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Juniper Bot a519a237e0 Updated book for master ***NO_CI***
2021-06-29 06:56:52 +00:00

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<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
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<a class="header" href="#subscriptions" id="subscriptions"><h1>Subscriptions</h1></a>
<a class="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,
but instead of immediately returning a single answer a result is sent every time a particular event happens on the
server.</p>
<p>In order to execute subscriptions you need a coordinator (that spawns connections)
and a GraphQL object that can be resolved into a stream--elements of which will then
be returned to the end user. The <a href="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>
<pre><code class="language-toml">[dependencies]
juniper = { git = &quot;https://github.com/graphql-rust/juniper&quot;, branch = &quot;master&quot; }
juniper_subscriptions = { git = &quot;https://github.com/graphql-rust/juniper&quot;, branch = &quot;master&quot; }
</code></pre>
<a class="header" href="#schema-definition" id="schema-definition"><h3>Schema Definition</h3></a>
<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 <a href="https://docs.rs/futures/0.3.4/futures/stream/trait.Stream.html">Stream</a>.</p>
<p>This example shows a subscription operation that returns two events, the strings <code>Hello</code> and <code>World!</code>
sequentially:</p>
<pre><pre class="playpen"><code class="language-rust"># extern crate futures;
# extern crate juniper;
# extern crate juniper_subscriptions;
# extern crate tokio;
# use juniper::{graphql_object, graphql_subscription, FieldError};
# use futures::Stream;
# use std::pin::Pin;
#
# #[derive(Clone)]
# pub struct Database;
# impl juniper::Context for Database {}
# pub struct Query;
# #[graphql_object(context = Database)]
# impl Query {
# fn hello_world() -&gt; &amp;str {
# &quot;Hello World!&quot;
# }
# }
pub struct Subscription;
type StringStream = Pin&lt;Box&lt;dyn Stream&lt;Item = Result&lt;String, FieldError&gt;&gt; + Send&gt;&gt;;
#[graphql_subscription(context = Database)]
impl Subscription {
async fn hello_world() -&gt; StringStream {
let stream = futures::stream::iter(vec![
Ok(String::from(&quot;Hello&quot;)),
Ok(String::from(&quot;World!&quot;))
]);
Box::pin(stream)
}
}
#
# fn main () {}
</code></pre></pre>
<a class="header" href="#coordinator" id="coordinator"><h3>Coordinator</h3></a>
<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
and shutdown logic.</p>
<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&lt;Connection, GraphQLError&gt;</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>
<pre><pre class="playpen"><code class="language-rust"># #![allow(dead_code)]
# extern crate futures;
# extern crate juniper;
# extern crate juniper_subscriptions;
# extern crate serde_json;
# extern crate tokio;
# use juniper::{
# http::GraphQLRequest,
# graphql_object, graphql_subscription,
# DefaultScalarValue, EmptyMutation, FieldError,
# RootNode, SubscriptionCoordinator,
# };
# use juniper_subscriptions::Coordinator;
# use futures::{Stream, StreamExt};
# use std::pin::Pin;
#
# #[derive(Clone)]
# pub struct Database;
#
# impl juniper::Context for Database {}
#
# impl Database {
# fn new() -&gt; Self {
# Self {}
# }
# }
#
# pub struct Query;
#
# #[graphql_object(context = Database)]
# impl Query {
# fn hello_world() -&gt; &amp;str {
# &quot;Hello World!&quot;
# }
# }
#
# pub struct Subscription;
#
# type StringStream = Pin&lt;Box&lt;dyn Stream&lt;Item = Result&lt;String, FieldError&gt;&gt; + Send&gt;&gt;;
#
# #[graphql_subscription(context = Database)]
# impl Subscription {
# async fn hello_world() -&gt; StringStream {
# let stream =
# futures::stream::iter(vec![Ok(String::from(&quot;Hello&quot;)), Ok(String::from(&quot;World!&quot;))]);
# Box::pin(stream)
# }
# }
type Schema = RootNode&lt;'static, Query, EmptyMutation&lt;Database&gt;, Subscription&gt;;
fn schema() -&gt; Schema {
Schema::new(Query {}, EmptyMutation::new(), Subscription {})
}
async fn run_subscription() {
let schema = schema();
let coordinator = Coordinator::new(schema);
let req: GraphQLRequest&lt;DefaultScalarValue&gt; = serde_json::from_str(
r#&quot;{
&quot;query&quot;: &quot;subscription { helloWorld }&quot;
}&quot;#,
)
.unwrap();
let ctx = Database::new();
let mut conn = coordinator.subscribe(&amp;req, &amp;ctx).await.unwrap();
while let Some(result) = conn.next().await {
println!(&quot;{}&quot;, serde_json::to_string(&amp;result).unwrap());
}
}
#
# fn main() { }
</code></pre></pre>
<a class="header" href="#web-integration-and-examples" id="web-integration-and-examples"><h3>Web Integration and Examples</h3></a>
<p>Currently there is an example of subscriptions with [warp][warp], but it still in an alpha state.
GraphQL over [WS][WS] is not fully supported yet and is non-standard.</p>
<ul>
<li><a href="https://github.com/graphql-rust/juniper/tree/master/examples/warp_subscriptions">Warp Subscription Example</a></li>
<li><a href="https://github.com/graphql-rust/juniper/tree/master/examples/basic_subscriptions">Small Example</a></li>
</ul>
<!-- TODO: Fix these links when the documentation for the `juniper_subscriptions` are defined in the docs. --->
[Coordinator]: https://docs.rs/juniper_subscriptions/0.15.0/struct.Coordinator.html
[SubscriptionCoordinator]: https://docs.rs/juniper_subscriptions/0.15.0/trait.SubscriptionCoordinator.html
[Connection]: https://docs.rs/juniper_subscriptions/0.15.0/struct.Connection.html
[SubscriptionConnection]: https://docs.rs/juniper_subscriptions/0.15.0/trait.SubscriptionConnection.html
<!--- --->
[Future]: https://docs.rs/futures/0.3.4/futures/future/trait.Future.html
[warp]: https://github.com/graphql-rust/juniper/tree/master/juniper_warp
[WS]: https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md
[GraphQLError]: https://docs.rs/juniper/0.14.2/juniper/enum.GraphQLError.html
[Schema]: ../schema/schemas_and_mutations.md
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