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<h1 class="post-title-main">HTTP API concepts</h1>
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<p>Ditto’s <a href="http-api-doc.html">HTTP API</a> follows some concepts which are documented on this page.</p>
<p>The entry point into the HTTP API is:</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>http://localhost:8080/api/&lt;apiVersion&gt;
</code></pre></div></div>
<h2 id="api-versioning">API versioning</h2>
<p>Ditto’s HTTP API is versioned in the URL: <code class="highlighter-rouge">/api/&lt;apiVersion&gt;</code>. Currently Ditto distinguishes between deprecated API version <code class="highlighter-rouge">1</code> and
API version <code class="highlighter-rouge">2</code>.</p>
<p>The API version is a promise that no HTTP resources (the static ones defined by Ditto itself) are modified in an
incompatible/breaking way. As the HTTP resources reflect the JSON structure of the <code class="highlighter-rouge">Thing</code> entity, that also applies for
this entity. In API version 1, the JSON structure of the <code class="highlighter-rouge">Thing</code> entity won’t be changed in a breaking way
(e.g. by removing or renaming a JSON field).</p>
<p>That is also the reason for Ditto having already 2 API versions. In API 2 the <code class="highlighter-rouge">Thing</code> structure was changed to no longer
contain the <a href="basic-acl.html">ACL</a> inline as payload of the Thing. Instead, the authorization information in API 2 is
managed by <a href="basic-policy.html">Policies</a>. The <code class="highlighter-rouge">acl</code> field was removed from the structure of the <code class="highlighter-rouge">Thing</code> and the
<code class="highlighter-rouge">policyId</code> was added - that’s why Ditto had to make this change in an API version 2.</p>
<h2 id="endpoints">Endpoints</h2>
<p>In the HTTP API, some endpoints are static and can be seen as the “schema” of Ditto. They are in sync with the JSON
representation of the model classes, e.g. <a href="basic-thing.html#model-specification">Thing</a> for the layout of the <code class="highlighter-rouge">/things</code>
endpoint and <a href="basic-policy.html">Policy</a> for the layout of the <code class="highlighter-rouge">/policies</code> endpoint.</p>
<h3 id="api-version-1---deprecated">API version 1 - Deprecated</h3>
<p>In API version 1, each <code class="highlighter-rouge">Thing</code> contains the information about the authorization in an inlined <a href="basic-acl.html">ACL</a>.</p>
<h4 id="migration-from-api-1-to-api-2">Migration from API 1 to API 2</h4>
<p>In case you need to migrate a thing which was created via API 1 to API 2,
please note that you need to migrate the access control list entries (ACL) into a <strong>policy</strong>, and to assign your thing to such a policy.</p>
<ol>
<li>
<p>Request the thing to be migrated, via API 2 and use the field-selector to specify that the inline policy (i.e. <code class="highlighter-rouge">_policy</code>) should also be retrieved.</p>
<p><code class="highlighter-rouge">GET /api/2/things/{$thingId}?fields=_policy</code></p>
<p><a href="https://www.eclipse.org/ditto/http-api-doc.html#/Things/get_things__thingId_">Retrieve a specific Thing</a></p>
</li>
<li>
<p>Create a new policy from the content of the requested inline policy, with a <code class="highlighter-rouge">policyId</code> of your choice (e.g. same as the <code class="highlighter-rouge">thingId</code>).</p>
<p><code class="highlighter-rouge">PUT /api/2/policies/{$policyId}</code></p>
<p><a href="https://www.eclipse.org/ditto/http-api-doc.html#/Policies/put_policies__policyId_">Create or update a Policy with a specified ID</a></p>
</li>
<li>
<p>Assign the new <code class="highlighter-rouge">policyId</code> to the thing to be migrated.</p>
<p><code class="highlighter-rouge">PUT /api/2/things/{$thingId}/policyId</code></p>
<p><a href="https://www.eclipse.org/ditto/http-api-doc.html#/Things/put_things__thingId__policyId">Create or update the Policy ID of a Thing</a></p>
</li>
</ol>
<p><strong>Note</strong>: Henceforth the thing cannot be read nor written via API 1.</p>
<h4 id="things-in-api-1"><code class="highlighter-rouge">/things</code> in API 1</h4>
<p>The base endpoint for accessing and working with <code class="highlighter-rouge">Things</code>.<br />
A <code class="highlighter-rouge">Thing</code> in API 1 has the following JSON structure:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">""</span><span class="p">,</span><span class="w">
</span><span class="s2">"acl"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>This maps to the following HTTP API endpoints:</p>
<ul>
<li><code class="highlighter-rouge">/things/{thingId}</code>: accessing complete <code class="highlighter-rouge">Thing</code></li>
<li><code class="highlighter-rouge">/things/{thingId}/acl</code>: accessing the ACL of the <code class="highlighter-rouge">Thing</code></li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes</code>: accessing the attributes of the <code class="highlighter-rouge">Thing</code></li>
<li><code class="highlighter-rouge">/things/{thingId}/features</code>: accessing the features of the <code class="highlighter-rouge">Thing</code></li>
