curl --resolve appears to do nothing

Question

The --help output for curl lists a --resolve option, which states

--resolve <host:port:address> Force resolve of HOST:PORT to ADDRESS

I'm not having any luck getting it to work though. The basic command I'm trying to run is

curl --resolve foo.example.com:443:localhost https://foo.example.com:443/

and I keep getting the response Couldn't resolve host 'foo.example.com'. I want do do this because I'm testing a certificate for foo.example.com, but I'm not testing it on the actual server. Instead, I'm testing it on a dummy machine. I know that I can edit /etc/hosts so that foo.example.com resolves to localhost, but this curl approach seems like it would be the "correct" way to go, if I could make it work.

Does anybody see what I'm doing wrong here?

Answer 1

It appears that the address needs to be a numeric IP address, not a hostname.

Try this:

curl --resolve foo.example.com:443:127.0.0.1 https://foo.example.com:443/

Answer 2

Some additional help in troubleshooting:

Ensure you're listing the right port for the protocol: http=80; https=443 & etc.

Also curl -v will give the HEADER information for the response server which can be helpful.

$ curl -v --resolve foo.example.com:443:127.0.0.1 https://foo.example.com:443/
## The client request headers prepended by >
> OPTIONS /v1/..
> HOSTS foo.example.com
## The server response prepended by <
< HTTP/1.1 501 Not Implemented
## The html returned
<H1>Unsupported Request</H1>

Basically in this case the OPTIONS HTTP method was not implemented at the edge server for the CDN.

Answer 3

I have the same problem. Very strange, but it seems like it depends on the version. I checked one server with curl --manual | grep resolve for version 7.19.7 and the --resolve parameter is missing. In version 7.29.0, I have this parameter, and resolving is working fine.