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| <li class="subfolders"> |
| <a href="#"><span></span>Client SDK</a> |
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| <li><a href="client-sdk-overview.html">Overview</a></li> |
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| <li><a href="client-sdk-java.html">Java</a></li> |
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| <li><a href="client-sdk-javascript.html">JavaScript</a></li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>Ditto Protocol</a> |
| <ul> |
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| <li><a href="protocol-overview.html">Overview</a></li> |
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| <li><a href="protocol-twinlive.html">Twin/live channel</a></li> |
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| <li><a href="protocol-specification.html">Specification</a></li> |
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| <li><a href="protocol-specification-topic.html">Protocol topic</a></li> |
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| <li><a href="protocol-specification-things.html">Things group</a></li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>→ commands/events</a> |
| <ul> |
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| <li><a href="protocol-specification-things-create-or-modify.html">Create/Modify</a></li> |
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| <li><a href="protocol-specification-things-merge.html">Merge</a></li> |
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| <li><a href="protocol-specification-things-retrieve.html">Retrieve</a></li> |
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| <li><a href="protocol-specification-things-delete.html">Delete</a></li> |
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| <li><a href="protocol-specification-acks.html">Acknowledgements</a></li> |
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| <li><a href="protocol-specification-errors.html">Errors</a></li> |
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| </ul> |
| </li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>→ search/messages</a> |
| <ul> |
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| <li><a href="protocol-specification-things-search.html">Search</a></li> |
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| <li><a href="protocol-specification-things-messages.html">Messages</a></li> |
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| </ul> |
| </li> |
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| <li><a href="protocol-specification-policies.html">Policies group</a></li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>→ commands/events</a> |
| <ul> |
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| <li><a href="protocol-specification-policies-create-or-modify.html">Create/Modify</a></li> |
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| <li><a href="protocol-specification-policies-retrieve.html">Retrieve</a></li> |
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| <li><a href="protocol-specification-policies-delete.html">Delete</a></li> |
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| <li><a href="protocol-specification-policies-announcement.html">Announcement</a></li> |
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| </ul> |
| </li> |
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| <li><a href="protocol-bindings.html">Bindings</a></li> |
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| <li><a href="protocol-examples.html">Examples</a></li> |
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| <li class="subfolders"> |
| <a href="#"><span></span>→ Things examples</a> |
| <ul> |
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| <li><a href="protocol-examples-creatething.html">Create a Thing</a></li> |
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| <li><a href="protocol-examples-deletething.html">Delete a Thing</a></li> |
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| <li><a href="protocol-examples-modifything.html">Modify a Thing</a></li> |
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| <li><a href="protocol-examples-retrievething.html">Retrieve a Thing</a></li> |
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| <li><a href="protocol-examples-retrievethings.html">Retrieve multiple Things</a></li> |
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| <li><a href="protocol-examples-modifypolicyid.html">Modify the Policy ID of a Thing</a></li> |
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| <li><a href="protocol-examples-createattributes.html">Create Attributes</a></li> |
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| <li><a href="protocol-examples-deleteattributes.html">Delete Attributes</a></li> |
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| <li><a href="protocol-examples-modifyattributes.html">Modify Attributes</a></li> |
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| <li><a href="protocol-examples-retrieveattributes.html">Retrieve Attributes</a></li> |
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| <li><a href="protocol-examples-createattribute.html">Create a single Attribute</a></li> |
