Interceptors

public class ModifyPublishOutboundInterceptor implements PublishOutboundInterceptor {
    @Override
    public void onOutboundPublish(final @NotNull PublishOutboundInput input, final @NotNull PublishOutboundOutput output) {
        final String clientId = input.getClientInformation().getClientId();
        final ModifiableOutboundPublish publish = output.getPublishPacket();
        final String originalTopic = publish.getTopic();

        publish.setTopic(originalTopic + "/" + clientId);
        publish.getUserProperties().addUserProperty("original-topic", originalTopic);

        publish.setResponseTopic("response/"+clientId);
    }
}

public class ModifyPublishOutboundInterceptor implements PublishOutboundInterceptor {
    @Override
    public void onOutboundPublish(final @NotNull PublishOutboundInput input, final @NotNull PublishOutboundOutput output) {
        final Async<PublishOutboundOutput> async = output.async(Duration.ofSeconds(10), TimeoutFallback.FAILURE);
        Services.extensionExecutorService().submit(() -> {
            final ModifiableOutboundPublish publish = output.getPublishPacket();
            final String payloadString = StandardCharsets.UTF_8.decode(publish.getPayload().get()).toString();
            final String newPayload = payloadString.toLowerCase();
            publish.setPayload(StandardCharsets.UTF_8.encode(newPayload));
            async.resume();
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubackInboundInterceptor interceptor = (pubackInboundInput, pubackInboundOutput) -> {
        log.debug("intercepted a PUBACK packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubackInboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubackInboundInterceptor implements PubackInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubackInboundInterceptor.class);

    @Override
    public void onInboundPuback(final @NotNull PubackInboundInput pubackInboundInput, final @NotNull PubackInboundOutput pubackInboundOutput) {
        //get the modifiable puback object from the output
        final ModifiablePubackPacket pubackPacket = pubackInboundOutput.getPubackPacket();

        // modify / overwrite parameters of a puback packet.

        try {
            if (pubackPacket.getReasonCode() != AckReasonCode.SUCCESS &&
                pubackPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                //Set reason string and reason code if reason code is not success.
                pubackPacket.setReasonString("The reason for the unsuccessful puback");
                pubackPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
            }

            pubackPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubackPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Puback inbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubackInboundInterceptor implements PubackInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubackInboundInterceptor.class);

    @Override
    public void onInboundPuback(final @NotNull PubackInboundInput pubackInboundInput, final @NotNull PubackInboundOutput pubackInboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubackInboundOutput> async = pubackInboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable puback object from the output
                final ModifiablePubackPacket pubackPacket = pubackInboundOutput.getPubackPacket();
                // modify / overwrite parameters of a puback packet.

                try {
                    if (pubackPacket.getReasonCode() != AckReasonCode.SUCCESS &&
                        pubackPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                        //Set reason string and reason code if reason code is not success.
                        pubackPacket.setReasonString("The reason for the unsuccessful puback");
                        pubackPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
                    }

                    pubackPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubackPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Puback inbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Puback inbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubackOutboundInterceptor interceptor = (pubackOutboundInput, pubackOutboundOutput) -> {
        log.debug("intercepted a PUBACK packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubackOutboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubackOutboundInterceptor implements PubackOutboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubackOutboundInterceptor.class);

    @Override
    public void onOutboundPuback(final @NotNull PubackOutboundInput pubackOutboundInput, final @NotNull PubackOutboundOutput pubackOutboundOutput) {
        //get the modifiable puback object from the output
        final ModifiablePubackPacket pubackPacket = pubackOutboundOutput.getPubackPacket();

        // modify / overwrite parameters of a puback packet.

        try {
            if (pubackPacket.getReasonCode() != AckReasonCode.SUCCESS &&
                pubackPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                //Set reason string and reason code if reason code is not success.
                pubackPacket.setReasonString("The reason for the unsuccessful puback");
                pubackPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
            }

            pubackPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubackPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Puback outbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubackOutboundInterceptor implements PubackOutboundPubackInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubackOutboundInterceptor.class);

