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HTTP Trailers: Headers After the Body

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Trailers: when you don't know the metadata until after the body

HTTP headers come before the body — which means you must know all metadata upfront. But some values can only be computed after the body is generated: a checksum requires hashing the full content, server timing includes body generation time, a gRPC status code depends on whether processing succeeded.

HTTP trailers solve this: they're headers sent after the body completes. The response starts flowing immediately (low latency), and metadata computed during streaming arrives at the end.

Packets in motion — click to inspect:

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