fix(client): be resilient to invalid response bodies

When an Http11Message knows that the previous response should not
have included a body per RFC7230, and fails to parse the following
response, the bytes are shuffled along, checking for the start of the
next response.

Closes #640

src/client/mod.rs

@@ -446,8 +446,10 @@ fn get_host_and_port(url: &Url) -> ::Result<(String, u16)> {
 
 #[cfg(test)]
 mod tests {
+    use std::io::Read;
     use header::Server;
     use super::{Client, RedirectPolicy};
+    use super::pool::Pool;
     use url::Url;
 
     mock_connector!(MockRedirectPolicy {
@@ -494,4 +496,31 @@ mod tests {
         let res = client.get("http://127.0.0.1").send().unwrap();
         assert_eq!(res.headers.get(), Some(&Server("mock2".to_owned())));
     }
+
+    mock_connector!(Issue640Connector {
+        b"HTTP/1.1 200 OK\r\nContent-Length: 3\r\n\r\n",
+        b"GET",
+        b"HTTP/1.1 200 OK\r\nContent-Length: 4\r\n\r\n",
+        b"HEAD",
+        b"HTTP/1.1 200 OK\r\nContent-Length: 4\r\n\r\n",
+        b"POST"
+    });
+
+    // see issue #640
+    #[test]
+    fn test_head_response_body_keep_alive() {
+        let client = Client::with_connector(Pool::with_connector(Default::default(), Issue640Connector));
+
+        let mut s = String::new();
+        client.get("http://127.0.0.1").send().unwrap().read_to_string(&mut s).unwrap();
+        assert_eq!(s, "GET");
+
+        let mut s = String::new();
+        client.head("http://127.0.0.1").send().unwrap().read_to_string(&mut s).unwrap();
+        assert_eq!(s, "");
+
+        let mut s = String::new();
+        client.post("http://127.0.0.1").send().unwrap().read_to_string(&mut s).unwrap();
+        assert_eq!(s, "POST");
+    }
 }