Add support for XEP-0422: Message Fastening

SMACK-884

documentation/extensions/index.md

@@ -120,6 +120,7 @@ Experimental Smack Extensions and currently supported XEPs of smack-experimental
 | [Consistent Color Generation](consistent_colors.md)       | [XEP-0392](https://xmpp.org/extensions/xep-0392.html)  | 0.6.0     | Generate consistent colors for identifiers like usernames to provide a consistent user experience. |
 | [Message Markup](messagemarkup.md)                        | [XEP-0394](https://xmpp.org/extensions/xep-0394.html)  | 0.1.0     | Style message bodies while keeping body and markup information separated. |
 | DNS Queries over XMPP (DoX)                               | [XEP-0418](https://xmpp.org/extensions/xep-0418.html)  | 0.1.0     | Send DNS queries and responses over XMPP. |
+| Message Fastening                                         | [XEP-0422](https://xmpp.org/extensions/xep-0422.html)  | 0.1.1     | Mark payloads on a message to be logistically fastened to a previous message. |
 
 Unofficial XMPP Extensions
 --------------------------

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/MessageFasteningManager.java

@@ -0,0 +1,107 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.message_fastening;
+
+import java.util.List;
+import java.util.WeakHashMap;
+
+import org.jivesoftware.smack.ConnectionCreationListener;
+import org.jivesoftware.smack.Manager;
+import org.jivesoftware.smack.XMPPConnection;
+import org.jivesoftware.smack.XMPPConnectionRegistry;
+import org.jivesoftware.smack.packet.MessageBuilder;
+import org.jivesoftware.smackx.disco.ServiceDiscoveryManager;
+import org.jivesoftware.smackx.message_fastening.element.FasteningElement;
+
+/**
+ * Smacks API for XEP-0422: Message Fastening.
+ * The API is still very bare bones, as the XEP intends Message Fastening to be used as a tool by other protocols.
+ *
+ * To enable / disable auto-announcing support for this feature, call {@link #setEnabledByDefault(boolean)} (default true).
+ *
+ * To fasten a payload to a previous message, create an {@link FasteningElement} using the builder provided by
+ * {@link FasteningElement#builder()}.
+ *
+ * You need to provide the {@link org.jivesoftware.smackx.sid.element.OriginIdElement} of the message you want to reference.
+ * Then add wrapped payloads using {@link FasteningElement.Builder#addWrappedPayloads(List)}
+ * and external payloads using {@link FasteningElement.Builder#addExternalPayloads(List)}.
+ *
+ * If you fastened some payloads onto the message previously and now want to replace the previous fastening, call
+ * {@link FasteningElement.Builder#isRemovingElement()}.
+ * Once you are finished, build the {@link FasteningElement} using {@link FasteningElement.Builder#build()} and add it to
+ * a stanza by calling {@link FasteningElement#applyTo(MessageBuilder)}.
+ *
+ * @see <a href="https://xmpp.org/extensions/xep-0422.html">XEP-0422: Message Fastening</a>
+ */
+public final class MessageFasteningManager extends Manager {
+
+    public static final String NAMESPACE = "urn:xmpp:fasten:0";
+
+    private static boolean ENABLED_BY_DEFAULT = true;
+
+    private static final WeakHashMap<XMPPConnection, MessageFasteningManager> INSTANCES = new WeakHashMap<>();
+
+    static {
+        XMPPConnectionRegistry.addConnectionCreationListener(new ConnectionCreationListener() {
+            @Override
+            public void connectionCreated(XMPPConnection connection) {
+                if (ENABLED_BY_DEFAULT) {
+                    MessageFasteningManager.getInstanceFor(connection).announceSupport();
+                }
+            }
+        });
+    }
+
+    private MessageFasteningManager(XMPPConnection connection) {
+        super(connection);
+    }
+
+    public static synchronized MessageFasteningManager getInstanceFor(XMPPConnection connection) {
+        MessageFasteningManager manager = INSTANCES.get(connection);
+        if (manager == null) {
+            manager = new MessageFasteningManager(connection);
+            INSTANCES.put(connection, manager);
+        }
+        return manager;
+    }
+
+    /**
+     * Enable or disable auto-announcing support for Message Fastening.
+     * Default is enabled.
+     *
+     * @param enabled enabled
+     */
+    public static synchronized void setEnabledByDefault(boolean enabled) {
+        ENABLED_BY_DEFAULT = enabled;
+    }
+
+    /**
+     * Announce support for Message Fastening via Service Discovery.
+     */
+    public void announceSupport() {
+        ServiceDiscoveryManager discoveryManager = ServiceDiscoveryManager.getInstanceFor(connection());
+        discoveryManager.addFeature(NAMESPACE);
+    }
+
+    /**
+     * Stop announcing support for Message Fastening.
+     */
+    public void stopAnnouncingSupport() {
+        ServiceDiscoveryManager discoveryManager = ServiceDiscoveryManager.getInstanceFor(connection());
+        discoveryManager.removeFeature(NAMESPACE);
+    }
+}

