some
cases.

Second, it created different behavior depending
on _how_ we detected the disconnection. That is,
depending on the value of the various return values
and error codes, we either threw or returned with
errno.

This treats all disconnection/unexpected socket
errors as EPIPE and returns 0.

Change-Id: Ia27a055a3cbcf639c62b82506f7cb683e99146f2
Signed-off-by: Ashod Nakashian <ashod.nakashian@collabora.co.uk>

net/SslSocket.hpp

@@ -461,8 +461,6 @@ class SslStreamSocket final : public StreamSocket
                     {
                         // Socket closed. Not an error.
                         oss << " (" << context << "): closed. " << bioErrStr;
-                        LOG_INF(oss.str());
-                        return 0;
                     }
                     else if (rc == -1)
                     {
@@ -479,9 +477,7 @@ class SslStreamSocket final : public StreamSocket
                 }
 
                 oss << bioErrStr;
-                const std::string msg = oss.str();
-                LOG_TRC("Throwing SSL Error ("
-                        << context << "): " << msg); // Locate the source of the exception.
+                LOG_DBG("SSL Error (" << context << "): " << oss.str());
 
                 handshakeFail();
 
@@ -490,13 +486,12 @@ class SslStreamSocket final : public StreamSocket
                 if (!sslVerifyResult.empty())
                     LOG_ERR("SSL verification warning (" << context << "): " << sslVerifyResult);
 
-                errno = last_errno; // Restore errno before throwing.
-                throw std::runtime_error(msg);
+                last_errno = last_errno ? last_errno : EPIPE; // Set errno if unset.
+                return 0; // EOF.
             }
             break;
         }
 
-        errno = last_errno; // Restore errno.
         return rc;
     }