Move MimeTypeResourceHandler before ThrottlingResourceHandler

content/browser/loader/mime_sniffing_resource_handler.cc

 // 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 "content/browser/loader/mime_type_resource_handler.h"
+#include "content/browser/loader/mime_sniffing_resource_handler.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/mime_util/mime_util.h"
 #include "content/browser/download/download_resource_handler.h"
 #include "content/browser/download/download_stats.h"
+#include "content/browser/loader/intercepting_resource_handler.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/loader/resource_request_info_impl.h"
 #include "content/browser/loader/stream_resource_handler.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/download_save_info.h"
 #include "content/public/browser/download_url_parameters.h"
 #include "content/public/browser/plugin_service.h"
 #include "content/public/browser/resource_context.h"
 #include "content/public/browser/resource_dispatcher_host_delegate.h"
 #include "content/public/common/resource_response.h"
 #include "content/public/common/webplugininfo.h"
 #include "net/base/io_buffer.h"
 #include "net/base/mime_sniffer.h"
 #include "net/base/mime_util.h"
-#include "net/base/net_errors.h"
 #include "net/http/http_content_disposition.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_request.h"
 
 namespace content {
 
 namespace {
 
 const char kAcceptHeader[] = "Accept";
 const char kFrameAcceptHeader[] =
     "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,"
     "*/*;q=0.8";
 const char kStylesheetAcceptHeader[] = "text/css,*/*;q=0.1";
 const char kImageAcceptHeader[] = "image/webp,image/*,*/*;q=0.8";
 const char kDefaultAcceptHeader[] = "*/*";
 
 // Used to write into an existing IOBuffer at a given offset.
 class DependentIOBuffer : public net::WrappedIOBuffer {
  public:
   DependentIOBuffer(net::IOBuffer* buf, int offset)
-      : net::WrappedIOBuffer(buf->data() + offset),
-        buf_(buf) {
-  }
+      : net::WrappedIOBuffer(buf->data() + offset), buf_(buf) {}
 
  private:
   ~DependentIOBuffer() override {}
 
   scoped_refptr<net::IOBuffer> buf_;
 };
 
 }  // namespace
 
-MimeTypeResourceHandler::MimeTypeResourceHandler(
+MimeSniffingResourceHandler::MimeSniffingResourceHandler(
     std::unique_ptr<ResourceHandler> next_handler,
     ResourceDispatcherHostImpl* host,
     PluginService* plugin_service,
+    InterceptingResourceHandler* intercepting_handler,
     net::URLRequest* request)
     : LayeredResourceHandler(request, std::move(next_handler)),
       state_(STATE_STARTING),
       host_(host),
-#if defined(ENABLE_PLUGINS)
       plugin_service_(plugin_service),
-#endif
+      must_download_(false),
+      must_download_is_set_(false),
       read_buffer_size_(0),
       bytes_read_(0),
-      must_download_(false),
-      must_download_is_set_(false),
-      weak_ptr_factory_(this) {
-}
+      intercepting_handler_(intercepting_handler),
+      weak_ptr_factory_(this) {}
 
-MimeTypeResourceHandler::~MimeTypeResourceHandler() {
-}
+MimeSniffingResourceHandler::~MimeSniffingResourceHandler() {}
 
-void MimeTypeResourceHandler::SetController(ResourceController* controller) {
+void MimeSniffingResourceHandler::SetController(
+    ResourceController* controller) {
   ResourceHandler::SetController(controller);
 
-  // Downstream handlers see us as their ResourceController, which allows us to
-  // consume part or all of the resource response, and then later replay it to
-  // downstream handler.
+  // Downstream handlers see the MimeSniffingResourceHandler as their
+  // ResourceController, which allows it to consume part or all of the resource
+  // response, and then later replay it to downstream handler.
   DCHECK(next_handler_.get());
   next_handler_->SetController(this);
 }
 
