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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 | 2x 2x 8x 2x 2x 4x 4x 9x 9x 4x 2x 28x 25x 6x 7x 6x 6x 4x | const arraySize = (arr: unknown[]): number => {
let size = 2;
for (let i = arr.length - 1; i >= 0; i--) size += jsonSizeFast(arr[i]);
return size;
};
const objectSize = (obj: Record<string, unknown>): number => {
let size = 2;
for (const key in obj)
if (
// biome-ignore lint: .hasOwnProperty access is intentional
obj.hasOwnProperty(key)
)
size += 2 + key.length + jsonSizeFast(obj[key]);
return size;
};
/**
* This function is the fastest way to approximate size of JSON object in bytes.
*
* It uses the following heuristics:
*
* - Boolean: 1 byte.
* - Null: 1 byte.
* - Number: 9 bytes (1 byte to store the number type, 8 bytes to store the number).
* - String: 4 bytes + string length. String length is encoded in UTF-8, so it is not
* exactly the same as the number of bytes in the string.
* - Array: 2 bytes + sum of sizes of elements.
* - Object: 2 bytes + 2 bytes for each key + length of each key + sum of sizes of values.
*
* Rationale:
*
* - Booleans and `null` are stored as one byte in MessagePack.
* - Maximum size of a number in MessagePack is 9 bytes (1 byte for the type,
* 8 bytes for the number).
* - Maximum overhead for string storage is 4 bytes in MessagePack. We use that, especially
* because we approximate the size of strings in UTF-8, which can consume more bytes if
* non-ASCII characters are present.
* - Maximum overhead for arrays is 4 bytes in MessagePack, but we use 2 bytes for the
* array length, as we don't expect most arrays to be longer than 65,535 elements.
* - Maximum overhead for objects is 4 bytes in MessagePack, but we use 2 bytes for the
* object length, as we don't expect most objects to have more than 65,535 keys.
* - For object keys we use 2 bytes overhead for each key, as we don't expect most
* keys to be longer than 65,535 characters.
*
* @param value JSON value to calculate approximate size of
* @returns Number of bytes required to store the JSON value
*/
export const jsonSizeFast = (value: unknown): number => {
if (value === null) return 1;
switch (typeof value) {
case 'number':
return 9;
case 'string':
return 4 + value.length;
case 'boolean':
return 1;
}
if (value instanceof Array) return arraySize(value);
return objectSize(value as Record<string, unknown>);
};
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