</ul>
<h4 id="things-in-api-1---dynamic-part"><code class="highlighter-rouge">/things</code> in API 1 - dynamic part</h4>
<p>Additionally to that “static part” of the HTTP API which is defined by Ditto, the API is dynamically enhanced by the JSON
structure of the Thing.<br /></p>
<div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> This automatically turns each small aspect of a <strong>digital twin</strong> into an API endpoint.</div>
<p>For example for a <code class="highlighter-rouge">Thing</code> with following content:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{thingId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"acl"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"{userId}"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"READ"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"WRITE"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"ADMINISTRATE"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="p">,</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"lamp"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"color"</span><span class="p">:</span><span class="w"> </span><span class="s2">"blue"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>The following additional API endpoints are automatically available:</p>
<ul>
<li><code class="highlighter-rouge">/things/{thingId}/acl/userId</code>: accessing the ACL entry for user <code class="highlighter-rouge">userId</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/manufacturer</code>: accessing the attribute <code class="highlighter-rouge">manufacturer</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/complex</code>: accessing the attribute <code class="highlighter-rouge">complex</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/complex/some</code>: accessing the attribute <code class="highlighter-rouge">complex/some</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/complex/serialNo</code>: accessing the attribute <code class="highlighter-rouge">complex/serialNo</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp</code>: accessing the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp/properties</code>: accessing all properties of the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp/properties/on</code>: accessing the <code class="highlighter-rouge">on</code> property of the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp/properties/color</code>: accessing the <code class="highlighter-rouge">color</code> properties of the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
</ul>
<h3 id="api-version-2">API version 2</h3>
<p>In API version 2, a <code class="highlighter-rouge">Thing</code> does no longer contain information about the authorization in an inlined <a href="basic-acl.html">ACL</a>,
but contains a <code class="highlighter-rouge">policyId</code>, which points to a <code class="highlighter-rouge">Policy</code> managed as another entity. Its API endpoint is <code class="highlighter-rouge">/policies</code>.</p>
<h4 id="things-in-api-2"><code class="highlighter-rouge">/things</code> in API 2</h4>
<p>The base endpoint for accessing and working with <code class="highlighter-rouge">Things</code>.<br />
A <code class="highlighter-rouge">Thing</code> in API 2 has the following JSON structure:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{thingId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"definition"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{definition}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>This maps to the following HTTP API endpoints:</p>
<ul>
<li><code class="highlighter-rouge">/things/{thingId}</code>: accessing a complete specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/policyId</code>: accessing the policy ID of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/definition</code>: accessing the definition of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes</code>: accessing the attributes of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features</code>: accessing the features of the specific thing</li>
</ul>
<h4 id="things-in-api-2---dynamic-part"><code class="highlighter-rouge">/things</code> in API 2 - dynamic part</h4>
<p>Additionally to that “static part” of the HTTP API which is defined by Ditto, the API is dynamically enhanced by the JSON
structure of the Thing.<br /></p>
<div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> This automatically turns each small aspect of a <strong>digital twin</strong> into an API endpoint.</div>
<p>For example for a <code class="highlighter-rouge">Thing</code> with following content:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{thingId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"definition"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{definition}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="p">,</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"lamp"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"color"</span><span class="p">:</span><span class="w"> </span><span class="s2">"blue"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>The following additional API endpoints are automatically available:</p>
