| // 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. |
| |
| #ifndef BASE_JSON_JSON_PARSER_H_ |
| #define BASE_JSON_JSON_PARSER_H_ |
| |
| #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 { |
| public: |
| explicit JSONParser(int options); |
| ~JSONParser(); |
| |
| // 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; |
| |
| private: |
| enum Token { |
| T_OBJECT_BEGIN, // { |
| T_OBJECT_END, // } |
| T_ARRAY_BEGIN, // [ |
| T_ARRAY_END, // ] |
| T_STRING, |
| T_NUMBER, |
| T_BOOL_TRUE, // true |
| T_BOOL_FALSE, // false |
| T_NULL, // null |
| T_LIST_SEPARATOR, // , |
| T_OBJECT_PAIR_SEPARATOR, // : |
| T_END_OF_INPUT, |
| T_INVALID_TOKEN, |
| }; |
| |
| // 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 { |
| public: |
| // Empty constructor. Used for creating a builder with which to Swap(). |
| StringBuilder(); |
| |
| // |pos| is the beginning of an input string, excluding the |"|. |
| explicit StringBuilder(const char* pos); |
| |
| ~StringBuilder(); |
| |
| // 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(); |
| |
| private: |
| // 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, NextChar); |
| FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeDictionary); |
| FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeList); |
| FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeString); |
| FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeLiterals); |
| FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ConsumeNumbers); |
| FRIEND_TEST_ALL_PREFIXES(JSONParserTest, ErrorMessages); |
| |
| DISALLOW_COPY_AND_ASSIGN(JSONParser); |
| }; |
| |
| } // namespace internal |
| } // namespace base |
| |
| #endif // BASE_JSON_JSON_PARSER_H_ |