Added DnsQuery class

net/base/dns_response.cc

+// Copyright (c) 2011 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.
+
+#include "net/base/dns_response.h"
+
+#include <netdb.h>            // for EAI_NONAME
+
+#include "net/base/address_list.h"
+#include "net/base/dns_util.h"
+
+namespace net {
+
+// RFC 1035, section 4.2.1: Messages carried by UDP are restricted to 512

[agl, 2011/05/30 18:35:30]

This is no longer true. The current recommendation is that clients SHOULD be
able to cope with 4K replies I believe.

[agayev, 2011/05/31 15:19:06]

Right.  I was thinking of adding EDNS0 support in another iteration to keep this
CL limited to RFC1035.

+// bytes (not counting the IP nor UDP headers).
+static const int kMaxResponseSize = 512;
+
+// TODO(agayev): decide on |error_|, should we emulate getaddrinfo error
+// messages and continue with net_error and os_error scheme or should we
+// define more net_error codes and get rid of os_error, since there is no
+// "OS" anymore.  Currently, |error_| is EAI_NONAME in case of an error, 0
+// otherwise.
+DnsResponse::DnsResponse(DnsQuery* query)
+    : error_(EAI_NONAME),
+      size_(kMaxResponseSize + 1),
+      query_(query),
+      io_buffer_(new IOBufferWithSize(size_)) {
+}
+
+bool DnsResponse::Parse(int nbytes, AddressList* results) {
+  DCHECK(query_->IsValid());
+
+  // Response includes query, it should be at least that size.
+  if (nbytes < query_->size() || nbytes > kMaxResponseSize)
+    return false;
+
+  size_ = nbytes;
+  DnsResponseBuffer response(reinterpret_cast<uint8*>(io_buffer_->data()),
+                             size_);
+
+  uint16 id;
+  if (!response.U16(&id) || id != query_->id()) // Make sure IDs match.
+    return false;
+
+  uint8 flags, rcode;
+  if (!response.U8(&flags) || !response.U8(&rcode))
+    return false;
+
+  if (flags & 2) // TC is set -- server wants TCP, we don't support it (yet?).
+    return false;
+
+  rcode &= 0x0f;
+  if (rcode && (rcode != 3)) // 3 means NXDOMAIN, the rest means server failed.
+    return false;
+
+  uint16 query_count, answer_count, authority_count, additional_count;
+  if (!response.U16(&query_count) ||
+      !response.U16(&answer_count) ||
+      !response.U16(&authority_count) ||
+      !response.U16(&additional_count))

[agl, 2011/05/30 18:35:30]

{ } around the body if the conditional is multi-line. (I'm not sure if it's a
style rule, so you can ignore this if you like.)

[agayev, 2011/05/31 15:19:06]

Will do.

+    return false;
+
+  if (query_count != 1) // Sent a single question, shouldn't have changed.
+    return false;
+
+  std::string hostname;
+  uint16 qtype, qclass;
+  if (!response.DNSName(&hostname) ||
+      !response.U16(&qtype) ||
+      !response.U16(&qclass) ||
+      hostname != query_->hostname() || // Make sure Question section
+      qtype != query_->qtype() ||       // echoed back.
+      qclass != query_->qclass())
+    return false;

[agl, 2011/05/30 18:35:30]

ditto

[agayev, 2011/05/31 15:19:06]

Will do.

+
+  if (answer_count < 1)

[agl, 2011/05/30 18:35:30]

This isn't a parse error of course. I feel that you would need to distinguish
error codes from this function into multiple families:
  * Invalid packet (dispatcher can stop processing)
  * Not for me (dispatcher can try to match against other outstanding requests)
  * For me, but I couldn't get a useful answer (SERVFAIL, NXDOMAIN, no records
etc)

[agayev, 2011/05/31 15:19:06]

Thanks for these.  As I've written in the comment on line 18, I need to decide
whether I should add more ERR_* codes or continue with the existing
host_resolver_proc method of reflecting back getaddrinfo errors, so will do.

+    return false;
+
+  std::vector<IPAddressNumber> rdatas;
+  while (answer_count--) {
+    uint32 ttl;
+    uint16 rdlength;
+    if (!response.DNSName(NULL) ||
+        !response.U16(&qtype) ||
+        !response.U16(&qclass) ||
+        !response.U32(&ttl) ||
+        !response.U16(&rdlength))
+      return false;

[agl, 2011/05/30 18:35:30]

ditto

[agayev, 2011/05/31 15:19:06]

Will do.

+
+    if (qtype == query_->qtype() &&
+        qclass == query_->qclass() &&
+        (rdlength == kIPv4AddressSize || rdlength == kIPv6AddressSize)) {
+      base::StringPiece rdata;
+      if (!response.Block(&rdata, rdlength))
+        return false;
+      rdatas.push_back(IPAddressNumber(rdata.begin(), rdata.end()));
+    } else if (!response.Skip(rdlength))
+      return false;
+  }
+
+  if (rdatas.empty())
+    return false;
+
+  *results = AddressList::CreateFromIPAddressList(rdatas, query_->port());
+  error_ = 0;
+  return true;
+}
+
+}  // namespace net