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| <li><a href="protocol-examples-deleteattribute.html">Delete a single Attribute</a></li> |
| |
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| <li><a href="protocol-examples-modifyattribute.html">Modify a single Attribute</a></li> |
| |
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| <li><a href="protocol-examples-retrieveattribute.html">Retrieve a single Attribute</a></li> |
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| <li><a href="protocol-examples-createthingdefinition.html">Create a Definition</a></li> |
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| <li><a href="protocol-examples-deletethingdefinition.html">Delete a Definition</a></li> |
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| <li><a href="protocol-examples-modifythingdefinition.html">Modify a Definition</a></li> |
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| <li><a href="protocol-examples-retrievethingdefinition.html">Retrieve a Definition</a></li> |
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| <li><a href="protocol-examples-createfeatures.html">Create Features</a></li> |
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| <li><a href="protocol-examples-deletefeatures.html">Delete Features</a></li> |
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| <li><a href="protocol-examples-modifyfeatures.html">Modify Features</a></li> |
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| <li><a href="protocol-examples-retrievefeatures.html">Retrieve Features</a></li> |
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| <li><a href="protocol-examples-createfeature.html">Create a single Feature</a></li> |
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| <li><a href="protocol-examples-deletefeature.html">Delete a single Feature</a></li> |
| |
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| <li><a href="protocol-examples-modifyfeature.html">Modify a single Feature</a></li> |
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| <li><a href="protocol-examples-retrievefeature.html">Retrieve a single Feature</a></li> |
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| <li><a href="protocol-examples-createdefinition.html">Create Feature Definition</a></li> |
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| <li><a href="protocol-examples-deletedefinition.html">Delete Feature Definition</a></li> |
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| <li><a href="protocol-examples-modifydefinition.html">Modify Feature Definition</a></li> |
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| <li><a href="protocol-examples-retrievedefinition.html">Retrieve Feature Definition</a></li> |
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| <li><a href="protocol-examples-createproperties.html">Create Feature Properties</a></li> |
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| <li><a href="protocol-examples-deleteproperties.html">Delete Feature Properties</a></li> |
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| <li><a href="protocol-examples-modifyproperties.html">Modify Feature Properties</a></li> |
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| <li><a href="protocol-examples-retrieveproperties.html">Retrieve Feature Properties</a></li> |
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| <li><a href="protocol-examples-createproperty.html">Create a single Property</a></li> |
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| <li><a href="protocol-examples-deleteproperty.html">Delete a single Property</a></li> |
| |
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| <li><a href="protocol-examples-modifyproperty.html">Modify a single Property</a></li> |
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| <li><a href="protocol-examples-retrieveproperty.html">Retrieve a single Property</a></li> |
| |
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| <li><a href="protocol-examples-createdesiredproperties.html">Create desired Feature Properties</a></li> |
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| <li><a href="protocol-examples-deletedesiredproperties.html">Delete desired Feature Properties</a></li> |
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| <li><a href="protocol-examples-modifydesiredproperties.html">Modify desired Feature Properties</a></li> |
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| <li><a href="protocol-examples-retrievedesiredproperties.html">Retrieve desired Feature Properties</a></li> |
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| <li><a href="protocol-examples-createdesiredproperty.html">Create a single desired Property</a></li> |
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| <li><a href="protocol-examples-deletedesiredproperty.html">Delete a single desired Property</a></li> |
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| <li><a href="protocol-examples-modifydesiredproperty.html">Modify a single desired Property</a></li> |
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| <li><a href="protocol-examples-retrievedesiredproperty.html">Retrieve a single desired Property</a></li> |
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| <li><a href="protocol-examples-errorresponses.html">Error responses</a></li> |
