Add support to ProxyService for downloading a PAC script on behalf of the Pro...

net/proxy/proxy_service.cc

Index: net/proxy/proxy_service.cc
===================================================================
--- net/proxy/proxy_service.cc	(revision 10072)
+++ net/proxy/proxy_service.cc	(working copy)
@@ -38,7 +38,35 @@
   }
 };
 
+// Strip away any reference fragments and the username/password, as they
+// are not relevant to proxy resolution.
+static GURL SanitizeURLForProxyResolver(const GURL& url) {
+  // TODO(eroman): The following duplicates logic from
+  // HttpUtil::SpecForRequest. Should probably live in net_util.h
+  GURL::Replacements replacements;
+  replacements.ClearUsername();
+  replacements.ClearPassword();
+  replacements.ClearRef();
+  return url.ReplaceComponents(replacements);
+}
 
+// Runs on the PAC thread to notify the proxy resolver of the fetched PAC
+// script contents. This task shouldn't outlive ProxyService, since
+// |resolver| is owned by ProxyService.
+class NotifyFetchCompletionTask : public Task {
+ public:
+  NotifyFetchCompletionTask(ProxyResolver* resolver, const std::string& bytes)
+      : resolver_(resolver), bytes_(bytes) {}
+
+  virtual void Run() {
+    resolver_->SetPacScript(bytes_);
+  }
+
+ private:
+  ProxyResolver* resolver_;
+  std::string bytes_;
+};
+
 // ProxyConfig ----------------------------------------------------------------
 
 // static
@@ -194,27 +222,44 @@
 class ProxyService::PacRequest :
     public base::RefCountedThreadSafe<ProxyService::PacRequest> {
  public:
+  // |service| -- the ProxyService that owns this request.
+  // |url|     -- the url of the query.
+  // |results| -- the structure to fill with proxy resolve results.
   PacRequest(ProxyService* service,
-             const GURL& pac_url,
+             const GURL& url,
+             ProxyInfo* results,
              CompletionCallback* callback)
       : service_(service),
         callback_(callback),
-        results_(NULL),
-        config_id_(service->config_id()),
-        pac_url_(pac_url),
+        results_(results),
+        url_(url),
+        is_started_(false),
         origin_loop_(MessageLoop::current()) {
     DCHECK(callback);
   }
 
-  void Query(const GURL& url, ProxyInfo* results) {
-    results_ = results;
-    // Execute Query asynchronously
+  // Start the resolve proxy request on the PAC thread.
+  void Query() {
+    is_started_ = true;
     AddRef();  // balanced in QueryComplete
+
+    GURL query_url = SanitizeURLForProxyResolver(url_);
+    const GURL& pac_url = service_->config_.pac_url;
+    results_->config_id_ = service_->config_.id();
+
     service_->pac_thread()->message_loop()->PostTask(FROM_HERE,
         NewRunnableMethod(this, &ProxyService::PacRequest::DoQuery,
-                          service_->resolver(), url, pac_url_));
+                          service_->resolver(), query_url, pac_url));
   }
 
+  // Run the request's callback on the current message loop.
+  void PostCallback(int result_code) {
+    AddRef();  // balanced in DoCallback
+    MessageLoop::current()->PostTask(FROM_HERE,
+        NewRunnableMethod(this, &ProxyService::PacRequest::DoCallback,
+            result_code));
+  }
+
   void Cancel() {
     // Clear these to inform QueryComplete that it should not try to
     // access them.
@@ -223,7 +268,12 @@
     results_ = NULL;
   }
 
+  // Returns true if Cancel() has been called.
+  bool was_cancelled() const { return callback_ == NULL; }
+
  private:
+  friend class ProxyService;
+
   // Runs on the PAC thread.
   void DoQuery(ProxyResolver* resolver,
                const GURL& query_url,
@@ -235,33 +285,43 @@
 
   // Runs the completion callback on the origin thread.
   void QueryComplete(int result_code) {
-    // The PacRequest may have been cancelled after it was started. If it was
-    // cancelled then |callback_|, |service_|, and |results_| will be NULL.
-    bool was_cancelled = callback_ == NULL;
+    // The PacRequest may have been cancelled after it was started.
+    if (!was_cancelled()) {
+      service_->DidCompletePacRequest(results_->config_id_, result_code);
 
-    if (!was_cancelled) {
-      service_->DidCompletePacRequest(config_id_, result_code);
-
       if (result_code == OK) {
         results_->Use(results_buf_);
         results_->RemoveBadProxies(service_->proxy_retry_info_);
       }
       callback_->Run(result_code);
+
+      // We check for cancellation once again, in case the callback deleted
+      // the owning ProxyService (whose destructor will in turn cancel us).
+      if (!was_cancelled())
+        service_->RemoveFrontOfRequestQueue(this);
     }
 
     Release();  // balances the AddRef in Query.  we may get deleted after
                 // we return.
   }
 
