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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.
#include <stddef.h>
#include <stdint.h>
#include <memory>
#include <string>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/gtest_prod_util.h"
#include "base/json/json_reader.h"
#include "base/macros.h"
#include "base/strings/string_piece.h"
namespace base {
class Value;
namespace internal {
class JSONParserTest;
// The implementation behind the JSONReader interface. This class is not meant
// to be used directly; it encapsulates logic that need not be exposed publicly.
// This parser guarantees O(n) time through the input string. It also optimizes
// base::StringValue by using StringPiece where possible when returning Value
// objects by using "hidden roots," discussed in the implementation.
// Iteration happens on the byte level, with the functions CanConsume and
// NextChar. The conversion from byte to JSON token happens without advancing
// the parser in GetNextToken/ParseToken, that is tokenization operates on
// the current parser position without advancing.
// Built on top of these are a family of Consume functions that iterate
// internally. Invariant: on entry of a Consume function, the parser is wound
// to the first byte of a valid JSON token. On exit, it is on the last byte
// of a token, such that the next iteration of the parser will be at the byte
// immediately following the token, which would likely be the first byte of the
// next token.
class BASE_EXPORT JSONParser {
explicit JSONParser(int options);
// Parses the input string according to the set options and returns the
// result as a Value owned by the caller.
std::unique_ptr<Value> Parse(StringPiece input);
// Returns the error code.
JSONReader::JsonParseError error_code() const;
// Returns the human-friendly error message.
std::string GetErrorMessage() const;
// Returns the error line number if parse error happened. Otherwise always
// returns 0.
int error_line() const;
// Returns the error column number if parse error happened. Otherwise always
// returns 0.
int error_column() const;
enum Token {
T_BOOL_TRUE, // true
T_BOOL_FALSE, // false
T_NULL, // null
// A helper class used for parsing strings. One optimization performed is to
// create base::Value with a StringPiece to avoid unnecessary std::string
// copies. This is not possible if the input string needs to be decoded from
// UTF-16 to UTF-8, or if an escape sequence causes characters to be skipped.
// This class centralizes that logic.
class StringBuilder {
// Empty constructor. Used for creating a builder with which to Swap().
// |pos| is the beginning of an input string, excluding the |"|.
explicit StringBuilder(const char* pos);
// Swaps the contents of |other| with this.
void Swap(StringBuilder* other);
// Either increases the |length_| of the string or copies the character if
// the StringBuilder has been converted. |c| must be in the basic ASCII
// plane; all other characters need to be in UTF-8 units, appended with
// AppendString below.
void Append(const char& c);
// Appends a string to the std::string. Must be Convert()ed to use.
void AppendString(const std::string& str);
// Converts the builder from its default StringPiece to a full std::string,
// performing a copy. Once a builder is converted, it cannot be made a
// StringPiece again.
void Convert();
// Returns whether the builder can be converted to a StringPiece.
bool CanBeStringPiece() const;
// Returns the StringPiece representation. Returns an empty piece if it
// cannot be converted.
StringPiece AsStringPiece();
// Returns the builder as a std::string.
const std::string& AsString();
// The beginning of the input string.
const char* pos_;
// Number of bytes in |pos_| that make up the string being built.
size_t length_;
// The copied string representation. NULL until Convert() is called.
// Strong. std::unique_ptr<T> has too much of an overhead here.
std::string* string_;
// Quick check that the stream has capacity to consume |length| more bytes.
bool CanConsume(int length);
// The basic way to consume a single character in the stream. Consumes one
// byte of the input stream and returns a pointer to the rest of it.
const char* NextChar();
// Performs the equivalent of NextChar N times.
void NextNChars(int n);
// Skips over whitespace and comments to find the next token in the stream.
// This does not advance the parser for non-whitespace or comment chars.
Token GetNextToken();
// Consumes whitespace characters and comments until the next non-that is
// encountered.
void EatWhitespaceAndComments();
// Helper function that consumes a comment, assuming that the parser is
// currently wound to a '/'.
bool EatComment();
// Calls GetNextToken() and then ParseToken(). Caller owns the result.
Value* ParseNextToken();
// Takes a token that represents the start of a Value ("a structural token"
// in RFC terms) and consumes it, returning the result as an object the
// caller owns.
Value* ParseToken(Token token);
// Assuming that the parser is currently wound to '{', this parses a JSON
// object into a DictionaryValue.
Value* ConsumeDictionary();
// Assuming that the parser is wound to '[', this parses a JSON list into a
// ListValue.
Value* ConsumeList();
// Calls through ConsumeStringRaw and wraps it in a value.
Value* ConsumeString();
// Assuming that the parser is wound to a double quote, this parses a string,
// decoding any escape sequences and converts UTF-16 to UTF-8. Returns true on
// success and Swap()s the result into |out|. Returns false on failure with
// error information set.
bool ConsumeStringRaw(StringBuilder* out);
// Helper function for ConsumeStringRaw() that consumes the next four or 10
// bytes (parser is wound to the first character of a HEX sequence, with the
// potential for consuming another \uXXXX for a surrogate). Returns true on
// success and places the UTF8 code units in |dest_string|, and false on
// failure.
bool DecodeUTF16(std::string* dest_string);
// Helper function for ConsumeStringRaw() that takes a single code point,
// decodes it into UTF-8 units, and appends it to the given builder. The
// point must be valid.
void DecodeUTF8(const int32_t& point, StringBuilder* dest);
// Assuming that the parser is wound to the start of a valid JSON number,
// this parses and converts it to either an int or double value.
Value* ConsumeNumber();
// Helper that reads characters that are ints. Returns true if a number was
// read and false on error.
bool ReadInt(bool allow_leading_zeros);
// Consumes the literal values of |true|, |false|, and |null|, assuming the
// parser is wound to the first character of any of those.
Value* ConsumeLiteral();
// Compares two string buffers of a given length.
static bool StringsAreEqual(const char* left, const char* right, size_t len);
// Sets the error information to |code| at the current column, based on
// |index_| and |index_last_line_|, with an optional positive/negative
// adjustment by |column_adjust|.
void ReportError(JSONReader::JsonParseError code, int column_adjust);
// Given the line and column number of an error, formats one of the error
// message contants from json_reader.h for human display.
static std::string FormatErrorMessage(int line, int column,
const std::string& description);
// base::JSONParserOptions that control parsing.
int options_;
// Pointer to the start of the input data.
const char* start_pos_;
// Pointer to the current position in the input data. Equivalent to
// |start_pos_ + index_|.
const char* pos_;
// Pointer to the last character of the input data.
const char* end_pos_;
// The index in the input stream to which the parser is wound.
int index_;
// The number of times the parser has recursed (current stack depth).
int stack_depth_;
// The line number that the parser is at currently.
int line_number_;
// The last value of |index_| on the previous line.
int index_last_line_;
// Error information.
JSONReader::JsonParseError error_code_;
int error_line_;
int error_column_;
friend class JSONParserTest;
FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeDictionary);
FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeLiterals);
} // namespace internal
} // namespace base