net: add DnsRRResovler to fetch arbitary DNS resource types.

net/base/dnsrr_resolver.h

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_DNSRR_RESOLVER_H_
+#define NET_BASE_DNSRR_RESOLVER_H_
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "build/build_config.h"
+#include "net/base/completion_callback.h"
+
+namespace net {
+
+// DnsRRResolver resolves arbitary DNS resource record types. It should not be
+// confused with HostResolver and should not be used to resolve A/AAAA records.
+//
+// HostResolver exists to lookup addresses and there are many details about
+// address resolution over and above DNS (i.e. Bonjour, VPNs etc).
+//
+// DnsRRResolver should only be used when the data is specifically DNS data and
+// the name is a fully qualified DNS domain.
+class DnsRRResolver {
+ public:
+  // Response contains the details of a successful request.
+  struct Response {
+    // name contains the canonical name of the resulting domain. If the queried
+    // name was a CNAME then this can differ.
+    std::string name;
+    // ttl contains the TTL of the resource records.
+    uint32 ttl;
+    // dnssec is true if the response was DNSSEC validated.
+    bool dnssec;
+    std::vector<std::string> rrdatas;
+    // sigs contains the RRSIG records returned.
+    std::vector<std::string> signatures;
+
+    // For testing only
+    bool ParseFromResponse(const uint8* data, unsigned len,
+                           uint16 rrtype_requested);
+  };
+
+  enum {
+    // Try harder to get a DNSSEC signed response. This doesn't mean that the
+    // Response will always have the dnssec bit set.
+    FLAG_WANT_DNSSEC = 1,
+  };
+
+  // Resolve starts the resolution process. When complete, |callback| is called
+  // with a result. If the result is |OK| then |response| is filled with the
+  // result of the resolution. Note the |callback| is called from a random
+  // worker thread.
+  static bool Resolve(const std::string& name, uint16 rrtype,
+                      uint16 flags, CompletionCallback* callback,
+                      Response* response);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DnsRRResolver);
+};
+
+}  // namespace net
+
+#endif // NET_BASE_DNSRR_RESOLVER_H_