/* Copyright (c) 2008, Adobe Systems Incorporated All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of Adobe Systems Incorporated nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ package com.adobe.serialization.json { public class JSONTokenizer { /** The object that will get parsed from the JSON string */ private var obj:Object; /** The JSON string to be parsed */ private var jsonString:String; /** The current parsing location in the JSON string */ private var loc:int; /** The current character in the JSON string during parsing */ private var ch:String; /** * Constructs a new JSONDecoder to parse a JSON string * into a native object. * * @param s The JSON string to be converted * into a native object */ public function JSONTokenizer( s:String ) { jsonString = s; loc = 0; // prime the pump by getting the first character nextChar(); } /** * Gets the next token in the input sting and advances * the character to the next character after the token */ public function getNextToken():JSONToken { var token:JSONToken = new JSONToken(); // skip any whitespace / comments since the last // token was read skipIgnored(); // examine the new character and see what we have... switch ( ch ) { case '{': token.type = JSONTokenType.LEFT_BRACE; token.value = '{'; nextChar(); break case '}': token.type = JSONTokenType.RIGHT_BRACE; token.value = '}'; nextChar(); break case '[': token.type = JSONTokenType.LEFT_BRACKET; token.value = '['; nextChar(); break case ']': token.type = JSONTokenType.RIGHT_BRACKET; token.value = ']'; nextChar(); break case ',': token.type = JSONTokenType.COMMA; token.value = ','; nextChar(); break case ':': token.type = JSONTokenType.COLON; token.value = ':'; nextChar(); break; case 't': // attempt to read true var possibleTrue:String = "t" + nextChar() + nextChar() + nextChar(); if ( possibleTrue == "true" ) { token.type = JSONTokenType.TRUE; token.value = true; nextChar(); } else { parseError( "Expecting 'true' but found " + possibleTrue ); } break; case 'f': // attempt to read false var possibleFalse:String = "f" + nextChar() + nextChar() + nextChar() + nextChar(); if ( possibleFalse == "false" ) { token.type = JSONTokenType.FALSE; token.value = false; nextChar(); } else { parseError( "Expecting 'false' but found " + possibleFalse ); } break; case 'n': // attempt to read null var possibleNull:String = "n" + nextChar() + nextChar() + nextChar(); if ( possibleNull == "null" ) { token.type = JSONTokenType.NULL; token.value = null; nextChar(); } else { parseError( "Expecting 'null' but found " + possibleNull ); } break; case '"': // the start of a string token = readString(); break; default: // see if we can read a number if ( isDigit( ch ) || ch == '-' ) { token = readNumber(); } else if ( ch == '' ) { // check for reading past the end of the string return null; } else { // not sure what was in the input string - it's not // anything we expected parseError( "Unexpected " + ch + " encountered" ); } } return token; } /** * Attempts to read a string from the input string. Places * the character location at the first character after the * string. It is assumed that ch is " before this method is called. * * @return the JSONToken with the string value if a string could * be read. Throws an error otherwise. */ private function readString():JSONToken { // the token for the string we'll try to read var token:JSONToken = new JSONToken(); token.type = JSONTokenType.STRING; // the string to store the string we'll try to read var string:String = ""; // advance past the first " nextChar(); while ( ch != '"' && ch != '' ) { // unescape the escape sequences in the string if ( ch == '\\' ) { // get the next character so we know what // to unescape nextChar(); switch ( ch ) { case '"': // quotation mark string += '"'; break; case '/': // solidus string += "/"; break; case '\\': // reverse solidus string += '\\'; break; case 'b': // bell string += '\b'; break; case 'f': // form feed string += '\f'; break; case 'n': // newline string += '\n'; break; case 'r': // carriage return string += '\r'; break; case 't': // horizontal tab string += '\t' break; case 'u': // convert a unicode escape sequence // to it's character value - expecting // 4 hex digits // save the characters as a string we'll convert to an int var hexValue:String = ""; // try to find 4 hex characters for ( var i:int = 0; i < 4; i++ ) { // get the next character and determine // if it's a valid hex digit or not if ( !isHexDigit( nextChar() ) ) { parseError( " Excepted a hex digit, but found: " + ch ); } // valid, add it to the value hexValue += ch; } // convert hexValue to an integer, and use that // integrer value to create a character to add // to our string. string += String.fromCharCode( parseInt( hexValue, 16 ) ); break; default: // couldn't unescape the sequence, so just // pass it through string += '\\' + ch; } } else { // didn't have to unescape, so add the character to the string string += ch; } // move to the next character nextChar(); } // we read past the end of the string without closing it, which // is a parse error if ( ch == '' ) { parseError( "Unterminated string literal" ); } // move past the closing " in the input string nextChar(); // attach to the string to the token so we can return it token.value = string; return token; } /** * Attempts to read a number from the input string. Places * the character location at the first character after the * number. * * @return The JSONToken with the number value if a number could * be read. Throws an error otherwise. */ private function