Initial revision for comment.

bindings/mqtt/core/pom.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>cloudevents-parent</artifactId>
+        <groupId>io.cloudevents</groupId>
+        <version>2.5.0-SNAPSHOT</version>
+        <relativePath>../../../pom.xml</relativePath>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>cloudevents-mqtt-core</artifactId>
+    <name>CloudEvents - MQTT Common</name>
+    <packaging>jar</packaging>
+
+    <properties>
+        <module-name>io.cloudevents.mqtt.core</module-name>
+    </properties>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-core</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+
+    </dependencies>
+
+</project>

bindings/mqtt/core/src/main/java/io/cloudevents/mqtt/core/BaseMqttBinaryMessageReader.java

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+package io.cloudevents.mqtt.core;
+
+import io.cloudevents.SpecVersion;
+import io.cloudevents.core.data.BytesCloudEventData;
+import io.cloudevents.core.message.impl.BaseGenericBinaryMessageReaderImpl;
+import io.cloudevents.core.v1.CloudEventV1;
+
+import java.util.function.BiConsumer;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Enable the hydration of a CloudEvent in binary mode from an MQTT message.
+ * <p>
+ * This abstract class provides common behavior across different MQTT
+ * client implementations.
+ */
+public abstract class BaseMqttBinaryMessageReader extends BaseGenericBinaryMessageReaderImpl<String, Object> {
+
+    /**
+     * CloudEvent attribute names must match this pattern.
+     */
+    private static final Pattern CE_ATTR_NAME_REGEX = Pattern.compile("^[a-z\\d]+$");
+    private final String contentType;
+
+    /**
+     * Initialise the binary message reader.
+     * @param version The CloudEvent message version.
+     * @param contentType The assigned media content type.
+     * @param payload The raw data payload from the MQTT message.
+     */
+    protected BaseMqttBinaryMessageReader(final SpecVersion version, final String contentType, final byte[] payload) {
+        super(version, payload != null && payload.length > 0 ? BytesCloudEventData.wrap(payload) : null);
+        this.contentType = contentType;
+    }
+
+    // --- Overrides
+
+    @Override
+    protected boolean isContentTypeHeader(String key) {
+        return false; // The content type is not defined in a user-property
+    }
+
+    @Override
+    protected boolean isCloudEventsHeader(String key) {
+
+        // The binding specification does not require name prefixing,
+        // as such any user-property is a potential CE Context Attribute.
+        //
+        // If the name complies with CE convention then we'll assume
+        // it's a context attribute.
+        //
+        Matcher m = CE_ATTR_NAME_REGEX.matcher(key);
+        return m.matches();
+    }
+
+    @Override
+    protected String toCloudEventsKey(String key) {
+        return key; // No special prefixing occurs in the MQTT binding spec.
+    }
+
+
+    @Override
+    protected void forEachHeader(BiConsumer<String, Object> fn) {
+
+        // If there is a content-type then we need set it.
+        // Inspired by AMQP/Proton code :-)
+
+        if (contentType != null) {
+            fn.accept(CloudEventV1.DATACONTENTTYPE, contentType);
+        }
+
+        // Now process each MQTT User Property.
+        forEachUserProperty(fn);
+
+    }
+
+    @Override
+    protected String toCloudEventsValue(Object value) {
+        return value.toString();
+    }
+
+    /**
+     * Visit each MQTT user-property and invoke the supplied function.
+     * @param fn The function to invoke for each MQTT User property.
+     */
+    protected abstract void forEachUserProperty(BiConsumer<String, Object> fn);
+}

bindings/mqtt/core/src/main/java/io/cloudevents/mqtt/core/MqttUtils.java

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+package io.cloudevents.mqtt.core;
+
+import io.cloudevents.core.format.EventFormat;
+import io.cloudevents.core.provider.EventFormatProvider;
+
+/**
+ * General MQTT Utilities and Helpers
+ */
+public class MqttUtils {
+
+    private MqttUtils() {}
+
+    private  static final String DEFAULT_FORMAT = "application/cloudevents+json";
+
+    /**
+     * Obtain the {@link EventFormat} to use when working with MQTT V3
+     * messages.
+     *
+     * @return An event format.
+     */
+    public static EventFormat getDefaultEventFormat () {
+
+        return EventFormatProvider.getInstance().resolveFormat(DEFAULT_FORMAT);
+
+    }
+
+    /**
+     * Get the default content type to assume for MQTT messages.
+     * @return A Content-Type
+     */
+    public static final String getDefaultContentType() {
+        return DEFAULT_FORMAT;
+    }
+
+}

bindings/mqtt/hivemq/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>cloudevents-parent</artifactId>
+        <groupId>io.cloudevents</groupId>
+        <version>2.5.0-SNAPSHOT</version>
+        <relativePath>../../../pom.xml</relativePath>
+    </parent>
+
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>cloudevents-mqtt-hivemq</artifactId>
+    <name>CloudEvents - MQTT HiveMQ Binding</name>
+    <packaging>jar</packaging>
+
+    <properties>
+        <module-name>io.cloudevents.mqtt.hivemq</module-name>
+        <hivemq.version>1.3.0</hivemq.version>
+    </properties>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-core</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-mqtt-core</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>com.hivemq</groupId>
+            <artifactId>hivemq-mqtt-client</artifactId>
+            <version>${hivemq.version}</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <!-- Testing Dependencies -->
+
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-core</artifactId>
+            <classifier>tests</classifier>
+            <type>test-jar</type>
+            <version>${project.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- We need a JSON Format for V3 compliance checking -->
+
+        <dependency>
+            <groupId>io.cloudevents</groupId>
+            <artifactId>cloudevents-json-jackson</artifactId>
+            <version>${project.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+</project>

bindings/mqtt/hivemq/src/main/java/io/cloudevents/mqtt/hivemq/BinaryMessageReader.java

