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/*
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 );
}
}
}
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