| |
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| </ul> |
| </li> |
| |
| |
| |
| <li class="subfolders"> |
| <a href="#"><span></span>→ Things merge examples</a> |
| <ul> |
| |
| |
| |
| <li><a href="protocol-examples-mergething.html">Merge a Thing</a></li> |
| |
| |
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| <li><a href="protocol-examples-mergepolicyid.html">Merge the Policy ID of a Thing</a></li> |
| |
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| <li><a href="protocol-examples-mergeattributes.html">Merge Attributes</a></li> |
| |
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| <li><a href="protocol-examples-mergeattribute.html">Merge a single Attribute</a></li> |
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| <li><a href="protocol-examples-mergethingdefinition.html">Merge a Definition</a></li> |
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| <li><a href="protocol-examples-mergefeatures.html">Merge Features</a></li> |
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| <li><a href="protocol-examples-mergefeature.html">Merge a single Feature</a></li> |
| |
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| <li><a href="protocol-examples-mergefeaturedefinition.html">Merge Feature Definition</a></li> |
| |
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| <li><a href="protocol-examples-mergeproperties.html">Merge Feature Properties</a></li> |
| |
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| <li><a href="protocol-examples-mergeproperty.html">Merge a single Property</a></li> |
| |
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| <li><a href="protocol-examples-mergedesiredproperties.html">Merge desired Feature Properties</a></li> |
| |
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| <li><a href="protocol-examples-mergedesiredproperty.html">Merge a single desired Property</a></li> |
| |
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| <li><a href="protocol-examples-errorresponses.html">Error responses</a></li> |
| |
| |
| |
| </ul> |
| </li> |
| |
| |
| |
| <li class="subfolders"> |
| <a href="#"><span></span>→ Policies examples</a> |
| <ul> |
| |
| |
| |
| <li><a href="protocol-examples-policies-createpolicy.html">Create a Policy</a></li> |
| |
| |
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| |
| <li><a href="protocol-examples-policies-deletepolicy.html">Delete a Policy</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-modifypolicy.html">Modify a Policy</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-retrievepolicy.html">Retrieve a Policy</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-modifypolicyentries.html">Modify entries</a></li> |
| |
| |
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| |
| <li><a href="protocol-examples-policies-retrievepolicyentries.html">Retrieve entries</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-createpolicyentry.html">Create a single entry</a></li> |
| |
| |
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| |
| <li><a href="protocol-examples-policies-deletepolicyentry.html">Delete a single entry</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-modifypolicyentry.html">Modify a single entry</a></li> |
| |
| |
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| |
| |
| <li><a href="protocol-examples-policies-retrievepolicyentry.html">Retrieve a single entry</a></li> |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-policies-modifysubjects.html">Modify subjects</a></li> |
| |
| |
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| |
| <li><a href="protocol-examples-policies-retrievesubjects.html">Retrieve subjects</a></li> |
| |
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| <li><a href="protocol-examples-policies-createsubject.html">Create a single subject</a></li> |
| |
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| <li><a href="protocol-examples-policies-deletesubject.html">Delete a single subject</a></li> |
| |
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| <li><a href="protocol-examples-policies-modifysubject.html">Modify a single subject</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-retrievesubject.html">Retrieve a single subject</a></li> |
| |
| |
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| |
| |
| <li><a href="protocol-examples-policies-modifyresources.html">Modify resources</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-retrieveresources.html">Retrieve resources</a></li> |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-policies-createresource.html">Create a single resource</a></li> |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-policies-deleteresource.html">Delete a single resource</a></li> |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-policies-modifyresource.html">Modify a single resource</a></li> |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-policies-retrieveresource.html">Retrieve a single resource</a></li> |
| |
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| |
| <li><a href="protocol-examples-policies-errorresponses.html">Error responses</a></li> |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-policies-announcement-subjectDeletion.html">Announcement for subject deletion</a></li> |
