// Copyright (c) 2012 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/proxy_resolution/dhcp_pac_file_fetcher_win.h"

#include <memory>
#include <vector>

#include "base/bind.h"
#include "base/bind_helpers.h"
#include "base/containers/queue.h"
#include "base/memory/free_deleter.h"
#include "base/synchronization/lock.h"
#include "base/task_runner.h"
#include "base/task_scheduler/post_task.h"
#include "base/threading/scoped_blocking_call.h"
#include "net/base/net_errors.h"
#include "net/proxy_resolution/dhcp_pac_file_adapter_fetcher_win.h"

#include <winsock2.h>
#include <iphlpapi.h>

namespace {

// Maximum number of DHCP lookup tasks running concurrently. This is chosen
// based on the following UMA data:
// - When OnWaitTimer fires, ~99.8% of users have 6 or fewer network
//   adapters enabled for DHCP in total.
// - At the same measurement point, ~99.7% of users have 3 or fewer pending
//   DHCP adapter lookups.
// - There is however a very long and thin tail of users who have
//   systems reporting up to 100+ adapters (this must be some very weird
//   OS bug (?), probably the cause of http://crbug.com/240034).
//
// Th value is chosen such that DHCP lookup tasks don't prevent other tasks from
// running even on systems that report a huge number of network adapters, while
// giving a good chance of getting back results for any responsive adapters.
constexpr int kMaxConcurrentDhcpLookupTasks = 12;

// How long to wait at maximum after we get results (a PAC file or
// knowledge that no PAC file is configured) from whichever network
// adapter finishes first.
constexpr base::TimeDelta kMaxWaitAfterFirstResult =
    base::TimeDelta::FromMilliseconds(400);

// A TaskRunner that never schedules more than |kMaxConcurrentDhcpLookupTasks|
// tasks concurrently.
class TaskRunnerWithCap : public base::TaskRunner {
 public:
  TaskRunnerWithCap() = default;

  bool PostDelayedTask(const base::Location& from_here,
                       base::OnceClosure task,
                       base::TimeDelta delay) override {
    // Delayed tasks are not supported.
    DCHECK(delay.is_zero());

    // Wrap the task in a callback that runs |task|, then tries to schedule a
    // task from |pending_tasks_|.
    base::OnceClosure wrapped_task =
        base::BindOnce(&TaskRunnerWithCap::RunTaskAndSchedulePendingTask, this,
                       std::move(task));

    {
      base::AutoLock auto_lock(lock_);

      // If |kMaxConcurrentDhcpLookupTasks| tasks are scheduled, move the task
      // to |pending_tasks_|.
      DCHECK_LE(num_scheduled_tasks_, kMaxConcurrentDhcpLookupTasks);
      if (num_scheduled_tasks_ == kMaxConcurrentDhcpLookupTasks) {
        pending_tasks_.emplace(from_here, std::move(wrapped_task));
        return true;
      }

      // If less than |kMaxConcurrentDhcpLookupTasks| tasks are scheduled,
      // increment |num_scheduled_tasks_| and schedule the task.
      ++num_scheduled_tasks_;
    }

    task_runner_->PostTask(from_here, std::move(wrapped_task));
    return true;
  }

  bool RunsTasksInCurrentSequence() const override {
    return task_runner_->RunsTasksInCurrentSequence();
  }

 private:
  struct LocationAndTask {
    LocationAndTask() = default;
    LocationAndTask(const base::Location& from_here, base::OnceClosure task)
        : from_here(from_here), task(std::move(task)) {}
    base::Location from_here;
    base::OnceClosure task;
  };

  ~TaskRunnerWithCap() override = default;

  void RunTaskAndSchedulePendingTask(base::OnceClosure task) {
    // Run |task|.
    std::move(task).Run();

    // If |pending_tasks_| is non-empty, schedule a task from it. Otherwise,
    // decrement |num_scheduled_tasks_|.
    LocationAndTask task_to_schedule;

