HeaderName::from_static requires all-lowercase HTTP2 compatible hea…

…der names

and was passed header names with uppercase characters instead, which
made it panic.

src/handshake/client.rs

@@ -105,7 +105,10 @@ fn generate_request(mut request: Request) -> Result<(Vec<u8>, String)> {
     .unwrap();
 
     // Headers that must be present in a correct request.
+    const KEY_HEADERNAME_LOWERCASE: &str = "sec-websocket-key";
     const KEY_HEADERNAME: &str = "Sec-WebSocket-Key";
+    const WEBSOCKET_HEADERS_LOWERCASE: [&str; 5] =
+        ["host", "connection", "upgrade", "sec-websocket-version", KEY_HEADERNAME_LOWERCASE];
     const WEBSOCKET_HEADERS: [&str; 5] =
         ["Host", "Connection", "Upgrade", "Sec-WebSocket-Version", KEY_HEADERNAME];
 
@@ -114,7 +117,9 @@ fn generate_request(mut request: Request) -> Result<(Vec<u8>, String)> {
         .headers()
         .get(KEY_HEADERNAME)
         .ok_or_else(|| {
-            Error::Protocol(ProtocolError::InvalidHeader(HeaderName::from_static(KEY_HEADERNAME)))
+            Error::Protocol(ProtocolError::InvalidHeader(HeaderName::from_static(
+                KEY_HEADERNAME_LOWERCASE,
+            )))
         })?
         .to_str()?
         .to_owned();
@@ -127,9 +132,11 @@ fn generate_request(mut request: Request) -> Result<(Vec<u8>, String)> {
     //
     // See similar problem in `hyper`: https://github.com/hyperium/hyper/issues/1492
     let headers = request.headers_mut();
-    for header in WEBSOCKET_HEADERS {
+    for (header_lowercase, &header) in
+        Iterator::zip(WEBSOCKET_HEADERS_LOWERCASE.iter(), WEBSOCKET_HEADERS.iter())
+    {
         let value = headers.remove(header).ok_or_else(|| {
-            Error::Protocol(ProtocolError::InvalidHeader(HeaderName::from_static(header)))
+            Error::Protocol(ProtocolError::InvalidHeader(HeaderName::from_static(header_lowercase)))
         })?;
         write!(req, "{header}: {value}\r\n", value = value.to_str()?).unwrap();
     }