<ul>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/manufacturer</code>: accessing the attribute <code class="highlighter-rouge">manufacturer</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/complex</code>: accessing the attribute <code class="highlighter-rouge">complex</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/complex/some</code>: accessing the attribute <code class="highlighter-rouge">complex/some</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/attributes/complex/serialNo</code>: accessing the attribute <code class="highlighter-rouge">complex/serialNo</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp</code>: accessing the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp/properties</code>: accessing all properties of the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp/properties/on</code>: accessing the <code class="highlighter-rouge">on</code> property of the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
<li><code class="highlighter-rouge">/things/{thingId}/features/lamp/properties/color</code>: accessing the <code class="highlighter-rouge">color</code> properties of the feature <code class="highlighter-rouge">lamp</code> of the specific thing</li>
</ul>
<h4 id="policies-in-api-2"><code class="highlighter-rouge">/policies</code> in API 2</h4>
<p>The base endpoint for accessing and working with <code class="highlighter-rouge">Policies</code>.<br />
A <code class="highlighter-rouge">Policy</code> in API 2 has the following JSON structure:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"entries"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"{entryLabel-1}"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"subjects"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"{subjectId1}"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"resources"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"{resource1}"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>This maps to the following HTTP API endpoints:</p>
<ul>
<li><code class="highlighter-rouge">/policies/{policyId}</code>: accessing complete <code class="highlighter-rouge">Policy</code></li>
<li><code class="highlighter-rouge">/policies/{policyId}/entries</code>: accessing the <code class="highlighter-rouge">Policy</code> entries</li>
<li><code class="highlighter-rouge">/policies/{policyId}/entries/{entryLabel-1}</code>: accessing a single <code class="highlighter-rouge">Policy</code> entry with the label <code class="highlighter-rouge">{entryLabel-1}</code></li>
<li><code class="highlighter-rouge">/policies/{policyId}/entries/{entryLabel-1}/subjects</code>: accessing the subjects of a single <code class="highlighter-rouge">Policy</code> entry with the label <code class="highlighter-rouge">{entryLabel-1}</code></li>
<li><code class="highlighter-rouge">/policies/{policyId}/entries/{entryLabel-1}/resources</code>: accessing the resources of a single <code class="highlighter-rouge">Policy</code> entry with the label <code class="highlighter-rouge">{entryLabel-1}</code></li>
</ul>
<h2 id="partial-updates">Partial updates</h2>
<p>As a benefit of the above mentioned mechanism that an API is automatically available based on the JSON structure, the
“partial update” pattern can be applied when modifying data.</p>
<p>The benefit of this is a reduction in payload to be transferred. Further, it is beneficial because other parts of the
<code class="highlighter-rouge">Thing</code> are not overwritten with a potentially outdated value - only the actually changed data part can be modified.</p>
<p>So instead of modifying a complete <code class="highlighter-rouge">Thing</code> only a specific part is affected.</p>
<p>Given, the <code class="highlighter-rouge">on</code> property of <code class="highlighter-rouge">lamp</code> should be changed to <code class="highlighter-rouge">true</code>.</p>
<p>Instead of<br />
<br />
<code class="highlighter-rouge">PUT .../things/{thingId}</code> with the complete payload:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{thingId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"definition"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{definition}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="p">,</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"lamp"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"color"</span><span class="p">:</span><span class="w"> </span><span class="s2">"blue"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>we can use a smarter request<br /><code class="highlighter-rouge">PUT .../things/{thingId}/features/lamp/properties/on</code> with a minimal payload:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kc">true</span><span class="w">
</span></code></pre></div></div>
<h2 id="partial-requests">Partial requests</h2>
<p>Similar to the partial updates from above, the HTTP API can also be used to retrieve a single value instead of a
complete <code class="highlighter-rouge">Thing</code>.</p>
<p>Again, the benefit is a reduction in response payload and that the caller can directly use the returned data value
(for example expect it to be a <code class="highlighter-rouge">boolean</code> and treat it accordingly).</p>