    {
      base::AutoLock auto_lock(lock_);

      DCHECK_GT(num_scheduled_tasks_, 0);
      if (pending_tasks_.empty()) {
        --num_scheduled_tasks_;
        return;
      }

      task_to_schedule = std::move(pending_tasks_.front());
      pending_tasks_.pop();
    }

    DCHECK(task_to_schedule.task);
    task_runner_->PostTask(task_to_schedule.from_here,
                           std::move(task_to_schedule.task));
  }

  const scoped_refptr<base::TaskRunner> task_runner_ =
      base::CreateTaskRunnerWithTraits(
          {base::MayBlock(), base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN,
           base::TaskPriority::USER_VISIBLE});

  // Synchronizes access to members below.
  base::Lock lock_;

  // Number of tasks that are currently scheduled.
  int num_scheduled_tasks_ = 0;

  // Tasks that are waiting to be scheduled.
  base::queue<LocationAndTask> pending_tasks_;

  DISALLOW_COPY_AND_ASSIGN(TaskRunnerWithCap);
};

}  // namespace

namespace net {

DhcpProxyScriptFetcherWin::DhcpProxyScriptFetcherWin(
    URLRequestContext* url_request_context)
    : state_(STATE_START),
      num_pending_fetchers_(0),
      destination_string_(NULL),
      url_request_context_(url_request_context),
      task_runner_(base::MakeRefCounted<TaskRunnerWithCap>()) {
  DCHECK(url_request_context_);
}

DhcpProxyScriptFetcherWin::~DhcpProxyScriptFetcherWin() {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  // Count as user-initiated if we are not yet in STATE_DONE.
  Cancel();
}

int DhcpProxyScriptFetcherWin::Fetch(base::string16* utf16_text,
                                     const CompletionCallback& callback) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  if (state_ != STATE_START && state_ != STATE_DONE) {
    NOTREACHED();
    return ERR_UNEXPECTED;
  }

  if (!url_request_context_)
    return ERR_CONTEXT_SHUT_DOWN;

  state_ = STATE_WAIT_ADAPTERS;
  callback_ = callback;
  destination_string_ = utf16_text;

  last_query_ = ImplCreateAdapterQuery();
  task_runner_->PostTaskAndReply(
      FROM_HERE,
      base::Bind(
          &DhcpProxyScriptFetcherWin::AdapterQuery::GetCandidateAdapterNames,
          last_query_.get()),
      base::Bind(&DhcpProxyScriptFetcherWin::OnGetCandidateAdapterNamesDone,
                 AsWeakPtr(), last_query_));

  return ERR_IO_PENDING;
}

void DhcpProxyScriptFetcherWin::Cancel() {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  CancelImpl();
}

void DhcpProxyScriptFetcherWin::OnShutdown() {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  // Back up callback, if there is one, as CancelImpl() will destroy it.
  net::CompletionCallback callback = std::move(callback_);

  // Cancel current request, if there is one.
  CancelImpl();

  // Prevent future network requests.
  url_request_context_ = nullptr;

  // Invoke callback with error, if present.
  if (callback)
    callback.Run(ERR_CONTEXT_SHUT_DOWN);
}

void DhcpProxyScriptFetcherWin::CancelImpl() {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  if (state_ != STATE_DONE) {
    callback_.Reset();
    wait_timer_.Stop();
    state_ = STATE_DONE;

    for (FetcherVector::iterator it = fetchers_.begin();
         it != fetchers_.end();
         ++it) {
      (*it)->Cancel();
    }

    fetchers_.clear();
  }
}

void DhcpProxyScriptFetcherWin::OnGetCandidateAdapterNamesDone(
    scoped_refptr<AdapterQuery> query) {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);

  // This can happen if this object is reused for multiple queries,
  // and a previous query was cancelled before it completed.
  if (query.get() != last_query_.get())
    return;
  last_query_ = NULL;

  // Enable unit tests to wait for this to happen; in production this function
  // call is a no-op.
  ImplOnGetCandidateAdapterNamesDone();

