I did this

After calling CURLOPT_RTSPREQ_SETUP my satip server has no more resources and sends back 503 with a No-More: parameter
(see https://www.satip.info/sites/satip/files/resource/satip_specification_version_1_2_2.pdf, page 53 - it's the only 5xx return code with optional body)

I captured the packet, it looks like this:

But: CURLOPT_WRITEFUNCTION doesn't get called at all! I tried CURLOPT_HEADER in the hope to get headers + data but all i get was this:

RTSP/1.0 503 Service Unavailable
CSeq:1001
Content-Length:18

CURLOPT_DEBUGFUNCTION returns as INFO Excess found: excess = 18 url = / (zero-length body)

I'm confused...

I expected the following

CURLOPT_WRITEFUNCTION without CURLOPT_HEADER enabled should return

No-More: sessions

or, with CURLOPT_HEADER enabled:

RTSP/1.0 503 Service Unavailable
CSeq:1001
Content-Length:18

No-More: sessions

curl/libcurl version

curl 8.4.0 (selfcompiled), but same with jammy version 7.81.0

operating system

Linux server 5.15.0-odroid-arm64 #​1 SMP PREEMPT Ubuntu 5.15.118-202306231801~jammy (2023-06-23) aarch64 aarch64 aarch64 GNU/Linux