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/element/ExternalElement.java

@@ -0,0 +1,84 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.message_fastening.element;
+
+import org.jivesoftware.smack.packet.NamedElement;
+import org.jivesoftware.smack.packet.XmlEnvironment;
+import org.jivesoftware.smack.util.XmlStringBuilder;
+
+/**
+ * Child element of {@link FasteningElement}.
+ * Reference to a top level element in the stanza that contains the {@link FasteningElement}.
+ */
+public class ExternalElement implements NamedElement {
+
+    public static final String ELEMENT = "external";
+    public static final String ATTR_NAME = "name";
+    public static final String ATTR_ELEMENT_NAMESPACE = "element-namespace";
+
+    private final String name;
+    private final String elementNamespace;
+
+    /**
+     * Create a new {@link ExternalElement} that references a top level element with the given name.
+     *
+     * @param name name of the top level element
+     */
+    public ExternalElement(String name) {
+        this(name, null);
+    }
+
+    /**
+     * Create a new {@link ExternalElement} that references a top level element with the given name and namespace.
+     *
+     * @param name name of the top level element
+     * @param elementNamespace namespace of the top level element
+     */
+    public ExternalElement(String name, String elementNamespace) {
+        this.name = name;
+        this.elementNamespace = elementNamespace;
+    }
+
+    @Override
+    public String getElementName() {
+        return ELEMENT;
+    }
+
+    @Override
+    public XmlStringBuilder toXML(XmlEnvironment xmlEnvironment) {
+        XmlStringBuilder xml = new XmlStringBuilder(this);
+        xml.attribute(ATTR_NAME, getName());
+        xml.optAttribute(ATTR_ELEMENT_NAMESPACE, getElementNamespace());
+        return xml.closeEmptyElement();
+    }
+
+    /**
+     * Name of the referenced top level element, eg. 'body'.
+     * @return element name
+     */
+    public String getName() {
+        return name;
+    }
+
+    /**
+     * Namespace of the referenced top level element, eg. 'urn:example:lik'.
+     * @return element namespace
+     */
+    public String getElementNamespace() {
+        return elementNamespace;
+    }
+}

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/element/FasteningElement.java

