add php.ini entry to set default user_agent for curl

Hi Michael,
Thanks for opening this conversation and the PR.

Most HTTP client libraries that need to set a custom user agent do so
with curl_setopt because it needs to contain a library version or
some sort of dynamic values. They will likely not benefit from this
change. On the other hand, libraries that do not bother to set a UA
string probably wanted it that way too, because Curl's default UA
string is useful as it contains the Curl version.

That said, if it comes to it that we add this feature, I'd be in favor
of a new curl.user_agent as opposed to inheriting the global
user_agent because that would be BC break. We already have
curl.cainfo INI setting, and adding a new curl.user_agent wouldn't
be a drastic change to configuration either.

-- Ayesh.

Dear Internals,
I'd like to suggest a new enhancement for 8.1 as outlined in the title.

The initial pull request is here:
https://github.com/php/php-src/pull/6834/files

--- Details:
Since quite a while PHP offers a dedicated user_agent php.ini entry, but it
affects only all internal implementations like file_get_contents. cURL has
no default and you need to modify CURLOPT_USERAGENT in the code and for the
SoapClient there is a parameter 'user-agent' in the constructor which can
be set.

Therefore I'd like to introduce an equal entry for curl.user_agent which
would set a default user_agent when making curl requests. Of course you can
override it with CURLOPT_USERAGENT if required. (I can implement the same
for SoapClient, if requested)

--- Alternative:
I could also use the default user_agent entry, but I wasn't sure what the
best practise is and went for the more "local" approach for the initial
implementation.

--- Bigger picture:
When the preferred solution is to use the default user_agent, we could also
try to determine more places where i could send the default user_agent to
give this php.ini entry a more consistent feeling.

Thanks for your consideration,
Michael

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Dear Internals,
I'd like to suggest a new enhancement for 8.1 as outlined in the title.

The initial pull request is here:
https://github.com/php/php-src/pull/6834/files

--- Details:
Since quite a while PHP offers a dedicated user_agent php.ini entry, but it
affects only all internal implementations like file_get_contents. cURL has
no default and you need to modify CURLOPT_USERAGENT in the code and for the
SoapClient there is a parameter 'user-agent' in the constructor which can
be set.

Therefore I'd like to introduce an equal entry for curl.user_agent which
would set a default user_agent when making curl requests. Of course you can
override it with CURLOPT_USERAGENT if required. (I can implement the same
for SoapClient, if requested)

--- Alternative:
I could also use the default user_agent entry, but I wasn't sure what the
best practise is and went for the more "local" approach for the initial
implementation.

--- Bigger picture:
When the preferred solution is to use the default user_agent, we could also
try to determine more places where i could send the default user_agent to
give this php.ini entry a more consistent feeling.

Thanks for your consideration,
Michael

Could you please describe what your use case for this change is?

I'm generally not a fan of adding more ini settings (aka global state)
without a strong motivation, and it's not immediately obvious what that
motivation is in this case. This seems useful if you have both a) one user
agent you want to use for everything and b) a lot of heterogeneous code
that doesn't use any common abstraction, which seems like a rather odd
situation to be in.

Regards,
Nikita