check for overly large header field in send_headers

src/codec/error.rs

@@ -35,6 +35,9 @@ pub enum UserError {
     /// The payload size is too big
     PayloadTooBig,
 
+    /// A header size is too big
+    HeaderTooBig,
+
     /// The application attempted to initiate too many streams to remote.
     Rejected,
 
@@ -131,6 +134,7 @@ impl error::Error for UserError {
             InactiveStreamId => "inactive stream",
             UnexpectedFrameType => "unexpected frame type",
             PayloadTooBig => "payload too big",
+            HeaderTooBig => "header too big",
             Rejected => "rejected",
             ReleaseCapacityTooBig => "release capacity too big",
             OverflowedStreamId => "stream ID overflowed",