<p>For example, we can request<br /><code class="highlighter-rouge">GET .../things/{thingId}/features/lamp/properties/on</code> and get as response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kc">true</span><span class="w">
</span></code></pre></div></div>
<h3 id="with-field-selector">With field selector</h3>
<p>A further mechanism in the API for partial requests is using a so-called field selector. This is useful when the JSON
structure of the <code class="highlighter-rouge">Thing</code> or other entity should be kept intact, but not all information is relevant.</p>
<p>The field selector is passed as a HTTP query parameter <code class="highlighter-rouge">fields</code> and contains a comma separated list of fields to include
in the response.</p>
<p>Given, you have the following Thing:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{thingId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"definition"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{definition}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="p">,</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="p">,</span><span class="w">
</span><span class="s2">"misc"</span><span class="p">:</span><span class="w"> </span><span class="s2">"foo"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"lamp"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="p">,</span><span class="w">
</span><span class="s2">"color"</span><span class="p">:</span><span class="w"> </span><span class="s2">"blue"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<h4 id="field-selector-examples">Field selector examples</h4>
<p>The following <code class="highlighter-rouge">GET</code> request examples with field selectors show how you can retrieve only the parts of a thing which
you are interested in:</p>
<p><code class="highlighter-rouge">GET .../things/{thingId}?fields=attributes</code><br />
Response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="p">,</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="p">,</span><span class="w">
</span><span class="s2">"misc"</span><span class="p">:</span><span class="w"> </span><span class="s2">"foo"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p><code class="highlighter-rouge">GET .../things/{thingId}?fields=attributes/manufacturer</code><br />
Response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p><code class="highlighter-rouge">GET .../things/{thingId}?fields=attributes/complex/serialNo</code><br />
Response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p><code class="highlighter-rouge">GET .../things/{thingId}?fields=attributes/complex/some,attributes/complex/serialNo</code><br />
Response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p><code class="highlighter-rouge">GET .../things/{thingId}?fields=attributes/complex(some,serialNo)</code><br />
Response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"some"</span><span class="p">:</span><span class="w"> </span><span class="kc">false</span><span class="p">,</span><span class="w">
</span><span class="s2">"serialNo"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p><code class="highlighter-rouge">GET .../things/{thingId}?fields=attributes/complex/misc,features/lamp/properties/on</code><br />
Response:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"complex"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"misc"</span><span class="p">:</span><span class="w"> </span><span class="s2">"foo"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"lamp"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"on"</span><span class="p">:</span><span class="w"> </span><span class="kc">true</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<h2 id="conditional-requests">Conditional Requests</h2>
<p>The HTTP API for <code class="highlighter-rouge">Things</code> and <code class="highlighter-rouge">Policies</code> partially supports <code class="highlighter-rouge">Conditional Requests</code> as defined in <a href="https://tools.ietf.org/html/rfc7232">RFC-7232</a>.</p>
<h3 id="etag">ETag</h3>
<p>A successful response on a <code class="highlighter-rouge">thing</code> or <code class="highlighter-rouge">policy</code> resource provides an <code class="highlighter-rouge">ETag</code> header.</p>
<ul>
<li>For read responses, it contains the current entity-tag of the resource.</li>
<li>For write responses, it contains the entity-tag after successful write.</li>
</ul>
<p>The <code class="highlighter-rouge">ETag</code> has a different format for top-level resources and sub-resources.</p>
<ul>
<li>Top-level resources (e.g. <code class="highlighter-rouge">.../things/{thingId}</code>): The entity-tag contains the revision of the
entity which is addressed by the resource in the format <code class="highlighter-rouge">"rev:&lt;revision&gt;"</code>, e.g. <code class="highlighter-rouge">"rev:2"</code>.</li>
<li>Sub-resources (e.g. <code class="highlighter-rouge">.../things/{thingId}/features/{featureId}</code>): The entity-tag contains a hash
of the current value of the addressed sub-resource in the format <code class="highlighter-rouge">"hash:&lt;calculated-hash&gt;"</code>, e.g.
