Isolates generic DnsClient from AsyncHostResolver.

net/dns/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/dns/dns_response.h"
 
-#include "net/base/dns_util.h"
+#include "net/base/big_endian.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
+#include "net/base/sys_byteorder.h"
+#include "net/dns/dns_protocol.h"
 #include "net/dns/dns_query.h"
 
 namespace net {
 
-// RFC 1035, section 4.2.1: Messages carried by UDP are restricted to 512
-// bytes (not counting the IP nor UDP headers).
-static const int kMaxResponseSize = 512;
+DnsRecordParser::DnsRecordParser() : packet_(NULL), length_(0), cur_(0) {
+}
 
-DnsResponse::DnsResponse(DnsQuery* query)
-    : query_(query),
-      io_buffer_(new IOBufferWithSize(kMaxResponseSize + 1)) {
-  DCHECK(query_);
+DnsRecordParser::DnsRecordParser(const void* packet,
+                                 size_t length,
+                                 size_t offset)
+    : packet_(reinterpret_cast<const char*>(packet)),
+      length_(length),
+      cur_(packet_ + offset) {
+  DCHECK(offset <= length);

[mmenke, 2011/12/06 20:43:01]

nit:  Use DCHECK_LE here and in ParseName, where applicable.

[szym, 2011/12/06 21:06:43]

Done.

+}
+
+int DnsRecordParser::ParseName(const void* const vpos, std::string* out) const {
+  const char* const pos = reinterpret_cast<const char*>(vpos);
+  DCHECK(packet_);
+  DCHECK(packet_ <= pos);
+  DCHECK(pos <= packet_ + length_);
+
+  const char* p = pos;
+  const char* end = packet_ + length_;
+  // Count number of seen bytes to detect loops.
+  size_t seen = 0;
+  // Remember how many bytes were consumed before first jump.
+  size_t consumed = 0;
+
+  if (pos >= end)
+    return 0;
+
+  if (out) {
+    out->clear();
+    out->reserve(dns_protocol::kMaxNameLength);
+  }
+
+  for (;;) {
+    // The two couple of bits of the length give the type of the length. It's
+    // either a direct length or a pointer to the remainder of the name.
+    switch (*p & dns_protocol::kLabelMask) {
+      case dns_protocol::kLabelPointer: {
+        if (p + sizeof(uint16) > end)
+          return 0;
+        if (consumed == 0) {
+          consumed = p - pos + sizeof(uint16);
+          if (!out)
+            return consumed;  // If name is not stored, that's all we need.
+        }
+        seen += sizeof(uint16);
+        // If seen the whole packet, then we must be in a loop.
+        if (seen > length_)
+          return 0;
+        uint16 offset;
+        ReadBigEndian<uint16>(p, &offset);
+        offset &= dns_protocol::kOffsetMask;
+        p = packet_ + offset;
+        if (p >= end)
+          return 0;
+        break;
+      }
+      case dns_protocol::kLabelDirect: {
+        uint8 label_len = *p;
+        ++p;
+        // Note: root domain (".") is NOT included.
+        if (label_len == 0) {
+          if (consumed == 0) {
+            consumed = p - pos;
+          }  // else we set |consumed| before first jump
+          return consumed;
+        }
+        if (p + label_len >= end)
+          return 0;  // Truncated or missing label.
+        if (out) {
+          if (!out->empty())
+            out->append(".");
+          out->append(p, label_len);
+        }
+        p += label_len;
+        seen += 1 + label_len;
+        break;
+      }
+      default:
+        // unhandled label type
+        return 0;
+    }
+  }
+}
+
+bool DnsRecordParser::ParseRecord(DnsResourceRecord* out) {
+  DCHECK(packet_);
+  size_t consumed = ParseName(cur_, &out->name);
+  if (!consumed)
+    return false;
+  BigEndianReader reader(cur_ + consumed,
+                         packet_ + length_ - (cur_ + consumed));
+  uint16 rdlen;
+  if (reader.ReadU16(&out->type) &&
+      reader.ReadU16(&out->klass) &&
+      reader.ReadU32(&out->ttl) &&
+      reader.ReadU16(&rdlen) &&
+      reader.ReadPiece(&out->rdata, rdlen)) {
+    cur_ = reader.ptr();
+    return true;
+  }
+  return false;
+}
+
+DnsResponse::DnsResponse()
+    : io_buffer_(new IOBufferWithSize(dns_protocol::kMaxUDPSize + 1)) {
+}
+
+DnsResponse::DnsResponse(const void* data,
+                         size_t length,
+                         size_t answer_offset)
+    : io_buffer_(new IOBufferWithSize(length)),
+      parser_(io_buffer_->data(), length, answer_offset) {
+  memcpy(io_buffer_->data(), data, length);
 }
 
