feat(server): Handle 100-continue

cc #838

tests/server.rs

@@ -523,3 +523,33 @@ fn test_server_disable_keep_alive() {
         }
     }
 }
+
+#[test]
+fn expect_continue() {
+    let server = serve();
+    let mut req = connect(server.addr());
+    server.reply().status(hyper::Ok);
+
+    req.write_all(b"\
+        POST /foo HTTP/1.1\r\n\
+        Host: example.domain\r\n\
+        Expect: 100-continue\r\n\
+        Content-Length: 5\r\n\
+        Connection: Close\r\n\
+        \r\n\
+    ").expect("write 1");
+
+    let msg = b"HTTP/1.1 100 Continue\r\n\r\n";
+    let mut buf = vec![0; msg.len()];
+    req.read_exact(&mut buf).expect("read 1");
+    assert_eq!(buf, msg);
+
+    let msg = b"hello";
+    req.write_all(msg).expect("write 2");
+
+    let mut body = String::new();
+    req.read_to_string(&mut body).expect("read 2");
+
+    let body = server.body();
+    assert_eq!(body, msg);
+}