readNumber():JSONToken { // the token for the number we'll try to read var token:JSONToken = new JSONToken(); token.type = JSONTokenType.NUMBER; // the string to accumulate the number characters // into that we'll convert to a number at the end var input:String = ""; // check for a negative number if ( ch == '-' ) { input += '-'; nextChar(); } // the number must start with a digit if ( !isDigit( ch ) ) { parseError( "Expecting a digit" ); } // 0 can only be the first digit if it // is followed by a decimal point if ( ch == '0' ) { input += ch; nextChar(); // make sure no other digits come after 0 if ( isDigit( ch ) ) { parseError( "A digit cannot immediately follow 0" ); } // Commented out - this should only be available when "strict" is false // // unless we have 0x which starts a hex number\ // else if ( ch == 'x' ) // { // // include the x in the input // input += ch; // nextChar(); // // // need at least one hex digit after 0x to // // be valid // if ( isHexDigit( ch ) ) // { // input += ch; // nextChar(); // } // else // { // parseError( "Number in hex format require at least one hex digit after \"0x\"" ); // } // // // consume all of the hex values // while ( isHexDigit( ch ) ) // { // input += ch; // nextChar(); // } // } } else { // read numbers while we can while ( isDigit( ch ) ) { input += ch; nextChar(); } } // check for a decimal value if ( ch == '.' ) { input += '.'; nextChar(); // after the decimal there has to be a digit if ( !isDigit( ch ) ) { parseError( "Expecting a digit" ); } // read more numbers to get the decimal value while ( isDigit( ch ) ) { input += ch; nextChar(); } } // check for scientific notation if ( ch == 'e' || ch == 'E' ) { input += "e" nextChar(); // check for sign if ( ch == '+' || ch == '-' ) { input += ch; nextChar(); } // require at least one number for the exponent // in this case if ( !isDigit( ch ) ) { parseError( "Scientific notation number needs exponent value" ); } // read in the exponent while ( isDigit( ch ) ) { input += ch; nextChar(); } } // convert the string to a number value var num:Number = Number( input ); if ( isFinite( num ) && !isNaN( num ) ) { token.value = num; return token; } else { parseError( "Number " + num + " is not valid!" ); } return null; } /** * Reads the next character in the input * string and advances the character location. * * @return The next character in the input string, or * null if we've read past the end. */ private function nextChar():String { return ch = jsonString.charAt( loc++ ); } /** * Advances the character location past any * sort of white space and comments */ private function skipIgnored():void { var originalLoc:int; // keep trying to skip whitespace and comments as long // as we keep advancing past the original location do { originalLoc = loc; skipWhite(); skipComments(); } while ( originalLoc != loc ); } /** * Skips comments in the input string, either * single-line or multi-line. Advances the character * to the first position after the end of the comment. */ private function skipComments():void { if ( ch == '/' ) { // Advance past the first / to find out what type of comment nextChar(); switch ( ch ) { case '/': // single-line comment, read through end of line // Loop over the characters until we find // a newline or until there's no more characters left do { nextChar(); } while ( ch != '\n' && ch != '' ) // move past the \n nextChar(); break; case '*': // multi-line comment, read until closing */ // move past the opening * nextChar(); // try to find a trailing */ while ( true ) { if ( ch == '*' ) { // check to see if we have a closing / nextChar(); if ( ch == '/') { // move past the end of the closing */ nextChar(); break; } } else { // move along, looking if the next character is a * nextChar(); } // when we're here we've read past the end of // the string without finding a closing */, so error if ( ch == '' ) { parseError( "Multi-line comment not closed" ); } } break; // Can't match a comment after a /, so it's a parsing error default: parseError( "Unexpected " + ch + " encountered (expecting '/' or '*' )" ); } } } /** * Skip any whitespace in the input string and advances * the character to the first character after any possible * whitespace. */ private function skipWhite():void { // As long as there are spaces in the input // stream, advance the current location pointer // past them while ( isWhiteSpace( ch ) ) { nextChar(); } } /** * Determines if a character is whitespace or not. * * @return True if the character passed in is a whitespace * character */ private function isWhiteSpace( ch:String ):Boolean { return ( ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r' ); } /** * Determines if a character is a digit [0-9]. * * @return True if the character passed in is a digit */ private function isDigit( ch:String ):Boolean { return ( ch >= '0' && ch <= '9' ); } /** * Determines if a character is a digit [0-9]. * * @return True if the character passed in is a digit */ private function isHexDigit( ch:String ):Boolean { // get the uppercase value of ch so we only have // to compare the value between 'A' and 'F' var uc:String = ch.toUpperCase(); // a hex digit is a digit of A-F, inclusive ( using // our uppercase constraint ) return ( isDigit( ch ) || ( uc >= 'A' && uc <= 'F' ) ); } /** * Raises a parsing error with a specified message, tacking * on the error location and the original string. * * @param message The message indicating why the error occurred */ public function parseError( message:String ):void { throw new JSONParseError( message, loc, jsonString ); } } }