fix(http2): add Date header if not present for HTTP2 server responses

src/proto/h1/date.rs

@@ -2,6 +2,7 @@ use std::cell::RefCell;
 use std::fmt::{self, Write};
 use std::str;
 
+use http::header::HeaderValue;
 use time::{self, Duration};
 
 // "Sun, 06 Nov 1994 08:49:37 GMT".len()
@@ -19,6 +20,15 @@ pub fn update() {
     })
 }
 
+pub(crate) fn update_and_header_value() -> HeaderValue {
+    CACHED.with(|cache| {
+        let mut cache = cache.borrow_mut();
+        cache.check();
+        HeaderValue::from_bytes(cache.buffer())
+            .expect("Date format should be valid HeaderValue")
+    })
+}
+
 struct CachedDate {
     bytes: [u8; DATE_VALUE_LENGTH],
     pos: usize,

src/proto/h1/mod.rs

@@ -11,7 +11,7 @@ pub use self::io::Cursor; //TODO: move out of h1::io
 pub use self::io::MINIMUM_MAX_BUFFER_SIZE;
 
 mod conn;
-mod date;
+pub(super) mod date;
 mod decode;
 pub(crate) mod dispatch;
 mod encode;