 DnsResponse::~DnsResponse() {
 }
 
-int DnsResponse::Parse(int nbytes, IPAddressList* ip_addresses) {
+bool DnsResponse::InitParse(int nbytes, const DnsQuery& query) {
   // Response includes query, it should be at least that size.
-  if (nbytes < query_->io_buffer()->size() || nbytes > kMaxResponseSize)
-    return ERR_DNS_MALFORMED_RESPONSE;
+  if (nbytes < query.io_buffer()->size() || nbytes > dns_protocol::kMaxUDPSize)
+    return false;
 
-  DnsResponseBuffer response(reinterpret_cast<uint8*>(io_buffer_->data()),
-                             io_buffer_->size());
-  uint16 id;
-  if (!response.U16(&id) || id != query_->id()) // Make sure IDs match.
-    return ERR_DNS_MALFORMED_RESPONSE;
+  // Match the query id.
+  if (ntohs(header()->id) != query.id())
+    return false;
 
-  uint8 flags, rcode;
-  if (!response.U8(&flags) || !response.U8(&rcode))
-    return ERR_DNS_MALFORMED_RESPONSE;
+  // Match question count.
+  if (ntohs(header()->qdcount) != 1)
+    return false;
 
-  if (flags & 2) // TC is set -- server wants TCP, we don't support it (yet?).
-    return ERR_DNS_SERVER_REQUIRES_TCP;
+  // Match the question section.
+  const size_t hdr_size = sizeof(dns_protocol::Header);
+  const base::StringPiece question = query.question();
+  if (question != base::StringPiece(io_buffer_->data() + hdr_size,
+                                    question.size()))

[mmenke, 2011/12/06 20:43:01]

nit:  Add parentheses.

[szym, 2011/12/06 21:06:43]

Done.

+    return false;
 
-  rcode &= 0x0f;         // 3 means NXDOMAIN, the rest means server failed.
-  if (rcode && (rcode != 3))
-    return ERR_DNS_SERVER_FAILED;
+  // Construct the parser.
+  parser_ = DnsRecordParser(io_buffer_->data(),
+                            nbytes,
+                            hdr_size + question.size());
+  return true;
+}
 
-  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)) {
-    return ERR_DNS_MALFORMED_RESPONSE;
-  }
+uint8 DnsResponse::flags0() const {
+  return header()->flags[0];
+}
 
-  if (query_count != 1) // Sent a single question, shouldn't have changed.
-    return ERR_DNS_MALFORMED_RESPONSE;
+uint8 DnsResponse::flags1() const {
+  return header()->flags[1] & ~(dns_protocol::kRcodeMask);
+}
 
-  base::StringPiece question; // Make sure question section is echoed back.
-  if (!response.Block(&question, query_->question_size()) ||
-      memcmp(question.data(), query_->question_data(),
-             query_->question_size())) {
-    return ERR_DNS_MALFORMED_RESPONSE;
-  }
+uint8 DnsResponse::rcode() const {
+  return header()->flags[1] & dns_protocol::kRcodeMask;
+}
 
-  if (answer_count < 1)
-    return ERR_NAME_NOT_RESOLVED;
+int DnsResponse::answer_count() const {
+  return ntohs(header()->ancount);
+}
 
-  IPAddressList rdatas;
-  while (answer_count--) {
-    uint32 ttl;
-    uint16 rdlength, qtype, qclass;
-    if (!response.DNSName(NULL) ||
-        !response.U16(&qtype) ||
-        !response.U16(&qclass) ||
-        !response.U32(&ttl) ||
-        !response.U16(&rdlength)) {
-      return ERR_DNS_MALFORMED_RESPONSE;
-    }
-    if (qtype == query_->qtype() &&
-        qclass == kClassIN &&
-        (rdlength == kIPv4AddressSize || rdlength == kIPv6AddressSize)) {
-      base::StringPiece rdata;
-      if (!response.Block(&rdata, rdlength))
-        return ERR_DNS_MALFORMED_RESPONSE;
-      rdatas.push_back(IPAddressNumber(rdata.begin(), rdata.end()));
-    } else if (!response.Skip(rdlength))
-      return ERR_DNS_MALFORMED_RESPONSE;
-  }
+DnsRecordParser DnsResponse::Parser() const {
+  DCHECK(parser_.IsValid());
+  return parser_;
+}
 
-  if (rdatas.empty())
-    return ERR_NAME_NOT_RESOLVED;
-
-  if (ip_addresses)
-    ip_addresses->swap(rdatas);
-  return OK;
+const dns_protocol::Header* DnsResponse::header() const {
+  return reinterpret_cast<const dns_protocol::Header*>(io_buffer_->data());
 }
 
 }  // namespace net