@@ -0,0 +1,325 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.message_fastening.element;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.jivesoftware.smack.packet.ExtensionElement;
+import org.jivesoftware.smack.packet.Message;
+import org.jivesoftware.smack.packet.MessageBuilder;
+import org.jivesoftware.smack.packet.Stanza;
+import org.jivesoftware.smack.packet.XmlEnvironment;
+import org.jivesoftware.smack.util.Objects;
+import org.jivesoftware.smack.util.XmlStringBuilder;
+import org.jivesoftware.smackx.message_fastening.MessageFasteningManager;
+import org.jivesoftware.smackx.sid.element.OriginIdElement;
+
+/**
+ * Message Fastening container element.
+ */
+public final class FasteningElement implements ExtensionElement {
+
+    public static final String ELEMENT = "apply-to";
+    public static final String NAMESPACE = MessageFasteningManager.NAMESPACE;
+    public static final String ATTR_ID = "id";
+    public static final String ATTR_CLEAR = "clear";
+    public static final String ATTR_SHELL = "shell";
+
+    private final OriginIdElement referencedStanzasOriginId;
+    private final List<ExternalElement> externalPayloads = new ArrayList<>();
+    private final List<ExtensionElement> wrappedPayloads = new ArrayList<>();
+    private final boolean clear;
+    private final boolean shell;
+
+    private FasteningElement(OriginIdElement originId,
+                             List<ExtensionElement> wrappedPayloads,
+                             List<ExternalElement> externalPayloads,
+                             boolean clear,
+                             boolean shell) {
+        this.referencedStanzasOriginId = Objects.requireNonNull(originId, "Fastening element MUST contain an origin-id.");
+        this.wrappedPayloads.addAll(wrappedPayloads);
+        this.externalPayloads.addAll(externalPayloads);
+        this.clear = clear;
+        this.shell = shell;
+    }
+
+    /**
+     * Return the {@link OriginIdElement origin-id} of the {@link Stanza} that the message fastenings are to be
+     * applied to.
+     *
+     * @return origin id of the referenced stanza
+     */
+    public OriginIdElement getReferencedStanzasOriginId() {
+        return referencedStanzasOriginId;
+    }
+
+    /**
+     * Return all wrapped payloads of this element.
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#wrapped-payloads">XEP-0422: §3.1. Wrapped Payloads</a>
+     *
+     * @return wrapped payloads.
+     */
+    public List<ExtensionElement> getWrappedPayloads() {
+        return Collections.unmodifiableList(wrappedPayloads);
+    }
+
+    /**
+     * Return all external payloads of this element.
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#external-payloads">XEP-0422: §3.2. External Payloads</a>
+     *
+     * @return external payloads.
+     */
+    public List<ExternalElement> getExternalPayloads() {
+        return Collections.unmodifiableList(externalPayloads);
+    }
+
+    /**
+     * Does this element remove a previously sent {@link FasteningElement}?
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#remove">
+     *     XEP-0422: Message Fastening §3.4 Removing fastenings</a>
+     *
+     * @return true if the clear attribute is set.
+     */
+    public boolean isRemovingElement() {
+        return clear;
+    }
+
+    /**
+     * Is this a shell element?
+     * Shell elements are otherwise empty elements that indicate that an encrypted payload of a message
+     * encrypted using XEP-420: Stanza Content Encryption contains a sensitive {@link FasteningElement}.
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#encryption">
+     *     XEP-0422: Message Fastening §3.5 Interaction with stanza encryption</a>
+     *
+     * @return true if this is a shell element.
+     */
+    public boolean isShellElement() {
+        return shell;
+    }
+
+    /**
+     * Return true if the provided {@link Message} contains a {@link FasteningElement}.
+     *
+     * @param message message
+     * @return true if the stanza has an {@link FasteningElement}.
+     */
+    public static boolean hasFasteningElement(Message message) {
+        return message.hasExtension(ELEMENT, MessageFasteningManager.NAMESPACE);
+    }
+
+    /**
+     * Return true if the provided {@link MessageBuilder} contains a {@link FasteningElement}.
+     *
+     * @param builder message builder
+     * @return true if the stanza has an {@link FasteningElement}.
+     */
+    public static boolean hasFasteningElement(MessageBuilder builder) {
+        return builder.hasExtension(FasteningElement.class);
+    }
+
+    @Override
+    public String getNamespace() {
+        return MessageFasteningManager.NAMESPACE;
+    }
+
+    @Override
+    public String getElementName() {
+        return ELEMENT;
+    }
+
+    @Override
+    public XmlStringBuilder toXML(XmlEnvironment xmlEnvironment) {
+        XmlStringBuilder xml = new XmlStringBuilder(this)
+                .attribute(ATTR_ID, referencedStanzasOriginId.getId())
+                .optBooleanAttribute(ATTR_CLEAR, isRemovingElement())
+                .optBooleanAttribute(ATTR_SHELL, isShellElement())
+                .rightAngleBracket();
+        addPayloads(xml);
+        return xml.closeElement(this);
+    }
+
+    private void addPayloads(XmlStringBuilder xml) {
+        for (ExternalElement external : externalPayloads) {
+            xml.append(external);
+        }
+        for (ExtensionElement wrapped : wrappedPayloads) {
+            xml.append(wrapped);
+        }
+    }
+
+    public static FasteningElement createShellElementForSensitiveElement(FasteningElement sensitiveElement) {
+        return createShellElementForSensitiveElement(sensitiveElement.getReferencedStanzasOriginId());
