fix(client): coerce HTTP_2 requests to HTTP_11

Closes #1770

src/client/mod.rs

@@ -236,13 +236,14 @@ where C: Connect + Sync + 'static,
         match req.version() {
             Version::HTTP_11 => (),
             Version::HTTP_10 => if is_http_connect {
-                debug!("CONNECT is not allowed for HTTP/1.0");
+                warn!("CONNECT is not allowed for HTTP/1.0");
                 return ResponseFuture::new(Box::new(future::err(::Error::new_user_unsupported_request_method())));
             },
-            other => if self.config.ver != Ver::Http2 {
-                error!("Request has unsupported version \"{:?}\"", other);
-                return ResponseFuture::new(Box::new(future::err(::Error::new_user_unsupported_version())));
-            }
+            other_h2 @ Version::HTTP_2 => if self.config.ver != Ver::Http2 {
+                return ResponseFuture::error_version(other_h2);
+            },
+            // completely unsupported HTTP version (like HTTP/0.9)!
+            other => return ResponseFuture::error_version(other),
         };
 
         let domain = match extract_domain(req.uri_mut(), is_http_connect) {
@@ -591,6 +592,11 @@ impl ResponseFuture {
             inner: fut,
         }
     }
+
+    fn error_version(ver: Version) -> Self {
+        warn!("Request has unsupported version \"{:?}\"", ver);
+        ResponseFuture::new(Box::new(future::err(::Error::new_user_unsupported_version())))
+    }
 }
 
 impl fmt::Debug for ResponseFuture {

src/proto/h1/role.rs

@@ -271,7 +271,7 @@ impl Http1Transaction for Server {
                     warn!("response with HTTP2 version coerced to HTTP/1.1");
                     extend(dst, b"HTTP/1.1 ");
                 },
-                _ => unreachable!(),
+                other => panic!("unexpected response version: {:?}", other),
             }
 
             extend(dst, msg.head.subject.as_str().as_bytes());
@@ -667,7 +667,11 @@ impl Http1Transaction for Client {
         match msg.head.version {
             Version::HTTP_10 => extend(dst, b"HTTP/1.0"),
             Version::HTTP_11 => extend(dst, b"HTTP/1.1"),
-            _ => unreachable!(),
+            Version::HTTP_2 => {
+                warn!("request with HTTP2 version coerced to HTTP/1.1");
+                extend(dst, b"HTTP/1.1");
+            },
+            other => panic!("unexpected request version: {:?}", other),
         }
         extend(dst, b"\r\n");