appservice-api: Add support for the appservice ping mechanism

According to MSC2659

crates/ruma-appservice-api/CHANGELOG.md

@@ -1,5 +1,9 @@
 # [unreleased]
 
+Improvements:
+
+- Add support for the appservice ping mechanism (MSC 2659 / Matrix 1.7)
+
 # 0.8.1
 
 Improvements:

crates/ruma-appservice-api/src/lib.rs

@@ -10,6 +10,7 @@
 use serde::{Deserialize, Serialize};
 
 pub mod event;
+pub mod ping;
 pub mod query;
 pub mod thirdparty;
 

crates/ruma-appservice-api/src/ping.rs

@@ -0,0 +1,3 @@
+//! Endpoint for pinging the application service.
+
+pub mod send_ping;

crates/ruma-appservice-api/src/ping/send_ping.rs

@@ -0,0 +1,53 @@
+//! `PUT /_matrix/app/*/ping`
+//!
+//! Endpoint to ping the application service.
+
+pub mod v1 {
+    //! `/v1/` ([spec])
+    //!
+    //! [spec]: https://spec.matrix.org/latest/application-service-api/#post_matrixappv1ping
+
+    use ruma_common::{
+        api::{request, response, Metadata},
+        metadata, OwnedTransactionId,
+    };
+
+    const METADATA: Metadata = metadata! {
+        method: POST,
+        rate_limited: false,
+        authentication: AccessToken,
+        history: {
+            unstable => "/_matrix/app/unstable/fi.mau.msc2659/ping",
+            1.7 => "/_matrix/app/v1/ping",
+        }
+    };
+
+    /// Request type for the `send_ping` endpoint.
+    #[request]
+    #[derive(Default)]
+    pub struct Request {
+        /// A transaction ID for the ping, copied directly from the `POST
+        /// /_matrix/client/v1/appservice/{appserviceId}/ping` call.
+        #[serde(skip_serializing_if = "Option::is_none")]
+        pub transaction_id: Option<OwnedTransactionId>,
+    }
+
+    /// Response type for the `send_ping` endpoint.
+    #[response]
+    #[derive(Default)]
+    pub struct Response {}
+
+    impl Request {
+        /// Creates a new empty `Request`.
+        pub fn new() -> Self {
+            Self::default()
+        }
+    }
+
+    impl Response {
+        /// Creates a new empty `Response`.
+        pub fn new() -> Self {
+            Self::default()
+        }
+    }
+}