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 <memory> 32 #include <string> 33 34 #include "base/base_export.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 // If set the parser replaces invalid characters with the Unicode replacement 60 // character (U+FFFD). If not set, invalid characters trigger a hard error and 61 // parsing fails. 62 JSON_REPLACE_INVALID_CHARACTERS = 1 << 2, 63 }; 64 65 class BASE_EXPORT JSONReader { 66 public: 67 // Error codes during parsing. 68 enum JsonParseError { 69 JSON_NO_ERROR = 0, 70 JSON_INVALID_ESCAPE, 71 JSON_SYNTAX_ERROR, 72 JSON_UNEXPECTED_TOKEN, 73 JSON_TRAILING_COMMA, 74 JSON_TOO_MUCH_NESTING, 75 JSON_UNEXPECTED_DATA_AFTER_ROOT, 76 JSON_UNSUPPORTED_ENCODING, 77 JSON_UNQUOTED_DICTIONARY_KEY, 78 JSON_PARSE_ERROR_COUNT 79 }; 80 81 // String versions of parse error codes. 82 static const char kInvalidEscape[]; 83 static const char kSyntaxError[]; 84 static const char kUnexpectedToken[]; 85 static const char kTrailingComma[]; 86 static const char kTooMuchNesting[]; 87 static const char kUnexpectedDataAfterRoot[]; 88 static const char kUnsupportedEncoding[]; 89 static const char kUnquotedDictionaryKey[]; 90 91 // Constructs a reader with the default options, JSON_PARSE_RFC. 92 JSONReader(); 93 94 // Constructs a reader with custom options. 95 explicit JSONReader(int options); 96 97 ~JSONReader(); 98 99 // Reads and parses |json|, returning a Value. 100 // If |json| is not a properly formed JSON string, returns nullptr. 101 // Wrap this in base::FooValue::From() to check the Value is of type Foo and 102 // convert to a FooValue at the same time. 103 static std::unique_ptr<Value> Read(StringPiece json); 104 105 // Same as Read() above, but the parser respects the given |options|. 106 static std::unique_ptr<Value> Read(StringPiece json, int options); 107 108 // Reads and parses |json| like Read(). |error_code_out| and |error_msg_out| 109 // are optional. If specified and nullptr is returned, they will be populated 110 // an error code and a formatted error message (including error location if 111 // appropriate). Otherwise, they will be unmodified. 112 static std::unique_ptr<Value> ReadAndReturnError( 113 const StringPiece& json, 114 int options, // JSONParserOptions 115 int* error_code_out, 116 std::string* error_msg_out, 117 int* error_line_out = nullptr, 118 int* error_column_out = nullptr); 119 120 // Converts a JSON parse error code into a human readable message. 121 // Returns an empty string if error_code is JSON_NO_ERROR. 122 static std::string ErrorCodeToString(JsonParseError error_code); 123 124 // Non-static version of Read() above. 125 std::unique_ptr<Value> ReadToValue(StringPiece json); 126 127 // Returns the error code if the last call to ReadToValue() failed. 128 // Returns JSON_NO_ERROR otherwise. 129 JsonParseError error_code() const; 130 131 // Converts error_code_ to a human-readable string, including line and column 132 // numbers if appropriate. 133 std::string GetErrorMessage() const; 134 135 private: 136 std::unique_ptr<internal::JSONParser> parser_; 137 }; 138 139 } // namespace base 140 141 #endif // BASE_JSON_JSON_READER_H_ 142