<code class="highlighter-rouge">"hash:87192253740"</code>. Note that this format may change in the future.</li>
</ul>
<h3 id="conditional-headers">Conditional Headers</h3>
<p>The following request headers can be used to issue a conditional request:</p>
<ul>
<li><code class="highlighter-rouge">If-Match</code>:
<ul>
<li>Read or write the resource only
<ul>
<li>if the current entity-tag matches at least one of the entity-tags provided in this header</li>
<li>or if the header is <code class="highlighter-rouge">*</code> and the entity exists</li>
</ul>
</li>
<li>The response will be:
<ul>
<li>in case of a match, the same response as if the header wouldn’t have been specified</li>
<li>in case of no match, status <code class="highlighter-rouge">412 (Precondition Failed)</code> with an error response containing detail information
and the current entity-tag of the resource as <code class="highlighter-rouge">ETag</code> header</li>
</ul>
</li>
</ul>
</li>
<li><code class="highlighter-rouge">If-None-Match</code>:
<ul>
<li>Read or write the resource only
<ul>
<li>if the current entity-tag does not match any one of the entity-tags provided in this header</li>
<li>or if the header is <code class="highlighter-rouge">*</code> and the entity does not exist</li>
</ul>
</li>
<li>The response will be:
<ul>
<li>in case of no match, the same response as if the header wouldn’t have been specified</li>
<li>in case of a match:
<ul>
<li>for write requests, status <code class="highlighter-rouge">412 (Precondition Failed)</code> with an error response containing detail information and
the current entity-tag of the resource as <code class="highlighter-rouge">ETag</code> header</li>
<li>for read requests, status <code class="highlighter-rouge">304 (Not Modified)</code> without response body, with the current entity-tag of the
resource as <code class="highlighter-rouge">ETag</code> header</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
<p>Note that the Ditto HTTP API always provides a <code class="highlighter-rouge">strong</code> entity-tag in the <code class="highlighter-rouge">ETag</code> header, thus you will never receive a
<code class="highlighter-rouge">weak</code> entity-tag (see <a href="https://tools.ietf.org/html/rfc7232#section-2.1">RFC-7232 Section 2.1</a>). If you convert this
strong entity-tag to a weak entity-tag and use it in a Conditional Header, Ditto will handle it according to RFC-7232.
However, we discourage the usage of weak entity-tags, because in the context of Ditto they only add unnecessary
complexity.</p>
<h3 id="exempted-fields">Exempted fields</h3>
<p>Assuming you have a thing with an associated policy. When querying the thing with</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>GET .../things/{thingId}?fields=_policy
</code></pre></div></div>
<p>you will get the thing containing its revision and associated policy.</p>
<p>If you now modify the associated policy, the revision of the thing will not change! This could lead to an
inconsistent state if the thing is getting refetched by using the <code class="highlighter-rouge">If-None-Match</code> header,
because this would return a <code class="highlighter-rouge">304 Not Modified</code>, even if the policy has changed.</p>
<p>To tackle this, Ditto has the following list of exempted fields which automatically bypass the precondition header check:</p>
<ul>
<li><code class="highlighter-rouge">_policy</code></li>
</ul>
<h3 id="examples">Examples</h3>
<p>The following examples show several scenarios on a top-level (Thing) resource. Nevertheless, these scenarios can
also be applied on any sub-resource in the same way.</p>
<h4 id="create-write-only-if-the-resource-does-not-exist">Create: Write only if the resource does not exist</h4>
<p>The following example request shows, how you can make sure that a <code class="highlighter-rouge">PUT</code> request does not overwrite existing data, i.e.
