I’m creating an object for making HTTP requests like this:

        $!ua = Cro::HTTP::Client.new(
            base-uri     => 'https://what.ever/api/',
            content-type => 'application/json'
        );

but one of the API endpoints requires using content-type: multipart/form-data instead.

Naively doing something like

        my $response = await $!ua.post(
            "add",
            content-type => 'multipart/form-data',
            body => [Cro::HTTP::Body::MultiPartFormData::Part.new(
                headers => [Cro::HTTP::Header.new(
                    name => 'content-type',
                    value => $mimetype
                )],
                name => $name,
                body-blob => $data,
            )]
        );

results in an error because both content types are concatenated:

    Could not parse media type 'application/json,multipart/form-data'

But how can I override the default content type here?

I’ve tried doing

        $!ua.content-type = '';
        LEAVE {
            $!ua.content-type = 'application/json';
        }

in the same function but this fails with

Cannot modify an immutable Str (application/json)

which I don’t fully understand (why assigning an empty string works but not for the non-empty one?), but I guess this is not the right way to do it anyhow. But which one is?

I can just create another client, of course, but this seems a bit wasteful. And I can avoid specifying the default content type, but then I’d have to do it in all the other requests (of which there are a few), which is not great neither.