--header "If-Modified-Since:" doesn't suppress that header

[psimonyi]

I did this

touch hello.txt
curl --silent --verbose --time-cond hello.txt --header "If-Modified-Since:" --remote-name http://localhost:8080/hello.txt

i.e. use --time-cond but suppress the header it generates with --header as described in the man page: "Remove an internal header by giving a replacement without content on the right side of the colon".

(For context, I'm also adding the If-None-Match header, so I do want the 304-means-keep-file behaviour that --time-cond provides, just with a different header.)

I expected the following

The generated If-Modified-Since header would be suppressed, like so:

GET /hello.txt HTTP/1.1
Host: localhost:8080
User-Agent: curl/7.64.0
Accept: */*

curl/libcurl version

$ curl -V
curl 7.64.0 (x86_64-redhat-linux-gnu) libcurl/7.64.0 OpenSSL/1.1.1c zlib/1.2.11 brotli/1.0.7 libidn2/2.2.0 libpsl/0.20.2 (+libidn2/2.0.5) libssh/0.8.7/openssl/zlib nghttp2/1.38.0
Release-Date: 2019-02-06
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp
Features: AsynchDNS IDN IPv6 Largefile GSS-API Kerberos SPNEGO NTLM NTLM_WB SSL libz brotli TLS-SRP HTTP2 UnixSockets HTTPS-proxy PSL Metalink

operating system

Fedora 30

[psimonyi]

I decided to take a stab at this myself :)