drupal_page_cache_header() should compare timestamp

I assume that “exact date comparison function” means comparing the date represented by the header, not the verbatim string.

Anyway, not returning a 304 is never forbidden, but it will give us better caching if we return 304 whenever possible.

I added a test that looks for 304 Not Modified, even if If-Modified-Since uses another date format that the one generated in drupal_page_cache_header().

In order to do this, drupal_web_test_case now allows setting request headers and inspecting response headers. I added type-hinting to the methods I touched (as suggested in #318016: Type hint array parameters).

The existing header parser in drupal_http_request() is moved to a seperate function. I changed drupalHead() to return a header => value array instead of a string — this seems more natural, now that we are able to parse the HTTP headers.

It may be a bit confusing that request headers are specified as array("header: value", …), while response headers are returned as array("header" => "value", …). Drupal already uses different conventions in drupal_set_header() and in $result->headers in drupal_http_request(). I don't know whether we should standardize on one format.

gmdate() in drupal_page_cache_header() now uses the named constant, DATE_RFC1123 (available as of PHP 5.1.1). RFC 1123 dates are mandated by section 3.3.1 in the HTTP/1.1 spec.

Chasing HEAD.

- The "header:" stuff is a little weird indeed until I saw the examples. It is weird to refer to it as "header: " -- it is just the regular HTTP-header format.

I have changed the variable names and documentation to refer to name/value rather than header/value. The HTTP spec refers to these as field name and field value. Though the "name: value" format is the regular format used by header(), I think it needs to be explicitly documented, because associative arrays are also sometimes used when working with HTTP headers.

I added some comments to curlExec() and some more tests. I think the test coverage is now more or less complete wrt If-Modified-Since. If-None-Match is a rather complicated subject that should have some more tests of its own. Would you like these in this issue?

This needs a reroll. Much of the header voodoo can probably be avoided by hooking into drupal_web_test_case::curlHeaderCallback() that was just added in #243532: Catch notices, warnings, errors and fatal errors from the tested side.

Reroll.

Now hooks into drupal_web_test_case::curlHeaderCallback() and leaves drupal_http_request() alone, except that it changes the $header/$name wording to $name/$value for consistency ($name/$value is already used in drupal_mail_send()).

The work on adding the ability to add and inspect headers in simpletests is continuing over in #330582: Retrieve HTTP response headers. I'll postpone this issue until that other issue is fixed.

[edit: I originally linked to this issue instead of #330582]

Now that #330582: Retrieve HTTP response headers has landed, the patch has been reduced in size. The patch now fixes drupal_page_cache_header(), adds a test, and adds the ability to specify HTTP request headers in drupal_web_test_case. The latter is relevant in other issues also, e.g. #43462: cache_set and cache_get base_url brokenosity.