[master] Merge branch 'trac5216'

src/lib/asiodns/io_fetch.cc

@@ -1,4 +1,4 @@
-// Copyright (C) 2011-2016 Internet Systems Consortium, Inc. ("ISC")
+// Copyright (C) 2011-2017 Internet Systems Consortium, Inc. ("ISC")
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -232,7 +232,11 @@ IOFetch::operator()(boost::system::error_code ec, size_t length) {
 
     if (data_->stopped) {
         return;
-    } else if (ec) {
+
+    // On Debian it has been often observed that boost::asio async
+    // operations result in EINPROGRESS. This doesn't neccessarily
+    // indicate an issue. Thus, we continue as if no error occurred.
+    } else if (ec && (ec.value() != boost::asio::error::in_progress)) {
         logIOFailure(ec);
         return;
     }