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fix(minvmd): bind a waiting declared forward when the row holding its listener is withdrawn - #2186
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norrietaylor merged 11 commits intoOct 13, 2026
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… listener is withdrawn Several boxes can declare one host ingress port at a shared loopback address. The egress gate keeps one attribution per host listener, so the second box's publish was relayed to the switch, refused there, and forgotten. When the holder's row was withdrawn the gate unbound the listener and nothing bound it again, so the port stayed dead. The unbind also reached the switch before the ledger dropped its entry, so a publish relayed in between was bound and attributed to no box, and was never unbound at its box's end. A publish for a listener the ledger attributes to another box's address is no longer relayed. The guest is answered with the status and body the switch gives a held listener (HTTP 500, "proxy already running"), which is what it read before. When the port is one the publishing row declared, the gate keeps the publish as that row's waiting forward: listener, the row's switch address, inside port and protocol, all from the guest's own request. At a row's withdrawal, the step that drops a listener's attribution gives the listener to one waiting forward and the gate sends the expose itself. Of several waiting forwards the one with the lowest box id is bound: the host mints the id as a UUIDv7 at registration, so that is the row registered earliest, whatever order the guest published in. The listener is never unheld in the ledger across the hand-over. A failed expose takes the attribution back out, is logged at warn with the listener and the row, and is retried on the unbind's own backoff. The hold on the withdrawn box's addresses does not wait on it. A waiting forward is dropped at its own row's withdrawal, and waiting forwards are bounded as the ledger is: past the bound a new one is refused and nothing is evicted.
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A rabbit watched the listener wait,
While forwards queued beside the gate.
The holder left; a claim took flight,
The switch replied by day or night.
If answers paused, retries began,
The rabbit bounded through the plan.
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Approved: every review thread resolved at @mitodrummer resolved the last thread, which releases the approval this review had withheld. Nothing to do. |
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Review comments at @crates/minvmd/src/net/egress_gate.rs:
- Around line 3091-3107: Update `forward_revoke::expose` and its callers to
distinguish an answered non-2xx refusal from an outcome where no status was
read. In `apply_waiting`, release the claim only for an answered refusal; for an
unanswered expose, settle and retain the claim and drop the waiting record so
withdrawal can unexpose it.
- Around line 2535-2544: Update claim_in to return a distinct result when the
row-held bound is reached, and record that listener in owed so retry_hand_overs
can retry the waiting forward after a ledger slot becomes available.
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…swered A hand-over expose that fails without a status read (a connect, write or read error, or a timeout) may still have been bound by the switch. The gate released the claim for every failure, so a forward the switch did bind had no attribution: the waiting row's withdrawal unbound nothing, released the address, and the next box leased there would receive the old listener's connections. The expose now tells a refusal from a lost answer. An unanswered claim keeps its attribution, so the waiting row's withdrawal unbinds it and no other box's publish for the listener is relayed, and keeps its waiting record, so the retries repeat the expose. Only an answered refusal takes the attribution back out. A hand-over the ledger had no row-held slot for is now owed a retry instead of being counted as settled, and the give-up line names both ways the listener is bound again.
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unsafe-libyaml is archived upstream with no maintained release. It is reached only through nickel-lang-core's non-optional serde_yaml dependency, so no version bump clears the advisory. (cherry picked from commit 4d0ffdf)
mitodrummer
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Oct 13, 2026
…nd for it A forward the gate binds at a hand-over is one the waiting box's daemon never asked for, so the box publishes it at its next attach. The ledger already attributes the listener to that box, so the publish was relayed, the switch refused it as already running, and the daemon, which treats any refused bind as fatal, failed the attach every time. The ledger now marks a listener its own expose bound, and a publish of that same forward from its own box is answered as bound without being relayed. A publish at the listener that dials another inside port or protocol is still relayed for the switch to decide. A hand-over's retries no longer come out of the unbinds' budget. They shared one iterator, so a box whose own unbinds used every wait left an owed hand-over none. An owed hand-over is now retried on the whole backoff again once the unbinds are done or given up. A waiting forward is filed only by its own box's publish. A test pins that a row whose box never published a declared port is bound nothing at the holder's withdrawal: the row names neither the inside port nor the protocol an expose needs.