-bool MimeTypeResourceHandler::OnResponseStarted(ResourceResponse* response,
-                                                bool* defer) {
-  response_ = response;
-
-  // A 304 response should not contain a Content-Type header (RFC 7232 section
-  // 4.1). The following code may incorrectly attempt to add a Content-Type to
-  // the response, and so must be skipped for 304 responses.
-  if (!(response_->head.headers.get() &&
-        response_->head.headers->response_code() == 304)) {
-    if (ShouldSniffContent()) {
-      state_ = STATE_BUFFERING;
-      return true;
-    }
-
-    if (response_->head.mime_type.empty()) {
-      // Ugg.  The server told us not to sniff the content but didn't give us
-      // a mime type.  What's a browser to do?  Turns out, we're supposed to
-      // treat the response as "text/plain".  This is the most secure option.
-      response_->head.mime_type.assign("text/plain");
-    }
-
-    // Treat feed types as text/plain.
-    if (response_->head.mime_type == "application/rss+xml" ||
-        response_->head.mime_type == "application/atom+xml") {
-      response_->head.mime_type.assign("text/plain");
-    }
-  }
-
-  state_ = STATE_PROCESSING;
-  return ProcessResponse(defer);
-}
-
-bool MimeTypeResourceHandler::OnWillStart(const GURL& url, bool* defer) {
+bool MimeSniffingResourceHandler::OnWillStart(const GURL& url, bool* defer) {
   const char* accept_value = nullptr;
   switch (GetRequestInfo()->GetResourceType()) {
     case RESOURCE_TYPE_MAIN_FRAME:
     case RESOURCE_TYPE_SUB_FRAME:
       accept_value = kFrameAcceptHeader;
       break;
     case RESOURCE_TYPE_STYLESHEET:
       accept_value = kStylesheetAcceptHeader;
       break;
     case RESOURCE_TYPE_IMAGE:
@@ skipping 19 matching lines @@
       NOTREACHED();
       break;
   }
 
   // The false parameter prevents overwriting an existing accept header value,
   // which is needed because JS can manually set an accept header on an XHR.
   request()->SetExtraRequestHeaderByName(kAcceptHeader, accept_value, false);
   return next_handler_->OnWillStart(url, defer);
 }
 
-bool MimeTypeResourceHandler::OnWillRead(scoped_refptr<net::IOBuffer>* buf,
-                                         int* buf_size,
-                                         int min_size) {
+bool MimeSniffingResourceHandler::OnResponseStarted(ResourceResponse* response,
+                                                    bool* defer) {
+  DCHECK_EQ(STATE_STARTING, state_);
+  response_ = response;
+
+  state_ = STATE_BUFFERING;
+
+  // A 304 response should not contain a Content-Type header (RFC 7232 section
+  // 4.1). The following code may incorrectly attempt to add a Content-Type to
+  // the response, and so must be skipped for 304 responses.
+  if (!(response_->head.headers.get() &&
+        response_->head.headers->response_code() == 304)) {
+    if (ShouldSniffContent())
+      return true;
+
+    if (response_->head.mime_type.empty()) {
+      // Ugg.  The server told us not to sniff the content but didn't give us a
+      // mime type.  What's a browser to do?  Turns out, we're supposed to
+      // treat the response as "text/plain".  This is the most secure option.
+      response_->head.mime_type.assign("text/plain");
+    }
+
+    // Treat feed types as text/plain.
+    if (response_->head.mime_type == "application/rss+xml" ||
+        response_->head.mime_type == "application/atom+xml") {
+      response_->head.mime_type.assign("text/plain");
+    }
+  }
+
+  return ProcessReplay(defer);
+}
+
+bool MimeSniffingResourceHandler::OnWillRead(scoped_refptr<net::IOBuffer>* buf,
+                                             int* buf_size,
+                                             int min_size) {
   if (state_ == STATE_STREAMING)
     return next_handler_->OnWillRead(buf, buf_size, min_size);
 
