fix(http2): allow TE "trailers" request headers

The HTTP/2 spec allows TE headers in requests if the value is
"trailers". Other TE headers are still stripped.

Closes #1642

src/proto/h2/client.rs

@@ -108,7 +108,7 @@ where
  }
  let (head, body) = req.into_parts();
  let mut req = ::http::Request::from_parts(head, ());
- super::strip_connection_headers(req.headers_mut());
+ super::strip_connection_headers(req.headers_mut(), true);
  if let Some(len) = body.content_length() {
  headers::set_content_length_if_missing(req.headers_mut(), len);
  }

src/proto/h2/mod.rs

@@ -15,15 +15,17 @@ mod server;
 pub(crate) use self::client::Client;
 pub(crate) use self::server::Server;
 
-fn strip_connection_headers(headers: &mut HeaderMap) {
+fn strip_connection_headers(headers: &mut HeaderMap, is_request: bool) {
  // List of connection headers from:
  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Connection
+ //
+ // TE headers are allowed in HTTP/2 requests as long as the value is "trailers", so they're
+ // tested separately.
  let connection_headers = [
  HeaderName::from_lowercase(b"keep-alive").unwrap(),
  HeaderName::from_lowercase(b"proxy-connection").unwrap(),
  PROXY_AUTHENTICATE,
  PROXY_AUTHORIZATION,
- TE,
  TRAILER,
  TRANSFER_ENCODING,
  UPGRADE,
@@ -35,6 +37,17 @@ fn strip_connection_headers(headers: &mut HeaderMap) {
  }
  }
 
+ if is_request {
+ if headers.get(TE).map(|te_header| te_header != "trailers").unwrap_or(false) {
+ warn!("TE headers not set to \"trailers\" are illegal in HTTP/2 requests");
+ headers.remove(TE);
+ }
+ } else {
+ if headers.remove(TE).is_some() {
+ warn!("TE headers illegal in HTTP/2 responses");
+ }
+ }
+
  if let Some(header) = headers.remove(CONNECTION) {
  warn!(
  "Connection header illegal in HTTP/2: {}",

src/proto/h2/server.rs

@@ -192,7 +192,7 @@ where
 
  let (head, body) = res.into_parts();
  let mut res = ::http::Response::from_parts(head, ());
- super::strip_connection_headers(res.headers_mut());
+ super::strip_connection_headers(res.headers_mut(), false);
  if let Some(len) = body.content_length() {
  headers::set_content_length_if_missing(res.headers_mut(), len);
  }

tests/integration.rs

@@ -184,6 +184,30 @@ t! {
  ;
 }
 
+t! {
+ get_allow_te_trailers_header,
+ client:
+ request:
+ uri: "/",
+ headers: {
+ // http2 strips connection headers other than TE "trailers"
+ "te" => "trailers",
+ },
+ ;
+ response:
+ status: 200,
+ ;
+ server:
+ request:
+ uri: "/",
+ headers: {
+ "te" => "trailers",
+ },
+ ;
+ response:
+ ;
+}
+
 t! {
  get_body_chunked,
  client: