1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 // 5 // A JSON parser. Converts strings of JSON into a Value object (see 6 // base/values.h). 7 // http://www.ietf.org/rfc/rfc4627.txt?number=4627 8 // 9 // Known limitations/deviations from the RFC: 10 // - Only knows how to parse ints within the range of a signed 32 bit int and 11 // decimal numbers within a double. 12 // - Assumes input is encoded as UTF8. The spec says we should allow UTF-16 13 // (BE or LE) and UTF-32 (BE or LE) as well. 14 // - We limit nesting to 100 levels to prevent stack overflow (this is allowed 15 // by the RFC). 16 // - A Unicode FAQ ("http://unicode.org/faq/utf_bom.html") writes a data 17 // stream may start with a Unicode Byte-Order-Mark (U+FEFF), i.e. the input 18 // UTF-8 string for the JSONReader::JsonToValue() function may start with a 19 // UTF-8 BOM (0xEF, 0xBB, 0xBF). 20 // To avoid the function from mis-treating a UTF-8 BOM as an invalid 21 // character, the function skips a Unicode BOM at the beginning of the 22 // Unicode string (converted from the input UTF-8 string) before parsing it. 23 // 24 // TODO(tc): Add a parsing option to to relax object keys being wrapped in 25 // double quotes 26 // TODO(tc): Add an option to disable comment stripping 27 28 #ifndef BASE_JSON_JSON_READER_H_ 29 #define BASE_JSON_JSON_READER_H_ 30 31 #include <string> 32 33 #include "base/base_export.h" 34 #include "base/memory/scoped_ptr.h" 35 #include "base/strings/string_piece.h" 36 37 namespace base { 38 39 class Value; 40 41 namespace internal { 42 class JSONParser; 43 } 44 45 enum JSONParserOptions { 46 // Parses the input strictly according to RFC 4627, except for where noted 47 // above. 48 JSON_PARSE_RFC = 0, 49 50 // Allows commas to exist after the last element in structures. 51 JSON_ALLOW_TRAILING_COMMAS = 1 << 0, 52 53 // The parser can perform optimizations by placing hidden data in the root of 54 // the JSON object, which speeds up certain operations on children. However, 55 // if the child is Remove()d from root, it would result in use-after-free 56 // unless it is DeepCopy()ed or this option is used. 57 JSON_DETACHABLE_CHILDREN = 1 << 1, 58 }; 59 60 class BASE_EXPORT JSONReader { 61 public: 62 // Error codes during parsing. 63 enum JsonParseError { 64 JSON_NO_ERROR = 0, 65 JSON_INVALID_ESCAPE, 66 JSON_SYNTAX_ERROR, 67 JSON_UNEXPECTED_TOKEN, 68 JSON_TRAILING_COMMA, 69 JSON_TOO_MUCH_NESTING, 70 JSON_UNEXPECTED_DATA_AFTER_ROOT, 71 JSON_UNSUPPORTED_ENCODING, 72 JSON_UNQUOTED_DICTIONARY_KEY, 73 JSON_PARSE_ERROR_COUNT 74 }; 75 76 // String versions of parse error codes. 77 static const char kInvalidEscape[]; 78 static const char kSyntaxError[]; 79 static const char kUnexpectedToken[]; 80 static const char kTrailingComma[]; 81 static const char kTooMuchNesting[]; 82 static const char kUnexpectedDataAfterRoot[]; 83 static const char kUnsupportedEncoding[]; 84 static const char kUnquotedDictionaryKey[]; 85 86 // Constructs a reader with the default options, JSON_PARSE_RFC. 87 JSONReader(); 88 89 // Constructs a reader with custom options. 90 explicit JSONReader(int options); 91 92 ~JSONReader(); 93 94 // Reads and parses |json|, returning a Value. The caller owns the returned 95 // instance. If |json| is not a properly formed JSON string, returns NULL. 96 static scoped_ptr<Value> Read(const StringPiece& json); 97 98 // Reads and parses |json|, returning a Value owned by the caller. The 99 // parser respects the given |options|. If the input is not properly formed, 100 // returns NULL. 101 static scoped_ptr<Value> Read(const StringPiece& json, int options); 102 103 // Reads and parses |json| like Read(). |error_code_out| and |error_msg_out| 104 // are optional. If specified and NULL is returned, they will be populated 105 // an error code and a formatted error message (including error location if 106 // appropriate). Otherwise, they will be unmodified. 107 static scoped_ptr<Value> ReadAndReturnError(const StringPiece& json, 108 int options, // JSONParserOptions 109 int* error_code_out, 110 std::string* error_msg_out, 111 int* error_line_out = nullptr, 112 int* error_column_out = nullptr); 113 114 // Converts a JSON parse error code into a human readable message. 115 // Returns an empty string if error_code is JSON_NO_ERROR. 116 static std::string ErrorCodeToString(JsonParseError error_code); 117 118 // Parses an input string into a Value that is owned by the caller. 119 scoped_ptr<Value> ReadToValue(const std::string& json); 120 121 // Returns the error code if the last call to ReadToValue() failed. 122 // Returns JSON_NO_ERROR otherwise. 123 JsonParseError error_code() const; 124 125 // Converts error_code_ to a human-readable string, including line and column 126 // numbers if appropriate. 127 std::string GetErrorMessage() const; 128 129 private: 130 scoped_ptr<internal::JSONParser> parser_; 131 }; 132 133 } // namespace base 134 135 #endif // BASE_JSON_JSON_READER_H_ 136