| |
| |
| |
| </ul> |
| </li> |
| |
| |
| |
| |
| |
| |
| <li><a href="protocol-examples-search.html">→ Search examples</a></li> |
| |
| |
| |
| |
| </ul> |
| </li> |
| |
| |
| |
| |
| |
| <li><a href="sandbox.html">Sandbox</a></li> |
| |
| |
| |
| |
| |
| <li><a href="presentations.html">Presentations</a></li> |
| |
| |
| |
| |
| |
| <li><a href="glossary.html">Glossary</a></li> |
| |
| |
| |
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| |
| <li><a href="feedback.html">Feedback</a></li> |
| |
| |
| |
| |
| |
| <p class="external"> |
| <a href="#" id="collapseAll">Collapse All</a> | <a href="#" id="expandAll">Expand All</a> |
| </p> |
| |
| </ul> |
| |
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| <script>$("li.active").parents('li').toggleClass("active"); |
| </script> |
| |
| </div> |
| |
| |
| |
| <!-- Content Column --> |
| <div class="col-md-9" id="tg-sb-content"> |
| <div class="post-header"> |
| <h1 class="post-title-main">Messages</h1> |
| </div> |
| |
| |
| |
| <div class="post-content"> |
| |
| |
| |
| |
| |
| <!-- this handles the automatic toc. use ## for subheads to auto-generate the on-page minitoc. if you use html tags, you must supply an ID for the heading element in order for it to appear in the minitoc. --> |
| <script> |
| $( document ).ready(function() { |
| // Handler for .ready() called. |
| |
| $('#toc').toc({ minimumHeaders: 0, listType: 'ul', showSpeed: 0, headers: 'h2,h3,h4' }); |
| |
| /* this offset helps account for the space taken up by the floating toolbar. */ |
| $('#toc').on('click', 'a', function() { |
| var target = $(this.getAttribute('href')) |
| , scroll_target = target.offset().top |
| |
| $(window).scrollTop(scroll_target - 10); |
| return false |
| }) |
| |
| }); |
| </script> |
| |
| <div id="toc"></div> |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| <p>Messages <em>do not affect</em> the state of a digital twin or an actual device. |
| Therefore Ditto does not handle messages like <a href="basic-signals-command.html">commands</a>: there are no responses which are |
| produced by Ditto and no events which are emitted for messages.</p> |
| |
| <div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> Ditto has no knowledge of the payload of messages but merely routes messages between |
| connected devices.</div> |
| |
| <p>Messages provide the possibility to send something <strong>to</strong> or <strong>from</strong> an actual device using an arbitrary subject/topic. |
| They contain a custom payload with a custom content-type, so you can choose what content best |
| fits your solution.</p> |
| |
| <p>Expressed differently, Messages</p> |
| <ul> |
| <li><strong>to</strong> devices are operations which should trigger an action on a device (e.g. with a subject <code class="highlighter-rouge">turnOff</code>),</li> |
| <li><strong>from</strong> devices are events/alarms which are emitted by devices (e.g. with a subject <code class="highlighter-rouge">smokeDetected</code>).</li> |
| </ul> |
| |
| <figure><img class="docimage" src="images/pages/basic/ditto-messages.png" alt="Ditto Messages" style="max-width: 600px" /><figcaption>How Ditto acts as router for Messages</figcaption></figure> |
| |
| <h2 id="characteristics-of-messages">Characteristics of Messages</h2> |
| |
| <p>Eclipse Ditto is not a message broker and does not want to offer features a message broker does.</p> |
| |
| <p>It can be seen as a message router which:</p> |
| <ul> |
| <li>accepts messages via 2 APIs (<a href="httpapi-messages.html">HTTP</a> and |
| <a href="protocol-specification-things-messages.html">Ditto Protocol</a>, e.g. via <a href="httpapi-protocol-bindings-websocket.html">WebSocket binding</a>)</li> |
| <li>checks for <strong>currently connected</strong> interested parties whether they may receive a specific Message |
| (performs <a href="basic-auth.html#authorization">authorization checks</a>)</li> |
| <li> |
| <p>routes the Message and reply Messages in between connected clients</p> |
| |
| <div class="alert alert-danger" role="alert"><i class="fa fa-exclamation-circle"></i> <b>Warning:</b> Ditto offers no message retention. If a device isn’t connected when a Message should |
| be routed, it will never receive the Message.</div> |
| |
| <div class="alert alert-danger" role="alert"><i class="fa fa-exclamation-circle"></i> <b>Warning:</b> Ditto makes no statement about Message QoS. Messages are routed <strong>at most once</strong>.</div> |
| |
| <div class="alert alert-danger" role="alert"><i class="fa fa-exclamation-circle"></i> <b>Warning:</b> Ditto does deliver messages only in “fan out” style, |
| if the same credentials are connected twice, both connections will receive Messages if the credential is authorized |
| to read a Message.</div> |
| </li> |
| </ul> |
| |
| <h2 id="elements">Elements</h2> |
| |
| <p>Ditto messages always have to have at least this elements:</p> |
| <ul> |
| <li><strong>Direction</strong>: <em>to</em> / <em>from</em>,</li> |
| <li><strong>Thing ID</strong>: the ID of the <code class="highlighter-rouge">Thing</code> (actual device) which should receive/send the message and</li> |
| <li><strong>Subject</strong>: the custom subject/topic.</li> |
| </ul> |
| |
