Create a mechanism define declarative rules via the extension manifest.

extensions/common/api/declarative/declarative_manifest_data.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 "extensions/common/api/declarative/declarative_manifest_data.h"
+
+#include "base/strings/utf_string_conversions.h"
+#include "extensions/common/api/extensions_manifest_types.h"

[not at google - send to devlin, 2015/06/08 21:44:58]

What are you using from this?

[danduong, 2015/06/09 01:21:26]

Done.

+#include "extensions/common/manifest_constants.h"
+
+using base::UTF8ToUTF16;
+
+namespace extensions {
+
+namespace {
+
+std::string ValueTypeToString(base::Value::Type type) {

[not at google - send to devlin, 2015/06/08 21:44:58]

You might as well pass the whole Value into here, rather than its type.

[danduong, 2015/06/09 01:21:26]

Done.

+  static const char* strings[] = {"null",
+                                  "boolean",
+                                  "integer",
+                                  "double",
+                                  "string",
+                                  "binary",
+                                  "dictionary",
+                                  "list"};
+  CHECK(static_cast<size_t>(type) < arraysize(strings));
+  return std::string(strings[type]);

[not at google - send to devlin, 2015/06/08 21:44:58]

you could also make it return a const char* if you prefer.

+}
+
+// Converts a rule defined in the manifest into a JSON internal format. The
+// difference is that actions and conditions use a "type" key to define the
+// type of rule/condition, while the internal format uses a "instanceType" key
+// for this. This function walks through all the conditions and rules to swap
+// the manifest key for the internal key.
+bool ConvertManifestRule(const linked_ptr<DeclarativeManifestData::Rule>& rule,
+                         base::string16* error) {
+  auto convert_list = [error](std::vector<linked_ptr<base::Value>>& list) {
+    for (const linked_ptr<base::Value>& value : list) {
+      base::DictionaryValue* dictionary = nullptr;
+      if (!value->GetAsDictionary(&dictionary)) {
+        if (error->length())
+          error->append(UTF8ToUTF16("; "));
+        error->append(UTF8ToUTF16("expected dictionary, got " +
+                                  ValueTypeToString(value->GetType())));
+        return false;
+      }
+      std::string type;
+      if (!dictionary->GetString("type", &type)) {
+        if (error->length())
+          error->append(UTF8ToUTF16("; "));
+        error->append(UTF8ToUTF16("'type' is required"));
+        return false;
+      }
+      dictionary->Remove("type", nullptr);
+      dictionary->SetString("instanceType", type);
+    }
+    return true;
+  };
+  return convert_list(rule->actions) && convert_list(rule->conditions);
+}
+
+}  // namespace
+
+DeclarativeManifestData::DeclarativeManifestData() {
+}
+
+DeclarativeManifestData::~DeclarativeManifestData() {
+}
+
+// static
+DeclarativeManifestData* DeclarativeManifestData::Get(
+    const Extension* extension) {
+  return static_cast<DeclarativeManifestData*>(
+      extension->GetManifestData(manifest_keys::kEventRules));
+}
+
+// static
+scoped_ptr<DeclarativeManifestData> DeclarativeManifestData::FromValue(
+    const base::Value& value,
+    base::string16* error) {
+  //  The following is an example of how an event programmatic rule definition
+  //  translates to a manifest definition.
+  //
+  //  From javascript:
+  //
+  //  chrome.declarativeContent.onPageChanged.addRules([{
+  //    actions: [
+  //      new chrome.declarativeContent.ShowPageAction()
+  //    ],
+  //    conditions: [
+  //      new chrome.declarativeContent.PageStateMatcher({css: ["video"]})
+  //    ]
+  //  }]);
+  //
+  //  In manifest:
+  //
+  //  "event_rules": [{
+  //    "event" : "declarativeContent.onPageChanged",
+  //    "actions" : [{
+  //      "type": "declarativeContent.ShowPageAction"
+  //    }],
+  //    "conditions" : [{
+  //      "css": ["video"],
+  //      "type" : "declarativeContent.PageStateMatcher"
+  //    }]
+  //  }]
+  //
+  //  The javascript objects get translated into JSON objects with a "type"
+  //  field to indicate the instance type. Instead of adding rules to a
+  //  specific event list, each rule has an "event" field to indicate which
+  //  event it applies to.
+  //
+  scoped_ptr<DeclarativeManifestData> result(new DeclarativeManifestData());
+  const base::ListValue* list = nullptr;
+  if (!value.GetAsList(&list)) {
+    if (error->length())
+      error->append(UTF8ToUTF16("; "));
+    error->append(UTF8ToUTF16("'event_rules' expected list, got " +
+                              ValueTypeToString(value.GetType())));
+    return scoped_ptr<DeclarativeManifestData>();
+  }
+

[not at google - send to devlin, 2015/06/08 21:44:58]

There is a lot of code here for generating errors... is it tested? You could
clean it up a lot by writing a quick ErrorBuilder class. It would let you (a)
remove all of the UTF8ToUTF16 calls, and (b) let you remove all of the semicolon
handling:


class ErrorBuilder {
 public:
  ErrorBuilder() {}

  const base::string16& error() { return error_; }

  // Appends a literal string |error|.
  void Append(const char* error) {
    if (error_.length())
      error_.append(UF8ToUTF16("; "));
    error_.append(UTF8ToUTF16(error));
  }

  // Appends a string |error| with the first %s replaced by |sub|.
  void Append(const char* error, const char* sub) {
    Append(base::StringPrintf(error, sub));
  }
  

 private:
  DISALLOW_COPY_AND_ASSIGN(ErrorBuilder);

  base::string16 error_;
}


here, assuming it's passed in as a pointer, use like:

error_builder->Append("'event_rules' expected list, got ",
                      ValueTypeToString(value));
... (later)
error_builder->Append("expected dictionary");


Would generally make the business logic easier to review as well.

[danduong, 2015/06/09 01:21:26]

Done.

+  for (size_t i = 0; i < list->GetSize(); ++i) {
+    const base::DictionaryValue* dict = nullptr;
+    if (!list->GetDictionary(i, &dict)) {
+      if (error->length())
+        error->append(base::UTF8ToUTF16("; "));
+      const base::Value* value = nullptr;
+      if (list->Get(i, &value))
+        error->append(base::UTF8ToUTF16("expected dictionary, got " +
+                                        ValueTypeToString(value->GetType())));
+      else
+        error->append(base::UTF8ToUTF16("expected dictionary"));
+      return scoped_ptr<DeclarativeManifestData>();
+    }
+    std::string event;
+    if (!dict->GetString("event", &event)) {
+      if (error->length())
+        error->append(UTF8ToUTF16("; "));
+      error->append(UTF8ToUTF16("'event' is required"));
+    }
+    linked_ptr<Rule> rule(new Rule());
+    if (Rule::Populate(*dict, rule.get()) && ConvertManifestRule(rule, error)) {
+      result->event_rules_map_[event].push_back(rule);
+    } else {
+      if (error->length())
+        error->append(UTF8ToUTF16("; "));
+      error->append(UTF8ToUTF16("rule failed to populate"));
+      return scoped_ptr<DeclarativeManifestData>();
+    }
+  }
+  return result.Pass();
+}
+
+std::vector<linked_ptr<DeclarativeManifestData::Rule>>&
+DeclarativeManifestData::RulesForEvent(const std::string& event) {
+  return event_rules_map_[event];
+}
+
+}  // namespace extensions