Bug in base64url decoding algorithm - undefined length

[tmcw]

Looks like this is here:

deno/ext/node/polyfills/internal/buffer.mjs

Line 1778 in 142449e

src = src.subarray(0, length);

And was introduced recently in #20158

blitBuffer refers to length, which isn't a local variable was probably intended to be byteLength or src.length. Testcase for this bug:

Deno 1.37.0
exit using ctrl+d, ctrl+c, or close()
REPL is running with all permissions allowed.
To specify permissions, run `deno repl` with allow flags.
> import { Buffer } from "node:buffer"
undefined
> Buffer.from('ZmRzYWZkYWZkc2E', 'base64url')
Uncaught ReferenceError: length is not defined
    at blitBuffer (ext:deno_node/internal/buffer.mjs:1778:27)
    at Uint8Array.base64urlWrite (ext:deno_node/internal/buffer.mjs:691:10)
    at Object.write (ext:deno_node/internal/buffer.mjs:2194:11)
    at Uint8Array.write (ext:deno_node/internal/buffer.mjs:794:14)
    at fromString (ext:deno_node/internal/buffer.mjs:214:22)
    at _from (ext:deno_node/internal/buffer.mjs:119:12)
    at Function.from (ext:deno_node/internal/buffer.mjs:157:10)
    at <anonymous>:2:8

This might be the root cause of #20563

[bartlomieju]

@aapoalas could you take a look?