JSON and Uint8Array

Problem with var x=JSON.parse(JSON.stringify(Obj));
When Obj contains an Uint8Array(N). x is undefined/

function A(){
 this.A=1;
 this.B= new Uint8Array(16);
 this.s= new Uint8Array(16);
}

A.prototype.setup=function(){
 var i;
 for(i=0;i<16;i++)this.B[i]=i;
};

function B(){
 this.B= 2; // new Uint8Array(16);
 this.s= 2; //new Uint8Array(16);
 this.A=1;
}


var a=new A();
a.setup();
console.log(a);
var e=JSON.stringify(a);
console.log(e);
var f=JSON.parse(e);
console.log("f= ",f);

console.log(" ");
var b=new B();
console.log(b);
var e1=JSON.stringify(b);
console.log(e1);
var f1=JSON.parse(e1);
console.log("f1= ",f1);

The output:

>echo(0);
{ "A": 1,
  "B": new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]),
  "s": new Uint8Array(16)
 }
{"A":1,"B":new Uint8Array([0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]),"s":new Uint8Array(16)}
f=  undefined
 
{ "B": 2, "s": 2, "A": 1 }
{"B":2,"s":2,"A":1}
f1=  { "B": 2, "s": 2, "A": 1 }

Almost a fix!
Replace the Uint8Array using E.toString()
do the JSON
Replace the strings using E.toUint8Array()

//jsontest1.js
//21aug2016
function A(){
 this.A=1;
 this.B= new Uint8Array(16);
 this.s= new Uint8Array(16);
}

A.prototype.setup=function(){
 var i;
 for(i=0;i<16;i++)this.B[i]=i;
};

function B(){
 this.B= 2; // new Uint8Array(16);
 this.s= 2; //new Uint8Array(16);
 this.A=1;
}


var a=new A();
a.setup();
console.log(a);
//Almost a fix
 a.B=E.toString(a.B);
 a.s=E.toString(a.s);
 console.log(a);
//
var e=JSON.stringify(a);
console.log(e);
var f=JSON.parse(e);
console.log("f= ",f);
//Almost a fix
 f.B=E.toUint8Array(f.B);
 f.s=E.toUint8Array(f.s);
console.log("f= ",f);

console.log(" ");
var b=new B();
console.log(b);
var e1=JSON.stringify(b);
console.log(e1);
var f1=JSON.parse(e1);
console.log("f1= ",f1);

The output:

>echo(0);
{ "A": 1,
  "B": new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]),
  "s": new Uint8Array(16)
 }
{ "A": 1,
  "B": "\x00\x01\x02\x03\x04\x05\x06\a\b\t\n\x0B\f\r\x0E\x0F",
  "s": "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
 }
{"A":1,"B":"\x00\x01\x02\x03\x04\x05\x06\a\b\t\n\x0B\f\r\x0E\x0F","s":"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"}
f=  { "A": 1,
  "B": "\x00\x01\x02\x03\x04\x05\x06a\b\t\n\x0B\f\r\x0E\x0F",
  "s": "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
 }
f=  { "A": 1,
  "B": new Uint8Array([0, 1, 2, 3, 4, 5, 6, 97, 8, 9, 10, 11, 12, 13, 14, 15]),
  "s": new Uint8Array(16)
 }
 
{ "B": 2, "s": 2, "A": 1 }
{"B":2,"s":2,"A":1}
f1=  { "B": 2, "s": 2, "A": 1 }

Problem the 7 gets changed to 97

2 Attachments

• jsontest1.js
• jsontest.js

A fix using atob() and btoa() functions.

//jsontest3.js
//21aug2016
function A(){
 this.A=1;
 this.B= new Uint8Array(16);
 this.s= new Uint8Array(16);
}

A.prototype.setup=function(){
 var i;
 for(i=0;i<16;i++)this.B[i]=i;
};

function B(){
 this.B= 2; // new Uint8Array(16);
 this.s= 2; //new Uint8Array(16);
 this.A=1;
}


var a=new A();
a.setup();
console.log(a);
//a fix
 a.B=btoa(a.B);
 a.s=btoa(a.s);
 console.log(a);
//
var e=JSON.stringify(a);
console.log(e);
var f=JSON.parse(e);
console.log("f= ",f);
//a fix
 f.B=E.toUint8Array(atob(f.B));
 f.s=E.toUint8Array(atob(f.s));
console.log("f= ",f);

console.log(" ");
var b=new B();
console.log(b);
var e1=JSON.stringify(b);
console.log(e1);
var f1=JSON.parse(e1);
console.log("f1= ",f1);

The output:

>echo(0);
{ "A": 1,
  "B": new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]),
  "s": new Uint8Array(16)
 }
{ "A": 1,
  "B": "AAECAwQFBgcICQoLDA0ODw==",
  "s": "AAAAAAAAAAAAAAAAAAAAAA=="
 }
{"A":1,"B":"AAECAwQFBgcICQoLDA0ODw==","s":"AAAAAAAAAAAAAAAAAAAAAA=="}
f=  { "A": 1,
  "B": "AAECAwQFBgcICQoLDA0ODw==",
  "s": "AAAAAAAAAAAAAAAAAAAAAA=="
 }
f=  { "A": 1,
  "B": new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]),
  "s": new Uint8Array(16)
 }
 
{ "B": 2, "s": 2, "A": 1 }
{"B":2,"s":2,"A":1}
f1=  { "B": 2, "s": 2, "A": 1 }

1 Attachment

• jsontest3.js

Thanks - yes, this is a bit of a pain... There's a bug open for it here: https://github.com/espruino/Espruino/issues/489

Basically the 'standard' JavaScript way of handling Typed Arrays is horrible (turning them into objects), and I don't really want to implement it - but then I don't want to implement something that's not standards compliant either.

If you want to parse the 'semi-JSON' you get from JSON.stringify with a Uint8Array then (as long as you trust the input!) you can use eval instead...