+    }
+
+    public static FasteningElement createShellElementForSensitiveElement(String originIdOfSensitiveElement) {
+        return createShellElementForSensitiveElement(new OriginIdElement(originIdOfSensitiveElement));
+    }
+
+    public static FasteningElement createShellElementForSensitiveElement(OriginIdElement originIdOfSensitiveElement) {
+        return FasteningElement.builder()
+                .setOriginId(originIdOfSensitiveElement)
+                .setShell()
+                .build();
+    }
+
+    /**
+     * Add this element to the provided message builder.
+     * Note: The stanza MUST NOT contain more than one apply-to elements at the same time.
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#rules">XEP-0422 §4: Business Rules</a>
+     *
+     * @param messageBuilder message builder
+     */
+    public void applyTo(MessageBuilder messageBuilder) {
+        if (FasteningElement.hasFasteningElement(messageBuilder)) {
+            throw new IllegalArgumentException("Stanza cannot contain more than one apply-to elements.");
+        } else {
+            messageBuilder.addExtension(this);
+        }
+    }
+
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    public static class Builder {
+        private OriginIdElement originId;
+        private final List<ExtensionElement> wrappedPayloads = new ArrayList<>();
+        private final List<ExternalElement> externalPayloads = new ArrayList<>();
+        private boolean isClear = false;
+        private boolean isShell = false;
+
+        /**
+         * Set the origin-id of the referenced message.
+         *
+         * @param originIdString origin id as String
+         * @return builder instance
+         */
+        public Builder setOriginId(String originIdString) {
+            return setOriginId(new OriginIdElement(originIdString));
+        }
+
+        /**
+         * Set the {@link OriginIdElement} of the referenced message.
+         *
+         * @param originId origin-id as element
+         * @return builder instance
+         */
+        public Builder setOriginId(OriginIdElement originId) {
+            this.originId = originId;
+            return this;
+        }
+
+        /**
+         * Add a wrapped payload.
+         *
+         * @param wrappedPayload wrapped payload
+         * @return builder instance
+         */
+        public Builder addWrappedPayload(ExtensionElement wrappedPayload) {
+            return addWrappedPayloads(Collections.singletonList(wrappedPayload));
+        }
+
+        /**
+         * Add multiple wrapped payloads at once.
+         *
+         * @param wrappedPayloads list of wrapped payloads
+         * @return builder instance
+         */
+        public Builder addWrappedPayloads(List<ExtensionElement> wrappedPayloads) {
+            this.wrappedPayloads.addAll(wrappedPayloads);
+            return this;
+        }
+
+        /**
+         * Add an external payload.
+         *
+         * @param externalPayload external payload
+         * @return builder instance
+         */
+        public Builder addExternalPayload(ExternalElement externalPayload) {
+            return addExternalPayloads(Collections.singletonList(externalPayload));
+        }
+
+        /**
+         * Add multiple external payloads at once.
+         *
+         * @param externalPayloads external payloads
+         * @return builder instance
+         */
+        public Builder addExternalPayloads(List<ExternalElement> externalPayloads) {
+            this.externalPayloads.addAll(externalPayloads);
+            return this;
+        }
+
+        /**
+         * Declare this {@link FasteningElement} to remove previous fastenings.
+         * Semantically the wrapped payloads of this element declares all wrapped payloads from the referenced
+         * fastening element that share qualified names as removed.
+         *
+         * @see <a href="https://xmpp.org/extensions/xep-0422.html#remove">
+         *     XEP-0422: Message Fastening §3.4 Removing fastenings</a>
+         *
+         * @return builder instance
+         */
+        public Builder setClear() {
+            isClear = true;
+            return this;
+        }
+
+        /**
+         * Declare this {@link FasteningElement} to be a shell element.
+         * Shell elements are used as hints that a Stanza Content Encryption payload contains another sensitive
+         * {@link FasteningElement}. The outer "shell" {@link FasteningElement} is used to do fastening collation.
+         *
+         * @see <a href="https://xmpp.org/extensions/xep-0422.html#encryption">XEP-0422: Message Fastening §3.5 Interaction with stanza encryption</a>
+         * @see <a href="https://xmpp.org/extensions/xep-0420.html">XEP-0420: Stanza Content Encryption</a>
+         *
+         * @return builder instance
+         */
+        public Builder setShell() {
+            isShell = true;
+            return this;
+        }
+
+        /**
+         * Build the element.
+         * @return built element.
+         */
+        public FasteningElement build() {
+            validateThatIfIsShellThenOtherwiseEmpty();
+            return new FasteningElement(originId, wrappedPayloads, externalPayloads, isClear, isShell);
+        }
+
+        private void validateThatIfIsShellThenOtherwiseEmpty() {
+            if (!isShell) {
+                return;
+            }
+
+            if (isClear || !wrappedPayloads.isEmpty() || !externalPayloads.isEmpty()) {
+                throw new IllegalArgumentException("A fastening that is a shell element must be otherwise empty " +
+                        "and cannot have a 'clear' attribute.");
+            }
+        }
+    }
+}