how you can enforce that the Thing can only be created by the request.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>PUT .../things/{thingId}
If-None-Match: *
</code></pre></div></div>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME crop"</span><span class="p">,</span><span class="w">
</span><span class="s2">"otherData"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>You will get one of the following responses:</p>
<ul>
<li><code class="highlighter-rouge">201 (Created)</code> in case the creation was successful, i.e. the Thing did not yet exist.</li>
<li><code class="highlighter-rouge">412 (Precondition Failed)</code> in case the creation failed, i.e. a Thing with the exactly same <code class="highlighter-rouge">{thingId}</code> already
exists.</li>
</ul>
<h4 id="update-write-only-if-the-resource-already-exists">Update: Write only if the resource already exists</h4>
<p>The following example request shows how you can make sure that a <code class="highlighter-rouge">PUT</code> request does not create the resource, i.e. how
you can enforce that the Thing can only be updated by the request, but you do not generate a duplicate by mistake.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>PUT .../things/{thingId}
If-Match: *
</code></pre></div></div>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME crop"</span><span class="p">,</span><span class="w">
</span><span class="s2">"otherData"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>You will get one of the following responses:</p>
<ul>
<li><code class="highlighter-rouge">204 (No Content)</code> in case the update was successful, i.e. the Thing already existed.</li>
<li><code class="highlighter-rouge">412 (Precondition Failed)</code> in case the update failed, i.e. the Thing does not yet exist.</li>
</ul>
<h4 id="optimistic-locking">Optimistic Locking</h4>
<p>First, <code class="highlighter-rouge">GET</code> the Thing in order to retrieve both: the current data and the entity-tag:</p>
<p><code class="highlighter-rouge">GET .../things/{thingId}</code>:</p>
<p>Response:</p>
<p><code class="highlighter-rouge">ETag: "rev:2"</code></p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{thingId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{policyId}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"definition"</span><span class="p">:</span><span class="w"> </span><span class="s2">"{definition}"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME crop"</span><span class="p">,</span><span class="w">
</span><span class="s2">"otherData"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>Assume that you have detected the typo in the manufacturer attribute (“ACME crop”) and want to fix this with a
top-level Thing PUT. You want to make sure, that no one else has modified the Thing in the meantime, because
otherwise his changes would be lost. (You could also achieve this with a PUT on the concrete attribute, but for this
example we assume that you want to use a top-level Thing PUT.)</p>
<p><code class="highlighter-rouge">PUT</code> the Thing with the changed data and the entity-tag from the preceding <code class="highlighter-rouge">GET</code> response in the <code class="highlighter-rouge">If-Match</code> header.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>PUT .../things/{thingId}
If-Match: "rev:2"
</code></pre></div></div>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"manufacturer"</span><span class="p">:</span><span class="w"> </span><span class="s2">"ACME corp"</span><span class="p">,</span><span class="w">
</span><span class="s2">"otherData"</span><span class="p">:</span><span class="w"> </span><span class="mi">4711</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>You will get one of the following responses:</p>
<ul>
<li><code class="highlighter-rouge">204 (No Content)</code> in case the update was successful, i.e. no one else has changed the Thing in the meantime.</li>
<li><code class="highlighter-rouge">412 (Precondition Failed)</code> in case the update was not successful, i.e. the Thing has been changed by someone else
in the meantime.</li>
</ul>
<div class="tags">
<b>Tags: </b>
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