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| 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/basictypes.h" | |
| 35 #include "base/memory/scoped_ptr.h" | |
| 36 #include "base/strings/string_piece.h" | |
| 37 | |
| 38 namespace base { | |
| 39 | |
| 40 class Value; | |
| 41 | |
| 42 namespace internal { | |
| 43 class JSONParser; | |
| 44 } | |
| 45 | |
| 46 enum JSONParserOptions { | |
| 47 // Parses the input strictly according to RFC 4627, except for where noted | |
| 48 // above. | |
| 49 JSON_PARSE_RFC = 0, | |
| 50 | |
| 51 // Allows commas to exist after the last element in structures. | |
| 52 JSON_ALLOW_TRAILING_COMMAS = 1 << 0, | |
| 53 | |
| 54 // The parser can perform optimizations by placing hidden data in the root of | |
| 55 // the JSON object, which speeds up certain operations on children. However, | |
| 56 // if the child is Remove()d from root, it would result in use-after-free | |
| 57 // unless it is DeepCopy()ed or this option is used. | |
| 58 JSON_DETACHABLE_CHILDREN = 1 << 1, | |
| 59 }; | |
| 60 | |
| 61 class BASE_EXPORT JSONReader { | |
| 62 public: | |
| 63 // Error codes during parsing. | |
| 64 enum JsonParseError { | |
| 65 JSON_NO_ERROR = 0, | |
| 66 JSON_INVALID_ESCAPE, | |
| 67 JSON_SYNTAX_ERROR, | |
| 68 JSON_UNEXPECTED_TOKEN, | |
| 69 JSON_TRAILING_COMMA, | |
| 70 JSON_TOO_MUCH_NESTING, | |
| 71 JSON_UNEXPECTED_DATA_AFTER_ROOT, | |
| 72 JSON_UNSUPPORTED_ENCODING, | |
| 73 JSON_UNQUOTED_DICTIONARY_KEY, | |
| 74 JSON_PARSE_ERROR_COUNT | |
| 75 }; | |
| 76 | |
| 77 // String versions of parse error codes. | |
| 78 static const char kInvalidEscape[]; | |
| 79 static const char kSyntaxError[]; | |
| 80 static const char kUnexpectedToken[]; | |
| 81 static const char kTrailingComma[]; | |
| 82 static const char kTooMuchNesting[]; | |
| 83 static const char kUnexpectedDataAfterRoot[]; | |
| 84 static const char kUnsupportedEncoding[]; | |
| 85 static const char kUnquotedDictionaryKey[]; | |
| 86 | |
| 87 // Constructs a reader with the default options, JSON_PARSE_RFC. | |
| 88 JSONReader(); | |
| 89 | |
| 90 // Constructs a reader with custom options. | |
| 91 explicit JSONReader(int options); | |
| 92 | |
| 93 ~JSONReader(); | |
| 94 | |
| 95 // Reads and parses |json|, returning a Value. The caller owns the returned | |
| 96 // instance. If |json| is not a properly formed JSON string, returns NULL. | |
| 97 static scoped_ptr<Value> Read(const StringPiece& json); | |
| 98 // TODO(estade): remove this bare pointer version. | |
| 99 static Value* DeprecatedRead(const StringPiece& json); | |
| 100 | |
| 101 // Reads and parses |json|, returning a Value owned by the caller. The | |
| 102 // parser respects the given |options|. If the input is not properly formed, | |
| 103 // returns NULL. | |
| 104 static scoped_ptr<Value> Read(const StringPiece& json, int options); | |
| 105 // TODO(estade): remove this bare pointer version. | |
| 106 static Value* DeprecatedRead(const 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 NULL 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 scoped_ptr<Value> ReadAndReturnError(const StringPiece& json, | |
| 113 int options, // JSONParserOptions | |
| 114 int* error_code_out, | |
| 115 std::string* error_msg_out); | |
| 116 // TODO(estade): remove this bare pointer version. | |
| 117 static Value* DeprecatedReadAndReturnError(const StringPiece& json, | |
| 118 int options, // JSONParserOptions | |
| 119 int* error_code_out, | |
| 120 std::string* error_msg_out); | |
| 121 | |
| 122 // Converts a JSON parse error code into a human readable message. | |
| 123 // Returns an empty string if error_code is JSON_NO_ERROR. | |
| 124 static std::string ErrorCodeToString(JsonParseError error_code); | |
| 125 | |
| 126 // Parses an input string into a Value that is owned by the caller. | |
| 127 scoped_ptr<Value> ReadToValue(const std::string& json); | |
| 128 | |
| 129 // Returns the error code if the last call to ReadToValue() failed. | |
| 130 // Returns JSON_NO_ERROR otherwise. | |
| 131 JsonParseError error_code() const; | |
| 132 | |
| 133 // Converts error_code_ to a human-readable string, including line and column | |
| 134 // numbers if appropriate. | |
| 135 std::string GetErrorMessage() const; | |
| 136 | |
| 137 private: | |
| 138 scoped_ptr<internal::JSONParser> parser_; | |
| 139 }; | |
| 140 | |
| 141 } // namespace base | |
| 142 | |
| 143 #endif // BASE_JSON_JSON_READER_H_ | |
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