非递归Javascript JSON解析器

浏览器中的JSON解析通常只使用eval完成,但在eval前面使用正则表达式“lint”,这应该可以安全地评估JSON。

维基百科上有一个这样的例子:

• http://en.wikipedia.org/wiki/JSON#Security_issues

如果eval抛出stackoverflow,您可以使用它

http://code.google.com/p/json-sans-eval/

一个根本不使用eval()的JSON解析器。

我已经用几种语言编写了JSON解析器,它们不是递归的,但直到现在还没有用JavaScript编写。它不是递归的,而是使用名为stack的本地数组。在actionscript中,这比递归快得多,内存效率也更高,我假设javascript也会类似。

此实现使用 eval 仅用于带反斜杠转义的带引号字符串,作为优化和简化。可以很容易地用任何其他解析器的字符串处理来替换。转义处理代码很长,与递归无关。

这个实现在(至少)以下方面并不严格。它将8位字符视为空白。它允许数字前导“+”和“0”。它允许在数组和对象中跟踪“”。它忽略第一个结果之后的输入。因此“[+09,]2”返回[9]并忽略“2”。

function parseJSON( inJSON ) {
    var result;
    var parent;
    var string;

    var depth = 0;
    var stack = new Array();
    var state = 0;

    var began , place = 0 , limit = inJSON.length;
    var letter;

    while ( place < limit ) {
        letter = inJSON.charCodeAt( place++ );

        if ( letter <= 0x20 || letter >= 0x7F ) {   //  whitespace or control
        } else if ( letter === 0x22 ) {             //  " string
            var slash = 0;
            var plain = true;

            began = place - 1;
            while ( place < limit ) {
                letter = inJSON.charCodeAt( place++ );

                if ( slash !== 0 ) {
                    slash = 0;
                } else if ( letter === 0x5C ) {     //  \ escape
                    slash = 1;
                    plain = false;
                } else if ( letter === 0x22 ) {     //  " string
                    if ( plain ) {
                        result = inJSON.substring( began + 1 , place - 1 );
                    } else {
                        string = inJSON.substring( began , place );
                        result = eval( string );    //  eval to unescape
                    }

                    break;
                }
            }
        } else if ( letter === 0x7B ) {             //  { object
            stack[depth++] = state;
            stack[depth++] = parent;
            parent = new Object();
            result = undefined;
            state = letter;
        } else if ( letter === 0x7D ) {             //  } object
            if ( state === 0x3A ) {
                parent[stack[--depth]] = result;
                state = stack[--depth];
            }

            if ( state === 0x7B ) {
                result = parent;
                parent = stack[--depth];
                state = stack[--depth];
            } else {
                //  error got } expected state {
                result = undefined;
                break;
            }
        } else if ( letter === 0x5B ) {             //  [ array
            stack[depth++] = state;
            stack[depth++] = parent;
            parent = new Array();
            result = undefined;
            state = letter;
        } else if ( letter === 0x5D ) {             //  ] array
            if ( state === 0x5B ) {
                if ( undefined !== result ) parent.push( result );

                result = parent;
                parent = stack[--depth];
                state = stack[--depth];
            } else {
                //  error got ] expected state [
                result = undefined;
                break;
            }
        } else if ( letter === 0x2C ) {             //  , delimiter
            if ( undefined === result ) {
                //  error got , expected previous value
                break;
            } else if ( state === 0x3A ) {
                parent[stack[--depth]] = result;
                state = stack[--depth];
                result = undefined;
            } else if ( state === 0x5B ) {
                parent.push( result );
                result = undefined;
            } else {
                //  error got , expected state [ or :
                result = undefined;
                break;
            }
        } else if ( letter === 0x3A ) {             //  : assignment
            if ( state === 0x7B ) {
                //  could verify result is string
                stack[depth++] = state;
                stack[depth++] = result;
                state = letter;
                result = undefined;
            } else {
                //  error got : expected state {
                result = undefined;
                break;
            }
        } else {
            if ( ( letter >= 0x30 && letter <= 0x39 ) || letter === 0x2B || letter === 0x2D || letter === 0x2E ) {
                var             exponent = -2;
                var             real = ( letter === 0x2E );
                var             digits = ( letter >= 0x30 && letter <= 0x39 ) ? 1 : 0;

                began = place - 1;
                while ( place < limit ) {
                    letter = inJSON.charCodeAt( place++ );

                    if ( letter >= 0x30 && letter <= 0x39 ) {           //  digit
                        digits += 1;
                    } else if ( letter === 0x2E ) {                     //  .
                        if ( real ) break;
                        else real = true;
                    } else if ( letter === 0x45 || letter === 0x65 ) {  //  e E
                        if ( exponent > began || 0 === digits ) break;
                        else exponent = place - 1;
                        real = true;
                    } else if ( letter === 0x2B || letter === 0x2D ) {  //  + -
                        if ( place != exponent + 2 ) break;
                    } else {
                        break;
                    }
                }

                place -= 1;
                string = inJSON.substring( began , place );

                if ( 0 === digits ) break;  //  error expected digits
                if ( real ) result = parseFloat( string );
                else result = parseInt( string , 10 );
            } else if ( letter === 0x6E && 'ull' === inJSON.substr( place , 3 ) ) {
                result = null;
                place += 3;
            } else if ( letter === 0x74 && 'rue' === inJSON.substr( place , 3 ) ) {
                result = true;
                place += 3;
            } else if ( letter === 0x66 && 'alse' === inJSON.substr( place , 4 ) ) {
                result = false;
                place += 4;
            } else {
                //  error unrecognized literal
                result = undefined;
                break;
            }
        }

        if ( 0 === depth ) break;
    }

    return result;
}

我建议您将JSON字符串分成块,并按需提供。可能也在使用Ajax,您可以有一个刚好适合您需要的配方。 使用“分而治之”机制,我认为您仍然可以使用常见的JSON解析方法。

希望能有所帮助,