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// 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/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 {
DnsRecordParser::DnsRecordParser() : packet_(NULL), length_(0), cur_(0) {
}
DnsRecordParser::DnsRecordParser(const void* packet,
size_t length,
size_t offset)
: packet_(reinterpret_cast<const char*>(packet)),
length_(length),
cur_(packet_ + offset) {
DCHECK_LE(offset, length);
}
int DnsRecordParser::ParseName(const void* const vpos, std::string* out) const {
const char* const pos = reinterpret_cast<const char*>(vpos);
DCHECK(packet_);
DCHECK_LE(packet_, pos);
DCHECK_LE(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() {
}
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 > dns_protocol::kMaxUDPSize)
return false;
// Match the query id.
if (ntohs(header()->id) != query.id())
return false;
// Match question count.
if (ntohs(header()->qdcount) != 1)
return false;
// 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())) {
return false;
}
// Construct the parser.
parser_ = DnsRecordParser(io_buffer_->data(),
nbytes,
hdr_size + question.size());
return true;
}
uint8 DnsResponse::flags0() const {
return header()->flags[0];
}
uint8 DnsResponse::flags1() const {
return header()->flags[1] & ~(dns_protocol::kRcodeMask);
}
uint8 DnsResponse::rcode() const {
return header()->flags[1] & dns_protocol::kRcodeMask;
}
int DnsResponse::answer_count() const {
return ntohs(header()->ancount);
}
DnsRecordParser DnsResponse::Parser() const {
DCHECK(parser_.IsValid());
return parser_;
}
const dns_protocol::Header* DnsResponse::header() const {
return reinterpret_cast<const dns_protocol::Header*>(io_buffer_->data());
}
} // namespace net
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