   DCHECK_EQ(-1, min_size);
 
   if (read_buffer_.get()) {
     CHECK_LT(bytes_read_, read_buffer_size_);
     *buf = new DependentIOBuffer(read_buffer_.get(), bytes_read_);
     *buf_size = read_buffer_size_ - bytes_read_;
   } else {
     if (!next_handler_->OnWillRead(buf, buf_size, min_size))
       return false;
 
     read_buffer_ = *buf;
     read_buffer_size_ = *buf_size;
     DCHECK_GE(read_buffer_size_, net::kMaxBytesToSniff * 2);
   }
   return true;
 }
 
-bool MimeTypeResourceHandler::OnReadCompleted(int bytes_read, bool* defer) {
+bool MimeSniffingResourceHandler::OnReadCompleted(int bytes_read, bool* defer) {
   if (state_ == STATE_STREAMING)
     return next_handler_->OnReadCompleted(bytes_read, defer);
 
   DCHECK_EQ(state_, STATE_BUFFERING);
   bytes_read_ += bytes_read;
 
-  if (!DetermineMimeType() && (bytes_read > 0))
-    return true;  // Needs more data, so keep buffering.
+  const std::string& type_hint = response_->head.mime_type;
 
-  state_ = STATE_PROCESSING;
-  return ProcessResponse(defer);
+  std::string new_type;
+  bool made_final_decision =
+      net::SniffMimeType(read_buffer_->data(), bytes_read_, request()->url(),
+                         type_hint, &new_type);
+
+  // SniffMimeType() returns false if there is not enough data to determine
+  // the mime type. However, even if it returns false, it returns a new type
+  // that is probably better than the current one.
+  response_->head.mime_type.assign(new_type);
+
+  if (!made_final_decision && (bytes_read > 0))
+    return true;
+
+  return ProcessReplay(defer);
 }
 
-void MimeTypeResourceHandler::OnResponseCompleted(
+void MimeSniffingResourceHandler::OnResponseCompleted(
     const net::URLRequestStatus& status,
     const std::string& security_info,
     bool* defer) {
   // Upon completion, act like a pass-through handler in case the downstream
   // handler defers OnResponseCompleted.
   state_ = STATE_STREAMING;
 
   next_handler_->OnResponseCompleted(status, security_info, defer);
 }
 
-void MimeTypeResourceHandler::Resume() {
-  switch (state_) {
-    case STATE_BUFFERING:
-    case STATE_PROCESSING:
-      NOTREACHED();
-      break;
-    case STATE_REPLAYING:
-      base::ThreadTaskRunnerHandle::Get()->PostTask(
-          FROM_HERE,
-          base::Bind(&MimeTypeResourceHandler::CallReplayReadCompleted,
-                     weak_ptr_factory_.GetWeakPtr()));
-      break;
-    case STATE_STARTING:
-    case STATE_STREAMING:
-      controller()->Resume();
-      break;
+void MimeSniffingResourceHandler::Resume() {
+  // If no information is currently being transmitted to downstream handlers,
+  // they should not attempt to resume the request.
+  if (state_ == STATE_BUFFERING) {
+    NOTREACHED();
+    return;
+  }
+
+  // If the BufferingHandler is acting as a pass-through handler, just ask the
+  // upwards ResourceController to resume the request.
+  if (state_ == STATE_STARTING || state_ == STATE_STREAMING) {
+    controller()->Resume();
+    return;
+  }
+
+  // Otherwise proceed with the replay of the response. If it is successful,
+  // it will resume the request.
+  ProceedWithReplay();
+}
+
+void MimeSniffingResourceHandler::Cancel() {
+  controller()->Cancel();
+}
+
+void MimeSniffingResourceHandler::CancelAndIgnore() {
+  controller()->CancelAndIgnore();
+}
+
+void MimeSniffingResourceHandler::CancelWithError(int error_code) {
+  controller()->CancelWithError(error_code);
+}
+
+void MimeSniffingResourceHandler::ProceedWithReplay() {
+  bool defer = false;
+  if (!ProcessReplay(&defer)) {
+    Cancel();
+  } else if (!defer) {
+    DCHECK_EQ(STATE_STREAMING, state_);
+    controller()->Resume();
   }
 }
 
