net: add DnsRRResovler to fetch arbitary DNS resource types.

net/base/dnsrr_resolver.cc

+// 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.
+
+#include "net/base/dnsrr_resolver.h"
+
+#if defined(OS_LINUX)
+#include <resolv.h>
+#endif
+
+#include "base/string_piece.h"
+#include "base/task.h"
+#include "base/worker_pool.h"
+#include "net/base/dns_reload_timer.h"
+#include "net/base/dns_util.h"
+#include "net/base/net_errors.h"
+
+namespace net {
+
+static const uint16 kClassIN = 1;
+
+#if defined(OS_LINUX)
+
+// A Buffer is used for walking over a DNS packet.
+class Buffer {
+ public:
+  Buffer(const uint8* p, unsigned len)
+      : p_(p),
+        packet_(p),
+        len_(len),
+        packet_len_(len) {
+  }
+
+  bool U8(uint8* v) {
+    if (len_ < 1)
+      return false;
+    *v = *p_;
+    p_++;
+    len_--;
+    return true;
+  }
+
+  bool U16(uint16* v) {
+    if (len_ < 2)
+      return false;
+    *v = static_cast<uint16>(p_[0]) << 8 |
+         static_cast<uint16>(p_[1]);
+    p_ += 2;
+    len_ -= 2;
+    return true;
+  }
+
+  bool U32(uint32* v) {
+    if (len_ < 4)
+      return false;
+    *v = static_cast<uint32>(p_[0]) << 24 |
+         static_cast<uint32>(p_[1]) << 16 |
+         static_cast<uint32>(p_[2]) << 8 |
+         static_cast<uint32>(p_[3]);
+    p_ += 4;
+    len_ -= 4;
+    return true;
+  }
+
+  bool Skip(unsigned n) {
+    if (len_ < n)
+      return false;
+    p_ += n;
+    len_ -= n;
+    return true;
+  }
+
+  bool Block(base::StringPiece* out, unsigned len) {
+    if (len_ < len)
+      return false;
+    *out = base::StringPiece(reinterpret_cast<const char*>(p_), len);
+    p_ += len;
+    len_ -= len;
+    return true;
+  }
+
+  // DNSName parses a (possibly compressed) DNS name from the packet. If |name|
+  // is not NULL, then the name is written into it. See RFC 1035 section 4.1.4.
+  bool DNSName(std::string* name) {
+    unsigned jumps = 0;
+    const uint8* p = p_;
+    unsigned len = len_;
+
+    if (name)
+      name->clear();
+
+    for (;;) {
+      if (len < 1)
+        return false;
+      uint8 d = *p;

[Mike Belshe, 2010/08/02 14:18:28]

nit: I hate all these 1 char variable names!

+      p++;
+      len--;
+
+      if ((d & 0xc0) == 0xc0) {

[Mike Belshe, 2010/08/02 14:18:28]

I'm sure 0xc0 is a mask of some sort; for those not intimately aware of the
protocol, it's not readable :-(

+        if (jumps > 100)

[Mike Belshe, 2010/08/02 14:18:28]

100 is a hardcoded limit for ???

+          return false;
+        if (len < 1)
+          return false;
+        uint16 offset = static_cast<uint16>(d) << 8 |
+                        static_cast<uint16>(p[0]);
+        offset &= 0x3ff;
+        p++;
+        len--;
+
+        if (jumps == 0) {
+          p_ = p;
+          len_ = len;
+        }
+        jumps++;
+
+        if (offset >= packet_len_)
+          return false;
+        p = &packet_[offset];
+      } else if ((d & 0xc0) == 0) {
+        uint8 label_len = d;
+        if (len < label_len)
+          return false;
+        if (name && label_len) {
+          if (!name->empty())
+            name->append(".");
+          name->append(reinterpret_cast<const char*>(p), label_len);
+        }
+        p += label_len;
+        len -= label_len;
+
+        if (jumps == 0) {
+          p_ = p;
+          len_ = len;
+        }
+
+        if (label_len == 0)
+          break;
+      } else {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+ private:
+  const uint8* p_;
+  const uint8* const packet_;
+  unsigned len_;
+  const unsigned packet_len_;
+};
+
+bool DnsRRResolver::Response::ParseFromResponse(const uint8* p, unsigned len,
+                                                uint16 rrtype_requested) {
+  name.clear();
+  ttl = 0;
+  dnssec = false;
+  rrdatas.clear();
+  signatures.clear();
+
+  // RFC 1035 section 4.4.1
+  uint8 flags2;
+  Buffer buf(p, len);
+  if (!buf.Skip(2) ||  // skip id
+      !buf.Skip(1) ||  // skip first flags byte
+      !buf.U8(&flags2)) {
+    return false;
+  }
+
+  // Bit 5 is the Authenticated Data (AD) bit. See
+  // http://tools.ietf.org/html/rfc2535#section-6.1
+  if (flags2 & 32) {
+    // AD flag is set. We'll trust it if it came from a local nameserver.
+    if (_res.nscount == 1 &&
+        memcmp(&_res.nsaddr_list[0].sin_addr,
+               "\x7f\x00\x00\x01" /* 127.0.0.1 */, 4) == 0) {

