ipc: support per-address max-connections options on -ipcbind #35037

enirox001 commented at 1:44 PM on April 9, 2026: contributor

This is a draft follow-up to #34978 to make the per-address IPC connection-limit approach concrete.

The branch extends -ipcbind to accept :max-connections=<n> options, for example -ipcbind=unix::max-connections=8 or -ipcbind=unix:/custom/path:max-connections=8, instead of introducing a separate global -ipcmaxconnections option.

It also adds the local listener limit support needed in libmultiprocess and threads the parsed per-address limit through to ListenConnections() so each listener can stop accepting new IPC connections after reaching its local cap and resume accepting after a disconnect.

The draft includes:

parser coverage for -ipcbind max-connections and invalid inputs
functional init coverage for FD reservation logging and init errors
an IPC behavior test verifying that with max_connections=1, a second client only becomes usable after the first disconnects

This is intended to help evaluate the per-address approach downstream against the global-limit direction in #34978.

DrahtBot commented at 1:44 PM on April 9, 2026: contributor

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Reviews

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Type	Reviewers
Concept ACK	ryanofsky, kevkevinpal

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Conflicts

Reviewers, this pull request conflicts with the following ones:

#35084 (ipc: Support for windows support by ryanofsky)
#34978 (init: Reserve file descriptors for IPC connections by enirox001)
#34806 (refactor: logging: Various API improvements by ajtowns)
#32427 ((RFC) kernel: Replace leveldb-based BlockTreeDB with flat-file based store by sedited)
#32387 (ipc: add windows support by ryanofsky)
#17783 (common: Disallow calling IsArgSet() on ALLOW_LIST options by ryanofsky)
#17581 (refactor: Remove settings merge reverse precedence code by ryanofsky)
#17580 (refactor: Add ALLOW_LIST flags and enforce usage in CheckArgFlags by ryanofsky)
#17493 (util: Forbid ambiguous multiple assignments in config file by ryanofsky)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

enirox001 renamed this:
~~04 26 ipcbind max connections draft~~
ipc: support per-address max-connections options on -ipcbind
on Apr 9, 2026

enirox001 force-pushed on Apr 9, 2026

DrahtBot added the label CI failed on Apr 9, 2026

enirox001 force-pushed on Apr 9, 2026

ryanofsky commented at 2:40 PM on April 9, 2026: contributor

Concept ACK. Looks like suggestions from #35036 (comment) apply here too (sorry, saw that PR first in my inbox).

IMO this is a better alternative to adding a new -ipcmaxconnections option like #34978, and I'd prefer this approach but both approaches seem reasonable. Main reason I prefer this approach is IPC is a pretty generic feature, so it seems useful to be able to set different limits for different purposes (like GUIs vs mining clients).

enirox001 force-pushed on Apr 9, 2026

enirox001 commented at 3:50 PM on April 9, 2026: contributor

Thanks for the review @ryanofsky

I pushed updates based on your review here as well

the bind-address type is now shared
parsing moved behind the interfaces::Ipc boundary
the parser handles trailing socket options
listenAddress() now takes the bind-address struct directly

in test/functional/interface_ipc_init.py:29 in aadc51fb5f outdated

  24 | +        super().setup_nodes()
  25 | +        self.nodes[0].args = [arg for arg in self.nodes[0].args if not arg.startswith("-ipcbind=")]
  26 | +        self.ipc_tmpdir = tempfile.TemporaryDirectory(prefix="btc-ipc-init-")
  27 | +        self.ipcbind_path = Path(self.ipc_tmpdir.name) / "ipcinit.sock"
  28 | +
  29 | +    def test_ipcbind_max_connections(self):

ViniciusCestarii commented at 5:21 PM on April 9, 2026:

Same suggestion I made on #34978. It would be good to have a functional test case where max-connections is not specified, to verify the default value is actually applied correctly

enirox001 commented at 11:49 AM on April 20, 2026:

Thanks for the suggestion, applied in the latest push

kevkevinpal commented at 3:43 PM on April 13, 2026: contributor

Concept ACK

I agree with Ryanofsky. I think this approach seems more reasonable than #34978, even though both can work and both make sense this seems cleaner. I think it makes sense to go with this approach instead of adding the -ipcmaxconnections option.

fanquake commented at 1:02 PM on April 14, 2026: member

cc @Sjors

enirox001 force-pushed on Apr 20, 2026

enirox001 force-pushed on Apr 21, 2026

ipc: update libmultiprocess subtree to include local connection limit support

git-subtree-dir: src/ipc/libmultiprocess
git-subtree-split: 8511c68f8b6827f4e9b306e0245929965a363930

540d55dc7c

enirox001 force-pushed on Apr 21, 2026

ipc: add per-address max-connections parsing and support for -ipcbind

Thread optional per-address max-connections values through the listener
implementation.

Update interfaces::Ipc and ipc::Protocol listen methods to accept an
optional connection limit, pass parsed -ipcbind limits from init, and
use ListenConnections(..., max_connections) support so each
listener stops accepting new IPC connections after reaching its local
cap and resumes accepting after a disconnect.

01f82cbc2a

ipc: test per-address connection limiting over unix sockets

Add an IPC test covering the local listener limit behavior
through ipc::Process and ipc::Protocol over a unix socket.

The new test starts a listener with max_connections=1, verifies the
first client is served immediately, checks that a second client remains
blocked while the first connection stays open, and then confirms the
second client becomes usable after the first disconnects.

2d214431d0

enirox001 force-pushed on Apr 21, 2026

enirox001 commented at 9:07 AM on April 21, 2026: contributor

Had a peer review with @Eunovo a few days ago, and I pushed a few follow-up changes to make the branch a bit easier to review:

Updated ParseBindAddress() to return util::Result, and adjusted the callers/tests accordingly.
Extended parser coverage to include 0, large valid values, and negative/overflow cases.
Cleaned up the commit structure so the branch is split into a subtree update, per-address integration, and tests.
Fixed the IPC limit test by correcting the async lifetime issue that could trigger disconnect errors.

The remaining subtree lint failure is expected for this draft, since the branch carries the libmultiprocess subtree update ahead of the upstream merge.