The set of listeners the gate's own expose bound was cleared only when a listener was attributed anew, so a hand-over whose box ended with no later publish left its entry for the gate's lifetime. The mark now goes wherever the attribution goes, which bounds the set by the row-held side of the ledger.
mitodrummer
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The bound-answer fix for the gate's own hand-over looks right, and the control-connection test covers it, thanks. The shared-address point is still open: by the updated Reach section this PR doesn't rebind the case it was written for, and whether the gate or the guest registry picks the new holder is a design call that has to agree with #2185 (which keeps a stopped holder). Let's settle that choice before merging the host half on its own, so we don't ship a waiting-forward path that the real guest never reaches.
When the box holding a shared-address port is destroyed, drops the port or moves address, the registry elects the next holder but nothing bound that box's forward until its next attach, so the port went dark for a running box. The registry now sends each hand-over to a subscriber. The session manager routes it to the elected box's actor, which posts the expose its own attach would have posted when its host is running, and tracks the forwarder with the running spawn so the spawn's teardown and the box's stop unbind it. A box that is not running is asked nothing and binds at its next attach, as before. A bind the switch refuses is logged and tracked nowhere: the election stands and the next attach binds the port. Behind a VM host's gate, the switch's "proxy already running" answer to the hand-over's expose is the gate still holding the old holder's listener; the forwarder is tracked and the gate binds it when that row is withdrawn.
The gate chose among the declared forwards waiting on a listener by lowest box id. The guest's registry is the one elector of a shared port's holder, by creation order with a running box first, and the two orders can differ. A publish for a held listener now replaces any other row's forward waiting on it, so one forward waits per listener: the one the guest published last, which names the box it elected. The gate applies that choice at the holder's row withdrawal and makes none of its own.
A box may declare TCP and UDP on one external port. The hand-over's guard against binding a forward twice was keyed by the listener alone, so the second protocol's forward was skipped once the first was tracked. The guard now matches the listener and the protocol. A port one of whose forwards the switch refused is no longer recorded on the box's record as bound.
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Taking the guest half in 0.7.0 with the gate change, no split. Thanks for building it as the guest-decides split.
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minimal-review — approved
Verdict APPROVE — every review thread is resolved; @mitodrummer closed the last one. The review of 9981e3c931b5 withheld this approval on the threads open then.
This was referenced Oct 13, 2026
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… listener is withdrawn (#2186) * fix(minvmd): bind a waiting declared forward when the row holding its listener is withdrawn Several boxes can declare one host ingress port at a shared loopback address. The egress gate keeps one attribution per host listener, so the second box's publish was relayed to the switch, refused there, and forgotten. When the holder's row was withdrawn the gate unbound the listener and nothing bound it again, so the port stayed dead. The unbind also reached the switch before the ledger dropped its entry, so a publish relayed in between was bound and attributed to no box, and was never unbound at its box's end. A publish for a listener the ledger attributes to another box's address is no longer relayed. The guest is answered with the status and body the switch gives a held listener (HTTP 500, "proxy already running"), which is what it read before. When the port is one the publishing row declared, the gate keeps the publish as that row's waiting forward: listener, the row's switch address, inside port and protocol, all from the guest's own request. At a row's withdrawal, the step that drops a listener's attribution gives the listener to one waiting forward and the gate sends the expose itself. Of several waiting forwards the one with the lowest box id is bound: the host mints the id as a UUIDv7 at registration, so that is the row registered earliest, whatever order the guest published in. The listener is never unheld in the ledger across the hand-over. A failed expose takes the attribution back out, is logged at warn with the listener and the row, and is retried on the unbind's own backoff. The hold on the withdrawn box's addresses does not wait on it. A waiting forward is dropped at its own row's withdrawal, and waiting forwards are bounded as the ledger is: past the bound a new one is refused and nothing is evicted. * fix(minvmd): keep a hand-over's attribution when its expose goes unanswered A hand-over expose that fails without a status read (a connect, write or read error, or a timeout) may still have been bound by the switch. The gate released the claim for every failure, so a forward the switch did bind had no attribution: the waiting row's withdrawal unbound