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<olclass="chapter"><liclass="affix"><ahref="../index.html">Introduction</a></li><liclass="affix"><ahref="../quickstart.html">Quickstart</a></li><liclass="affix"><ahref="../types/index.html">Type System</a></li><li><ahref="../types/objects/defining_objects.html"><strongaria-hidden="true">1.</strong> Defining objects</a></li><li><olclass="section"><li><ahref="../types/objects/complex_fields.html"><strongaria-hidden="true">1.1.</strong> Complex fields</a></li><li><ahref="../types/objects/using_contexts.html"><strongaria-hidden="true">1.2.</strong> Using contexts</a></li><li><ahref="../types/objects/error_handling.html"><strongaria-hidden="true">1.3.</strong> Error handling</a></li></ol></li><li><ahref="../types/other-index.html"><strongaria-hidden="true">2.</strong> Other types</a></li><li><olclass="section"><li><ahref="../types/enums.html"><strongaria-hidden="true">2.1.</strong> Enums</a></li><li><ahref="../types/interfaces.html"><strongaria-hidden="true">2.2.</strong> Interfaces</a></li><li><ahref="../types/input_objects.html"><strongaria-hidden="true">2.3.</strong> Input objects</a></li><li><ahref="../types/scalars.html"><strongaria-hidden="true">2.4.</strong> Scalars</a></li><li><ahref="../types/unions.html"><strongaria-hidden="true">2.5.</strong> Unions</a></li></ol></li><li><ahref="../schema/schemas_and_mutations.html"><strongaria-hidden="true">3.</strong> Schemas and mutations</a></li><li><ahref="../servers/index.html"><strongaria-hidden="true">4.</strong> Adding A Server</a></li><li><olclass="section"><li><ahref="../servers/official.html"><strongaria-hidden="true">4.1.</strong> Official Server Integrations</a></li><li><olclass="section"><li><ahref="../servers/warp.html"><strongaria-hidden="true">4.1.1.</strong> Warp</a></li><li><ahref="../servers/rocket.html"><strongaria-hidden="true">4.1.2.</strong> Rocket</a></li><li><ahref="../servers/iron.html"><strongaria-hidden="true">4.1.3.</strong> Iron</a></li><li><ahref="../servers/hyper.html"><strongaria-hidden="true">4.1.4.</strong> Hyper</a></li></ol></li><li><ahref="../servers/third-party.html"><strongaria-hidden="true">4.2.</strong> Third Party Integrations</a></li></ol></li><li><ahref="../advanced/index.html"><strongaria-hidden="true">5.</strong> Advanced Topics</a></li><li><olclass="section"><li><ahref="../advanced/introspection.html"><strongaria-hidden="true">5.1.</strong> Introspection</a></li><li><ahref="../advanced/non_struct_objects.html"><strongaria-hidden="true">5.2.</strong> Non-struct objects</a></li><li><ahref="../advanced/objects_and_generics.html"><strongaria-hidden="true">5.3.</strong> Objects and generics</a></li><li><ahref="../advanced/multiple_ops_per_request.html"><strongaria-hidden="true">5.4.</strong> Multiple operations per request</a></li><li><ahref="../advanced/dataloaders.html"><strongaria-hidden="true">5.5.</strong> Dataloaders</a></li><li><ahref="../advanced/subscriptions.html"class="active"><strongaria-hidden="true">5.6.</strong> Subscriptions</a></li></ol></li></ol>
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<h1class="menu-title">Juniper - GraphQL Server for Rust</h1>
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<aclass="header"href="#how-to-achieve-realtime-data-with-graphql-subscriptions"id="how-to-achieve-realtime-data-with-graphql-subscriptions"><h3>How to achieve realtime data with GraphQL subscriptions</h3></a>
<p>GraphQL subscriptions are a way to push data from the server to clients requesting real-time messages
from the server. Subscriptions are similar to queries in that they specify a set of fields to be delivered to the client,
be returned to the end user. The <ahref="https://github.com/graphql-rust/juniper/tree/master/juniper_subscriptions"><code>juniper_subscriptions</code></a> crate
provides a default connection implementation. Currently subscriptions are only supported on the <code>master</code> branch. Add the following to your <code>Cargo.toml</code>:</p>
<p>The <code>Subscription</code> is just a GraphQL object, similar to the query root and mutations object that you defined for the
operations in your [Schema][Schema]. For subscriptions all fields/operations should be async and should return a <ahref="https://docs.rs/futures/0.3.4/futures/stream/trait.Stream.html">Stream</a>.</p>
<p>Subscriptions require a bit more resources than regular queries and provide a great vector for DOS attacks. This can can bring down a server easily if not handled correctly. The [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] trait provides coordination logic to enable functionality like DOS attack mitigation and resource limits.</p>
<p>The [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] contains the schema and can keep track of opened connections, handle subscription
start and end, and maintain a global subscription id for each subscription. Each time a connection is established,<br/>
the [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] spawns a [<code>SubscriptionConnection</code>][SubscriptionConnection]. The [<code>SubscriptionConnection</code>][SubscriptionConnection] handles a single connection, providing resolver logic for a client stream as well as reconnection
<p>While you can implement [<code>SubscriptionCoordinator</code>][SubscriptionCoordinator] yourself, Juniper contains a simple and generic implementation called [<code>Coordinator</code>][Coordinator]. The <code>subscribe</code>
operation returns a [<code>Future</code>][Future] with an <code>Item</code> value of a <code>Result<Connection, GraphQLError></code>,
where [<code>Connection</code>][Connection] is a <code>Stream</code> of values returned by the operation and [<code>GraphQLError</code>][GraphQLError] is the error when the subscription fails.</p>
