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<ol class="chapter"><li class="affix"><a href="../index.html">Introduction</a></li><li class="affix"><a href="../quickstart.html">Quickstart</a></li><li class="affix"><a href="../types/index.html">Type System</a></li><li><a href="../types/objects/defining_objects.html"><strong aria-hidden="true">1.</strong> Defining objects</a></li><li><ol class="section"><li><a href="../types/objects/complex_fields.html"><strong aria-hidden="true">1.1.</strong> Complex fields</a></li><li><a href="../types/objects/using_contexts.html"><strong aria-hidden="true">1.2.</strong> Using contexts</a></li><li><a href="../types/objects/error_handling.html"><strong aria-hidden="true">1.3.</strong> Error handling</a></li></ol></li><li><a href="../types/other-index.html"><strong aria-hidden="true">2.</strong> Other types</a></li><li><ol class="section"><li><a href="../types/enums.html"><strong aria-hidden="true">2.1.</strong> Enums</a></li><li><a href="../types/interfaces.html"><strong aria-hidden="true">2.2.</strong> Interfaces</a></li><li><a href="../types/input_objects.html"><strong aria-hidden="true">2.3.</strong> Input objects</a></li><li><a href="../types/scalars.html"><strong aria-hidden="true">2.4.</strong> Scalars</a></li><li><a href="../types/unions.html"><strong aria-hidden="true">2.5.</strong> Unions</a></li></ol></li><li><a href="../schema/schemas_and_mutations.html"><strong aria-hidden="true">3.</strong> Schemas and mutations</a></li><li><a href="../servers/index.html"><strong aria-hidden="true">4.</strong> Adding A Server</a></li><li><ol class="section"><li><a href="../servers/official.html"><strong aria-hidden="true">4.1.</strong> Official Server Integrations</a></li><li><ol class="section"><li><a href="../servers/warp.html"><strong aria-hidden="true">4.1.1.</strong> Warp</a></li><li><a href="../servers/rocket.html"><strong aria-hidden="true">4.1.2.</strong> Rocket</a></li><li><a href="../servers/iron.html"><strong aria-hidden="true">4.1.3.</strong> Iron</a></li><li><a href="../servers/hyper.html"><strong aria-hidden="true">4.1.4.</strong> Hyper</a></li></ol></li><li><a href="../servers/third-party.html"><strong aria-hidden="true">4.2.</strong> Third Party Integrations</a></li></ol></li><li><a href="../advanced/index.html"><strong aria-hidden="true">5.</strong> Advanced Topics</a></li><li><ol class="section"><li><a href="../advanced/introspection.html"><strong aria-hidden="true">5.1.</strong> Introspection</a></li><li><a href="../advanced/non_struct_objects.html"><strong aria-hidden="true">5.2.</strong> Non-struct objects</a></li><li><a href="../advanced/objects_and_generics.html"><strong aria-hidden="true">5.3.</strong> Objects and generics</a></li><li><a href="../advanced/multiple_ops_per_request.html"><strong aria-hidden="true">5.4.</strong> Multiple operations per request</a></li><li><a href="../advanced/dataloaders.html"><strong aria-hidden="true">5.5.</strong> Dataloaders</a></li><li><a href="../advanced/subscriptions.html" class="active"><strong aria-hidden="true">5.6.</strong> Subscriptions</a></li></ol></li></ol>
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<h1 class="menu-title">Juniper - GraphQL Server for Rust</h1>
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<main>
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<a class="header" href="#subscriptions" id="subscriptions"><h1>Subscriptions</h1></a>
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<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>
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<p>GraphQL subscriptions are a way to push data from the server to clients requesting real-time messages
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from the server. Subscriptions are similar to queries in that they specify a set of fields to be delivered to the client,
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but instead of immediately returning a single answer, a result is sent every time a particular event happens on the
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server.</p>
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<p>In order to execute subscriptions you need a coordinator (that spawns connections)
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and a GraphQL object that can be resolved into a stream--elements of which will then
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be returned to the end user. The <a href="https://github.com/graphql-rust/juniper/tree/master/juniper_subscriptions">juniper_subscriptions</a> crate
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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>
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<pre><code class="language-toml">[dependencies]
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juniper = { git = "https://github.com/graphql-rust/juniper", branch = "master" }
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juniper_subscriptions = { git = "https://github.com/graphql-rust/juniper", branch = "master" }
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</code></pre>
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<a class="header" href="#schema-definition" id="schema-definition"><h3>Schema Definition</h3></a>
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<p>The Subscription is just a GraphQL object, similar to the Query root and Mutations object that you defined for the
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operations in your [Schema][Schema], the difference is that all the operations defined there should be async and the return of it
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should be a <a href="https://docs.rs/futures/0.3.4/futures/stream/trait.Stream.html">Stream</a>.</p>
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<p>This example shows a subscription operation that returns two events, the strings <code>Hello</code> and <code>World!</code>
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sequentially:</p>
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<pre><pre class="playpen"><code class="language-rust"># use juniper::http::GraphQLRequest;
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# use juniper::{DefaultScalarValue, FieldError, SubscriptionCoordinator};
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# use juniper_subscriptions::Coordinator;
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# use futures::{Stream, StreamExt};
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# use std::pin::Pin;
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# #[derive(Clone)]
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# pub struct Database;
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# impl juniper::Context for Database {}
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# impl Database {
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# fn new() -> Self {
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# Self {}
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# }
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# }
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# pub struct Query;
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# #[juniper::graphql_object(Context = Database)]
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# impl Query {
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# fn hello_world() -> &str {
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# "Hello World!"
