Read absence accurately
A response without Content-Length has not thereby declared a zero-byte body. HTTP message framing depends on the protocol and response context. RFC 9112 describes chunked transfer in HTTP/1.1, which can carry content whose final size was not known when headers were sent.
Keep the method and response status with the observation. A header-only response and a media GET answer different questions. Do not compare their apparent body sizes without accounting for that difference.
Observe completion separately
Record actual bytes received and the transport's completion or error result. Unknown size in advance and an interrupted transfer are distinct conditions. A progress indicator without a percentage may reflect missing advance size information rather than failed media delivery.
For an invented generated response, the producer starts transmitting before it knows the final encoded size. That can be a reasonable reason not to supply an advance length. It does not excuse malformed framing or establish that the resulting media can be decoded.
Choose the appropriate acceptance check
For a published stable file, compare the received artifact with the intended release identity and review partial retrieval if the application needs it. For a generated stream, define how normal completion and cancellation are recorded. Use the relevant protocol's framing rules rather than applying HTTP/1.1 chunk syntax to every HTTP version.
If a monitoring rule currently marks every missing size header as an outage, refine it to measure the actual requirement. Keep a distinct alert for incomplete or incorrect content. This is a monitoring design example, not an observed production response.
Questions answered
Does absent Content-Length mean Content-Length zero?
No. They are different observations.
Can a response with Content-Length still be incomplete?
Yes. The declaration is not proof that all intended bytes arrived successfully.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.