-void MimeTypeResourceHandler::Cancel() {
-  controller()->Cancel();
+bool MimeSniffingResourceHandler::ProcessReplay(bool* defer) {
+  bool return_value = true;
+  while (!*defer && return_value && state_ != STATE_STREAMING) {
+    switch (state_) {
+      case STATE_BUFFERING:
+        return_value = MaybeCheckForInterception(defer);
+        break;
+      case STATE_INTERCEPTION_CHECK_DONE:
+        return_value = ReplayResponseReceived(defer);
+        break;
+      case STATE_REPLAYING_RESPONSE_RECEIVED:
+        return_value = ReplayReadCompleted(defer);
+        break;
+      default:
+        NOTREACHED();
+        break;
+    }
+  }
+  return return_value;
 }
 
-void MimeTypeResourceHandler::CancelAndIgnore() {
-  controller()->CancelAndIgnore();
-}
-
-void MimeTypeResourceHandler::CancelWithError(int error_code) {
-  controller()->CancelWithError(error_code);
-}
-
-bool MimeTypeResourceHandler::ProcessResponse(bool* defer) {
-  DCHECK_EQ(STATE_PROCESSING, state_);
-
-  // TODO(darin): Stop special-casing 304 responses.
-  if (!(response_->head.headers.get() &&
-        response_->head.headers->response_code() == 304)) {
-    if (!SelectNextHandler(defer))
-      return false;
-    if (*defer)
-      return true;
-  }
-
-  state_ = STATE_REPLAYING;
-
-  if (!next_handler_->OnResponseStarted(response_.get(), defer))
+bool MimeSniffingResourceHandler::MaybeCheckForInterception(bool* defer) {
+  DCHECK_EQ(STATE_BUFFERING, state_);
+  // If a request that can be intercepted failed the check for interception
+  // step, it should be canceled.
+  if (CanBeIntercepted() && !CheckForInterception(defer))

[mmenke, 2016/07/18 18:50:42]

Maybe move CanBeIntercepted() to the first line of CheckForInterception?

[clamy, 2016/07/19 14:24:55]

Done.

     return false;
 
-  if (!read_buffer_.get()) {
-    state_ = STATE_STREAMING;
-    return true;
-  }
-
   if (!*defer)
-    return ReplayReadCompleted(defer);
+    state_ = STATE_INTERCEPTION_CHECK_DONE;
 
   return true;
 }
 
-bool MimeTypeResourceHandler::ShouldSniffContent() {
+bool MimeSniffingResourceHandler::ReplayResponseReceived(bool* defer) {
+  DCHECK_EQ(STATE_INTERCEPTION_CHECK_DONE, state_);
+  state_ = STATE_REPLAYING_RESPONSE_RECEIVED;
+  return next_handler_->OnResponseStarted(response_.get(), defer);
+}
+
+bool MimeSniffingResourceHandler::ReplayReadCompleted(bool* defer) {
+  DCHECK_EQ(STATE_REPLAYING_RESPONSE_RECEIVED, state_);
+
+  state_ = STATE_STREAMING;
+
+  if (!read_buffer_.get())
+    return true;
+
+  bool result = next_handler_->OnReadCompleted(bytes_read_, defer);
+
+  read_buffer_ = NULL;
+  read_buffer_size_ = 0;
+  bytes_read_ = 0;
+
+  return result;
+}
+
+bool MimeSniffingResourceHandler::ShouldSniffContent() {
   const std::string& mime_type = response_->head.mime_type;
 
   std::string content_type_options;
   request()->GetResponseHeaderByName("x-content-type-options",
                                      &content_type_options);
 
