Added a PolicySchema class.

chrome/browser/policy/policy_schema.cc

+// Copyright (c) 2013 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 "chrome/browser/policy/policy_schema.h"
+
+#include "base/json/json_reader.h"
+#include "base/logging.h"
+#include "chrome/common/json_schema/json_schema_constants.h"
+#include "chrome/common/json_schema/json_schema_validator.h"
+
+namespace policy {
+
+namespace {
+
+const char kJSONSchemaVersion[] = "http://json-schema.org/draft-03/schema#";
+
+bool SchemaTypeToValueType(const std::string& type_string,
+                           base::Value::Type* type) {
+  // Note: "any" is not an accepted type.
+  static const struct {
+    const char* schema_type;
+    base::Value::Type value_type;
+  } kSchemaToValueTypeMap[] = {
+    { json_schema_constants::kArray,        base::Value::TYPE_LIST        },
+    { json_schema_constants::kBoolean,      base::Value::TYPE_BOOLEAN     },
+    { json_schema_constants::kInteger,      base::Value::TYPE_INTEGER     },
+    { json_schema_constants::kNull,         base::Value::TYPE_NULL        },
+    { json_schema_constants::kNumber,       base::Value::TYPE_DOUBLE      },
+    { json_schema_constants::kObject,       base::Value::TYPE_DICTIONARY  },
+    { json_schema_constants::kString,       base::Value::TYPE_STRING      },
+  };
+  for (size_t i = 0; i < ARRAYSIZE_UNSAFE(kSchemaToValueTypeMap); ++i) {
+    if (kSchemaToValueTypeMap[i].schema_type == type_string) {
+      *type = kSchemaToValueTypeMap[i].value_type;
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
+// static
+scoped_ptr<PolicySchema> PolicySchema::Parse(const std::string& content,
+                                             std::string* error) {
+  // Validate as a generic JSON schema.
+  scoped_ptr<base::DictionaryValue> schema =
+      JSONSchemaValidator::IsValidSchema(content, error);
+  if (!schema)
+    return scoped_ptr<PolicySchema>();
+
+  // Validate the schema version.
+  std::string string_value;
+  if (!schema->GetString(json_schema_constants::kSchema, &string_value) ||
+      string_value != kJSONSchemaVersion) {
+    *error = "Must declare JSON Schema v3 version in \"$schema\"";

[Mattias Nissler (ping if slow), 2013/05/15 10:04:12]

Is this a good idea? This will prevent upgrading to later Schema versions, even
if they are forward-compatible.

[Joao da Silva, 2013/05/19 13:17:08]

If a new format is introduced then Chrome X will start supporting that version,
and it becomes publicly supported in Chrome X+1 or X+2.

I don't think it's a good idea to relax this and accept schemas that "look like
v3". It's possible that "v4" parses as v3 but has different semantics.

+    return scoped_ptr<PolicySchema>();
+  }
+
+  // Validate the main type.
+  if (!schema->GetString(json_schema_constants::kType, &string_value) ||
+      string_value != json_schema_constants::kObject) {
+    *error = "The main schema must have a type attribute with \"object\" value";
+    return scoped_ptr<PolicySchema>();
+  }
+
+  // Validate the properties and convert into a TypeMap.
+  if (schema->HasKey(json_schema_constants::kAdditionalProperties) ||
+      schema->HasKey(json_schema_constants::kPatternProperties)) {
+    *error = "\"additionalProperties\" and \"patternProperties\" are not "
+             "supported at the main schema";

[Mattias Nissler (ping if slow), 2013/05/15 10:04:12]

Ditto: Should this be a hard error or merely a warning if you consider
forward-compatibility?

[Joao da Silva, 2013/05/19 13:17:08]

This restriction is forced because some policy loaders need the exact policy
name to find it. If that isn't needed anymore in the future then we do the X+1
or 2 roll to relax this.

If we relaxed this now then policy names that aren't declared in "properties"
are never loaded, which would be more confusing.

+    return scoped_ptr<PolicySchema>();
+  }
+
+  TypeMap map;
+  const base::DictionaryValue* properties = NULL;
+  if (schema->GetDictionary(json_schema_constants::kProperties, &properties)) {
+    for (base::DictionaryValue::Iterator it(*properties);
+         !it.IsAtEnd(); it.Advance()) {
+      const base::DictionaryValue* dict = NULL;
+      // This should have been verified by the JSONSchemaValidator.
+      CHECK(it.value().GetAsDictionary(&dict));
+      std::string type_string;
+      if (!dict->GetString(json_schema_constants::kType, &type_string)) {
+        *error = "The types of the main properties must be string values";
+        return scoped_ptr<PolicySchema>();
+      }
+      base::Value::Type type = base::Value::TYPE_NULL;
+      if (!SchemaTypeToValueType(type_string, &type)) {
+        *error = "The type of main properties can't be \"any\"";

[Mattias Nissler (ping if slow), 2013/05/15 10:04:12]

Forward-compatibility?

[Joao da Silva, 2013/05/19 13:17:08]

Same rationale again; we can roll an updated version, and for now we need the
exact type.

+        return scoped_ptr<PolicySchema>();
+      }
+      map[it.key()] = type;
+    }
+  }
+
+  scoped_ptr<PolicySchema> policy_schema(new PolicySchema());
+  policy_schema->type_map_.swap(map);
+  return policy_schema.Pass();
+}
+
+PolicySchema::~PolicySchema() {}
+
+PolicySchema::PolicySchema() {}
+
+}  // namespace policy