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+package io.cloudevents.mqtt.hivemq;
+
+import com.hivemq.client.mqtt.mqtt5.message.publish.Mqtt5Publish;
+import io.cloudevents.SpecVersion;
+import io.cloudevents.mqtt.core.BaseMqttBinaryMessageReader;
+
+import java.util.function.BiConsumer;
+
+final class BinaryMessageReader extends BaseMqttBinaryMessageReader {
+
+    Mqtt5Publish message;
+
+    BinaryMessageReader(final SpecVersion version, final String contentType, Mqtt5Publish message) {
+        super(version, contentType, message.getPayloadAsBytes());
+
+        this.message = message;
+    }
+
+    @Override
+    protected void forEachUserProperty(BiConsumer<String, Object> fn) {
+
+        message.getUserProperties().asList().forEach(up -> {
+
+            final String key = up.getName().toString();
+            final String val = up.getValue().toString();
+
+            if (key != null && val != null) {
+                fn.accept(key, val);
+            }
+        });
+
+    }
+}

bindings/mqtt/hivemq/src/main/java/io/cloudevents/mqtt/hivemq/MqttMessageFactory.java

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+package io.cloudevents.mqtt.hivemq;
+
+import com.hivemq.client.mqtt.datatypes.MqttUtf8String;
+import com.hivemq.client.mqtt.mqtt3.message.publish.Mqtt3Publish;
+import com.hivemq.client.mqtt.mqtt3.message.publish.Mqtt3PublishBuilder;
+import com.hivemq.client.mqtt.mqtt5.datatypes.Mqtt5UserProperty;
+import com.hivemq.client.mqtt.mqtt5.message.publish.Mqtt5Publish;
+import com.hivemq.client.mqtt.mqtt5.message.publish.Mqtt5PublishBuilder;
+import io.cloudevents.core.message.MessageReader;
+import io.cloudevents.core.message.MessageWriter;
+import io.cloudevents.core.message.impl.GenericStructuredMessageReader;
+import io.cloudevents.core.message.impl.MessageUtils;
+import io.cloudevents.core.v1.CloudEventV1;
+import io.cloudevents.mqtt.core.MqttUtils;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * A factory to obtain:
+ * - {@link MessageReader} instances to read CloudEvents from MQTT messages.
+ * - {@link MessageWriter} instances to write CloudEvents into MQTT messages.
+ *
+ */
+public class MqttMessageFactory {
+
+    // Prevent Instantiation.
+    private MqttMessageFactory() {
+    }
+
+    /**
+     * Create a {@link MessageReader} for an MQTT V3 message.
+     * <p>
+     * As-Per MQTT Binding specification this only supports
+     * a structured JSON Format message.
+     *
+     * @param message An MQTT V3 message.
+     * @return MessageReader.
+     */
+    public static MessageReader createReader(Mqtt3Publish message) {
+        return new GenericStructuredMessageReader(MqttUtils.getDefaultEventFormat(), message.getPayloadAsBytes());
+    }
+
+    /**
+     * Create a {@link MessageReader} for an MQTT V5 message
+     *
+     * @param message An MQTT V5 message.
+     * @return A message reader.
+     */
+    public static MessageReader createReader(Mqtt5Publish message) {
+
+        Optional<MqttUtf8String> cType = message.getContentType();
+
+        String contentType = cType.isPresent() ? cType.get().toString() : null;
+
+        return MessageUtils.parseStructuredOrBinaryMessage(
+            () -> contentType,
+            format -> new GenericStructuredMessageReader(format, message.getPayloadAsBytes()),
+            () -> getSpecVersion(message),
+            sv -> new BinaryMessageReader(sv, contentType, message)
+        );
+    }
+
+
+    /**
+     * Create a {@link MessageWriter} for an MQTT V5 Message.
+     *
+     * @param builder {@link Mqtt5PublishBuilder.Complete}
+     * @return A message writer.
+     */
+    public static MessageWriter createWriter(Mqtt5PublishBuilder.Complete builder) {
+        return new V5MessageWriter(builder);
+    }
+
+    /**
+     * Create a {@link MessageWriter} for an MQTT V3 Message.
+     *
+     * Only supports structured messages.
+     *
+     * @param builder {@link Mqtt3PublishBuilder.Complete}
+     * @return A message writer.
+     */
+    public static MessageWriter createWriter(Mqtt3PublishBuilder.Complete builder) {
+        return new V3MessageWriter(builder);
+    }
+
+
+    // -- Private functions
+
+    /**
+     * Find the value of the CloudEvent 'specversion' in the MQTT V5 User Properties.
+     * @param message An MQTT message.
+     * @return spec version attribute content.
+     */
+    private static String getSpecVersion(Mqtt5Publish message) {
+
+        List<Mqtt5UserProperty> props = (List<Mqtt5UserProperty>) message.getUserProperties().asList();
+
+        Optional<Mqtt5UserProperty> up = props.stream().filter(p -> p.getName().toString().equals(CloudEventV1.SPECVERSION)).findFirst();
+
+        return (up.isPresent()) ? up.get().getValue().toString() : null;
+
+    }
+
+}