[core] Make AccountManager.getRegistrationInfo() public

[stokito]

The getRegistrationInfo() returns a registration form that may also contain a CAPTCHA. We need to get the full Registration object to get the fields. Also it should be possible to call it multiple times to update the form.

This is related to igniterealtime/Spark#877

[stokito]

Also we'll need to process more fields from response. Here is a real world example:

<!-- request for registration form -->
<iq xmlns="jabber:client" to="conversations.im" type="get" id="65081b4b-8131-4b17-afdd-b317f9560348">
  <query xmlns="jabber:iq:register" />
</iq>

<!-- response with form -->
<iq xmlns="jabber:client" xml:lang="en" from="conversations.im" type="result" id="65081b4b-8131-4b17-afdd-b317f9560348">
  <query xmlns="jabber:iq:register">
    <x type="form" xmlns="jabber:x:data">
      <instructions>Choose a username and password to register with this server</instructions>
      <field var="FORM_TYPE" type="hidden">
        <value>jabber:iq:register</value>
</field>
      <field var="username" type="text-single" label="User">
        <required />
</field>
      <field var="password" type="text-private" label="Password">
        <required />
</field>
      <field var="captcha-fallback-text" type="fixed">
        <value>If you don't see the CAPTCHA image here, visit the web page.</value>
</field>
      <field var="captcha-fallback-url" type="text-single" label="CAPTCHA web page">
        <value>https://xmpp.conversations.im/captcha/7183915110689270672/image</value>
</field>
      <field var="from" type="hidden" label="Attribute 'to' of stanza that triggered challenge">
        <value>conversations.im</value>
</field>
      <field var="challenge" type="hidden" label="Challenge ID">
        <required />
        <value>7183915110689270672</value>
</field>
      <field var="sid" type="hidden" label="Stanza ID">
        <value>65081b4b-8131-4b17-afdd-b317f9560348</value>
</field>
      <field var="ocr" type="text-single" label="Enter the text you see">
        <media xmlns="urn:xmpp:media-element">
          <uri type="image/png">cid:[email protected]</uri>
</media>
        <required />
</field>
</x>
    <data type="image/png" max-age="0" cid="[email protected]" xmlns="urn:xmpp:bob">BASE64_OF_PNG_HERE</data>
    <instructions>You need a client that supports x:data and CAPTCHA to register</instructions>
</query>
</iq>

So we should process the last <data> element that contains a CAPTCHA content.

[Flowdalic]

I don't have any issues with having a public getRegistrationInfo() method. However, the method should per default use the cached value (if any). So something like this should do the trick:

    public synchronized Registration getRegistrationInfo() throws NoResponseException, XMPPErrorException, NotConnectedException, InterruptedException {
        return getRegistrationInfo(true);
    }

    public synchronized Registration getRegistrationInfo(boolean useCached) throws NoResponseException, XMPPErrorException, NotConnectedException, InterruptedException {
        if (useCached && info != null) {
            return info;
        }

        Registration reg = new Registration();
        reg.setTo(connection().getXMPPServiceDomain());
        info = createStanzaCollectorAndSend(reg).nextResultOrThrow();
        return info;
    }

[stokito]

I intentionally kept it to always fetch info but store locally. See, unlike simple registrations here we can't keep a state with a form internally.

If a user can't see a CAPTCHA then it will need to press a button "Start registration" again and receive a new info with the new image.
In the same time the getInstructions() and createAccount() will use the newer version of form stored.

So the full flow will be:

• Call the getRegistrationInfo() and store the form to a variable. Internally the form will be also stored to a the private info field for a cache.
• Call supportsAccountCreation() that internally will check the cached info. The method can be moved into the Registration itself.
• If the info contains a form (captcha, email etc.) then render it. We should also get instructions from the from instead of those from info.
• Call createAccount() and pass values from the form as attributes.

Check my pr to the Spark to see it in action. igniterealtime/Spark@9d8876b#diff-35302a6fb74fb0dde4631403f2d85abd379231a22283c69ce058b12de8c69abfR240

You may try the conversations.im server to see a form with a captcha.