Fix for #2989 - Cryptomator using the configured proxy

[odouglsantos]

Given issue closes #2989 Cryptomator is not using system proxy to connect to Cryptomator update checker or hub.

During the debug I noticed that it was missing to inject the ProxySelector.getDefault() that returns the default proxy of the system. I performed the configurant tests via JVM Args and the JAVA_TOOL_OPTIONS environment variable both using the parameters -Djava.net.useSystemProxies=true -Dhttp.proxyHost=186.248.206.147 -Dhttp.proxyPort=8080.

Remembering that without the definition of these attributes, the check update works normally

Unfortunately I was only able to test it on MacOS.

[CLAassistant]

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[overheadhunter]

I assumed the system proxy was used anyway. You live and learn.

We do use the java.net.http.HttpClient in various other places as well. So I think we should add the ProxySelector in each of these places.

[odouglsantos]

I assumed the system proxy was used anyway. You live and learn.

We do use the java.net.http.HttpClient in various other places as well. So I think we should add the ProxySelector in each of these places.

Hello,

I uploaded the updates including ProxySelector in all HttpClient builders and I took the liberty of adding in this PR also small improvements in some code snippets that use Optional and replacing the exception NullPointerException to IllegalArgumentException, therefore, it is the best approach for a must-have item.

[overheadhunter]

Thank you, lgtm!

However I wonder why the provideHttpClient() returns an Optional in the first place... 😅

[infeo]

I already wondered, that this PR changes something, because in testing with a colleague only using the proxy selector the update checker still used the "normal" internet connection.

Not specifying the proxy let's automatically use the default proxy, see also the JDK implementation of the HttpClientImpl:

private HttpClientImpl(HttpClientBuilderImpl builder, SingleFacadeFactory facadeFactory) {
    /* ... some code */
    this.userProxySelector = builder.proxy;
    this.proxySelector = Optional.ofNullable(userProxySelector)
            .orElseGet(HttpClientImpl::getDefaultProxySelector);
    /*...*/
}

What's doing the trick is using the property java.net.useSystemProxies=true. And this property needs to be set in our build scripts.