    @Override
    public void onOutboundPuback(final @NotNull PubackOutboundInput pubackOutboundInput, final @NotNull PubackOutboundOutput pubackOutboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubackOutboundOutput> async = pubackOutboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable puback object from the output
                final ModifiablePubackPacket pubackPacket = pubackOutboundOutput.getPubackPacket();
                // modify / overwrite parameters of a puback packet.

                try {
                    if (pubackPacket.getReasonCode() != AckReasonCode.SUCCESS &&
                        pubackPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                        //Set reason string and reason code if reason code is not success.
                        pubackPacket.setReasonString("The reason for the unsuccessful puback");
                        pubackPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
                    }

                    pubackPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubackPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Puback outbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Puback outbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubrecInboundInterceptor interceptor = (pubrecInboundInput, pubrecInboundOutput) -> {
        log.debug("intercepted a PUBREC packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubrecInboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubrecInboundInterceptor implements PubrecInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubrecInboundInterceptor.class);

    @Override
    public void onInboundPubrec(final @NotNull PubrecInboundInput pubrecInboundInput, final @NotNull PubrecInboundOutput pubrecInboundOutput) {
        //get the modifiable pubrec object from the output
        final ModifiablePubrecPacket pubrecPacket = pubrecInboundOutput.getPubrecPacket();

        // modify / overwrite parameters of a pubrec packet.

        try {
            if (pubrecPacket.getReasonCode() != AckReasonCode.SUCCESS&&
                pubrecPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                //Set reason string and reason code if reason code is not success.
                pubrecPacket.setReasonString("The reason for the unsuccessful pubrec");
                pubrecPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
            }

            pubrecPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubrecPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Pubrec inbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubrecInboundInterceptor implements PubrecInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubrecInboundInterceptor.class);

    @Override
    public void onInboundPubrec(final @NotNull PubrecInboundInput pubrecInboundInput, final @NotNull PubrecInboundOutput pubrecInboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubrecInboundOutput> async = pubrecInboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable pubrec object from the output
                final ModifiablePubrecPacket pubrecPacket = pubrecInboundOutput.getPubrecPacket();
                // modify / overwrite parameters of a pubrec packet.

                try {
                    if (pubrecPacket.getReasonCode() != AckReasonCode.SUCCESS&&
                        pubrecPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                        //Set reason string and reason code if reason code is not success.
                        pubrecPacket.setReasonString("The reason for the unsuccessful pubrec");
                        pubrecPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
                    }

                    pubrecPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubrecPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Pubrec inbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Pubrec inbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubrecOutboundInterceptor interceptor = (pubrecOutboundInput, pubrecOutboundOutput) -> {
        log.debug("intercepted a PUBREC packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubrecOutboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubrecOutboundInterceptor implements PubrecOutboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubrecOutboundInterceptor.class);

    @Override
    public void onOutboundPubrec(final @NotNull PubrecOutboundInput pubrecOutboundInput, final @NotNull PubrecOutboundOutput pubrecOutboundOutput) {
        //get the modifiable pubrec object from the output
        final ModifiablePubrecPacket pubrecPacket = pubrecOutboundOutput.getPubrecPacket();

        // modify / overwrite parameters of a pubrec packet.

        try {
            if (pubrecPacket.getReasonCode() != AckReasonCode.SUCCESS&&
                pubrecPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                //Set reason string and reason code if reason code is not success.
                pubrecPacket.setReasonString("The reason for the unsuccessful pubrec");
                pubrecPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
            }

            pubrecPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubrecPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Pubrec outbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubrecOutboundInterceptor implements PubrecOutboundPubrecInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubrecOutboundInterceptor.class);