  // We may have been cancelled.
  if (state_ != STATE_WAIT_ADAPTERS)
    return;

  state_ = STATE_NO_RESULTS;

  const std::set<std::string>& adapter_names = query->adapter_names();

  if (adapter_names.empty()) {
    TransitionToDone();
    return;
  }

  for (std::set<std::string>::const_iterator it = adapter_names.begin();
       it != adapter_names.end();
       ++it) {
    std::unique_ptr<DhcpProxyScriptAdapterFetcher> fetcher(
        ImplCreateAdapterFetcher());
    fetcher->Fetch(
        *it, base::Bind(&DhcpProxyScriptFetcherWin::OnFetcherDone,
                        base::Unretained(this)));
    fetchers_.push_back(std::move(fetcher));
  }
  num_pending_fetchers_ = fetchers_.size();
}

std::string DhcpProxyScriptFetcherWin::GetFetcherName() const {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  return "win";
}

const GURL& DhcpProxyScriptFetcherWin::GetPacURL() const {
  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
  DCHECK_EQ(state_, STATE_DONE);

  return pac_url_;
}

void DhcpProxyScriptFetcherWin::OnFetcherDone(int result) {
  DCHECK(state_ == STATE_NO_RESULTS || state_ == STATE_SOME_RESULTS);

  if (--num_pending_fetchers_ == 0) {
    TransitionToDone();
    return;
  }

  // If the only pending adapters are those less preferred than one
  // with a valid PAC script, we do not need to wait any longer.
  for (FetcherVector::iterator it = fetchers_.begin();
       it != fetchers_.end();
       ++it) {
    bool did_finish = (*it)->DidFinish();
    int result = (*it)->GetResult();
    if (did_finish && result == OK) {
      TransitionToDone();
      return;
    }
    if (!did_finish || result != ERR_PAC_NOT_IN_DHCP) {
      break;
    }
  }

  // Once we have a single result, we set a maximum on how long to wait
  // for the rest of the results.
  if (state_ == STATE_NO_RESULTS) {
    state_ = STATE_SOME_RESULTS;
    wait_timer_.Start(FROM_HERE,
        ImplGetMaxWait(), this, &DhcpProxyScriptFetcherWin::OnWaitTimer);
  }
}

void DhcpProxyScriptFetcherWin::OnWaitTimer() {
  DCHECK_EQ(state_, STATE_SOME_RESULTS);

  TransitionToDone();
}

void DhcpProxyScriptFetcherWin::TransitionToDone() {
  DCHECK(state_ == STATE_NO_RESULTS || state_ == STATE_SOME_RESULTS);

  int result = ERR_PAC_NOT_IN_DHCP;  // Default if no fetchers.
  if (!fetchers_.empty()) {
    // Scan twice for the result; once through the whole list for success,
    // then if no success, return result for most preferred network adapter,
    // preferring "real" network errors to the ERR_PAC_NOT_IN_DHCP error.
    // Default to ERR_ABORTED if no fetcher completed.
    result = ERR_ABORTED;
    for (FetcherVector::iterator it = fetchers_.begin();
         it != fetchers_.end();
         ++it) {
      if ((*it)->DidFinish() && (*it)->GetResult() == OK) {
        result = OK;
        *destination_string_ = (*it)->GetPacScript();
        pac_url_ = (*it)->GetPacURL();
        break;
      }
    }
    if (result != OK) {
      destination_string_->clear();
      for (FetcherVector::iterator it = fetchers_.begin();
           it != fetchers_.end();
           ++it) {
        if ((*it)->DidFinish()) {
          result = (*it)->GetResult();
          if (result != ERR_PAC_NOT_IN_DHCP) {
            break;
          }
        }
      }
    }
  }

  CompletionCallback callback = callback_;
  CancelImpl();
  DCHECK_EQ(state_, STATE_DONE);
  DCHECK(fetchers_.empty());
  DCHECK(callback_.is_null());  // Invariant of data.

