Error: "Expected header TE: Trailers, but null is received"

Products

• Cloud Secure Web Gateway - Cloud SWG

Issue/Introduction

Users accessing internet via Cloud SWG using IPSEC access method.

Cloud SWG is managed via UPE policy.

When deploying a gRPC based application (uses HTTP/2), users reported the application would fail with the following error message:

"Expected header TE: Trailers, but null is received.  This means some intermediate proxy may not support trailers".

Enabling SSL interception for the destination domain works around the issue.

Environment

gRPC compatible application.

Cloud SWG.

Cause

Cloud SWG Proxy stripping the TE headers.

Using curl to simulate the required headers shows the TE header is stripped.

$ curl -k https://example.com/headers.php -H "TE: trailers" -H "User: Name"
<li>Host: example.com</li>
<li>User-Agent: curl/8.9.0</li>
<li>Accept: */*</li>
<li>User: Name</li>

Resolution

The August 2025 Proxy update allows for the retention of the "TE: Trailers" header per the gRPC specifications, but the following policy changes must be applied to enable it.

<Proxy Preserve_TE_Trailers>
    url.domain=example.com http.request.preserve_te_trailers_header(yes)