    @Override
    public void onOutboundPubrec(final @NotNull PubrecOutboundInput pubrecOutboundInput, final @NotNull PubrecOutboundOutput pubrecOutboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubrecOutboundOutput> async = pubrecOutboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable pubrec object from the output
                final ModifiablePubrecPacket pubrecPacket = pubrecOutboundOutput.getPubrecPacket();
                // modify / overwrite parameters of a pubrec packet.

                try {
                    if (pubrecPacket.getReasonCode() != AckReasonCode.SUCCESS&&
                        pubrecPacket.getReasonCode() != AckReasonCode.NO_MATCHING_SUBSCRIBERS) {

                        //Set reason string and reason code if reason code is not success.
                        pubrecPacket.setReasonString("The reason for the unsuccessful pubrec");
                        pubrecPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
                    }

                    pubrecPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubrecPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Pubrec outbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Pubrec outbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubrelInboundInterceptor interceptor = (pubrelInboundInput, pubrelInboundOutput) -> {
        log.debug("intercepted a PUBREL packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubrelInboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubrelInboundInterceptor implements PubrelInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubrelInboundInterceptor.class);

    @Override
    public void onInboundPubrel(final @NotNull PubrelInboundInput pubrelInboundInput, final @NotNull PubrelInboundOutput pubrelInboundOutput) {
        //get the modifiable pubrel object from the output
        final ModifiablePubrelPacket pubrelPacket = pubrelInboundOutput.getPubrelPacket();

        // modify / overwrite parameters of a pubrel packet.

        try {
            if (pubrelPacket.getReasonCode() != PubrelReasonCode.SUCCESS) {
                //Set reason string if reason code is not success.
                pubrelPacket.setReasonString("The reason for the unsuccessful pubrel");
            }

            pubrelPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubrelPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Pubrel inbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubrelInboundInterceptor implements PubrelInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubrelInboundInterceptor.class);

    @Override
    public void onInboundPubrel(final @NotNull PubrelInboundInput pubrelInboundInput, final @NotNull PubrelInboundOutput pubrelInboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubrelInboundOutput> async = pubrelInboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable pubrel object from the output
                final ModifiablePubrelPacket pubrelPacket = pubrelInboundOutput.getPubrelPacket();
                // modify / overwrite parameters of a pubrel packet.

                try {
                    if (pubrelPacket.getReasonCode() != PubrelReasonCode.SUCCESS) {
                        //Set reason string if reason code is not success.
                        pubrelPacket.setReasonString("The reason for the unsuccessful pubrel");
                    }

                    pubrelPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubrelPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Pubrel inbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Pubrel inbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubrelOutboundInterceptor interceptor = (pubrelOutboundInput, pubrelOutboundOutput) -> {
        log.debug("intercepted a PUBREL packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubrelOutboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubrelOutboundInterceptor implements PubrelOutboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubrelOutboundInterceptor.class);

    @Override
    public void onOutboundPubrel(final @NotNull PubrelOutboundInput pubrelOutboundInput, final @NotNull PubrelOutboundOutput pubrelOutboundOutput) {
        //get the modifiable pubrel object from the output
        final ModifiablePubrelPacket pubrelPacket = pubrelOutboundOutput.getPubrelPacket();

        // modify / overwrite parameters of a pubrel packet.

        try {
            if (pubrelPacket.getReasonCode() != PubrelReasonCode.SUCCESS) {
                //Set reason string if reason code is not success.
                pubrelPacket.setReasonString("The reason for the unsuccessful pubrel");
            }

            pubrelPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubrelPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Pubrel outbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubrelOutboundInterceptor implements PubrelOutboundPubrelInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubrelOutboundInterceptor.class);

    @Override
    public void onOutboundPubrel(final @NotNull PubrelOutboundInput pubrelOutboundInput, final @NotNull PubrelOutboundOutput pubrelOutboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubrelOutboundOutput> async = pubrelOutboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable pubrel object from the output
                final ModifiablePubrelPacket pubrelPacket = pubrelOutboundOutput.getPubrelPacket();
                // modify / overwrite parameters of a pubrel packet.

