add support to retrieve registration

src/main/java/im/conversations/android/xmpp/manager/RegistrationManager.java

@@ -1,13 +1,22 @@
 package im.conversations.android.xmpp.manager;
 
 import android.content.Context;
+import androidx.annotation.NonNull;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.MoreExecutors;
+import eu.siacs.conversations.utils.Patterns;
+import eu.siacs.conversations.xml.Namespace;
 import im.conversations.android.xmpp.XmppConnection;
+import im.conversations.android.xmpp.model.data.Data;
+import im.conversations.android.xmpp.model.oob.OutOfBandData;
+import im.conversations.android.xmpp.model.register.Instructions;
+import im.conversations.android.xmpp.model.register.Password;
 import im.conversations.android.xmpp.model.register.Register;
 import im.conversations.android.xmpp.model.register.Remove;
+import im.conversations.android.xmpp.model.register.Username;
 import im.conversations.android.xmpp.model.stanza.Iq;
+import java.util.regex.Matcher;
 
 public class RegistrationManager extends AbstractManager {
 
@@ -33,9 +42,74 @@ public class RegistrationManager extends AbstractManager {
                 connection.sendIqPacket(iq), r -> null, MoreExecutors.directExecutor());
     }
 
-    // TODO support registration
-    // 3 possible responses:
-    // 1) username + password
-    // 2) Captcha as shown here: https://xmpp.org/extensions/xep-0158.html#register
-    // 3) Redirection as show here: https://xmpp.org/extensions/xep-0077.html#redirect
+    public ListenableFuture<Registration> getRegistration() {
+        final var iq = new Iq(Iq.Type.SET);
+        iq.addExtension(new Register());
+        return Futures.transform(
+                connection.sendIqPacket(iq),
+                result -> {
+                    final var register = result.getExtension(Register.class);
+                    if (register == null) {
+                        throw new IllegalStateException(
+                                "Server did not include register in response");
+                    }
+                    if (register.hasExtension(Username.class)
+                            && register.hasExtension(Password.class)) {
+                        return new SimpleRegistration();
+                    }
+                    final var data = register.getExtension(Data.class);
+                    if (data != null && Namespace.REGISTER.equals(data.getFormType())) {
+                        return new ExtendedRegistration(data);
+                    }
+                    final var oob = register.getExtension(OutOfBandData.class);
+                    final var instructions = register.getExtension(Instructions.class);
+                    final String instructionsText =
+                            instructions == null ? null : instructions.getContent();
+                    final String redirectUrl = oob == null ? null : oob.getURL();
+                    if (redirectUrl != null) {
+                        return new RedirectRegistration(redirectUrl);
+                    }
+                    if (instructionsText != null) {
+                        final Matcher matcher = Patterns.WEB_URL.matcher(instructionsText);
+                        if (matcher.find()) {
+                            final String instructionsUrl =
+                                    instructionsText.substring(matcher.start(), matcher.end());
+                            return new RedirectRegistration(instructionsUrl);
+                        }
+                    }
+                    throw new IllegalStateException("No supported registration method found");
+                },
+                MoreExecutors.directExecutor());
+    }
+
+    private abstract static class Registration {}
+
+    // only requires Username + Password
+    public static class SimpleRegistration extends Registration {}
+
+    // Captcha as shown here: https://xmpp.org/extensions/xep-0158.html#register
+    public static class ExtendedRegistration extends Registration {
+        private final Data data;
+
+        public ExtendedRegistration(Data data) {
+            this.data = data;
+        }
+
+        public Data getData() {
+            return this.data;
+        }
+    }
+
+    // Redirection as show here: https://xmpp.org/extensions/xep-0077.html#redirect
+    public static class RedirectRegistration extends Registration {
+        private final String url;
+
+        public RedirectRegistration(@NonNull final String url) {
+            this.url = url;
+        }
+
+        public @NonNull String getURL() {
+            return this.url;
+        }
+    }
 }

src/main/java/im/conversations/android/xmpp/model/oob/OutOfBandData.java

@@ -1,5 +1,6 @@
 package im.conversations.android.xmpp.model.oob;
 
+import com.google.common.base.Strings;
 import im.conversations.android.annotation.XmlElement;
 import im.conversations.android.xmpp.model.Extension;
 
@@ -12,6 +13,6 @@ public class OutOfBandData extends Extension {
 
     public String getURL() {
         final URL url = this.getExtension(URL.class);
-        return url == null ? null : url.getContent();
+        return url == null ? null : Strings.emptyToNull(url.getContent());
     }
 }

src/main/java/im/conversations/android/xmpp/model/register/Instructions.java

@@ -0,0 +1,10 @@
+package im.conversations.android.xmpp.model.register;
+
+import im.conversations.android.xmpp.model.Extension;
+
+public class Instructions extends Extension {
+
+    public Instructions() {
+        super(Instructions.class);
+    }
+}