test: reduce repetition in metrics tests (#860)

Currently, the metrics tests have a bunch of code that's repeated
between tests in the inbound and outbound directions. This makes
modifying the tests much more painful, since the code needs to be
changed multiple times. Also, the file is hard to navigate.

This commit changes this by factoring out the shared code into functions
which are called by the differing code (e.g. metrics labels) as
parameters. This means that the common behavior is only defined once, so
it should be somewhat easier to edit. This has a significant advantage
over the approach we use elsewhere, where similar tests are generated by
macros: it doesn't mess up the compiler diagnostics for errors in the
tests. We may want to refactor other tests to use a similar style in the
future.

Signed-off-by: Eliza Weisman <[email protected]>

Author: hawkw

linkerd/app/integration/src/client.rs

@@ -83,6 +83,8 @@ pub fn tcp(addr: SocketAddr) -> tcp::TcpClient {
     tcp::client(addr)
 }
 pub struct Client {
+    addr: SocketAddr,
+    run: Run,
     authority: String,
     /// This is a future that completes when the associated connection for
     /// this Client has been dropped.
@@ -93,6 +95,13 @@ pub struct Client {
     tls: Option<TlsConfig>,
 }
 
+pub struct Reconnect {
+    addr: SocketAddr,
+    authority: String,
+    run: Run,
+    tls: Option<TlsConfig>,
+}
+
 impl Client {
     fn new(addr: SocketAddr, authority: String, r: Run, tls: Option<TlsConfig>) -> Client {
         let v = match r {
@@ -101,6 +110,8 @@ impl Client {
         };
         let (tx, task, running) = run(addr, r, tls.clone());
         Client {
+            addr,
+            run: r,
             authority,
             running,
             task,
@@ -172,18 +183,39 @@ impl Client {
         self.running.await
     }
 
-    pub async fn shutdown(self) {
+    /// Shut down the client, returning a type that can be used to initiate a
+    /// new client connection to that target.
+    pub async fn shutdown(self) -> Reconnect {
         let Self {
-            tx, task, running, ..
+            tx,
+            task,
+            running,
+            run,
+            addr,
+            authority,
+            tls,
+            ..
         } = self;
         // signal the client task to shut down now.
         drop(tx);
         task.await.unwrap();
         running.await;
+        Reconnect {
+            authority,
+            run,
+            addr,
+            tls,
+        }
+    }
+}
+
+impl Reconnect {
+    pub fn reconnect(self) -> Client {
+        Client::new(self.addr, self.authority, self.run, self.tls)
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy)]
 enum Run {
     Http1 { absolute_uris: bool },
     Http2,