Introduce the NotificationIdGenerator in //content.

content/browser/notifications/notification_id_generator.cc

+// Copyright 2015 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/notifications/notification_id_generator.h"
+
+#include <sstream>
+
+#include "base/files/file_path.h"
+#include "base/hash.h"
+#include "base/logging.h"
+#include "base/strings/string_number_conversions.h"
+#include "content/public/browser/browser_context.h"
+#include "url/gurl.h"
+
+namespace content {
+
+NotificationIdGenerator::NotificationIdGenerator(
+    BrowserContext* browser_context,
+    int render_process_id)
+    : browser_context_(browser_context),
+      render_process_id_(render_process_id) {}
+
+NotificationIdGenerator::~NotificationIdGenerator() {}
+
+std::string NotificationIdGenerator::GenerateForPersistentNotification(
+    const GURL& origin,
+    const std::string& tag,
+    int64_t persistent_notification_id) const {
+  DCHECK(origin.is_valid());
+  DCHECK_EQ(origin, origin.GetOrigin());
+
+  std::stringstream stream;
+
+  stream <<
+      BASE_HASH_NAMESPACE::hash<base::FilePath>()(browser_context_->GetPath());

[johnme, 2015/05/27 18:18:35]

I'm still uncomfortable with using a hash function that has 18742 collisions
after hashing just 216553 strings[1].

[1]: http://programmers.stackexchange.com/a/145633/122643

[Peter Beverloo, 2015/05/28 12:51:44]

Switched to SHA-1 after talking to bauerb@. Generated IDs are now ~50 characters
long, which is on the long side, but still OK.

+  stream << browser_context_->IsOffTheRecord();
+  stream << origin;
+
+  // Persistent notification ids are unique for the lifetime of the notification
+  // database, orthogonal to the renderer that created the notification.
+
+  stream << !!tag.size();
+  if (tag.size())
+    stream << tag;
+  else
+    stream << base::Int64ToString(persistent_notification_id);
+
+  return stream.str();
+}
+
+std::string NotificationIdGenerator::GenerateForNonPersistentNotification(
+    const GURL& origin,
+    const std::string& tag,
+    int non_persistent_notification_id) const {
+  DCHECK(origin.is_valid());
+  DCHECK_EQ(origin, origin.GetOrigin());
+
+  std::stringstream stream;
+
+  stream <<
+      BASE_HASH_NAMESPACE::hash<base::FilePath>()(browser_context_->GetPath());
+  stream << browser_context_->IsOffTheRecord();
+  stream << origin;
+
+  // Non-persistent notification ids are unique per renderer process when no
+  // tag is being used. Tags still identify uniqueness for the given origin.
+
+  stream << !!tag.size();
+  if (!tag.size()) {
+    const std::string render_process_id_string =
+        base::IntToString(render_process_id_);
+
+    stream << render_process_id_string.size();

[johnme, 2015/05/27 18:18:35]

This is also ambiguous. Whilst it appears to be true that
string(string_of_digits.size()) + string_of_digits is unambiguous (but I
consider that non-obvious), concatenating it with the
non_persistent_notification_id becomes ambiguous.

Please add appropriate separator characters (i.e. at least add one between
render_process_id_string and non_persistent_notification_id; and either add one
between render_process_id_string.size() and render_process_id_string or add a
comment explaining that that concatenation is in fact unambiguous).

[Peter Beverloo, 2015/05/28 12:51:44]

Done.

+    stream << render_process_id_string;
+
+    stream << base::IntToString(non_persistent_notification_id);
+  } else {
+    stream << tag;
+  }
+
+  return stream.str();
+}
+
+}  // namespace content