Bug 507523

SUMMARY
Using KIO::storedGet sends an http request which includes the header, "Content-Length: 0". Current RFC says that header shouldn't be sent.

STEPS TO REPRODUCE
Use whatever method you choose to observe the http request headers. One possibility is:
$ kioclient cat https://httpbin.org/headers

OBSERVED RESULT
{
  "headers": {
    "Accept-Encoding": "zstd, br, gzip, deflate", 
    "Accept-Language": "en-US,*", 
    "Content-Length": "0", 
    "Host": "httpbin.org", 
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64) KIO/6.16 kioworker/6.16.0"
  }
}
EXPECTED RESULT
Based on the RFC, the Content-Length header shouldn't be sent. For comparison, curl sends:
$ curl https://httpbin.org/headers
{
  "headers": {
    "Accept": "*/*", 
    "Host": "httpbin.org", 
    "User-Agent": "curl/8.14.1"
  }
}

SOFTWARE/OS VERSIONS
KDE Frameworks Version: 6.16.0
Qt Version: 6.9.1

ADDITIONAL INFORMATION
RFC9110, https://www.rfc-editor.org/rfc/rfc9110.html#name-content-length, says:
> A user agent SHOULD NOT send a Content-Length header field when the request message does not contain content
> and the method semantics do not anticipate such data.
An older one, RFC2616, https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.13, is worded differently.
> Any Content-Length greater than or equal to zero is a valid value.
There doesn't seem to be anything that distinguishes method semantics in the older RFC.

Various other reports suggest this could be an issue with some CDNs.
https://github.com/http-kit/http-kit/issues/583
https://github.com/httprb/http/issues/487