[Mike Belshe, 2010/08/02 14:18:28]

Is there any ipv6 issue here?  Maybe a TODO

+      dnssec = true;
+    }
+  }
+
+  uint16 query_count, answer_count, authority_count, additional_count;
+  if (!buf.U16(&query_count) ||
+      !buf.U16(&answer_count) ||
+      !buf.U16(&authority_count) ||
+      !buf.U16(&additional_count)) {
+    return false;
+  }
+
+  if (query_count != 1)
+    return false;
+
+  uint16 type, klass;
+  if (!buf.DNSName(NULL) ||
+      !buf.U16(&type) ||
+      !buf.U16(&klass) ||
+      type != rrtype_requested ||
+      klass != kClassIN) {
+    return false;
+  }
+
+  if (answer_count < 1)
+    return false;
+
+  for (uint32 i = 0; i < answer_count; i++) {
+    std::string* name = NULL;
+    if (i == 0)
+      name = &this->name;
+    uint32 ttl;
+    uint16 rrdata_len;
+    if (!buf.DNSName(name) ||
+        !buf.U16(&type) ||
+        !buf.U16(&klass) ||
+        !buf.U32(&ttl) ||
+        !buf.U16(&rrdata_len)) {
+      return false;
+    }
+
+    base::StringPiece rrdata;
+    if (!buf.Block(&rrdata, rrdata_len))
+      return false;
+
+    if (klass == kClassIN && type == rrtype_requested) {
+      if (i == 0)
+        this->ttl = ttl;
+      rrdatas.push_back(std::string(rrdata.data(), rrdata.size()));
+    } else if (klass == kClassIN && type == kDNS_RRSIG) {
+      signatures.push_back(std::string(rrdata.data(), rrdata.size()));
+    }
+  }
+
+  return true;
+}
+
+class ResolveTask : public Task {
+ public:
+  ResolveTask(const std::string& name, uint16 rrtype,
+              uint16 flags, CompletionCallback* callback,
+              DnsRRResolver::Response* response)
+      : name_(name),
+        rrtype_(rrtype),
+        flags_(flags),
+        callback_(callback),
+        response_(response) {
+  }
+
+  virtual void Run() {
+    // Runs on a worker thread.
+
+    if ((_res.options & RES_INIT) == 0) {
+      if (res_ninit(&_res) != 0)
+        return Failure();
+    }
+
+    unsigned long saved_options = _res.options;
+    bool r = Do();
+    if (!r && DnsReloadTimerHasExpired()) {
+      res_nclose(&_res);
+      if (res_ninit(&_res) == 0)
+        r = Do();
+    }
+    _res.options = saved_options;
+    int error = r ? OK : ERR_NAME_NOT_RESOLVED;
+    callback_->Run(error);
+  }
+
+  bool Do() {
+    // For DNSSEC, a 4K buffer is suggested
+    static const unsigned kMaxDNSPayload = 4096;
+
+    // We set the options explicitly. Note that this removes several default
+    // options: RES_DEFNAMES and RES_DNSRCH (see res_init(3)).
+    _res.options = RES_INIT | RES_RECURSE | RES_USE_EDNS0 | RES_USE_DNSSEC;
+    uint8 answer[kMaxDNSPayload];
+    int len = res_search(name_.c_str(), kClassIN, rrtype_, answer,
+                         sizeof(answer));
+    if (len == -1)
+      return false;
+
+    return response_->ParseFromResponse(answer, len, rrtype_);
+  }
+
+ private:
+  void Failure() {
+    callback_->Run(ERR_NAME_NOT_RESOLVED);
+  }
+
+  const std::string name_;
+  const uint16 rrtype_;
+  const uint16 flags_;
+  CompletionCallback* const callback_;
+  DnsRRResolver::Response* const response_;
+};
+#else  // OS_LINUX
+// On non-Linux platforms we fail everything for now.
+class ResolveTask {
+ public:
+  ResolveTask(const std::string& name, uint16 rrtype,
+              uint16 flags, CompletionCallback* callback,
+              Response* response) {
+  }
+
+  virtual void Run() {
+    callback_->Run(ERR_NAME_NOT_RESOLVED);
+  }
+};
+#endif
+
+// static
+bool DnsRRResolver::Resolve(const std::string& name, uint16 rrtype,
+                            uint16 flags, CompletionCallback* callback,
+                            Response* response) {
+  if (!callback || !response || name.empty())
+    return false;
+
+  // Don't allow queries of type ANY
+  if (rrtype == kDNS_ANY)
+    return false;
+
+  ResolveTask* task = new ResolveTask(name, rrtype, flags, callback, response);
+
+  return WorkerPool::PostTask(FROM_HERE, task, true /* task is slow */);
+}
+
+}  // namespace net