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/element/package-info.java

@@ -0,0 +1,25 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * XEP-0422: Message Fastening.
+ *
+ * @see <a href="https://xmpp.org/extensions/xep-0422.html">XEP-0422: Message
+ *      Fastening</a>
+ *
+ */
+package org.jivesoftware.smackx.message_fastening.element;

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/package-info.java

@@ -0,0 +1,25 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * XEP-0422: Message Fastening.
+ *
+ * @see <a href="https://xmpp.org/extensions/xep-0422.html">XEP-0422: Message
+ *      Fastening</a>
+ *
+ */
+package org.jivesoftware.smackx.message_fastening;

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/provider/FasteningElementProvider.java

@@ -0,0 +1,80 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.message_fastening.provider;
+
+import java.io.IOException;
+
+import org.jivesoftware.smack.packet.ExtensionElement;
+import org.jivesoftware.smack.packet.XmlEnvironment;
+import org.jivesoftware.smack.parsing.SmackParsingException;
+import org.jivesoftware.smack.provider.ExtensionElementProvider;
+import org.jivesoftware.smack.util.PacketParserUtils;
+import org.jivesoftware.smack.util.ParserUtils;
+import org.jivesoftware.smack.xml.XmlPullParser;
+import org.jivesoftware.smack.xml.XmlPullParserException;
+import org.jivesoftware.smackx.message_fastening.MessageFasteningManager;
+import org.jivesoftware.smackx.message_fastening.element.ExternalElement;
+import org.jivesoftware.smackx.message_fastening.element.FasteningElement;
+
+public class FasteningElementProvider extends ExtensionElementProvider<FasteningElement> {
+
+    public static final FasteningElementProvider TEST_INSTANCE = new FasteningElementProvider();
+
+    @Override
+    public FasteningElement parse(XmlPullParser parser, int initialDepth, XmlEnvironment xmlEnvironment) throws XmlPullParserException, IOException, SmackParsingException {
+        FasteningElement.Builder builder = FasteningElement.builder();
+        builder.setOriginId(parser.getAttributeValue("", FasteningElement.ATTR_ID));
+        if (ParserUtils.getBooleanAttribute(parser, FasteningElement.ATTR_CLEAR, false)) {
+            builder.setClear();
+        }
+        if (ParserUtils.getBooleanAttribute(parser, FasteningElement.ATTR_SHELL, false)) {
+            builder.setShell();
+        }
+
+        outerloop: while (true) {
+            XmlPullParser.Event tag = parser.next();
+            switch (tag) {
+                case START_ELEMENT:
+                    String name = parser.getName();
+                    String namespace = parser.getNamespace();
+
+                    // Parse external payload
+                    if (MessageFasteningManager.NAMESPACE.equals(namespace) && ExternalElement.ELEMENT.equals(name)) {
+                        ExternalElement external = new ExternalElement(
+                                parser.getAttributeValue("", ExternalElement.ATTR_NAME),
+                                parser.getAttributeValue("", ExternalElement.ATTR_ELEMENT_NAMESPACE));
+                        builder.addExternalPayload(external);
+                        continue;
+                    }
+
+                    // Parse wrapped payload
+                    ExtensionElement wrappedPayload = PacketParserUtils.parseExtensionElement(name, namespace, parser, xmlEnvironment);
+                    builder.addWrappedPayload(wrappedPayload);
+                    break;
+
+                case END_ELEMENT:
+                    if (parser.getDepth() == initialDepth) {
+                        break outerloop;
+                    }
+                    break;
+                default:
+                    break;
+            }
+        }
+        return builder.build();
+    }
+}