   bool sniffing_blocked =
       base::LowerCaseEqualsASCII(content_type_options, "nosniff");
   bool we_would_like_to_sniff =
       net::ShouldSniffMimeType(request()->url(), mime_type);
 
   if (!sniffing_blocked && we_would_like_to_sniff) {
     // We're going to look at the data before deciding what the content type
     // is.  That means we need to delay sending the ResponseStarted message
     // over the IPC channel.
     VLOG(1) << "To buffer: " << request()->url().spec();
     return true;
   }
 
   return false;
 }
 
-bool MimeTypeResourceHandler::DetermineMimeType() {
-  DCHECK_EQ(STATE_BUFFERING, state_);
-
-  const std::string& type_hint = response_->head.mime_type;
-
-  std::string new_type;
-  bool made_final_decision =
-      net::SniffMimeType(read_buffer_->data(), bytes_read_, request()->url(),
-                         type_hint, &new_type);
-
-  // SniffMimeType() returns false if there is not enough data to determine
-  // the mime type. However, even if it returns false, it returns a new type
-  // that is probably better than the current one.
-  response_->head.mime_type.assign(new_type);
-
-  return made_final_decision;
-}
-
-bool MimeTypeResourceHandler::SelectPluginHandler(bool* defer,
-                                                  bool* handled_by_plugin) {
-  *handled_by_plugin = false;
-#if defined(ENABLE_PLUGINS)
-  ResourceRequestInfoImpl* info = GetRequestInfo();
-  bool allow_wildcard = false;
-  bool stale;
-  WebPluginInfo plugin;
-  bool has_plugin = plugin_service_->GetPluginInfo(
-      info->GetChildID(), info->GetRenderFrameID(), info->GetContext(),
-      request()->url(), GURL(), response_->head.mime_type, allow_wildcard,
-      &stale, &plugin, NULL);
-
-  if (stale) {
-    // Refresh the plugins asynchronously.
-    plugin_service_->GetPlugins(
-        base::Bind(&MimeTypeResourceHandler::OnPluginsLoaded,
-                   weak_ptr_factory_.GetWeakPtr()));
-    request()->LogBlockedBy("MimeTypeResourceHandler");
-    *defer = true;
-    return true;
-  }
-
-  if (has_plugin && plugin.type != WebPluginInfo::PLUGIN_TYPE_BROWSER_PLUGIN) {
-    *handled_by_plugin = true;
-    return true;
-  }
-
-  // Attempt to intercept the request as a stream.
-  base::FilePath plugin_path;
-  if (has_plugin)
-    plugin_path = plugin.path;
-  std::string payload;
-  std::unique_ptr<ResourceHandler> handler(host_->MaybeInterceptAsStream(
-      plugin_path, request(), response_.get(), &payload));
-  if (handler) {
-    *handled_by_plugin = true;
-    return UseAlternateNextHandler(std::move(handler), payload);
-  }
-#endif
-  return true;
-}
-
-bool MimeTypeResourceHandler::SelectNextHandler(bool* defer) {
+bool MimeSniffingResourceHandler::CheckForInterception(bool* defer) {
   DCHECK(!response_->head.mime_type.empty());
 
   ResourceRequestInfoImpl* info = GetRequestInfo();
   const std::string& mime_type = response_->head.mime_type;
 
   // https://crbug.com/568184 - Temporary hack to track servers that aren't
   // setting Content-Disposition when sending x-x509-user-cert and expecting
   // the browser to automatically install certificates; this is being
   // deprecated and will be removed upon full <keygen> removal.
   if (mime_type == "application/x-x509-user-cert") {
     UMA_HISTOGRAM_BOOLEAN(
         "UserCert.ContentDisposition",
         response_->head.headers->HasHeader("Content-Disposition"));
   }
 
