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// 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.
#ifndef NET_BASE_HOST_RESOLVER_H_
#define NET_BASE_HOST_RESOLVER_H_
#include <string>
#include <vector>
#include "base/basictypes.h"
#include "base/lock.h"
#include "base/ref_counted.h"
#include "net/base/completion_callback.h"
#include "net/base/host_cache.h"
class MessageLoop;
namespace net {
class AddressList;
class HostMapper;
// This class represents the task of resolving hostnames (or IP address
// literal) to an AddressList object.
//
// HostResolver handles multiple requests at a time, so when cancelling a
// request the Request* handle that was returned by Resolve() needs to be
// given. A simpler alternative for consumers that only have 1 outstanding
// request at a time is to create a SingleRequestHostResolver wrapper around
// HostResolver (which will automatically cancel the single request when it
// goes out of scope).
//
// For each hostname that is requested, HostResolver creates a
// HostResolver::Job. This job gets dispatched to a thread in the global
// WorkerPool, where it runs "getaddrinfo(hostname)". If requests for that same
// host are made while the job is already outstanding, then they are attached
// to the existing job rather than creating a new one. This avoids doing
// parallel resolves for the same host.
//
// The way these classes fit together is illustrated by:
//
//
// +------------- HostResolver ---------------+
// | | |
// Job Job Job
// (for host1) (for host2) (for hostX)
// / | | / | | / | |
// Request ... Request Request ... Request Request ... Request
// (port1) (port2) (port3) (port4) (port5) (portX)
//
//
// When a HostResolver::Job finishes its work in the threadpool, the callbacks
// of each waiting request are run on the origin thread.
//
// Thread safety: This class is not threadsafe, and must only be called
// from one thread!
//
class HostResolver {
public:
// Creates a HostResolver that caches up to |max_cache_entries| for
// |cache_duration_ms| milliseconds.
//
// TODO(eroman): Get rid of the default parameters as it violate google
// style. This is temporary to help with refactoring.
HostResolver(int max_cache_entries = 100, int cache_duration_ms = 60000);
// If any completion callbacks are pending when the resolver is destroyed,
// the host resolutions are cancelled, and the completion callbacks will not
// be called.
~HostResolver();
// Opaque type used to cancel a request.
class Request;
// Resolves the given hostname (or IP address literal), filling out the
// |addresses| object upon success. The |port| parameter will be set as the
// sin(6)_port field of the sockaddr_in{6} struct. Returns OK if successful
// or an error code upon failure.
//
// When callback is null, the operation completes synchronously.
//
// When callback is non-null, the operation will be performed asynchronously.
// ERR_IO_PENDING is returned if it has been scheduled successfully. Real
// result code will be passed to the completion callback. If |req| is
// non-NULL, then |*req| will be filled with a handle to the async request.
// This handle is not valid after the request has completed.
int Resolve(const std::string& hostname, int port,
AddressList* addresses, CompletionCallback* callback,
Request** req);
// Cancels the specified request. |req| is the handle returned by Resolve().
// After a request is cancelled, its completion callback will not be called.
void CancelRequest(Request* req);
private:
class Job;
typedef std::vector<Request*> RequestsList;
typedef base::hash_map<std::string, scoped_refptr<Job> > JobMap;
// Adds a job to outstanding jobs list.
void AddOutstandingJob(Job* job);
// Returns the outstanding job for |hostname|, or NULL if there is none.
Job* FindOutstandingJob(const std::string& hostname);
// Removes |job| from the outstanding jobs list.
void RemoveOutstandingJob(Job* job);
// Callback for when |job| has completed with |error| and |addrlist|.
void OnJobComplete(Job* job, int error, const AddressList& addrlist);
// Cache of host resolution results.
HostCache cache_;
// Map from hostname to outstanding job.
JobMap jobs_;
// The job that OnJobComplete() is currently processing (needed in case
// HostResolver gets deleted from within the callback).
scoped_refptr<Job> cur_completing_job_;
DISALLOW_COPY_AND_ASSIGN(HostResolver);
};
// This class represents the task of resolving a hostname (or IP address
// literal) to an AddressList object. It wraps HostResolver to resolve only a
// single hostname at a time and cancels this request when going out of scope.
class SingleRequestHostResolver {
public:
explicit SingleRequestHostResolver(HostResolver* resolver);
// If a completion callback is pending when the resolver is destroyed, the
// host resolution is cancelled, and the completion callback will not be
// called.
~SingleRequestHostResolver();
// Resolves the given hostname (or IP address literal), filling out the
// |addresses| object upon success. See HostResolver::Resolve() for details.
int Resolve(const std::string& hostname, int port,
AddressList* addresses, CompletionCallback* callback);
private:
// Callback for when the request to |resolver_| completes, so we dispatch
// to the user's callback.
void OnResolveCompletion(int result);
// The actual host resolver that will handle the request.
HostResolver* resolver_;
// The current request (if any).
HostResolver::Request* cur_request_;
CompletionCallback* cur_request_callback_;
// Completion callback for when request to |resolver_| completes.
net::CompletionCallbackImpl<SingleRequestHostResolver> callback_;
DISALLOW_COPY_AND_ASSIGN(SingleRequestHostResolver);
};
// A helper class used in unit tests to alter hostname mappings. See
// SetHostMapper for details.
class HostMapper : public base::RefCountedThreadSafe<HostMapper> {
public:
virtual ~HostMapper() {}
// Returns possibly altered hostname, or empty string to simulate
// a failed lookup.
virtual std::string Map(const std::string& host) = 0;
protected:
// Ask previous host mapper (if set) for mapping of given host.
std::string MapUsingPrevious(const std::string& host);
private:
friend class ScopedHostMapper;
// Set mapper to ask when this mapper doesn't want to modify the result.
void set_previous_mapper(HostMapper* mapper) {
previous_mapper_ = mapper;
}
scoped_refptr<HostMapper> previous_mapper_;
};
#ifdef UNIT_TEST
// This function is designed to allow unit tests to override the behavior of
// HostResolver. For example, a HostMapper instance can force all hostnames
// to map to a fixed IP address such as 127.0.0.1.
//
// The previously set HostMapper (or NULL if there was none) is returned.
//
// NOTE: This function is not thread-safe, so take care to only call this
// function while there are no outstanding HostResolver instances.
//
// NOTE: In most cases, you should use ScopedHostMapper instead, which is
// defined in host_resolver_unittest.h
//
HostMapper* SetHostMapper(HostMapper* host_mapper);
#endif
} // namespace net
#endif // NET_BASE_HOST_RESOLVER_H_
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