nothing, released the address, and the next box leased there would receive the old listener's connections. The expose now tells a refusal from a lost answer. An unanswered claim keeps its attribution, so the waiting row's withdrawal unbinds it and no other box's publish for the listener is relayed, and keeps its waiting record, so the retries repeat the expose. Only an answered refusal takes the attribution back out. A hand-over the ledger had no row-held slot for is now owed a retry instead of being counted as settled, and the give-up line names both ways the listener is bound again. * chore(deny): ignore RUSTSEC-2024-0449 until nickel moves off serde_yaml unsafe-libyaml is archived upstream with no maintained release. It is reached only through nickel-lang-core's non-optional serde_yaml dependency, so no version bump clears the advisory. (cherry picked from commit 4d0ffdf) * fix(minvmd): answer a box's publish of a forward the gate already bound for it A forward the gate binds at a hand-over is one the waiting box's daemon never asked for, so the box publishes it at its next attach. The ledger already attributes the listener to that box, so the publish was relayed, the switch refused it as already running, and the daemon, which treats any refused bind as fatal, failed the attach every time. The ledger now marks a listener its own expose bound, and a publish of that same forward from its own box is answered as bound without being relayed. A publish at the listener that dials another inside port or protocol is still relayed for the switch to decide. A hand-over's retries no longer come out of the unbinds' budget. They shared one iterator, so a box whose own unbinds used every wait left an owed hand-over none. An owed hand-over is now retried on the whole backoff again once the unbinds are done or given up. A waiting forward is filed only by its own box's publish. A test pins that a row whose box never published a declared port is bound nothing at the holder's withdrawal: the row names neither the inside port nor the protocol an expose needs. * docs(minvmd): reword the hand-over sentence in the revocation's doc comment * fix(minvmd): drop a hand-over's mark with its attribution The set of listeners the gate's own expose bound was cleared only when a listener was attributed anew, so a hand-over whose box ended with no later publish left its entry for the gate's lifetime. The mark now goes wherever the attribution goes, which bounds the set by the row-held side of the ledger. * test(minimald): pin the live bind of a shared port when its holder is destroyed * fix(minimald): bind a shared port for the running box that takes it over When the box holding a shared-address port is destroyed, drops the port or moves address, the registry elects the next holder but nothing bound that box's forward until its next attach, so the port went dark for a running box. The registry now sends each hand-over to a subscriber. The session manager routes it to the elected box's actor, which posts the expose its own attach would have posted when its host is running, and tracks the forwarder with the running spawn so the spawn's teardown and the box's stop unbind it. A box that is not running is asked nothing and binds at its next attach, as before. A bind the switch refuses is logged and tracked nowhere: the election stands and the next attach binds the port. Behind a VM host's gate, the switch's "proxy already running" answer to the hand-over's expose is the gate still holding the old holder's listener; the forwarder is tracked and the gate binds it when that row is withdrawn. * fix(minvmd): bind the publish the guest sent last, not the lowest box id The gate chose among the declared forwards waiting on a listener by lowest box id. The guest's registry is the one elector of a shared port's holder, by creation order with a running box first, and the two orders can differ. A publish for a held listener now replaces any other row's forward waiting on it, so one forward waits per listener: the one the guest published last, which names the box it elected. The gate applies that choice at the holder's row withdrawal and makes none of its own. * fix(minimald): tell a handed-over forward apart by its protocol A box may declare TCP and UDP on one external port. The hand-over's guard against binding a forward twice was keyed by the listener alone, so the second protocol's forward was skipped once the first was tracked. The guard now matches the listener and the protocol. A port one of whose forwards the switch refused is no longer recorded on the box's record as bound. (cherry picked from commit e5913b5)
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What
When the box holding a shared-address port gives it up, the running box that takes it over now serves it without a new attach.
minimald): the registry's election is acted on at once. The daemon posts the elected box's expose when that box is running and tracks the forward with its running spawn.minvmd, VM-backed hosts): a publish for a listener another box's row still holds is kept as a waiting forward. The egress gate binds it when the holding row is withdrawn. The gate applies the guest's choice and makes none of its own.Why
The registry elected a new holder at a hand-over and only logged it. The new holder's forward was bound at its next attach, so the port went dark for a box that was already running.
