Possible memory corruption fix

[benubois]

Hi,

Since upgrading to http ~> 6, I've seen a new sporadic exception.

The backtrace ends at an http file, but I think it's at a point where it reading data from llhttp:

TypeError: wrong argument type Hash (expected Class) parser << data ^^^^

[GEM_ROOT]/gems/http-6.0.4/lib/http/response/parser.rb#57 in HTTP::Response::Parser#add
[GEM_ROOT]/gems/http-6.0.4/lib/http/connection/internals.rb#134 in HTTP::Connection::Internals#read_more

I have zero understanding of the C extension, so sorry if this is slop, but Claude came up with the below solution and explanation.

Here's the value I was able to add on top of the LLM:

1. Tests pass in llhttp
2. Tests pass with this fix in http
3. I'm running the patched llhttp in production in a Sidekiq cluster which downloads around 600 urls per second and haven't seen this exception come back

Thank you!

Warning

LLM output below

LLHttp::Parser caches the delegate in its C struct: parserData->delegate = rb_iv_get(self, "@delegate"); but the data type registered no GC mark callback ({0, rb_llhttp_free, rb_llhttp_memsize}). The @delegate ivar keeps the object alive, yet under GC compaction the delegate is relocated: the ivar reference is updated, while the cached copy in the struct is not. The next callback then dispatches against a stale/reused slot, producing a hard interpreter crash or a type-confusion error such as TypeError: wrong argument type Hash (expected Class) — even for perfectly valid input.

This is timing-dependent (compaction must run between parser creation and use), which is why it surfaces intermittently in high-throughput, GC-heavy workloads rather than in simple scripts.

Fix

Add a mark function that marks the cached delegate and register it for both the TypedData and legacy Data_Make_Struct paths. rb_gc_mark also pins the delegate, which is what's needed since a bare VALUE cached outside the Ruby heap can't tolerate being moved. Works across the whole supported Ruby range (>= 2.6.7) with no version guards.

Test

spec/integration/compaction_spec.rb builds a parser whose delegate is reachable only through the ivar, forces relocation with GC.verify_compaction_references(expand_heap: true, toward: :empty), then parses. It runs in a child process because the pre-fix failure can be an uncatchable crash. The test fails (child crashes) without the fix and passes with it.