Gracefully handling panics

[olegbespalov]

What?

During the preparation of #65 I faced the case where using incorrect data, I ended up with panic in k6

Here is an example of script that causes the panic:

import { crypto } from "k6/experimental/webcrypto";

export default async function () {
  const keyData = new Uint8Array([
    7, 152, 164, 45, 255, 169, 164, 66, 164, 163, 20, 197, 194, 223, 48, 213,
    93, 115, 173, 86, 215, 81, 128, 188, 45, 237, 156, 92, 163, 197, 248, 114,
  ]);

  const transmittedData = new Uint8Array([
    167, 9, 89, 202, 97, 13, 137, 77, 223, 24, 226, 161, 225, 228, 121, 248,
    181, 4, 25, 202, 215, 230, 193, 94, 143, 77, 187, 231, 84, 3, 198, 75, 22,
    211, 83, 101, 241, 159, 117, 124, 155, 229, 244, 173, 58, 149, 57, 18,
  ]);

  const iv = new Uint8Array(transmittedData.slice(0, 16));

  // here was my mistake, I cut the transmittedData from 12 to the end
  const encryptedData = new Uint8Array(transmittedData.slice(12));

  const importedKey = await crypto.subtle.importKey(
    "raw",
    keyData,
    { name: "AES-CBC", length: "256" },
    true,
    ["encrypt", "decrypt"]
  );

  // since I wrongly cut the transmittedData the decryption should fail with error
  // but it panics instead
  await crypto.subtle.decrypt(
    {
      name: "AES-CBC",
      iv: iv,
    },
    importedKey,
    encryptedData
  );
}

if I run this, I'll get:

panic: crypto/cipher: input not full blocks

goroutine 104 [running]:
crypto/cipher.(*cbcDecrypter).CryptBlocks(0x1be5890?, {0xc0003587b0?, 0xc000b8e080?, 0x10?}, {0xc000358780?, 0xc000f1c000?, 0xc002515707?})
        /home/olegbespalov/.go/src/crypto/cipher/cbc.go:145 +0x40b
github.com/grafana/xk6-webcrypto/webcrypto.(*AESCBCParams).Decrypt(0xc000b94900, {0xc000358780, 0x24, 0x24}, {{0x181d1fd, 0x6}, 0x1, {0x169f220, 0xc0003ce6c0}, {0xc000e2fa20, ...}, ...})
        /home/olegbespalov/go/pkg/mod/github.com/grafana/[email protected]/webcrypto/aes.go:308 +0xf1
github.com/grafana/xk6-webcrypto/webcrypto.(*SubtleCrypto).Decrypt.func1()
        /home/olegbespalov/go/pkg/mod/github.com/grafana/[email protected]/webcrypto/subtle_crypto.go:187 +0x235
created by github.com/grafana/xk6-webcrypto/webcrypto.(*SubtleCrypto).Decrypt in goroutine 101
        /home/olegbespalov/go/pkg/mod/github.com/grafana/[email protected]/webcrypto/subtle_crypto.go:175 +0x4d7

The panic happens in the go-sdk, but we should catch this and return the user a meaningful error instead. That particular case is related to the cbcDecrypter, but it could be so that not only this algorithm could produce them, so we should be ready and convert it to regular error.

Why?

There should be no panic, but a meaningful error instead.