smack-experimental/src/main/java/org/jivesoftware/smackx/message_fastening/provider/package-info.java

@@ -0,0 +1,25 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * XEP-0422: Message Fastening.
+ *
+ * @see <a href="https://xmpp.org/extensions/xep-0422.html">XEP-0422: Message
+ *      Fastening</a>
+ *
+ */
+package org.jivesoftware.smackx.message_fastening.provider;

smack-experimental/src/main/resources/org.jivesoftware.smack.experimental/experimental.providers

@@ -292,6 +292,12 @@
       <className>org.jivesoftware.smackx.dox.provider.DnsIqProvider</className>
     </iqProvider>
 
+    <!-- XEP-0422: Message Fastening -->
+    <extensionProvider>
+      <elementName>apply-to</elementName>
+      <namespace>urn:xmpp:fasten:0</namespace>
+      <className>org.jivesoftware.smackx.message_fastening.provider.FasteningElementProvider</className>
+    </extensionProvider>
 
     <!-- XEP-xxxx: Multi-User Chat Light -->
     <iqProvider>

smack-experimental/src/main/resources/org.jivesoftware.smack.experimental/experimental.xml

@@ -8,5 +8,6 @@
 		<className>org.jivesoftware.smackx.eme.ExplicitMessageEncryptionManager</className>
         <className>org.jivesoftware.smackx.sid.StableUniqueStanzaIdManager</className>
         <className>org.jivesoftware.smackx.xmlelement.DataFormsXmlElementManager</className>
+        <className>org.jivesoftware.smackx.message_fastening.MessageFasteningManager</className>
     </startupClasses>
 </smack>

smack-experimental/src/test/java/org/jivesoftware/smackx/message_fastening/MessageFasteningElementsTest.java