  // We may be deleted re-entrantly within this outcall.
  callback.Run(result);
}

int DhcpProxyScriptFetcherWin::num_pending_fetchers() const {
  return num_pending_fetchers_;
}

URLRequestContext* DhcpProxyScriptFetcherWin::url_request_context() const {
  return url_request_context_;
}

scoped_refptr<base::TaskRunner> DhcpProxyScriptFetcherWin::GetTaskRunner() {
  return task_runner_;
}

DhcpProxyScriptAdapterFetcher*
    DhcpProxyScriptFetcherWin::ImplCreateAdapterFetcher() {
  return new DhcpProxyScriptAdapterFetcher(url_request_context_, task_runner_);
}

DhcpProxyScriptFetcherWin::AdapterQuery*
    DhcpProxyScriptFetcherWin::ImplCreateAdapterQuery() {
  return new AdapterQuery();
}

base::TimeDelta DhcpProxyScriptFetcherWin::ImplGetMaxWait() {
  return kMaxWaitAfterFirstResult;
}

bool DhcpProxyScriptFetcherWin::GetCandidateAdapterNames(
    std::set<std::string>* adapter_names) {
  DCHECK(adapter_names);
  adapter_names->clear();

  // The GetAdaptersAddresses MSDN page recommends using a size of 15000 to
  // avoid reallocation.
  ULONG adapters_size = 15000;
  std::unique_ptr<IP_ADAPTER_ADDRESSES, base::FreeDeleter> adapters;
  ULONG error = ERROR_SUCCESS;
  int num_tries = 0;

  do {
    adapters.reset(static_cast<IP_ADAPTER_ADDRESSES*>(malloc(adapters_size)));
    // Return only unicast addresses, and skip information we do not need.
    base::ScopedBlockingCall scoped_blocking_call(
        base::BlockingType::MAY_BLOCK);
    error = GetAdaptersAddresses(AF_UNSPEC,
                                 GAA_FLAG_SKIP_ANYCAST |
                                 GAA_FLAG_SKIP_MULTICAST |
                                 GAA_FLAG_SKIP_DNS_SERVER |
                                 GAA_FLAG_SKIP_FRIENDLY_NAME,
                                 NULL,
                                 adapters.get(),
                                 &adapters_size);
    ++num_tries;
  } while (error == ERROR_BUFFER_OVERFLOW && num_tries <= 3);

  if (error == ERROR_NO_DATA) {
    // There are no adapters that we care about.
    return true;
  }

  if (error != ERROR_SUCCESS) {
    LOG(WARNING) << "Unexpected error retrieving WPAD configuration from DHCP.";
    return false;
  }

  IP_ADAPTER_ADDRESSES* adapter = NULL;
  for (adapter = adapters.get(); adapter; adapter = adapter->Next) {
    if (adapter->IfType == IF_TYPE_SOFTWARE_LOOPBACK)
      continue;
    if ((adapter->Flags & IP_ADAPTER_DHCP_ENABLED) == 0)
      continue;

    DCHECK(adapter->AdapterName);
    adapter_names->insert(adapter->AdapterName);
  }

  return true;
}

DhcpProxyScriptFetcherWin::AdapterQuery::AdapterQuery() {
}

void DhcpProxyScriptFetcherWin::AdapterQuery::GetCandidateAdapterNames() {
  ImplGetCandidateAdapterNames(&adapter_names_);
}

const std::set<std::string>&
    DhcpProxyScriptFetcherWin::AdapterQuery::adapter_names() const {
  return adapter_names_;
}

bool DhcpProxyScriptFetcherWin::AdapterQuery::ImplGetCandidateAdapterNames(
    std::set<std::string>* adapter_names) {
  return DhcpProxyScriptFetcherWin::GetCandidateAdapterNames(adapter_names);
}

DhcpProxyScriptFetcherWin::AdapterQuery::~AdapterQuery() {
}

}  // namespace net