                try {
                    if (pubrelPacket.getReasonCode() != PubrelReasonCode.SUCCESS) {
                        //Set reason string if reason code is not success.
                        pubrelPacket.setReasonString("The reason for the unsuccessful pubrel");
                    }

                    pubrelPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubrelPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Pubrel outbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Pubrel outbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubcompInboundInterceptor interceptor = (pubcompInboundInput, pubcompInboundOutput) -> {
        log.debug("intercepted a PUBCOMP packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubcompInboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubcompInboundInterceptor implements PubcompInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubcompInboundInterceptor.class);

    @Override
    public void onInboundPubcomp(final @NotNull PubcompInboundInput pubcompInboundInput, final @NotNull PubcompInboundOutput pubcompInboundOutput) {
        //get the modifiable pubcomp object from the output
        final ModifiablePubcompPacket pubcompPacket = pubcompInboundOutput.getPubcompPacket();

        // modify / overwrite parameters of a pubcomp packet.

        try {
            if (pubcompPacket.getReasonCode() != PubcompReasonCode.SUCCESS) {
                //Set reason string if reason code is not success.
                pubcompPacket.setReasonString("The reason for the unsuccessful pubcomp");
            }

            pubcompPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubcompPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Pubcomp inbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubcompInboundInterceptor implements PubcompInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubcompInboundInterceptor.class);

    @Override
    public void onInboundPubcomp(final @NotNull PubcompInboundInput pubcompInboundInput, final @NotNull PubcompInboundOutput pubcompInboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubcompInboundOutput> async = pubcompInboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable pubcomp object from the output
                final ModifiablePubcompPacket pubcompPacket = pubcompInboundOutput.getPubcompPacket();
                // modify / overwrite parameters of a pubcomp packet.

                try {
                    if (pubcompPacket.getReasonCode() != PubcompReasonCode.SUCCESS) {
                        //Set reason string if reason code is not success.
                        pubcompPacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);
                    }

                    pubcompPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubcompPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Pubcomp inbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Pubcomp inbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

...
@Override
public void extensionStart(final @NotNull ExtensionStartInput esi, final @NotNull ExtensionStartOutput eso) {

    final PubcompOutboundInterceptor interceptor = (pubcompOutboundInput, pubcompOutboundOutput) -> {
        log.debug("intercepted a PUBCOMP packet.");
    };

    Services.initializerRegistry().setClientInitializer((initializerInput, clientContext) -> {
        clientContext.addPubcompOutboundInterceptor(interceptor);
    });
}
...

public class ModifyingPubcompOutboundInterceptor implements PubcompOutboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingPubcompOutboundInterceptor.class);

    @Override
    public void onOutboundPubcomp(final @NotNull PubcompOutboundInput pubcompOutboundInput, final @NotNull PubcompOutboundOutput pubcompOutboundOutput) {
        //get the modifiable pubcomp object from the output
        final ModifiablePubcompPacket pubcompPacket = pubcompOutboundOutput.getPubcompPacket();

        // modify / overwrite parameters of a pubcomp packet.

        try {
            if (pubcompPacket.getReasonCode() != PubcompReasonCode.SUCCESS) {
                //Set reason string if reason code is not success.
                pubcompPacket.setReasonString("The reason for the unsuccessful pubcomp");
            }

            pubcompPacket.getUserProperties().addUserProperty("my-prop", "some value");
            pubcompPacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Pubcomp outbound interception failed:", e);
        }
    }
}

public class AsyncModifyingPubcompOutboundInterceptor implements PubcompOutboundPubcompInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingPubcompOutboundInterceptor.class);

    @Override
    public void onOutboundPubcomp(final @NotNull PubcompOutboundInput pubcompOutboundInput, final @NotNull PubcompOutboundOutput pubcompOutboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<PubcompOutboundOutput> async = pubcompOutboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable pubcomp object from the output
                final ModifiablePubcompPacket pubcompPacket = pubcompOutboundOutput.getPubcompPacket();
                // modify / overwrite parameters of a pubcomp packet.

