Clock

A Clock wraps the guest's wall clock. Operations dispatch to the agent, which adjusts the kernel's CLOCK_REALTIME (and equivalents) under the hood.

The clock is signed — you can move the guest backwards in time. This matters for testing time-dependent code: certificate expiry, timeout handling, leap-second handling, retry backoff.

Constructing #

Methods #

clock:get() #

Returns the current time as seconds-since-epoch (float). For sub-microsecond accuracy use :get_ns().

local t = vm:clock():get()
-- t ≈ 1700000000.0

clock:get_ns() #

Returns nanoseconds-since-epoch as a 64-bit signed integer. Lua 5.4 integers are 64-bit so no precision is lost.

clock:set(seconds) #

Set the wall clock to seconds seconds since epoch. Accepts integers or floats. Negative values are allowed — the guest goes pre-epoch, useful for testing time_t boundary handling.

Errors on NaN or infinity (clock:set: value must be a finite number (got NaN/inf)). Without this guard, the integer cast would silently saturate or round to zero.

clock:set_ns(ns) #

Set the wall clock to ns nanoseconds since epoch (i64). Same semantics as :set but at full precision.

clock:sleep(duration) #

Sleep for duration seconds. Accepts:

• Integer / float — seconds.
• String — "100ms" / "5s" / "5m" / "2h".

Errors on NaN, infinity, or negative.

clock:advance(duration) #

Advance the wall clock by duration seconds (signed). Unlike :sleep, this does not block — the kernel's CLOCK_REALTIME jumps forward (or backward).

Negative values are explicitly allowed (clock:advance(-3600) rolls the guest back an hour). Errors on NaN or infinity but not on negative.

Example: certificate expiry test #

test("client refuses an expired cert", function(t)
    local vm = provium:vm("v", "peios"):boot()
    -- Set the clock to before the cert was issued.
    vm:clock():set(1500000000)  -- 2017-07-14
    local r = vm:run("openssl s_client -connect server:443 < /dev/null")
    r:assert_ok()  -- baseline: cert is valid

    -- Jump past expiry.
    vm:clock():advance(20 * 365 * 24 * 3600)  -- +20 years
    local r2 = vm:run("openssl s_client -connect server:443 < /dev/null")
    t:assert(not r2:ok())  -- cert is now expired
    t:assert(r2.stderr:find("certificate has expired"))
end)

Notes #

• clock:get() (float) loses precision below ~250 ns at modern epoch values because of f64 mantissa width. Use :get_ns() if you need exact ns roundtrip.
• The clock is not a guest namespace — every process inside the guest sees the same time axis after :set / :advance.
• Boot-time initial clock is set via boot_opts.initial_time (see VM boot opts). The Clock methods are for adjustment after boot.

See also #

• VM — vm:clock() and the boot_opts.initial_time boot-time setter.