On a VM-backed host the listener of a declared forward is unbound only when its row is withdrawn. A publish for that listener from another box was relayed to the switch and refused, and after the withdrawal nothing bound the port. The gate also unbound the listener before dropping its attribution, so a publish arriving in between was bound without an attribution.
Reach
500 proxy already running, and binds it at the row's withdrawal. The guest reads that answer as held by the host and tracks the forward.Changes
minimald/src/net/dns.rs: the registry sends eachPortHandOverto a subscriber, and answers whether a box holds a shared port of record.minimald/src/sessions.rs: the session manager subscribes and routes each hand-over to the elected box's session.minimald/src/session.rs: the session binds the handed-over port when its host is running, one forward per declared protocol, tracks each forwarder, and records the port as one it bound when none was refused. Its stop releases the forward.minimald/src/net/policy.rs:bind_handed_portposts the one expose and reads the answer.proxy already runningis held-by-host behind a VM host's gate and an error on a native host.minimald/src/net/provider.rs,net/gvproxy_network.rs: forwards bound at a hand-over are kept with the running spawn and released at its teardown.minvmd/src/net/egress_gate.rs: a publish for a listener attributed to another row is not relayed. A declared one is kept as a waiting forward and bound at the holder's row withdrawal. One forward waits per listener: a later publish replaces any other waiting on it, so the gate binds the publish the guest sent last. The gate no longer picks by lowest box id.minvmd/src/net/egress_gate.rs: a forward the gate bound at a hand-over is marked. When its own box later publishes that same forward, the gate answers it as bound and does not relay it.minvmd/src/net/forward_revoke.rs: a host-originated expose beside the existing unexpose. An expose the switch refuses leaves no attribution. One that goes unanswered keeps its attribution and is retried. Hand-over retries run on the whole backoff again after the box's own unbinds.Known limits
release/0.7.0today and is not changed here.Verification
a_destroyed_holders_shared_port_is_bound_for_the_running_box_that_takes_iton the test-only commit7759dc0f1failed on Linux with "the switch was asked fewer than 1 request(s): []".9981e3c93:just testandjust clippy.just test:Summary [ 46.873s] 3769 tests run: 3769 passed (1 leaky), 24 skipped. One earlier run on the same commit failedlisten_publish_and_runtime_expose_never_double_bindonce; it passed alone and in the full rerun, and this change does not touch its path.just clippy:Finished `dev` profile, no warnings.ab21fd057(the later commit changes onlyminimald, which macOS does not build):just test:1174 tests run: 1174 passed, 21 skipped.just clippyandjust clippy-strict origin/release/0.7.0clean.every_hand_over_is_sent_to_the_subscriber(drop a port, move address, destroy),a_destroyed_holders_shared_port_is_bound_for_the_running_box_that_takes_it,a_destroyed_holders_shared_port_is_not_bound_for_a_box_that_is_not_running,a_hand_over_bind_the_switch_refuses_leaves_the_election_standing,a_port_taken_over_while_running_comes_down_with_its_spawn_and_binds_at_the_next_attach,a_bound_hand_over_hands_back_the_forwarder_to_track,an_already_running_answer_is_held_only_behind_a_vm_hosts_gate.net::egress_gate::tests, includingwaiting_declared_forward_bound_when_holder_row_withdrawn,of_two_publishes_for_a_held_listener_the_later_one_waits_and_is_bound,a_publish_of_a_forward_the_gate_bound_is_answered_as_bound_and_not_relayedanda_declared_port_its_box_never_published_is_not_bound_at_the_holders_withdrawal.127.0.0.1interim, which a host takes when the reserved local range is absent from its loopback. A Linux host's probe always reads the range present, and the macOS host these runs used has the range installed system-wide. The tests above use stand-in switches. No e2e case covers two boxes declaring one port at one address.Summary by CodeRabbit