                try {
                    if (pubcompPacket.getReasonCode() != PubcompReasonCode.SUCCESS) {
                        //Set reason string if reason code is not success.
                        pubcompPacket.setReasonString("The reason for the unsuccessful pubcomp");
                    }

                    pubcompPacket.getUserProperties().addUserProperty("my-prop", "some value");
                    pubcompPacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Pubcomp outbound interception failed:", e);
                }
            }
        });

        //wait for completion of the task
        taskFuture.whenComplete(new BiConsumer<Object, Throwable>() {
            @Override
            public void accept(final @Nullable Object o, final @Nullable Throwable throwable) {
                if (throwable != null) {
                    log.debug("Pubcomp outbound interception failed:", throwable);
                }

                //resume output to tell HiveMQ it's done.
                async.resume();
            }
        });
    }
}

public class ModifyingUnsubscribeInboundInterceptor implements UnsubscribeInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(ModifyingUnsubscribeInboundInterceptor.class);

    @Override
    public void onInboundUnsubscribe(final @NotNull UnsubscribeInboundInput unsubscribeInboundInput, final @NotNull UnsubscribeInboundOutput unsubscribeInboundOutput) {
        //get the modifiable disconnect object from the output
        final ModifiableUnsubscribePacket unsubscribePacket = unsubscribeInboundOutput.getUnsubscribePacket();
        // modify / overwrite parameters of the disconnect packet.
        try {

            unsubscribePacket.getUserProperties().addUserProperty("my-prop", "some value");
            unsubscribePacket.getUserProperties().addUserProperty("my-prop-2", "other value");
        } catch (final Exception e) {
            log.debug("Unsubscribe inbound interception failed:", e);
        }
    }
}

public class AsyncModifyingUnsubscribeInboundInterceptor implements UnsubscribeInboundInterceptor {

    private static final Logger log = LoggerFactory.getLogger(AsyncModifyingUnsubscribeInboundInterceptor.class);

    @Override
    public void onInboundUnsubscribe(final @NotNull UnsubscribeInboundInput unsubscribeInboundInput, final @NotNull UnsubscribeInboundOutput unsubscribeInboundOutput) {

        //make output object async with a duration of 10 seconds
        final Async<UnsubscribeInboundOutput> async = unsubscribeInboundOutput.async(Duration.ofSeconds(10));

        final CompletableFuture<?> taskFuture = Services.extensionExecutorService().submit(new Runnable() {
            @Override
            public void run() {

                //get the modifiable unsubscribe object from the output
                final ModifiableUnsubscribePacket unsubscribePacket = unsubscribeInboundOutput.getUnsubscribePacket();

                // modify / overwrite parameters of a unsubscribe packet.
                try {
                    //Set reason string and reason code.
                    unsubscribePacket.setReasonString("The reason for the unsuccessful puback");
                    unsubscribePacket.setReasonCode(AckReasonCode.UNSPECIFIED_ERROR);

                    unsubscribePacket.getUserProperties().addUserProperty("my-prop", "some value");
                    unsubscribePacket.getUserProperties().addUserProperty("my-prop-2", "other value");

                } catch (final Exception e) {
                    log.debug("Unsubscribe inbound interception failed:", e);
                }

                async.resume();
            }
        });
    }
}

public class SessionExpiryDisconnectInboundInterceptor implements DisconnectInboundInterceptor {

    @Override
    public void onInboundDisconnect(final @NotNull DisconnectInboundInput disconnectInboundInput, final @NotNull DisconnectInboundOutput disconnectInboundOutput) {
        if (disconnectInboundInput.getDisconnectPacket().getSessionExpiryInterval().isPresent()) {
            if (disconnectInboundInput.getDisconnectPacket().getSessionExpiryInterval().get() != 0) {
                disconnectInboundOutput.getDisconnectPacket().setSessionExpiryInterval(10L);
            }
        }
    }
}