Export ext/curl's primary header

[morrisonlevi]

This makes it more accessible to extensions.

Disclaimer: I have no idea if this is helpful or correct on Windows builds.

[nikic]

Which part of the header do you need? We may need to do a public/private split, in particular to avoid exporting structures for ABI reasons.

[cmb69]

Windows part looks good to me (headers are then available in devel-packs).

[morrisonlevi]

I'm not 100% sure at this point. For things like OpenTelemetry (and of course ddtrace) I want to add the W3C trace context automatically to curl requests. We started work in the past for ddtrace, but hit some blockers that I don't remember. One pain point was that these headers weren't exported at all, which is why I am exporting it now.

[morrisonlevi]

If this makes you nervous, perhaps we could write a new function which handles the use case of appending some headers and just export that? I'm worried that may not be sufficient for everyone, but something is better than nothing, which is what we had before.

[nikic]

@morrisonlevi Would it be sufficient for you to get access to the CURL handle?

[morrisonlevi]

I don't think so. PHP stores the headers in a PHP array (I think, if I am reading this correctly) and then at exec time it converts it to a curl_slist and sends it. Regardless of how it works, I need access to the curl_slists so I can add those headers, and I don't think curl provides this in the API, but I could be wrong on that.

I think there are other things that would be nice, such as having access to HTTP method and URL. I think these can be accessed from the CURL handle.

[cmb69]

[…] and then at exec time it converts it […]

That happens either during the respective curl_setopt() call, or when curl_copy_handle() is called, so on entry of curl_exec() they would be available via the CURL handle.

[morrisonlevi]

Immediate thoughts on that:

1. How? I don't see how to get the header slist out of a CURL.
2. Even if I can, curl doesn't copy the slist, and the caller is responsible for freeing it. In this case ext/curl holds the list; if I don't update that list then I will have free issues.

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I think minimizing the API exposed to extensions and such is a good idea, but I don't think the current code is set up very well for that. So far, my best idea would be to expose only the CURL bit and the curl_slist for the headers through some new functions we add.

[cmb69]

Ah, now I understand (I thought it is about the postfields). If you need to append to CURLOPT_HTTPHEADER, there should indeed be a dedicated function, because accessing _php_curl_free->slist is not really helpful for copied (cloned) CURL handles, and accessing a free list looks hackish anyway.

[kocsismate]

I don't know if it's useful information for you, but I wanted to share just in case, that I started working on migrating the curl handle to an object.

[morrisonlevi]

@kocsismate Glad to hear it! How close is the work to being ready for review?

[kocsismate]

@morrisonlevi I haven't reached far yet because I gave priority to other stuff, but I'll come back to this task this week.