Adds Lo-Fi fallback support for new Data Reduction Proxy protocol.

content/renderer/previews_state_helper.cc

Index: content/renderer/previews_state_helper.cc
diff --git a/content/renderer/previews_state_helper.cc b/content/renderer/previews_state_helper.cc
new file mode 100644
index 0000000000000000000000000000000000000000..808ccc3eb39a2a8407f013b319a6915fc990d6ed
--- /dev/null
+++ b/content/renderer/previews_state_helper.cc
@@ -0,0 +1,91 @@
+// Copyright 2017 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/renderer/previews_state_helper.h"
+
+#include "base/strings/string_split.h"
+
+namespace {

[megjablon, 2017/06/05 23:47:58]

move the anonymous namespace inside content namespace

[dougarnett, 2017/06/06 16:49:46]

Done.

+
+// Chrome Proxy Previews header and directives.
+const char kChromeProxyHeader[] = "chrome-proxy";
+const char kChromeProxyContentTransformHeader[] =
+    "chrome-proxy-content-transform";
+const char kChromeProxyPagePoliciesDirective[] = "page-policies";
+const char kChromeProxyEmptyImageDirective[] = "empty-image";
+const char kChromeProxyLitePageDirective[] = "lite-page";
+
+bool HasEmptyPageDirective(const blink::WebURLResponse& web_url_response) {

[megjablon, 2017/06/05 23:47:59]

s/HasEmptyPageDirective/HasEmptyImageDirective/?

[dougarnett, 2017/06/06 16:49:46]

Yuck! Thanks!

+  std::string chrome_proxy_value =

[megjablon, 2017/06/05 23:47:59]

#include <string>

[dougarnett, 2017/06/06 16:49:46]

Done.

+      web_url_response
+          .HttpHeaderField(blink::WebString::FromUTF8(kChromeProxyHeader))

[megjablon, 2017/06/05 23:47:58]

#include "third_party/WebKit/public/platform/WebString.h"

[dougarnett, 2017/06/06 16:49:46]

Done.

+          .Utf8();
+  for (const auto& directive :
+       base::SplitStringPiece(chrome_proxy_value, ",", base::TRIM_WHITESPACE,
+                              base::SPLIT_WANT_NONEMPTY)) {
+    if (!base::StartsWith(directive, kChromeProxyPagePoliciesDirective,

[megjablon, 2017/06/05 23:47:58]

#include "base/strings/string_util.cc"

[dougarnett, 2017/06/06 16:49:46]

Done.

+                          base::CompareCase::INSENSITIVE_ASCII)) {
+      continue;
+    }
+
+    // Check policy directive for empty-image entry.
+    base::StringPiece page_policies_value = base::StringPiece(directive).substr(

[megjablon, 2017/06/05 23:47:59]

#include "base/strings/string_piece.h"

[dougarnett, 2017/06/06 16:49:46]

Done.

+        arraysize(kChromeProxyPagePoliciesDirective));

[megjablon, 2017/06/05 23:47:58]

#include "src/base/macros.h"

[dougarnett, 2017/06/06 16:49:46]

Done.

+    for (const auto& policy :
+         base::SplitStringPiece(page_policies_value, "|", base::TRIM_WHITESPACE,
+                                base::SPLIT_WANT_NONEMPTY)) {
+      if (base::LowerCaseEqualsASCII(policy, kChromeProxyEmptyImageDirective)) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
+namespace content {
+
+PreviewsState UpdatePreviewsStateFromMainFrameResponse(
+    PreviewsState original_state,
+    const blink::WebURLResponse& web_url_response) {
+  // Only update the state if there was a server preview requested.
+  if (!(original_state & SERVER_LITE_PAGE_ON) &&
+      !(original_state & SERVER_LOFI_ON))
+    return original_state;

[megjablon, 2017/06/05 23:47:58]

if statement is more than two lines, add braces.

[dougarnett, 2017/06/06 16:49:46]

Done.

+
+  // Next handle legacy path where Lite Page not enabled but Lo-Fi is enabled.
+  if (!(original_state & SERVER_LITE_PAGE_ON) &&
+      (original_state & SERVER_LOFI_ON)) {

[megjablon, 2017/06/05 23:47:58]

Just want to make sure, in the updated protocol can we ever end up in a state
where Lo-Fi is enabled, but not Lite Page, for the main frame?

[dougarnett, 2017/06/06 16:49:46]

We don't want to since SERVER_LITE_PAGE_ON => accept lite-page => server
previews enabled for page.
The server takes responsibility for the country restrictions and will handle the
fallback to Lo-Fi.

This is not true of the current ShouldAcceptLitePages though. The other open CL
will address this.

+    return original_state;
+  }
+
+  // At this point, we have a proxy main frame response for which we want

[megjablon, 2017/06/05 23:47:58]

Don't use we. 

[dougarnett, 2017/06/06 16:49:46]

Done.

+  // to update the PreviewsState from what was enabled/accepted by the client
+  // to what the client should actually do based on the server response.
+
+  PreviewsState updated_state = original_state;
+
+  // Clear the Lite Page bit if Lite Page transformation did not occur.
+  if (web_url_response
+          .HttpHeaderField(
+              blink::WebString::FromUTF8(kChromeProxyContentTransformHeader))
+          .Utf8() != kChromeProxyLitePageDirective) {
+    updated_state &= ~(SERVER_LITE_PAGE_ON);
+  }
+
+  // Determine whether to keep or clear Lo-Fi bits. We need to receive the
+  // empty-image policy directive and have SERVER_LOFI_ON in order to retain
+  // Lo-Fi bits.
+  if (!(updated_state & SERVER_LOFI_ON)) {

[megjablon, 2017/06/05 23:47:59]

Even though it's the same, I'd use original_state since we want to check that
the original had server lofi on.

[dougarnett, 2017/06/06 16:49:46]

Done.

+    // Server Lo-Fi not enabled so ensure Client Lo-Fi off for this request.
+    updated_state &= ~(CLIENT_LOFI_ON);
+  } else if (!HasEmptyPageDirective(web_url_response)) {
+    updated_state &= ~(SERVER_LOFI_ON | CLIENT_LOFI_ON);
+  }
+

[megjablon, 2017/06/05 23:47:58]

Can we check here if we cleared all the bits and if so return PREVIEWS_OFF
instead of PREVIEWS_UNSPECIFIED?

Also, maybe we should do that at the top too. We can immediately check if
PREVIEWS_UNSPECIFIED and return PREVIEWS_OFF.

[dougarnett, 2017/06/06 16:49:46]

Done.

+  return updated_state;
+}
+
+}  // namespace content