For FILE buckets, the behaviour of apr_bucket_setaside() is to take *full* ownership of the underlying apr_file, that is: allocate/move the file/cleanup to the new pool AND set the old file's fd to -1 (see apr_file_setaside, [1]).
This can be problematic in an output filters chain whenever a FILE bucket gets splitted. Suppose that an FTYPE_RESOURCE output filter splits a FILE bucket in two and sends the first one through the chain, and then due to network congestion the core output filter needs to set the FILE bucket aside. It happens that the second FILE bucket becomes a dangling bucket (with fd == -1). The case I'm facing is a bit different but similar. A handler is saving large bodies into a file and inserts an input filter for mod_proxy to use the file bucket as request body (much like mod_request). The file is still needed/used after mod_proxy (in an output filter), so I don't expect the file to be invalidated by mod_proxy's output filtering. It seems to be an issue for mod_http2 too, judging by this workaround [2]. I don't think the caller should have to handle this kind of things, and for the output filters splitting case it's really too much to ask. I can only think of one way to address this: move file buckets from the user brigade to the setaside brigade in ap_filter_setaside_brigade(), assuming correct lifetime for the bucket and apr_file (like we do for buckets with length == -1 already). After a look at our codebase, this would work as is, all of the FILE buckets we pass through output filters are from r->pool, so the lifetime is within the EOR scope (I'm not totally sure about the http2 beam case, Stefan?). So, how about we do that? Would look like the attached patch (which also removes the misleading AP_BUCKET_IS_MORPHING() macro, as discussed previouly, and talks/comments about opaque buckets for ->length == -1, and morphing buckets for both opaque and FILE buckets, as an attempt to clarify things..). Regards, Yann. [1] https://github.com/apache/apr/blob/trunk/file_io/unix/filedup.c#L155 [2] https://github.com/apache/httpd/blob/trunk/modules/http2/h2_bucket_beam.c#L1019
