Add syslog stream and datagram listeners (#9)

* Add syslog stream and datagram listeners

Adds two syslog transports to the server alongside HTTP, both delivering
complete messages to a Ruby handler on the existing worker threads:

- a stream listener (Unix socket or TCP) framed with RFC 6587 octet
  counting and a newline fallback, with optional PROXY v2 parsing to
  recover the peer address, and
- a UDP listener with SO_REUSEPORT where one datagram is one message,
  with receive-buffer truncation detected and dropped.

Undelivered messages are bounded per connection and overall; a refused
message stalls stream reads and is retried, while a refused datagram is
dropped and counted. Listener readiness and transport counters are
exposed as syslog_listening? and syslog_stats.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Share worker threads fairly between requests and syslog

The worker fast path always drained requests first, so sustained request
load could starve syslog delivery indefinitely and stall every sender
behind the per-connection backpressure. The two channels now alternate
which is asked first, and the blocking select already picks uniformly
between them. Workers with no syslog listener configured keep the
original single-channel path.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Apply syslog listener review fixes

Licence: the framing module, including its test data, is a port of
Vector 0.48.0's octet counting decoder, so the file, the README and the
licence file record that it is MPL-2.0 rather than MIT.

Framing: a read boundary landing on a digit inside an oversize body no
longer restarts octet counting and hands that body over as messages.

Delivery: the per-connection queue is bounded separately from the
listener-wide one, so a stalled sender cannot take every credit; the
handler is given a stable message id and attempt number, its exceptions
are counted apart from refusals, and retries end when shutdown starts.
Messages the drain could not admit are counted instead of vanishing.

Lifecycle: a cancellation token replaces the per-connection broadcast so
a connection accepted in the same round as the shutdown still sees it,
and stop() takes owned handles before releasing the GVL. Connection and
idle limits bound stream resources, and datagram receive errors back
off. A PROXY header naming a Unix or unspecified family falls back to
the transport peer, with read failures counted separately.

Workers may take several syslog messages per request, so a busy request
queue cannot pace syslog delivery. The handler now reports :stream or
:datagram, a peerless stream gives nil, the datagram buffer keys are
named for what they bound, and the handler stays reachable through the
server object rather than a permanent GC root.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Yield syslog messages to the worker block

Requests and syslog messages now reach Ruby the same way: the block
given to run_worker receives either a Request, which it answers with a
Response, or a SyslogMessage, which it answers with an admission
verdict. The separate configured handler, and the GC root it needed, are
gone; delivery, limits, retries and accounting are unchanged.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Declare both of the gem's licences

The framing module is MPL-2.0 while the rest is MIT, so the gem metadata
lists both.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Tighten how a syslog message is answered and held

A block that answers a syslog message with a response was not giving a
verdict, but its response read as truthy and admitted the message. That
now logs once and refuses, counted as a handler error, and the failure
log names the message and its transport.

The message object is freed as soon as it is collected and reports its
payload to the GC, its string is built without revalidating bytes the
framer already checked, and inspect prints the transport as the reader
returns it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Correct the syslog and licence notes

The README described the removed callable, and the extension manifest
named only one of the two licences the gem declares.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Author: alistairjevans

Cargo.lock

@@ -19,3 +19,12 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
+
+Third-party components
+----------------------
+
+ext/hyper_ruby/src/syslog/framing.rs is a port of Vector 0.48.0's
+lib/codecs/src/decoding/framing/octet_counting.rs
+(https://github.com/vectordotdev/vector) and is licensed under the Mozilla
+Public License 2.0 (https://www.mozilla.org/en-US/MPL/2.0/), not the MIT
+licence above.

LICENSE.txt

@@ -10,10 +10,23 @@ After checking out the repo, run `bin/setup` to install dependencies. Then, run
 
 To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).
 
+## Syslog listeners
+
+Alongside HTTP, the server can accept syslog over a stream socket (Unix socket
+or TCP, optionally behind a PROXY v2 header) and over UDP. Each complete message
+is yielded to the same `Server#run_worker` block as requests, as a
+`HyperRuby::SyslogMessage` the block answers with an admission verdict. See the
+configuration keys documented at the top of `lib/hyper_ruby.rb`.
+
 ## License
 
 The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
 
+`ext/hyper_ruby/src/syslog/framing.rs` is an exception: it is a port of
+Vector 0.48.0's `lib/codecs/src/decoding/framing/octet_counting.rs` and is
+licensed under the [Mozilla Public License 2.0](https://www.mozilla.org/en-US/MPL/2.0/),
+which is why the gem's metadata lists both licences.
+
 ## Code of Conduct
 
 Everyone interacting in the HyperRuby project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/[USERNAME]/hyper_ruby/blob/master/CODE_OF_CONDUCT.md).

README.md

@@ -3,7 +3,7 @@ name = "hyper_ruby"
 version = "0.1.0"
 edition = "2021"
 authors = ["alistairjevans <alistair@betterstack.com>"]
-license = "MIT"
+license = "MIT AND MPL-2.0"
 publish = false
 
 [lib]
@@ -26,3 +26,5 @@ async-stream = "0.3.5"
 env_logger = "0.11"
 log = "0.4"
 form_urlencoded = "1.2.1"
+tokio-util = { version = "0.7", features = ["codec", "rt"] }
+socket2 = "0.5"