Refactorings surrounding HostResolver:

(1) Extract HostResolver to an interface.

The existing concrete implementation is now named HostResolverImpl. This makes it possible to create mocks with more complex behavior (i.e. choose via rules if response will be sync vs async).

(2) Transform HostMapper into HostResolverProc.

Conceptually HostResolverProc maps a hostname to a socket address, whereas HostMapper mapped a hostname to another hostname (so you were still at the mercy of the system's host resolver). With HostResolverProc you can specify the exact AddressList, making it possible to run tests requiring IPv6 socketaddrs on systems (like WinXP) that don't actually support it.

(3) Add a MockHostResolver implementation of HostResolver.

This replaces the [ScopedHostMapper + RuleBasedHostMapper + HostResolver] combo. It is less clunky and a bit more expressive.

BUG=http://crbug.com/16452
R=willchan
TEST=existing

Review URL: http://codereview.chromium.org/149511

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@20795 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 180 insertions, 0 deletions

diff --git a/net/base/host_resolver_proc.cc b/net/base/host_resolver_proc.cc
new file mode 100644
index 0000000..585a33e
--- /dev/null
+++ b/net/base/host_resolver_proc.cc
@@ -0,0 +1,180 @@
+// Copyright (c) 2006-2008 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/host_resolver_proc.h"
+
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <ws2tcpip.h>
+#include <wspiapi.h>  // Needed for Win2k compat.
+#elif defined(OS_POSIX)
+#include <netdb.h>
+#include <sys/socket.h>
+#endif
+#if defined(OS_LINUX)
+#include <resolv.h>
+#endif
+
+#include "base/logging.h"
+#include "base/time.h"
+#include "net/base/address_list.h"
+#include "net/base/net_errors.h"
+
+#if defined(OS_LINUX)
+#include "base/singleton.h"
+#include "base/thread_local_storage.h"
+#endif
+
+namespace net {
+
+HostResolverProc* HostResolverProc::default_proc_ = NULL;
+
+HostResolverProc::HostResolverProc(HostResolverProc* previous) {
+  set_previous_proc(previous);
+
+  // Implicitly fall-back to the global default procedure.
+  if (!previous)
+    set_previous_proc(default_proc_);
+}
+
+// static
+HostResolverProc* HostResolverProc::SetDefault(HostResolverProc* proc) {
+  HostResolverProc* old = default_proc_;
+  default_proc_ = proc;
+  return old;
+}
+
+// static
+HostResolverProc* HostResolverProc::GetDefault() {
+  return default_proc_;
+}
+
+int HostResolverProc::ResolveUsingPrevious(const std::string& host,
+                                           AddressList* addrlist) {
+  if (previous_proc_)
+    return previous_proc_->Resolve(host, addrlist);
+
+  // Final fallback is the system resolver.
+  return SystemHostResolverProc(host, addrlist);
+}
+
+#if defined(OS_LINUX)
+// On Linux changes to /etc/resolv.conf can go unnoticed thus resulting in
+// DNS queries failing either because nameservers are unknown on startup
+// or because nameserver info has changed as a result of e.g. connecting to
+// a new network. Some distributions patch glibc to stat /etc/resolv.conf
+// to try to automatically detect such changes but these patches are not
+// universal and even patched systems such as Jaunty appear to need calls
+// to res_ninit to reload the nameserver information in different threads.
+//
+// We adopt the Mozilla solution here which is to call res_ninit when
+// lookups fail and to rate limit the reloading to once per second per
+// thread.
+
+// Keep a timer per calling thread to rate limit the calling of res_ninit.
+class DnsReloadTimer {
+ public:
+  DnsReloadTimer() {
+    tls_index_.Initialize(SlotReturnFunction);
+  }
+
+  ~DnsReloadTimer() { }
+
+  // Check if the timer for the calling thread has expired. When no
+  // timer exists for the calling thread, create one.
+  bool Expired() {
+    const base::TimeDelta kRetryTime = base::TimeDelta::FromSeconds(1);
+    base::TimeTicks now = base::TimeTicks::Now();
+    base::TimeTicks* timer_ptr =
+      static_cast<base::TimeTicks*>(tls_index_.Get());
+
+    if (!timer_ptr) {
+      timer_ptr = new base::TimeTicks();
+      *timer_ptr = base::TimeTicks::Now();
+      tls_index_.Set(timer_ptr);
+      // Return true to reload dns info on the first call for each thread.
+      return true;
+    } else if (now - *timer_ptr > kRetryTime) {
+      *timer_ptr = now;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  // Free the allocated timer.
+  static void SlotReturnFunction(void* data) {
+    base::TimeTicks* tls_data = static_cast<base::TimeTicks*>(data);
+    delete tls_data;
+  }
+
+ private:
+  // We use thread local storage to identify which base::TimeTicks to
+  // interact with.
+  static ThreadLocalStorage::Slot tls_index_ ;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsReloadTimer);
+};
+
+// A TLS slot to the TimeTicks for the current thread.
+// static
+ThreadLocalStorage::Slot DnsReloadTimer::tls_index_(base::LINKER_INITIALIZED);
+
+#endif  // defined(OS_LINUX)
+
+int SystemHostResolverProc(const std::string& host, AddressList* addrlist) {
+  struct addrinfo* ai = NULL;
+  struct addrinfo hints = {0};
+  hints.ai_family = AF_UNSPEC;
+
+#if defined(OS_WIN)
+  // DO NOT USE AI_ADDRCONFIG ON WINDOWS.
+  //
+  // The following comment in <winsock2.h> is the best documentation I found
+  // on AI_ADDRCONFIG for Windows:
+  //   Flags used in "hints" argument to getaddrinfo()
+  //       - AI_ADDRCONFIG is supported starting with Vista
+  //       - default is AI_ADDRCONFIG ON whether the flag is set or not
+  //         because the performance penalty in not having ADDRCONFIG in
+  //         the multi-protocol stack environment is severe;
+  //         this defaulting may be disabled by specifying the AI_ALL flag,
+  //         in that case AI_ADDRCONFIG must be EXPLICITLY specified to
+  //         enable ADDRCONFIG behavior
+  //
+  // Not only is AI_ADDRCONFIG unnecessary, but it can be harmful.  If the
+  // computer is not connected to a network, AI_ADDRCONFIG causes getaddrinfo
+  // to fail with WSANO_DATA (11004) for "localhost", probably because of the
+  // following note on AI_ADDRCONFIG in the MSDN getaddrinfo page:
+  //   The IPv4 or IPv6 loopback address is not considered a valid global
+  //   address.
+  // See http://crbug.com/5234.
+  hints.ai_flags = 0;
+#else
+  hints.ai_flags = AI_ADDRCONFIG;
+#endif
+
+  // Restrict result set to only this socket type to avoid duplicates.
+  hints.ai_socktype = SOCK_STREAM;
+
+  int err = getaddrinfo(host.c_str(), NULL, &hints, &ai);
+#if defined(OS_LINUX)
+  net::DnsReloadTimer* dns_timer = Singleton<net::DnsReloadTimer>::get();
+  // If we fail, re-initialise the resolver just in case there have been any
+  // changes to /etc/resolv.conf and retry. See http://crbug.com/11380 for info.
+  if (err && dns_timer->Expired()) {
+    res_nclose(&_res);
+    if (!res_ninit(&_res))
+      err = getaddrinfo(host.c_str(), NULL, &hints, &ai);
+  }
+#endif
+
+  if (err)
+    return ERR_NAME_NOT_RESOLVED;
+
+  addrlist->Adopt(ai);
+  return OK;
+}
+
+}  // namespace net