Is there a way to convert ArrayBuffer to a ByteArray?

# javascript

[galex]

Is there a way to convert ArrayBuffer to a ByteArray?

[Dico]

Copy the contents

[Svyatoslav Kuzmich [JB]]

You can create Int8Array around the buffer and then unsafe cast it to ByteArray

[Svyatoslav Kuzmich [JB]]

You can find other type mappings here: https://kotlinlang.org/docs/reference/js-to-kotlin-interop.html#representing-kotlin-types-in-javascript

[Dico]

Oh that's cool

[galex]

Thank you so much !!!!! It worked ! For days I am trying to get a file to upload correctly to a backend through ktor-client !

[galex]

@Suppress("CAST_NEVER_SUCCEEDS")
fun ArrayBuffer?.asByteArray(): ByteArray? = this?.run { Int8Array(this) as ByteArray }

[Svyatoslav Kuzmich [JB]]

Great! We highly appreciate feedback. Please let us know if you have any inconveniences.

[galex]

I’d like that function to be part of kotlin/js by default

[galex]

Would have been useful

[Svyatoslav Kuzmich [JB]]

Since we know for sure that ByteArray and Int8Array are the same things on runtime we can use:

fun ArrayBuffer?.asByteArray(): ByteArray? =
   this?.run { Int8Array(this).unsafeCast<ByteArray>() }

This will eliminate unnecesary type check and we don't have to use @Suppress

Generated code for unsafeCast would be:

return $receiver != null ? new Int8Array($receiver) : null;

compared to as version:

var tmp$;
    if ($receiver != null) {
      var tmp$_0;
      tmp$ = Kotlin.isByteArray(tmp$_0 = new Int8Array($receiver)) ? tmp$_0 : throwCCE();
    }
     else
      tmp$ = null;
    return tmp$;

[Svyatoslav Kuzmich [JB]]

I’d like that function to be part of kotlin/js by default

Could you file a feature request at kotl.in/issue?

[galex]

Nice I will use that then

[galex]

Yes I will submit a feature request

[galex]

I didn’t know about unsafeCast, I am going to apply it everywhere needed now

[Svyatoslav Kuzmich [JB]]

unsafeCast has downsides, if cast fails your program will fail the JavaScript way: usually farther down the execution with ambiguous error message 😁

[galex]

ahah

[galex]

https://youtrack.jetbrains.com/issue/KT-30098?project=kt