Add a basic health check to the router (apollographql#252)

* Add a basic health check to the router

Provide a health check endpoint which behaves in the same way as the
health check on the gateway.

At this point in time it always returns pass because we don't have a
different health status to set.

resolves: apollographql#54

apollo-router/src/snapshots/apollo_router__warp_http_server_factory__tests__it_provides_health_status_body.snap

@@ -0,0 +1,6 @@
+---
+source: apollo-router/src/warp_http_server_factory.rs
+expression: "String::from_utf8_lossy(res.body())"
+
+---
+"{\"status\":\"pass\"}"

apollo-router/src/snapshots/apollo_router__warp_http_server_factory__tests__it_provides_health_status_header.snap

@@ -0,0 +1,6 @@
+---
+source: apollo-router/src/warp_http_server_factory.rs
+expression: "hdrs[\"content-type\"].to_str().unwrap()"
+
+---
+application/json

apollo-router/src/warp_http_server_factory.rs

@@ -6,6 +6,7 @@ use bytes::Bytes;
 use futures::{channel::oneshot, prelude::*};
 use hyper::server::conn::Http;
 use opentelemetry::propagation::Extractor;
+use std::collections::HashMap;
 use std::pin::Pin;
 use std::sync::Arc;
 use tokio::net::TcpListener;
@@ -61,7 +62,8 @@ impl HttpServerFactory for WarpHttpServerFactory {
                 .map(tracing::Dispatch::new)
                 .unwrap_or_default();
 
-            let routes = get_graphql_request_or_redirect(Arc::clone(&router))
+            let routes = get_health_request()
+                .or(get_graphql_request_or_redirect(Arc::clone(&router)))
                 .or(post_graphql_request(router))
                 .with(cors);
 
@@ -229,6 +231,19 @@ fn redirect_to_studio(host: Option<Authority>) -> Box<dyn Reply> {
     }
 }
 
+fn get_health_request() -> impl Filter<Extract = (Box<dyn Reply>,), Error = Rejection> + Clone {
+    warp::get()
+        .and(warp::path(".well-known"))
+        .and(warp::path("apollo"))
+        .and(warp::path("server-health"))
+        .and_then(move || async {
+            let mut result = HashMap::new();
+            result.insert("status", "pass");
+            let reply = Box::new(warp::reply::json(&result)) as Box<dyn Reply>;
+            Ok::<_, Rejection>(reply)
+        })
+}
+
 fn post_graphql_request<Router, PreparedQuery>(
     router: Arc<Router>,
 ) -> impl Filter<Extract = (Box<dyn Reply>,), Error = Rejection> + Clone
@@ -337,6 +352,7 @@ impl<'a> Extractor for HeaderMapCarrier<'a> {
 mod tests {
     use super::*;
     use crate::configuration::Cors;
+    use insta::{assert_json_snapshot, assert_snapshot};
     use mockall::{mock, predicate::*};
     use reqwest::header::{
         ACCEPT, ACCESS_CONTROL_ALLOW_HEADERS, ACCESS_CONTROL_ALLOW_METHODS,
@@ -676,4 +692,36 @@ mod tests {
             .iter()
             .for_each(|accepts| assert!(!prefers_html(accepts.to_string())));
     }
+
+    #[test(tokio::test)]
+    async fn it_provides_health_status_body() -> Result<(), FederatedServerError> {
+        let filter = get_health_request();
+
+        let res = warp::test::request()
+            .path("/.well-known/apollo/server-health")
+            .reply(&filter)
+            .await;
+
+        assert_eq!(res.status(), 200);
+        assert_json_snapshot!(String::from_utf8_lossy(res.body()));
+
+        Ok(())
+    }
+
+    #[test(tokio::test)]
+    async fn it_provides_health_status_header() -> Result<(), FederatedServerError> {
+        let filter = get_health_request();
+
+        let res = warp::test::request()
+            .path("/.well-known/apollo/server-health")
+            .reply(&filter)
+            .await;
+
+        let hdrs = res.headers();
+
+        assert_eq!(res.status(), 200);
+        assert_snapshot!(hdrs["content-type"].to_str().unwrap());
+
+        Ok(())
+    }
 }