Re: Outputting URL components

On 30-Mar-23 03:28, Daniel Stenberg via curl-users wrote:
> On Wed, 29 Mar 2023, Rich Gray via curl-users wrote:
>
>> If it's not already possible, it seems like it would be useful to 
>> give curl a URL solely for the purpose of write outs (no transfer 
>> operation).  Curl would be able to function as a URL parser for scripts.
>>
>>  curl --noop http://www.example.com:123/test -w'%{url.port}\n'
>>
>> would echo out 123 on a line by itself.
>>
>> --noop could also be useful for testing a curl command line for 
>> validity without doing a transfer.  (Could this speed up some tests?)
>
> Yeah, that exact thought crossed my mind as well. I'm hesitating 
> though, because I'm a little afraid of where such an option might take 
> us.
>
>
Hesitation is appropriate.

This seems rather limited, since you can't get much without doing some 
(usually network) IO.  Resolving a name requires DNS, getting an 
effective URL requires following redirects, resolving service names to 
ports requires access to /etc/services, ... and obviously you can't get 
transfer statistics or most of the other -w parameters.

If you're not going to do a transfer, what's the point?  Most use cases 
evaporate on inspection.

This is rather like the file tests (is a file readable? Writable?)  It 
turns out that while they superficially work, it's pretty common to pass 
the test but have an actual open fail.  And vice-versa.  (E.g. where the 
test uses stat's mode, but there's an ACL.  Or an anti-virus block.  
Or...)  The only reliable way to know if an operation will work is to 
try it.

It's not clear that curl ought to be a text processor.

But if you go there anyhow, use a useful name, e.g. --parse-only.  The 
request isn't a NOP.  And there are protocols that actually have a NOP 
operation defined..


Timothe Litt
ACM Distinguished Engineer
--------------------------
This communication may not represent the ACM or my employer's views,
if any, on the matters discussed.

-- 
Unsubscribe: https://lists.haxx.se/mailman/listinfo/curl-users
Etiquette:   https://curl.se/mail/etiquette.html