Re: Improve Error Handling message to become user friendly

On Fri, 15 Aug 2025, cyber security via curl-users wrote:

> └─$ curl https://127.0.0.0.1.1
> curl: (6) Failed to parse the ip 127.0.0.0.1.1 excepted. must have 4 octets
> (e.g, 127.0.0.1).

This is harder than it may seem.

First: an IPv4 address in a URL can be specified using one, two, three or four 
numbers (not octets) so the suggested error message is not exactly right.

Then: when the string provided is not a valid IPv4 address (as proposed 
above), it is by defintion "a hostname" and that's why it doesn't get reported 
as a bad IP address. Let me show you:

$ grep 127.0.0.0.1.1 /etc/hosts
127.0.0.1 127.0.0.0.1.1

$ curl http://127.0.0.0.1.1 -o /dev/null
$ echo $?
$ 0

> └─$ curl -6 http://127.0.0.1
> curl: (7) This not valid IPv6. It seems ipv4 tries to remove -6.

Fair. But remember that you can specify any amount of URLs and they can use 
mixed versions:

   curl -6 http://127.0.0.1 http://[::1] https://example.com/

... so it can't just error on it. The messaging can however probably be 
improved of course.

> improve it to ┌──(relun㉿relunsec)-[~/Test]
> └─$ curl https://httpbin.org --tls-max 1
> curl: option --tls-max: Invalid TLS Version choose from 1.0,1.1,1.2,1.3
> curl: try 'curl --help' or 'curl --manual' for more information

Yep, that would be neat.

> and also you can improve other error messages you can adjust if you would.

There is certainly always room for improvements. Feel free to dig in and help 
us!

-- 

  / daniel.haxx.se || https://rock-solid.curl.dev

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