   // Allow requests for object/embed tags to be intercepted as streams.
   if (info->GetResourceType() == content::RESOURCE_TYPE_OBJECT) {
     DCHECK(!info->allow_download());
 
     bool handled_by_plugin;
-    if (!SelectPluginHandler(defer, &handled_by_plugin))
+    if (!CheckForPluginHandler(defer, &handled_by_plugin))
       return false;
     if (handled_by_plugin || *defer)
       return true;
   }
 
   if (!info->allow_download())
     return true;
 
   // info->allow_download() == true implies
   // info->GetResourceType() == RESOURCE_TYPE_MAIN_FRAME or
   // info->GetResourceType() == RESOURCE_TYPE_SUB_FRAME.
   DCHECK(info->GetResourceType() == RESOURCE_TYPE_MAIN_FRAME ||
          info->GetResourceType() == RESOURCE_TYPE_SUB_FRAME);
 
   bool must_download = MustDownload();
   if (!must_download) {
     if (mime_util::IsSupportedMimeType(mime_type))
       return true;
 
     bool handled_by_plugin;
-    if (!SelectPluginHandler(defer, &handled_by_plugin))
+    if (!CheckForPluginHandler(defer, &handled_by_plugin))
       return false;
     if (handled_by_plugin || *defer)
       return true;
   }
 
-  // Install download handler
+  // This is request is a download,

[mmenke, 2016/07/18 18:50:42]

This comment seems weird, just above a "CheckInterceptionIsValid() -> fail
request" call.

[clamy, 2016/07/19 14:24:54]

Added a blank line to make it clearer that it's not related to the check itself.

+  if (!CheckInterceptionIsValid())

[mmenke, 2016/07/18 18:50:42]

We have:

CanBeIntercepted(), CheckForInterception(), CheckInterceptionIsValid().  These
names seem very confusing to me.

Maybe:

CheckInterceptionIsValid() -> CheckResponseIsNotProvisional() [Per spec, 100
responses are "provisional".  We may not even need the method, but getting rid
of it is beyond the scope of this CL, of course].  May maybe even better,
CheckResponseCanBeDownloaded().  Note that this check is just used for
downloads, not plugin interceptions, so "CheckInterceptionIsValid()" seems
inaccurate as well as confusing.

[clamy, 2016/07/19 14:24:55]

I went with CheckResponseIsNotProvisional. We do call the method in
CheckForPluginHandler, so CheckResponseCanBeDownloaded seemed false.

+    return false;
+
   info->set_is_download(true);
   std::unique_ptr<ResourceHandler> handler(
       host_->CreateResourceHandlerForDownload(request(),
                                               true,  // is_content_initiated
                                               must_download));
-  return UseAlternateNextHandler(std::move(handler), std::string());
+  intercepting_handler_->UseNewHandler(std::move(handler), std::string());
+  return true;
 }
 