+  // Runs the completion callback on the origin thread.
+  void DoCallback(int result_code) {
+    if (!was_cancelled()) {
+      callback_->Run(result_code);
+    }
+    Release();  // balances the AddRef in PostCallback.
+  }
+
   // Must only be used on the "origin" thread.
   ProxyService* service_;
   CompletionCallback* callback_;
   ProxyInfo* results_;
-  ProxyConfig::ID config_id_;
+  GURL url_;
+  bool is_started_;
 
   // Usable from within DoQuery on the PAC thread.
   ProxyInfo results_buf_;
-  GURL pac_url_;
   MessageLoop* origin_loop_;
 };
 
@@ -272,7 +332,12 @@
     : config_service_(config_service),
       resolver_(resolver),
       config_is_bad_(false),
-      config_has_been_updated_(false) {
+      config_has_been_updated_(false),
+      ALLOW_THIS_IN_INITIALIZER_LIST(proxy_script_fetcher_callback_(
+          this, &ProxyService::OnScriptFetchCompletion)),
+      fetched_pac_config_id_(ProxyConfig::INVALID_ID),
+      fetched_pac_error_(OK),
+      in_progress_fetch_config_id_(ProxyConfig::INVALID_ID) {
 }
 
 // static
@@ -309,15 +374,32 @@
                                CompletionCallback* callback,
                                PacRequest** pac_request) {
   DCHECK(callback);
-  // The overhead of calling ProxyConfigService::GetProxyConfig is very low.
-  const TimeDelta kProxyConfigMaxAge = TimeDelta::FromSeconds(5);
 
-  // Periodically check for a new config.
-  if (!config_has_been_updated_ ||
-      (TimeTicks::Now() - config_last_update_time_) > kProxyConfigMaxAge)
-    UpdateConfig();
+  // Check if the request can be completed right away. This is the case when
+  // using a direct connection, or when the config is bad.
+  UpdateConfigIfOld();
+  int rv = TryToCompleteSynchronously(url, result);
+  if (rv != ERR_IO_PENDING)
+    return rv;
+
+  // Otherwise, push the request into the work queue.
+  scoped_refptr<PacRequest> req = new PacRequest(this, url, result, callback);
+  pending_requests_.push_back(req);
+  ProcessPendingRequests(req.get());
+
+  // Completion will be notifed through |callback|, unless the caller cancels
+  // the request using |pac_request|.
+  if (pac_request)
+    *pac_request = req.get();
+  return rv;  // ERR_IO_PENDING
+}
+
+int ProxyService::TryToCompleteSynchronously(const GURL& url,
+                                             ProxyInfo* result) {
   result->config_id_ = config_.id();
 
+  DCHECK(config_.id() != ProxyConfig::INVALID_ID);
+
   // Fallback to a "direct" (no proxy) connection if the current configuration
   // is known to be bad.
   if (config_is_bad_) {
@@ -369,40 +451,112 @@
     }
 
     if (config_.pac_url.is_valid() || config_.auto_detect) {
-      if (!pac_thread_.get()) {
-        pac_thread_.reset(new base::Thread("pac-thread"));
-        pac_thread_->Start();
+      // If we failed to download the PAC script, return the network error
+      // from the failed download. This is only going to happen for the first
+      // request after the failed download -- after that |config_is_bad_| will
+      // be set to true, so we short-cuircuit sooner.
+      if (fetched_pac_error_ != OK && !IsFetchingPacScript()) {
+        DidCompletePacRequest(fetched_pac_config_id_, fetched_pac_error_);
+        return fetched_pac_error_;
       }
+      return ERR_IO_PENDING;
+    }
+  }
 
-      scoped_refptr<PacRequest> req =
-          new PacRequest(this, config_.pac_url, callback);
+  // otherwise, we have no proxy config
+  result->UseDirect();
+  return OK;
+}
 
-      // Strip away any reference fragments and the username/password, as they
-      // are not relevant to proxy resolution.
-      GURL sanitized_url;
-      { // TODO(eroman): The following duplicates logic from
-        // HttpUtil::SpecForRequest. Should probably live in net_util.h
-        GURL::Replacements replacements;
-        replacements.ClearUsername();
-        replacements.ClearPassword();
-        replacements.ClearRef();
-        sanitized_url = url.ReplaceComponents(replacements);
-      }
+void ProxyService::InitPacThread() {
+  if (!pac_thread_.get()) {
+    pac_thread_.reset(new base::Thread("pac-thread"));
+    pac_thread_->Start();
+  }
+}
 
-      req->Query(sanitized_url, result);
+ProxyService::~ProxyService() {
+  // Cancel the inprogress request (if any), and free the rest.
+  for (PendingRequestsQueue::iterator it = pending_requests_.begin();
+       it != pending_requests_.end();
+       ++it) {
+    (*it)->Cancel();
+  }
+}
 
