Foundational for the restore wizard's tree browser. The wizard needs to
lazy-load directory contents from a snapshot as the operator drills
down; this lands the transport.
- internal/api adds MsgTreeList (server → agent) + MsgTreeListResult
(agent → server) with TreeListRequestPayload / TreeListEntry /
TreeListResultPayload types. Reply correlates by Envelope.ID.
- internal/restic.ListTreeChildren wraps 'restic ls --json' and
filters its recursive output to direct children of the requested
path. Parser + path-normalisation + isDirectChild are unit-tested.
- internal/server/ws/rpc.go introduces a generic SendRPC helper on
Hub: register a buffered channel keyed by ULID, send the request,
block on ctx.Done()/timeout/reply. Reply routing piggybacks on the
existing dispatchAgentMessage by adding a MsgTreeListResult case
that forwards to the registered waiter; if no waiter is registered
(caller already gave up) the stray reply is dropped quietly.
- cmd/agent gains a tree.list handler that runs ListTreeChildren on a
fresh per-call context (60s ceiling) and ships the matching
tree.list.result envelope. Errors surface in result.Error rather
than as transport failures so the server-side waiter can render a
sensible UI message.
- internal/server/http/tree_cache.go is the per-wizard-session cache
layer (~30min TTL, sweep-on-access) that fetchTreeWithCache uses
before falling through to SendRPC. Cached on success only; agent
errors aren't cached so a transient failure doesn't poison the
session.
Tests:
- internal/restic/ls_test.go covers parseLsChildren at root / mid-tree
/ leaf, plus normalizeTreePath and isDirectChild edge cases.
- internal/server/ws/rpc_test.go unit-tests the registry: round-trip,
release semantics, concurrent waiters, ctx-cancel.
- internal/server/http/tree_rpc_test.go is the full round-trip: server
SendRPC → fake-agent over a real WS → reply → server gets the
payload. Plus a timeout test that confirms ~300ms timeouts terminate
in ~300ms rather than waiting forever.
The cache is plumbed but no UI handler hits fetchTreeWithCache yet —
that lands with P3-01 (wizard backend). The unused-linter is suppressed
via nolint until the wizard wires it in.
