Snapshot and LabSnapshot

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vm:snapshot() returns a Snapshot wrapping a single file. lab:snapshot() returns a LabSnapshot wrapping a directory containing per-VM snapshot files plus a lab.json index.

Both are thin handles over filesystem paths. They have no agent-side state — once the snapshot file or directory is on disk, the userdata just gives you ergonomic access to it.

Snapshot #

Constructing #

A fixture's chunk returns a Snapshot (single-VM fixture); the harness reads the path, compresses + sparsifies the file, and installs it into the cache.

Methods #

snap:path() #

Returns the on-disk path as a Lua string.

snap:size() #

Returns the file size in bytes. Returns 0 rather than ENOENT if the file has been moved or deleted (idempotent with :delete()).

snap:delete() #

Best-effort delete. Idempotent — calling on a path that's already gone is fine. Returns nothing.

LabSnapshot #

Constructing #

A lab fixture's chunk returns a LabSnapshot; the harness moves the directory into the cache as <key>.lab/.

Methods #

lab_snap:path() #

Returns the on-disk directory path as a Lua string.

lab_snap:size() #

Returns the sum of file sizes directly under the directory (one level deep, doesn't recurse). Useful for picking large fixtures out of the cache.

lab_snap:delete() #

Recursively deletes the directory. Idempotent — calling on a path that's already gone is fine.

Example: build a fixture #

-- tests/fixtures/base.fixture.lua
local vm = provium:vm("base", "peios"):boot()
vm:run("seq 1000000 > /srv/corpus"):assert_ok()
return vm:snapshot()

-- tests/fixtures/cluster.fixture.lua
provium:bridge("lan")
local a = provium:vm("a", "peios"):boot()
local b = provium:vm("b", "peios"):boot()
provium.lan:attach({a, b})
a:run("ip addr add 10.0.0.1/24 dev eth0 && ip link set eth0 up")
b:run("ip addr add 10.0.0.2/24 dev eth0 && ip link set eth0 up")
return provium:snapshot()

-- tests/uses-base.test.lua
test("base fixture has the corpus pre-built", function(t)
    local vm = provium:vm_fixture("fixtures/base")
    vm:run("test -s /srv/corpus"):assert_ok()
end)

test("cluster fixture brings two VMs", function(t)
    local cluster = provium:lab_fixture("fixtures/cluster")
    cluster.a:run("ping -c 1 10.0.0.2"):assert_ok()
end)

See also #

• VM — vm:snapshot(), vm:restore().
• Lab — lab:snapshot(), lab:restore(), lab:vm_fixture(), lab:lab_fixture().
• Fixtures and dependencies — how snapshots become cached fixtures.

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