Fix filter-related bugHEADmaster

Apparently, an Apache filter can be invoked more than once for a
single request, depending on the size of the contents [1].

Luckily, though, a filter can save state in the ctx field [1,2].

The solution isn't perfect, as it can't handle arbitrary long heads,
but they're very unlikely.

[1] https://httpd.apache.org/docs/2.4/developer/output-filters.html#invocation
[2] https://perl.apache.org/docs/2.0/user/handlers/filters.html#Introducing_Filters

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/Apache/Inject.pm b/lib/Apache/Inject.pm
index 1d6f49b..68e003e 100644
--- a/lib/Apache/Inject.pm
+++ b/lib/Apache/Inject.pm
@@ -182,6 +182,10 @@ intelligently and forwards their combined contents.
 
 =head1 CAVEATS
 
+=over
+
+=item *
+
 Apache::Inject::Filter uses a regular expression to determine the
 proper location of the injected header.  It supports all valid HTML.
 However, it does not parse embedded CSS and JavaScript, which means
@@ -204,10 +208,22 @@ This specific type of document, however, is I<incredibly> unlikely.
 In this case, an ad-hoc solution is simpler, more efficient and
 more maintainable than a general one.
 
+=item *
+
+Because of how Apache filters work, Inject may fail to find the end
+of the E<lt>headE<gt> if the E<lt>headE<gt> is very long (in my
+experience over 7000 characters).  If this happens, it will decline
+the request, and the contents will be served as though Inject had
+not been enabled.
+
+=item *
+
 On FreeBSD, you may need to enable the accf_http kernel module in
 order for the tests to work.  Note that Apache::Inject works fine
 without the module; it is only the tests that require it.
 
+=back
+
 =head1 DIAGNOSTICS
 
 Apache::Inject and Apache::Inject::Filter log all errors and