41 lines
2.7 KiB
Markdown
41 lines
2.7 KiB
Markdown
# mesh-delivery-gate
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The `mesh-delivery-gate` module of the mesh catalogue: the gate of design 47. It claims the seat `mesh-delivery`, whose
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name stays (ADR 0437 §11), and takes over from the module `mesh-delivery` (ADR 0437 §3, ADR 0450 §6). Its buckets are
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`mesh-delivery-gate_*`.
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## Files it does not know
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Each directory or archive this module declares says how it treats a file it did not write (ADR 0422, ADR 0416).
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- `${dir:state}`: everything in it is the program's; the mesh moves nothing out (ADR 0422 §2).
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## A backup that failed before the send
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The controller backs up the data of the modules a delivery moves before it asks or sends anything (ADR 0404). When its
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walk's record, in `plan-moved`, names a backup that failed or stayed silent and nothing of the plan was sent, the
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delivery goes from delivering to held (the observed row `backup failed`); the held reason names the machine, the
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module and the backup's words, and the pull request's comment shows it. The hold does not lift by itself. `release`
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of such a delivery asks the controller (`delivery-backups-again`) to take the backups again and the delivery goes on
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delivering; a record from before the controller cleared the failure does not hold it again. A held delivery already
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ends as covered or delivered when a later merge covers it.
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## Taking the seat over from today's module
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The gate claims the seat `mesh-delivery` beside the module `mesh-delivery`, which the catalogue no longer holds. The controller
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keeps a module that is assigned (it refuses to forget it), so the running module goes by a handover of verbs after the merge,
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never by hand on a machine (novox/hq ADR 0449 §4, ADR 0450 §6):
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1. assign `mesh-delivery-gate` to the machine that holds the seat (`mesh-controller.assign`);
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2. check that `mesh-controller.seats` still names `mesh-delivery`, held by the running module;
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3. unassign `mesh-delivery` from that machine (`mesh-controller.unassign`) and push it (`mesh-controller.push`);
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4. the seat passes: the gate reads the controller's assignments and the node-engine's have keys, finds the module on no machine,
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carries its deliveries, groups and pull keys over once (the key `carried` in its `deliveries` says it did), reads the controller's
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walks and the forge's open pull requests, and acts.
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Until then the gate is silent: it takes no event, writes no key, asks nothing and answers no verb but `delivery_status`, which
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says why (`holds-the-seat`, `seat-waits`).
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The catalogue holds the names of the old module that the handover needs, and no others: the three buckets the gate carries
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over, and the event the issue tracker and the tool runner hear until the module is forgotten (`catalogue_test.go`).
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