====== PHP RFC: Default User-Agent for cURL======
  * Version: 1.0
  * Date: 2021-06-25
  * Author: Michael Maroszek (maroszek@gmx.net)
  * Proposed Version: PHP 8.2
  * Status: Under Discussion
  * First Published at: http://wiki.php.net/rfc/curl_user_agent


===== Introduction =====
PHP has a user_agent php.ini entry for decades, which can be set as a default value. But it is considered for stream based operations like file_get_contents. This RFC proposes a new curl.user_agent php.ini entry which would allow setting a default user_agent for all cURL request. This would benefit in better consistency for setting a default user_agent. This feature will mainly be used in a SAPI context in my use-case, which i will illustrate later.

===== Proposal =====
Add a new php.ini entry for cURL named curl.user_agent, which will set the default User-Agent HTTP Header for all cURL related requests. Of course anyone can override the default value using curl_setopt.

An alternative approach would be to reuse the existing (global) user_agent ini setting also for cURL, but this would touch backwards compatibility, which isn't favorable.

===== Backward Incompatible Changes =====
None

===== Proposed PHP Version(s) =====
8.1

===== RFC Impact =====

==== To SAPIs ====
This feature is especially useful for SAPI usage, as it allows a default header for all HTTP requests (independently if stream based or cURL based) that will allow the remote side to detect the application. At the moment you need to have a workflow or a wrapper that will ensure that the User-Agent is set for all streams and cURL requests. In our use-case the user is also allowed to create PHP scripts by himself. In this situation the user will most probably not set the User-Agent at all, but rely on the defaults.

==== To Existing Extensions ====
No impact. By default the new entry is empty and will not do anything.

==== To Opcache ====
No impact.

==== New Constants ====
No

==== php.ini Defaults ====
curl.user_agent is unset by default for development and production.

===== Open Issues =====
Discussion if the ini visibility should be PHP_INI_ALL or PHP_INI_SYSTEM
https://github.com/php/php-src/pull/6834/files#r628774432

===== Unaffected PHP Functionality =====
This feature does not affect PHP very much and there does not collide with any currently proposed RFCs.

===== Future Scope =====
This RFC does not have any future scope.

===== Proposed Voting Choices =====
At the moment the php.ini option is proposed inside the curl section. If the discussion should not end unanimously we should consider adding a voting option if the curl section or the global section should be targeted for the user_agent entry.


===== Patches and Tests =====
Tests are included in the following PR.

===== Implementation =====
https://github.com/php/php-src/pull/6834

===== References =====
https://www.mail-archive.com/internals@lists.php.net/msg106186.html


===== Rejected Features =====
None yet