-bool MimeTypeResourceHandler::UseAlternateNextHandler(
-    std::unique_ptr<ResourceHandler> new_handler,
-    const std::string& payload_for_old_handler) {
-  if (response_->head.headers.get() &&  // Can be NULL if FTP.
-      response_->head.headers->response_code() / 100 != 2) {
-    // The response code indicates that this is an error page, but we don't
-    // know how to display the content.  We follow Firefox here and show our
-    // own error page instead of triggering a download.
-    // TODO(abarth): We should abstract the response_code test, but this kind
-    //               of check is scattered throughout our codebase.
-    request()->CancelWithError(net::ERR_INVALID_RESPONSE);
+bool MimeSniffingResourceHandler::CheckForPluginHandler(
+    bool* defer,
+    bool* handled_by_plugin) {
+  *handled_by_plugin = false;
+#if defined(ENABLE_PLUGINS)
+  ResourceRequestInfoImpl* info = GetRequestInfo();
+  bool allow_wildcard = false;
+  bool stale;
+  WebPluginInfo plugin;
+  bool has_plugin = plugin_service_->GetPluginInfo(
+      info->GetChildID(), info->GetRenderFrameID(), info->GetContext(),
+      request()->url(), GURL(), response_->head.mime_type, allow_wildcard,
+      &stale, &plugin, NULL);
+
+  if (stale) {
+    // Refresh the plugins asynchronously.
+    plugin_service_->GetPlugins(
+        base::Bind(&MimeSniffingResourceHandler::OnPluginsLoaded,
+                   weak_ptr_factory_.GetWeakPtr()));
+    request()->LogBlockedBy("MimeSniffingResourceHandler");
+    *defer = true;
+    return true;
+  }
+
+  if (has_plugin && plugin.type != WebPluginInfo::PLUGIN_TYPE_BROWSER_PLUGIN) {
+    *handled_by_plugin = true;
+    return true;
+  }
+
+  // Attempt to intercept the request as a stream.
+  base::FilePath plugin_path;
+  if (has_plugin)
+    plugin_path = plugin.path;
+  std::string payload;
+  std::unique_ptr<ResourceHandler> handler(host_->MaybeInterceptAsStream(
+      plugin_path, request(), response_.get(), &payload));
+  if (handler) {
+    if (!CheckInterceptionIsValid())
+      return false;
+    *handled_by_plugin = true;
+    intercepting_handler_->UseNewHandler(std::move(handler), payload);

[mmenke, 2016/07/18 17:58:37]

I'm not a big fan of having this dig into intercepting_handler.

It looks like all we need from this class that we weren't getting is the
is_download bit?  Given the "DCHECK(!info->allow_download());" in the plugin
path, I think we can just have MimeSniffingResourceHandler::CheckForInterception
set the is_download bit, and not set up the next handler, and then have the
intercepting_handler use that bit itself, as well as checking for a plugin?

Not great, but I think it's better than this.

[clamy, 2016/07/19 14:24:55]

We also need the info->is_stream bit that is set in
ResourceDispatcherHostImpl::MaybeInterceptAsStream which creates the
ResourceHandler for the stream. So we need to call it as well, and I'm not sure
if we can call it twice.

Ideally, we would modify the public API so we can have a call to teh embedder to
ask if this is a download or a stream, but which doesn't set up the new
ResourceHandler. Then the intercepting_handler would make a call to a different
function to actually get the new ResourceHandler. But the patch is already big
enough (and I'm not very familiar with the chromium code) that I did not want to
include this in the patch.

[mmenke, 2016/07/19 17:43:45]

I'm not seeing where is_stream is used in this file.  Do you mean you need the
is_stream bit for the X-Frame-Options logic, and streams are exempt from
X-Frame-Options?

I certainly agree that we don't want to make this patch any bigger than it
already is.

+  }
+#endif
+  return true;
+}
+
+bool MimeSniffingResourceHandler::CanBeIntercepted() {
+  if (response_->head.headers.get() &&
+      response_->head.headers->response_code() == 304) {
     return false;
   }
 
-  // Inform the original ResourceHandler that this will be handled entirely by
-  // the new ResourceHandler.
-  // TODO(darin): We should probably check the return values of these.
-  bool defer_ignored = false;
-  next_handler_->OnResponseStarted(response_.get(), &defer_ignored);
-  // Although deferring OnResponseStarted is legal, the only downstream handler
-  // which does so is CrossSiteResourceHandler. Cross-site transitions should
-  // not trigger when switching handlers.
-  DCHECK(!defer_ignored);
-  if (payload_for_old_handler.empty()) {
-    net::URLRequestStatus status(net::URLRequestStatus::CANCELED,
-                                 net::ERR_ABORTED);
-    next_handler_->OnResponseCompleted(status, std::string(), &defer_ignored);
-    DCHECK(!defer_ignored);
-  } else {
-    scoped_refptr<net::IOBuffer> buf;
-    int size = 0;
+  return true;
+}
 
