feat!(client): expose whether a connection is reused from the pool

This introduces a new type `ErrorConnectInfo` that contains information
about connection pool as well as transport-related data. This new type
can now be obtained from the `Error::connect_info()` method, which means
that this is a breaking change as the return type from the method has
changed. That said, all information that was available on the previous
return type is available on the new type through various getter methods.

src/client/legacy/client.rs

@@ -57,7 +57,7 @@ pub struct Error {
     kind: ErrorKind,
     source: Option<Box<dyn StdError + Send + Sync>>,
     #[cfg(any(feature = "http1", feature = "http2"))]
-    connect_info: Option<Connected>,
+    connect_info: Option<ErroredConnectInfo>,
 }
 
 #[derive(Debug)]
@@ -71,6 +71,34 @@ enum ErrorKind {
     SendRequest,
 }
 
+/// Extra information about a failed connection.
+pub struct ErroredConnectInfo {
+    conn_info: Connected,
+    is_reused: bool,
+}
+
+impl ErroredConnectInfo {
+    /// Determines if the connected transport is to an HTTP proxy.
+    pub fn is_proxied(&self) -> bool {
+        self.conn_info.is_proxied()
+    }
+
+    /// Copies the extra connection information into an `Extensions` map.
+    pub fn get_extras(&self, extensions: &mut http::Extensions) {
+        self.conn_info.get_extras(extensions);
+    }
+
+    /// Determines if the connected transport negotiated HTTP/2 as its next protocol.
+    pub fn is_negotiated_h2(&self) -> bool {
+        self.conn_info.is_negotiated_h2()
+    }
+
+    /// Determines if the connection is a reused one from the connection pool.
+    pub fn is_reused(&self) -> bool {
+        self.is_reused
+    }
+}
+
 macro_rules! e {
     ($kind:ident) => {
         Error {
@@ -282,7 +310,7 @@ where
             if req.version() == Version::HTTP_2 {
                 warn!("Connection is HTTP/1, but request requires HTTP/2");
                 return Err(TrySendError::Nope(
-                    e!(UserUnsupportedVersion).with_connect_info(pooled.conn_info.clone()),
+                    e!(UserUnsupportedVersion).with_connect_info(&pooled),
                 ));
             }
 
@@ -317,14 +345,12 @@ where
             Err(mut err) => {
                 return if let Some(req) = err.take_message() {
                     Err(TrySendError::Retryable {
-                        error: e!(Canceled, err.into_error())
-                            .with_connect_info(pooled.conn_info.clone()),
+                        error: e!(Canceled, err.into_error()).with_connect_info(&pooled),
                         req,
                     })
                 } else {
                     Err(TrySendError::Nope(
-                        e!(SendRequest, err.into_error())
-                            .with_connect_info(pooled.conn_info.clone()),
+                        e!(SendRequest, err.into_error()).with_connect_info(&pooled),
                     ))
                 }
             }
@@ -464,7 +490,7 @@ where
                 Ok(checked_out)
             }
             // Connect won, checkout can just be dropped.
-            Either::Right((Ok(connected), _checkout)) => Ok(connected),
+            Either::Right((Ok(connected), _checkout)) => Ok(connected)
             // Either checkout or connect could get canceled:
             //
             // 1. Connect is canceled if this is HTTP/2 and there is
@@ -1619,14 +1645,20 @@ impl Error {
 
     /// Returns the info of the client connection on which this error occurred.
     #[cfg(any(feature = "http1", feature = "http2"))]
-    pub fn connect_info(&self) -> Option<&Connected> {
+    pub fn connect_info(&self) -> Option<&ErroredConnectInfo> {
         self.connect_info.as_ref()
     }
 
     #[cfg(any(feature = "http1", feature = "http2"))]
-    fn with_connect_info(self, connect_info: Connected) -> Self {
+    fn with_connect_info<B>(self, pooled: &pool::Pooled<PoolClient<B>, PoolKey>) -> Self
+    where
+        B: Send + 'static,
+    {
         Self {
-            connect_info: Some(connect_info),
+            connect_info: Some(ErroredConnectInfo {
+                conn_info: pooled.conn_info.clone(),
+                is_reused: pooled.is_reused(),
+            }),
             ..self
         }
     }

src/client/legacy/connect/mod.rs

@@ -99,6 +99,7 @@ pub trait Connection {
 pub struct Connected {
     pub(super) alpn: Alpn,
     pub(super) is_proxied: bool,
+    pub(super) is_reused: bool,
     pub(super) extra: Option<Extra>,
     pub(super) poisoned: PoisonPill,
 }
@@ -149,6 +150,7 @@ impl Connected {
         Connected {
             alpn: Alpn::None,
             is_proxied: false,
+            is_reused: false,
             extra: None,
             poisoned: PoisonPill::healthy(),
         }
@@ -226,6 +228,7 @@ impl Connected {
         Connected {
             alpn: self.alpn,
             is_proxied: self.is_proxied,
+            is_reused: self.is_reused,
             extra: self.extra.clone(),
             poisoned: self.poisoned.clone(),
         }