-      if (pac_request)
-        *pac_request = req;
+void ProxyService::ProcessPendingRequests(PacRequest* recent_req) {
+  if (pending_requests_.empty())
+    return;
 
-      return ERR_IO_PENDING;  // Wait for callback.
+  // While the PAC script is being downloaded, requests are blocked.
+  if (IsFetchingPacScript())
+    return;
+
+  // Get the next request to process (FIFO).
+  PacRequest* req = pending_requests_.front().get();
+  if (req->is_started_)
+    return;
+
+  // The configuration may have changed since |req| was added to the
+  // queue. It could be this request now completes synchronously.
+  if (req != recent_req) {
+    UpdateConfigIfOld();
+    int rv = TryToCompleteSynchronously(req->url_, req->results_);
+    if (rv != ERR_IO_PENDING) {
+      req->PostCallback(rv);
+      RemoveFrontOfRequestQueue(req);
+      return;
     }
   }
 
-  // otherwise, we have no proxy config
-  result->UseDirect();
-  return OK;
+  // Check if a new PAC script needs to be downloaded.
+  DCHECK(config_.id() != ProxyConfig::INVALID_ID);
+  if (!resolver_->does_fetch() && config_.id() != fetched_pac_config_id_) {
+    // For auto-detect we use the well known WPAD url.
+    GURL pac_url = config_.auto_detect ?
+        GURL("http://wpad/wpad.dat") : config_.pac_url;
+    
+    in_progress_fetch_config_id_ = config_.id();
+
+    proxy_script_fetcher_->Fetch(
+        pac_url, &in_progress_fetch_bytes_, &proxy_script_fetcher_callback_);
+    return;
+  }
+
+  // The only choice left now is to actually run the ProxyResolver on
+  // the PAC thread.
+  InitPacThread();
+  req->Query();
 }
 
+void ProxyService::RemoveFrontOfRequestQueue(PacRequest* expected_req) {
+  DCHECK(pending_requests_.front().get() == expected_req);
+  pending_requests_.pop_front();
+
+  // Start next work item.
+  ProcessPendingRequests(NULL);
+}
+
+void ProxyService::OnScriptFetchCompletion(int result) {
+  DCHECK(IsFetchingPacScript());
+  DCHECK(!resolver_->does_fetch());
+
+  // Notify the ProxyResolver of the new script data (will be empty string if
+  // result != OK).
+  InitPacThread();
+  pac_thread()->message_loop()->PostTask(FROM_HERE,
+      new NotifyFetchCompletionTask(
+          resolver_.get(), in_progress_fetch_bytes_));
+
+  fetched_pac_config_id_ = in_progress_fetch_config_id_;
+  fetched_pac_error_ = result;
+  in_progress_fetch_config_id_ = ProxyConfig::INVALID_ID;
+  in_progress_fetch_bytes_.clear();
+
+  // Start a pending request if any.
+  ProcessPendingRequests(NULL);
+}
+
 int ProxyService::ReconsiderProxyAfterError(const GURL& url,
                                             ProxyInfo* result,
                                             CompletionCallback* callback,
@@ -453,8 +607,30 @@
   return OK;
 }
 
-void ProxyService::CancelPacRequest(PacRequest* pac_request) {
-  pac_request->Cancel();
+// There are four states of the request we need to handle:
+// (1) Not started (just sitting in the queue).
+// (2) Executing PacRequest::DoQuery in the PAC thread.
+// (3) Waiting for PacRequest::QueryComplete to be run on the origin thread.
+// (4) Waiting for PacRequest::DoCallback to be run on the origin thread.
+void ProxyService::CancelPacRequest(PacRequest* req) {
+  DCHECK(req);
+
+  bool is_active_request = req->is_started_ && !pending_requests_.empty() &&
+      pending_requests_.front().get() == req;
+
+  req->Cancel();
+
+  if (is_active_request) {
+    RemoveFrontOfRequestQueue(req);
+    return;
+  }
+
+  // Otherwise just delete the request from the queue.
+  PendingRequestsQueue::iterator it = std::find(
+      pending_requests_.begin(), pending_requests_.end(), req);
+  if (it != pending_requests_.end()) {
+    pending_requests_.erase(it);
+  }
 }
 
 void ProxyService::DidCompletePacRequest(int config_id, int result_code) {
@@ -487,6 +663,16 @@
   proxy_retry_info_.clear();
 }
 
+void ProxyService::UpdateConfigIfOld() {
+  // The overhead of calling ProxyConfigService::GetProxyConfig is very low.
+  const TimeDelta kProxyConfigMaxAge = TimeDelta::FromSeconds(5);
+
+  // Periodically check for a new config.
+  if (!config_has_been_updated_ ||
+      (TimeTicks::Now() - config_last_update_time_) > kProxyConfigMaxAge)
+    UpdateConfig();
+}
+
 bool ProxyService::ShouldBypassProxyForURL(const GURL& url) {
   std::string url_domain = url.scheme();
   if (!url_domain.empty())