@@ -0,0 +1,229 @@
+/**
+ *
+ * Copyright 2019 Paul Schaub
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.message_fastening;
+
+import static org.jivesoftware.smack.test.util.XmlUnitUtils.assertXmlSimilar;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.util.Arrays;
+
+import org.jivesoftware.smack.packet.MessageBuilder;
+import org.jivesoftware.smack.packet.StandardExtensionElement;
+import org.jivesoftware.smack.packet.StanzaFactory;
+import org.jivesoftware.smack.packet.id.StandardStanzaIdSource;
+import org.jivesoftware.smack.parsing.SmackParsingException;
+import org.jivesoftware.smack.test.util.SmackTestUtil;
+import org.jivesoftware.smack.test.util.TestUtils;
+import org.jivesoftware.smack.xml.XmlPullParserException;
+import org.jivesoftware.smackx.message_fastening.element.ExternalElement;
+import org.jivesoftware.smackx.message_fastening.element.FasteningElement;
+import org.jivesoftware.smackx.message_fastening.provider.FasteningElementProvider;
+import org.jivesoftware.smackx.sid.element.OriginIdElement;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+
+public class MessageFasteningElementsTest {
+
+    private final StanzaFactory stanzaFactory = new StanzaFactory(new StandardStanzaIdSource());
+
+    /**
+     * Test XML serialization of the {@link FasteningElement} using the example provided by
+     * the XEP.
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#wrapped-payloads">XEP-0422 §3.1 Wrapped Payloads</a>
+     */
+    @Test
+    public void fasteningElementSerializationTest() {
+        String xml = "" +
+                "<apply-to xmlns='urn:xmpp:fasten:0' id='origin-id-1'>" +
+                "    <i-like-this xmlns='urn:example:like'/>" +
+                "</apply-to>";
+
+        FasteningElement applyTo = FasteningElement.builder()
+                .setOriginId("origin-id-1")
+                .addWrappedPayload(new StandardExtensionElement("i-like-this", "urn:example:like"))
+                .build();
+
+        assertXmlSimilar(xml, applyTo.toXML().toString());
+    }
+
+    @ParameterizedTest
+    @EnumSource(SmackTestUtil.XmlPullParserKind.class)
+    public void fasteningDeserializationTest(SmackTestUtil.XmlPullParserKind parserKind) throws XmlPullParserException, IOException, SmackParsingException {
+        String xml = "" +
+                "<apply-to xmlns='urn:xmpp:fasten:0' id='origin-id-1'>" +
+                "    <i-like-this xmlns='urn:example:like'/>" +
+                "    <external name='custom' element-namespace='urn:example:custom'/>" +
+                "    <external name='body'/>" +
+                "</apply-to>";
+
+        FasteningElement parsed = SmackTestUtil.parse(xml, FasteningElementProvider.class, parserKind);
+
+        assertNotNull(parsed);
+        assertEquals(new OriginIdElement("origin-id-1"), parsed.getReferencedStanzasOriginId());
+        assertFalse(parsed.isRemovingElement());
+        assertFalse(parsed.isShellElement());
+
+        assertEquals(1, parsed.getWrappedPayloads().size());
+        assertEquals("i-like-this", parsed.getWrappedPayloads().get(0).getElementName());
+        assertEquals("urn:example:like", parsed.getWrappedPayloads().get(0).getNamespace());
+
+        assertEquals(2, parsed.getExternalPayloads().size());
+        ExternalElement custom = parsed.getExternalPayloads().get(0);
+        assertEquals("custom", custom.getName());
+        assertEquals("urn:example:custom", custom.getElementNamespace());
+        ExternalElement body  = parsed.getExternalPayloads().get(1);
+        assertEquals("body", body.getName());
+        assertNull(body.getElementNamespace());
+    }
+
+    @Test
+    public void fasteningDeserializationClearTest() throws XmlPullParserException, IOException, SmackParsingException {
+        String xml = "" +
+                "<apply-to xmlns='urn:xmpp:fasten:0' id='origin-id-1' clear='true'>" +
+                "    <i-like-this xmlns='urn:example:like'/>" +
+                "</apply-to>";
+
+        FasteningElement parsed = FasteningElementProvider.TEST_INSTANCE.parse(TestUtils.getParser(xml));
+
+        assertTrue(parsed.isRemovingElement());
+    }
+
+    @Test
+    public void fasteningElementWithExternalElementsTest() {
+        String xml = "" +
+                "<apply-to xmlns='urn:xmpp:fasten:0' id='origin-id-2'>" +
+                "    <external name='body'/>" +
+                "    <external name='custom' element-namespace='urn:example:custom'/>" +
+                "    <edit xmlns='urn:example.edit'/>" +
+                "</apply-to>";
