SERVER-31061 Add `mongo+srv://` support for URIs.

The shell now supports parsing and handling `mongo+srv://` style URIs,
as part of the DNS Seedlist support.  These URIs require DNS SRV and
TXT record lookups, for extra configuration options.  The shell also
supports a (limited) form of connection-failover -- when initially
connecting to a non-replica-set cluster, the shell will try each
host listed, in order, until a connection can be established.

1 files changed, 119 insertions, 0 deletions

diff --git a/src/mongo/util/dns_query.cpp b/src/mongo/util/dns_query.cpp
new file mode 100644
index 00000000000..9ce9e8743c6
--- /dev/null
+++ b/src/mongo/util/dns_query.cpp
@@ -0,0 +1,119 @@
+/**
+ *    Copyright (C) 2017 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/util/dns_query.h"
+
+#include <array>
+#include <cassert>
+#include <cstdint>
+#include <exception>
+#include <iostream>
+#include <memory>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <boost/noncopyable.hpp>
+
+// It is safe to include the implementation "headers" in an anonymous namespace, as the code is
+// meant to live in a single TU -- this one.  Include one of these headers last.
+#define MONGO_UTIL_DNS_QUERY_PLATFORM_INCLUDE_WHITELIST
+#ifdef WIN32
+#include "mongo/util/dns_query_windows-impl.h"
+#else
+#include "mongo/util/dns_query_posix-impl.h"
+#endif
+#undef MONGO_UTIL_DNS_QUERY_PLATFORM_INCLUDE_WHITELIST
+
+using std::begin;
+using std::end;
+using namespace std::literals::string_literals;
+
+namespace mongo {
+
+/**
+ * Returns a string with the IP address or domain name listed...
+ */
+std::vector<std::string> dns::lookupARecords(const std::string& service) {
+    DNSQueryState dnsQuery;
+    auto response = dnsQuery.lookup(service, DNSQueryClass::kInternet, DNSQueryType::kAddress);
+
+    if (response.size() == 0) {
+        throw DBException(ErrorCodes::DNSProtocolError,
+                          "Looking up " + service + " A record yielded no results.");
+    }
+
+    std::vector<std::string> rv;
+    std::transform(begin(response), end(response), back_inserter(rv), [](const auto& entry) {
+        return entry.addressEntry();
+    });
+
+    return rv;
+}
+
+std::vector<dns::SRVHostEntry> dns::lookupSRVRecords(const std::string& service) {
+    DNSQueryState dnsQuery;
+
+    auto response = dnsQuery.lookup(service, DNSQueryClass::kInternet, DNSQueryType::kSRV);
+
+    std::vector<SRVHostEntry> rv;
+
+    std::transform(begin(response), end(response), back_inserter(rv), [](const auto& entry) {
+        return entry.srvHostEntry();
+    });
+    return rv;
+}
+
+std::vector<std::string> dns::lookupTXTRecords(const std::string& service) {
+    DNSQueryState dnsQuery;
+
+    auto response = dnsQuery.lookup(service, DNSQueryClass::kInternet, DNSQueryType::kTXT);
+
+    std::vector<std::string> rv;
+
+    for (auto& entry : response) {
+        auto txtEntry = entry.txtEntry();
+        rv.insert(end(rv),
+                  std::make_move_iterator(begin(txtEntry)),
+                  std::make_move_iterator(end(txtEntry)));
+    }
+    return rv;
+}
+
+std::vector<std::string> dns::getTXTRecords(const std::string& service) try {
+    return lookupTXTRecords(service);
+} catch (const DBException& ex) {
+    if (ex.code() == ErrorCodes::DNSHostNotFound) {
+        return {};
+    }
+    throw;
+}
+}  // namespace mongo