Trailer

The HTTP Trailer response header is used to grant permission to the client to include additional metadata at the end of a chunked message.

Usage

The HTTP Trailer header is used to allow clients to append certain HTTP headers to the end of a chunked message. It has a single directive, which is the list of HTTP header names that will be included.

Not Allowed

Several HTTP header fields cannot be used as part of the HTTP Trailer header, including:

• Routing HTTP headers, such as HTTP Host;
• Message framing headers, such as HTTP Transfer-Encoding and HTTP Content-Length;
• Authentication HTTP headers, such as HTTP Authorization and HTTP Set-Cookie;
• HTTP request modifiers such as Cache-Control and Max-Forwards;
• HTTP Content-Encoding, Content-Type, Content-Range, and Trailer are explicitly banned.

Takeaway

The HTTP Trailer header is used to inform the client that it is allowed to append HTTP headers at the end of the message to include metadata such as a digital signature.

See also

• HTTP headers