+
+        FasteningElement element = FasteningElement.builder()
+                .setOriginId("origin-id-2")
+                .addExternalPayloads(Arrays.asList(
+                        new ExternalElement("body"),
+                        new ExternalElement("custom", "urn:example:custom")
+                ))
+                .addWrappedPayload(
+                        new StandardExtensionElement("edit", "urn:example.edit"))
+                .build();
+
+        assertXmlSimilar(xml, element.toXML().toString());
+    }
+
+    @Test
+    public void createShellElementSharesOriginIdTest() {
+        OriginIdElement originIdElement = new OriginIdElement("sensitive-stanza-1");
+        FasteningElement sensitiveFastening = FasteningElement.builder()
+                .setOriginId(originIdElement)
+                .build();
+
+        FasteningElement shellElement = FasteningElement.createShellElementForSensitiveElement(sensitiveFastening);
+
+        assertEquals(originIdElement, shellElement.getReferencedStanzasOriginId());
+    }
+
+    @Test
+    public void fasteningRemoveSerializationTest() {
+        String xml =
+                "<apply-to xmlns='urn:xmpp:fasten:0' id='origin-id-1' clear='true'>" +
+                        "      <i-like-this xmlns='urn:example:like'>Very much</i-like-this>" +
+                        "</apply-to>";
+
+        FasteningElement element = FasteningElement.builder()
+                .setOriginId("origin-id-1")
+                .setClear()
+                .addWrappedPayload(StandardExtensionElement.builder("i-like-this", "urn:example:like")
+                        .setText("Very much")
+                        .build())
+                .build();
+
+        assertXmlSimilar(xml, element.toXML().toString());
+    }
+
+    @Test
+    public void hasFasteningElementTest() {
+        MessageBuilder messageBuilderWithFasteningElement = MessageBuilder.buildMessage()
+                .setBody("Hi!")
+                .addExtension(FasteningElement.builder().setOriginId("origin-id-1").build());
+        MessageBuilder messageBuilderWithoutFasteningElement = MessageBuilder.buildMessage()
+                .setBody("Ho!");
+
+        assertTrue(FasteningElement.hasFasteningElement(messageBuilderWithFasteningElement));
+        assertFalse(FasteningElement.hasFasteningElement(messageBuilderWithoutFasteningElement));
+    }
+
+    @Test
+    public void shellElementMustNotHaveClearAttributeTest() {
+        assertThrows(IllegalArgumentException.class, () ->
+                FasteningElement.builder()
+                        .setShell()
+                        .setClear()
+                        .build());
+    }
+
+    @Test
+    public void shellElementMustNotContainAnyPayloads() {
+        assertThrows(IllegalArgumentException.class, () ->
+                FasteningElement.builder()
+                        .setShell()
+                        .addWrappedPayload(new StandardExtensionElement("edit", "urn:example.edit"))
+                        .build());
+
+        assertThrows(IllegalArgumentException.class, () ->
+                FasteningElement.builder()
+                        .setShell()
+                        .addExternalPayload(new ExternalElement("body"))
+                        .build());
+    }
+
+    @Test
+    public void ensureAddFasteningElementToStanzaWorks() {
+        MessageBuilder message = stanzaFactory.buildMessageStanza();
+        FasteningElement fasteningElement = FasteningElement.builder().setOriginId("another-apply-to").build();
+
+        // Adding only one element is allowed
+        fasteningElement.applyTo(message);
+    }
+
+    /**
+     * Ensure, that {@link FasteningElement#applyTo(MessageBuilder)}
+     * throws when trying to add an {@link FasteningElement} to a {@link MessageBuilder} that already contains one
+     * such element.
+     *
+     * @see <a href="https://xmpp.org/extensions/xep-0422.html#rules">XEP-0422: §4. Business Rules</a>
+     */
+    @Test
+    public void ensureStanzaCanOnlyContainOneFasteningElement() {
+        MessageBuilder messageWithFastening = stanzaFactory.buildMessageStanza();
+        FasteningElement.builder().setOriginId("origin-id").build().applyTo(messageWithFastening);
+
+        // Adding a second fastening MUST result in exception
+        Assertions.assertThrows(IllegalArgumentException.class, () ->
+                FasteningElement.builder().setOriginId("another-apply-to").build()
+                        .applyTo(messageWithFastening));
+    }
+}