| <p>Additionally, they can contain more information:</p> |
| <ul> |
| <li><strong>Feature ID</strong>: if a message should be addressed to the <a href="basic-feature.html">Feature</a> of a Thing, this specifies |
| its ID.</li> |
| <li><strong>content-type</strong>: defines which content-type the optional payload has.</li> |
| <li><strong>correlation-id</strong>: Ditto can route message responses back to the issuer of a message. Therefore, a correlation-id has |
| to be present in the message.</li> |
| </ul> |
| |
| <h2 id="payload">Payload</h2> |
| |
| <p>A message can optionally contain a payload. As Ditto does neither have to understand the message nor its payload, the |
| content-type and serialization is arbitrary.</p> |
| |
| <h2 id="apis">APIs</h2> |
| |
| <p>Messages can be sent via</p> |
| <ul> |
| <li>the <a href="httpapi-protocol-bindings-websocket.html">WebSocket API</a> as <a href="protocol-overview.html">Ditto Protocol</a> messages,</li> |
| <li>the <a href="httpapi-overview.html">HTTP API</a> either as “fire and forget” messages or, when expecting a response, in a |
| blocking way at the <a href="http-api-doc.html#/Messages">Messages HTTP API endpoint</a></li> |
| </ul> |
| |
| <p>Messages can, however, be received only via the <a href="httpapi-protocol-bindings-websocket.html">WebSocket API</a> as |
| <a href="protocol-overview.html">Ditto Protocol</a> messages.</p> |
| |
| <h2 id="receiving-messages">Receiving Messages</h2> |
| |
| <p>To be able to receive Messages for a Thing, you need to have <code class="highlighter-rouge">READ</code> access on that Thing. |
| When a Message is sent to or from a Thing, <strong>every</strong> connected WebSocket or |
| <a href="basic-connections.html#targets">connection target</a> with the correct |
| access rights will receive the Message.</p> |
| |
| <p>If there is more than one response to a message received by multiple consumers, only the |
| first response will be routed back to the initial issuer of a Message.</p> |
| |
| <h2 id="sending-messages">Sending Messages</h2> |
| |
| <p>If you want to send a Message to or from a Thing, you need <code class="highlighter-rouge">WRITE</code> permissions on that Thing. |
| Every WebSocket or <a href="basic-connections.html#targets">connection target</a> that is able to receive Messages for the |
| Thing (<code class="highlighter-rouge">READ</code> permission), will receive your message.</p> |
| |
| <h2 id="responding-to-messages">Responding to Messages</h2> |
| |
| <p>Since messages are stateless there is no <em>direct</em> response to a Message.</p> |
| |
| <p>For Ditto to be able to route the response of a Message back to the issuer, the |
| correlation-ids need to match. E.g. when the sender uses correlation-id <code class="highlighter-rouge">random-aa98s</code>, |
| any receiver can reply by using the same correlation-id <code class="highlighter-rouge">random-aa98s</code>.</p> |
| |
| <h2 id="permissions">Permissions</h2> |
| |
| <h3 id="api-version-1">API version 1</h3> |
| |
| <p>Permissions in API version 1 are simple for the Message API. If you want to receive Messages of a Thing, |
| you need <code class="highlighter-rouge">READ</code> access on the Thing. To be able to send Messages to or from a Thing |
| you need to have <code class="highlighter-rouge">WRITE</code> permissions.</p> |
| |
| <p>There is one sole exception, which are <a href="#claim-messages">Claim Messages</a>. You do |
| not need the access rights for sending them.</p> |
| |
| <h3 id="api-version-2">API version 2</h3> |
| |
| <p>Permissions in API version 2 can be more fine grained. In order to be able to receive all Messages of a Thing, |
| you need <code class="highlighter-rouge">READ</code> permission for the <code class="highlighter-rouge">message:/</code> resource in the used <a href="basic-policy.html#message">Policy</a>.<br /> |
| There can however be specified that you may only receive specific Messages (with a defined subject), also |
| expressed via <a href="basic-policy.html#message">Policy entry</a>.<br /> |
| The same applies for being able to send Messages, here a <code class="highlighter-rouge">WRITE</code> permission is required either globally for |
| all messages via the <code class="highlighter-rouge">message:/</code> resource or only for specific ones.</p> |
| |
| <p>There is one sole exception, which are <a href="#claim-messages">Claim Messages</a>. You do |
| not need the access rights for sending them.</p> |
| |
| <h2 id="claim-messages">Claim Messages</h2> |
| |
| <p>A Claim Message is used to gain access to a Thing. For this purpose a Claim Messages has two specifics:</p> |
| <ul> |
| <li>the predefined message subject is always <em>claim</em></li> |
| <li>you do not require <code class="highlighter-rouge">WRITE</code> permission to send a Claim Message</li> |
| </ul> |
| |
| <p>Apart from that the Claim Message is handled like a standard Message. It is forwarded to all Ditto Protocol bindings |
| that registered for Claim Messages of the specific Thing. The decision whether to grant access (by setting permissions) |
| is completely up to the receiver of the Claim Message e.g. after verifying the payload of the Message.</p> |
| |
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