Added concurrent db connections

Author: Kixiron

src/web/metrics.rs

@@ -71,6 +71,12 @@ lazy_static::lazy_static! {
         "Number of attempted and failed connections to the database"
     )
     .unwrap();
+
+    pub static ref CONCURRENT_DB_CONNECTIONS: IntGauge = register_int_gauge!(
+        "docsrs_db_connections",
+        "The number of currently used database connections"
+    )
+    .unwrap();
 }
 
 pub fn metrics_handler(req: &mut Request) -> IronResult<Response> {
@@ -87,6 +93,9 @@ pub fn metrics_handler(req: &mut Request) -> IronResult<Response> {
             .get(0),
     );
 
+    let pool = extension!(req, Pool);
+    CONCURRENT_DB_CONNECTIONS.set(pool.connections() as i64);
+
     let mut buffer = Vec::new();
     let families = prometheus::gather();
     ctry!(TextEncoder::new().encode(&families, &mut buffer));

src/web/pool.rs

@@ -42,6 +42,15 @@ impl Pool {
             )),
         }
     }
+
+    pub(crate) fn connections(&self) -> u32 {
+        match self {
+            Self::R2D2(conn) => conn.state().connections,
+
+            #[cfg(test)]
+            Self::Simple(..) => 0,
+        }
+    }
 }
 
 impl typemap::Key for Pool {