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# }
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# }
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pub struct Subscription;
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type StringStream = Pin<Box<dyn Stream<Item = Result<String, FieldError>> + Send>>;
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#[juniper::graphql_subscription(Context = Database)]
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impl Subscription {
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async fn hello_world() -> StringStream {
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let stream = tokio::stream::iter(vec![
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Ok(String::from("Hello")),
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Ok(String::from("World!"))
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]);
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Box::pin(stream)
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}
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}
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# fn main () {}
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</code></pre></pre>
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<a class="header" href="#coordinator" id="coordinator"><h3>Coordinator</h3></a>
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<p>Subscriptions require a bit more resources than regular queries, since they can provide a great vector
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for DOS attacks and can bring down a server easily if not handled right. [SubscriptionCoordinator][SubscriptionCoordinator] trait provides the coordination logic.
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It contains the schema and can keep track of opened connections, handle subscription
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start and maintains a global subscription id. Once connection is established, subscription
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coordinator spawns a [SubscriptionConnection][SubscriptionConnection], which handles a
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single connection, provides resolver logic for a client stream and can provide re-connection
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and shutdown logic.</p>
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<p>The [Coordinator][Coordinator] struct is a simple implementation of the trait [SubscriptionCoordinator][SubscriptionCoordinator]
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that is responsible for handling the execution of subscription operation into your schema. The execution of the <code>subscribe</code>
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operation returns a [Future][Future] with a Item value of a Result<[Connection][Connection], [GraphQLError][GraphQLError]>,
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where the connection is the Stream of values returned by the operation and the GraphQLError is the error that occurred in the
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resolution of this connection, which means that the subscription failed.</p>
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<pre><pre class="playpen"><code class="language-rust"># use juniper::http::GraphQLRequest;
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# use juniper::{DefaultScalarValue, EmptyMutation, FieldError, RootNode, SubscriptionCoordinator};
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# use juniper_subscriptions::Coordinator;
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# use futures::{Stream, StreamExt};
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# use std::pin::Pin;
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# use tokio::runtime::Runtime;
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# use tokio::task;
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#
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# #[derive(Clone)]
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# pub struct Database;
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#
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# impl juniper::Context for Database {}
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#
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# impl Database {
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# fn new() -> Self {
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# Self {}
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# }
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# }
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#
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# pub struct Query;
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#
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# #[juniper::graphql_object(Context = Database)]
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# impl Query {
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# fn hello_world() -> &str {
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# "Hello World!"
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# }
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# }
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#
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# pub struct Subscription;
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#
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# type StringStream = Pin<Box<dyn Stream<Item = Result<String, FieldError>> + Send>>;
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#
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# #[juniper::graphql_subscription(Context = Database)]
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# impl Subscription {
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# async fn hello_world() -> StringStream {
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# let stream =
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# tokio::stream::iter(vec![Ok(String::from("Hello")), Ok(String::from("World!"))]);
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# Box::pin(stream)
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# }
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# }
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type Schema = RootNode<'static, Query, EmptyMutation<Database>, Subscription>;
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fn schema() -> Schema {
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Schema::new(Query {}, EmptyMutation::new(), Subscription {})
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}
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async fn run_subscription() {
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let schema = schema();
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let coordinator = Coordinator::new(schema);
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let req: GraphQLRequest<DefaultScalarValue> = serde_json::from_str(
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r#"
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{
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"query": "subscription { helloWorld }"
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}
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"#,
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)
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.unwrap();
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let ctx = Database::new();
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let mut conn = coordinator.subscribe(&req, &ctx).await.unwrap();
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while let Some(result) = conn.next().await {
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println!("{}", serde_json::to_string(&result).unwrap());
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}
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}
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# fn main() { }
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</code></pre></pre>
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<a class="header" href="#web-integration-and-examples" id="web-integration-and-examples"><h3>Web Integration and Examples</h3></a>
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<p>Currently there is an example of subscriptions with [warp][warp], but it still in an alpha state.
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GraphQL over [WS][WS] is not fully supported yet and is non-standard.</p>
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<ul>
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||
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<li><a href="https://github.com/graphql-rust/juniper/tree/master/examples/warp_subscriptions">Warp Subscription Example</a></li>
|
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|
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<li><a href="https://github.com/graphql-rust/juniper/tree/master/examples/basic_subscriptions">Small Example</a></li>
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||
|
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</ul>
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|
|
<!-- TODO: Fix these links when the documentation for the `juniper_subscriptions` are defined in the docs. --->
|
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[Coordinator]: https://docs.rs/juniper_subscriptions/0.15.0/struct.Coordinator.html
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[SubscriptionCoordinator]: https://docs.rs/juniper_subscriptions/0.15.0/trait.SubscriptionCoordinator.html
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[Connection]: https://docs.rs/juniper_subscriptions/0.15.0/struct.Connection.html
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[SubscriptionConnection]: https://docs.rs/juniper_subscriptions/0.15.0/trait.SubscriptionConnection.html
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<!--- --->
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[Future]: https://docs.rs/futures/0.3.4/futures/future/trait.Future.html
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[warp]: https://github.com/graphql-rust/juniper/tree/master/juniper_warp
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||
|
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[WS]: https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md
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||
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[GraphQLError]: https://docs.rs/juniper/0.14.2/juniper/enum.GraphQLError.html
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[Schema]: ../schema/schemas_and_mutations.md
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