efficient u8a-style slice() & ensure byte arrays have clean-bounds

lib/2bytes.js

@@ -1,11 +1,11 @@
 import { Token, Type } from './token.js'
 import { assertEnoughData } from './common.js'
 import * as uint from './0uint.js'
-import { compare, fromString } from './byte-utils.js'
+import { compare, fromString, slice } from './byte-utils.js'
 
 function toToken (data, pos, prefix, length) {
   assertEnoughData(data, pos, prefix + length)
-  const buf = data.subarray(pos + prefix, pos + prefix + length)
+  const buf = slice(data, pos + prefix, pos + prefix + length)
   return new Token(Type.bytes, buf, prefix + length)
 }
 

lib/bl.js

@@ -16,7 +16,7 @@
  */
 
 // TODO: ipjs doesn't support this, only for test files: https://github.com/mikeal/ipjs/blob/master/src/package/testFile.js#L39
-import { alloc, concat } from './byte-utils.js'
+import { alloc, concat, slice } from './byte-utils.js'
 
 const defaultChunkSize = 1024
 
@@ -151,7 +151,7 @@ class Bl {
         this._initReuseChunk = null
         this.chunks = []
       } else {
-        byts = Uint8Array.prototype.slice.call(this.chunks[0], 0, this.cursor)
+        byts = slice(this.chunks[0], 0, this.cursor)
       }
     } else {
       byts = concat(this.chunks, this.cursor)

lib/byte-utils.js

@@ -38,6 +38,18 @@ export const fromArray = (arr) => {
   return Uint8Array.from(arr)
 }
 
+export const slice = useBuffer
+  ? (bytes, start, end) => {
+      if (isBuffer(bytes)) {
+        return new Uint8Array(bytes.subarray(start, end))
+      }
+      return bytes.slice(start, end)
+    }
+  /* c8 ignore next 3 */
+  : (bytes, start, end) => {
+      return bytes.slice(start, end)
+    }
+
 export const concat = useBuffer
   ? (chunks, length) => {
       // might get a stray plain Array here