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// 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.
// A JSON parser. Converts strings of JSON into a Value object (see
// base/values.h).
// Known limitations/deviations from the RFC:
// - Only knows how to parse ints within the range of a signed 32 bit int and
// decimal numbers within a double.
// - Assumes input is encoded as UTF8. The spec says we should allow UTF-16
// (BE or LE) and UTF-32 (BE or LE) as well.
// - We limit nesting to 100 levels to prevent stack overflow (this is allowed
// by the RFC).
// - A Unicode FAQ ("") writes a data
// stream may start with a Unicode Byte-Order-Mark (U+FEFF), i.e. the input
// UTF-8 string for the JSONReader::JsonToValue() function may start with a
// UTF-8 BOM (0xEF, 0xBB, 0xBF).
// To avoid the function from mis-treating a UTF-8 BOM as an invalid
// character, the function skips a Unicode BOM at the beginning of the
// Unicode string (converted from the input UTF-8 string) before parsing it.
// TODO(tc): Add a parsing option to to relax object keys being wrapped in
// double quotes
// TODO(tc): Add an option to disable comment stripping
#include <string>
#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/string_piece.h"
#include "base/memory/scoped_ptr.h"
namespace base {
class Value;
namespace internal {
class JSONParser;
namespace base {
enum JSONParserOptions {
// Parses the input strictly according to RFC 4627, except for where noted
// above.
// Allows commas to exist after the last element in structures.
// The parser can perform optimizations by placing hidden data in the root of
// the JSON object, which speeds up certain operations on children. However,
// if the child is Remove()d from root, it would result in use-after-free
// unless it is DeepCopy()ed or this option is used.
// If set the parser replaces invalid characters with the Unicode replacement
// character (U+FFFD). If not set, invalid characters trigger a hard error
// and parsing fails.
class BASE_EXPORT JSONReader {
// Error codes during parsing.
enum JsonParseError {
// String versions of parse error codes.
static const char* kInvalidEscape;
static const char* kSyntaxError;
static const char* kUnexpectedToken;
static const char* kTrailingComma;
static const char* kTooMuchNesting;
static const char* kUnexpectedDataAfterRoot;
static const char* kUnsupportedEncoding;
static const char* kUnquotedDictionaryKey;
// Constructs a reader with the default options, JSON_PARSE_RFC.
// Constructs a reader with custom options.
explicit JSONReader(int options);
// Reads and parses |json|, returning a Value. The caller owns the returned
// instance. If |json| is not a properly formed JSON string, returns NULL.
static Value* Read(const StringPiece& json);
// Reads and parses |json|, returning a Value owned by the caller. The
// parser respects the given |options|. If the input is not properly formed,
// returns NULL.
static Value* Read(const StringPiece& json, int options);
// Reads and parses |json| like Read(). |error_code_out| and |error_msg_out|
// are optional. If specified and NULL is returned, they will be populated
// an error code and a formatted error message (including error location if
// appropriate). Otherwise, they will be unmodified.
static Value* ReadAndReturnError(const StringPiece& json,
int options, // JSONParserOptions
int* error_code_out,
std::string* error_msg_out);
// Converts a JSON parse error code into a human readable message.
// Returns an empty string if error_code is JSON_NO_ERROR.
static std::string ErrorCodeToString(JsonParseError error_code);
// Parses an input string into a Value that is owned by the caller.
Value* ReadToValue(const std::string& json);
// Returns the error code if the last call to ReadToValue() failed.
// Returns JSON_NO_ERROR otherwise.
JsonParseError error_code() const;
// Converts error_code_ to a human-readable string, including line and column
// numbers if appropriate.
std::string GetErrorMessage() const;
scoped_ptr<internal::JSONParser> parser_;
} // namespace base