int64 validation is incorrect

[klntsky]

ajv-formats/src/formats.ts

Line 252 in 4dd6544

// JSON and javascript max Int is 2**53, so any int that passes isInteger is valid for Int64

// JSON and javascript max Int is 2**53, so any int that passes isInteger is valid for Int64

The second part of the sentence does not follow from the first. Neither JS nor JSON do not throw on overflows.

Consider this:

> Number.isInteger(JSON.parse('' + (2 ** 65)))
true

[klntsky]

I'm not familiar with the overflow behavior in JS, but letting it overflow on platforms that don't support long integers and perform the exact comparison on platforms that do would seemingly be better.

This is not a proposed fix, just an illustration of the idea:

> (JSON.parse('' + (2 ** 63))) < 2 ** 64
true
> (JSON.parse('' + (2 ** 64))) < 2 ** 64
false

[leeleahulkcs]

From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#number_type

• The Number type is a double-precision 64-bit binary format IEEE 754 value. It is capable of storing positive floating-point numbers between 2^-1074 (Number.MIN_VALUE) and 2¹⁰²³ × (2 - 2^-52) (Number.MAX_VALUE) as well as negative floating-point numbers of the same magnitude, but it can only safely store integers in the range -(2⁵³ − 1) (Number.MIN_SAFE_INTEGER) to 2⁵³ − 1 (Number.MAX_SAFE_INTEGER). Outside this range, JavaScript can no longer safely represent integers; they will instead be represented by a double-precision floating point approximation. You can check if a number is within the range of safe integers using Number.isSafeInteger().

From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isSafeInteger

• The Number.isSafeInteger() static method determines whether the provided value is a number that is a safe integer.

You could override the format, or create a new format (i.e. int64safe), and set the validation function to use Number.isSafeInteger().

Using Node.js:

> Number.isInteger(Number.MAX_SAFE_INTEGER)
true
> Number.isSafeInteger(Number.MAX_SAFE_INTEGER)
true
> Number.isInteger(Number.MAX_SAFE_INTEGER+1)
true
> Number.isSafeInteger(Number.MAX_SAFE_INTEGER+1)
false
> Number.isInteger(Number.MIN_SAFE_INTEGER)
true
> Number.isSafeInteger(Number.MIN_SAFE_INTEGER)
true
> Number.isInteger(Number.MIN_SAFE_INTEGER-1)
true
> Number.isSafeInteger(Number.MIN_SAFE_INTEGER-1)
false