-    next_handler_->OnWillRead(&buf, &size, -1);
-    CHECK_GE(size, static_cast<int>(payload_for_old_handler.length()));
-
-    memcpy(buf->data(), payload_for_old_handler.c_str(),
-           payload_for_old_handler.length());
-
-    next_handler_->OnReadCompleted(payload_for_old_handler.length(),
-                                   &defer_ignored);
-    DCHECK(!defer_ignored);
-
-    net::URLRequestStatus status(net::URLRequestStatus::SUCCESS, 0);
-    next_handler_->OnResponseCompleted(status, std::string(), &defer_ignored);
-    DCHECK(!defer_ignored);
+bool MimeSniffingResourceHandler::CheckInterceptionIsValid() {
+  if (!response_->head.headers.get() ||
+      response_->head.headers->response_code() / 100 == 2) {
+    return true;
   }
 
-  // This is handled entirely within the new ResourceHandler, so just reset the
-  // original ResourceHandler.
-  next_handler_ = std::move(new_handler);
-  next_handler_->SetController(this);
-
-  return CopyReadBufferToNextHandler();
+  // The response code indicates that this is an error page, but we don't
+  // know how to display the content.  We follow Firefox here and show our
+  // own error page instead of intercepting the request as a stream or a
+  // download.
+  // TODO(abarth): We should abstract the response_code test, but this kind
+  // of check is scattered throughout our codebase.
+  request()->CancelWithError(net::ERR_INVALID_RESPONSE);
+  return false;
 }
 
-bool MimeTypeResourceHandler::ReplayReadCompleted(bool* defer) {
-  DCHECK(read_buffer_.get());
-
-  bool result = next_handler_->OnReadCompleted(bytes_read_, defer);
-
-  read_buffer_ = NULL;
-  read_buffer_size_ = 0;
-  bytes_read_ = 0;
-
-  state_ = STATE_STREAMING;
-
-  return result;
-}
-
-void MimeTypeResourceHandler::CallReplayReadCompleted() {
-  bool defer = false;
-  if (!ReplayReadCompleted(&defer)) {
-    controller()->Cancel();
-  } else if (!defer) {
-    state_ = STATE_STREAMING;
-    controller()->Resume();
-  }
-}
-
-bool MimeTypeResourceHandler::MustDownload() {
+bool MimeSniffingResourceHandler::MustDownload() {
   if (must_download_is_set_)
     return must_download_;
 
   must_download_is_set_ = true;
 
   std::string disposition;
   request()->GetResponseHeaderByName("content-disposition", &disposition);
   if (!disposition.empty() &&
       net::HttpContentDisposition(disposition, std::string()).is_attachment()) {
     must_download_ = true;
   } else if (host_->delegate() &&
              host_->delegate()->ShouldForceDownloadResource(
                  request()->url(), response_->head.mime_type)) {
     must_download_ = true;
   } else {
     must_download_ = false;
   }
 
   return must_download_;
 }
 
-bool MimeTypeResourceHandler::CopyReadBufferToNextHandler() {
-  if (!read_buffer_.get())
-    return true;
-
-  scoped_refptr<net::IOBuffer> buf;
-  int buf_len = 0;
-  if (!next_handler_->OnWillRead(&buf, &buf_len, bytes_read_))
-    return false;
-
-  CHECK((buf_len >= bytes_read_) && (bytes_read_ >= 0));
-  memcpy(buf->data(), read_buffer_->data(), bytes_read_);
-  return true;
-}
-
-void MimeTypeResourceHandler::OnPluginsLoaded(
+void MimeSniffingResourceHandler::OnPluginsLoaded(
     const std::vector<WebPluginInfo>& plugins) {
+  // No longer blocking on the plugins being loaded.
   request()->LogUnblocked();
-  bool defer = false;
-  if (!ProcessResponse(&defer)) {
-    controller()->Cancel();
-  } else if (!defer) {
-    controller()->Resume();
-  }
+  if (state_ == STATE_BUFFERING)
+    ProceedWithReplay();
 }
 
 }  // namespace content