React-native bigint64 deserialization problem - refactoring/bigint64le

src/readBig.ts

@@ -1,5 +1,3 @@
-import { Buffer } from 'buffer'
-
 // https://github.com/nodejs/node/blob/v14.17.0/lib/internal/errors.js#L758
 const ERR_BUFFER_OUT_OF_BOUNDS = () => new Error('Attempt to access memory outside buffer bounds')
 
@@ -28,30 +26,41 @@ function boundsError(value: number, length: number) {
   throw ERR_OUT_OF_RANGE('offset', `>= 0 and <= ${length}`, value)
 }
 
-// https://github.com/nodejs/node/blob/v14.17.0/lib/internal/buffer.js#L129-L145
-export function readBigInt64LE(buffer: Buffer, offset = 0): bigint {
-  validateNumber(offset, 'offset')
-  const first = buffer[offset]
-  const last = buffer[offset + 7]
-  if (first === undefined || last === undefined) boundsError(offset, buffer.length - 8)
-  // tslint:disable-next-line:no-bitwise
-  const val = buffer[offset + 4] + buffer[offset + 5] * 2 ** 8 + buffer[offset + 6] * 2 ** 16 + (last << 24) // Overflow
-  return (
-    (BigInt(val) << BigInt(32)) + // tslint:disable-line:no-bitwise
-    BigInt(first + buffer[++offset] * 2 ** 8 + buffer[++offset] * 2 ** 16 + buffer[++offset] * 2 ** 24)
-  )
-}
-
-// https://github.com/nodejs/node/blob/v14.17.0/lib/internal/buffer.js#L89-L107
+// This function works with react-native >= 0.66.1
 export function readBigUInt64LE(buffer: Buffer, offset = 0): bigint {
-  validateNumber(offset, 'offset')
-  const first = buffer[offset]
-  const last = buffer[offset + 7]
-  if (first === undefined || last === undefined) boundsError(offset, buffer.length - 8)
+  buffer = buffer.slice(offset)
+
+  const bufferLenght = Math.min(buffer.length, 8)
+
+  let tot: number = 0
+  const maxIndex = Math.log2(Number.MAX_VALUE)
+  for(let index = 0; index < bufferLenght; index++) {
+      const value = buffer[index]
+      const exponent = 8*index
+
+      if(exponent > maxIndex)
+          throw new Error("out of range")
 
-  const lo = first + buffer[++offset] * 2 ** 8 + buffer[++offset] * 2 ** 16 + buffer[++offset] * 2 ** 24
+      const addend = value * Math.pow(2, exponent)
+
+      tot += addend
 
-  const hi = buffer[++offset] + buffer[++offset] * 2 ** 8 + buffer[++offset] * 2 ** 16 + last * 2 ** 24
+      // console.log("index: " + index + ", buffer value: " + value + ", decimal value: " + addend + ", tot: " + tot)
+  }
 
-  return BigInt(lo) + (BigInt(hi) << BigInt(32)) // tslint:disable-line:no-bitwise
+  return BigInt(tot)
 }
+
+// This function works with react-native >= 0.66.1
+export function readBigInt64LE(buffer: Buffer, offset = 0): bigint {
+  const resultUnsigned = readBigUInt64LE(buffer, offset)
+
+  const FFFFFFFFFFFFFFFF = BigInt(2**64 - 1);
+
+  if(buffer.length >= 8) {
+    if(buffer[7] >= 128)
+      return resultUnsigned - FFFFFFFFFFFFFFFF;    
+  }
+
+  return resultUnsigned
+}