chore: reorganize rust crates

crates/api/src/middleware/ratelimit.lua

@@ -0,0 +1,61 @@
+-- this script has side-effects, so it requires replicate commands mode
+-- redis.replicate_commands()
+
+local rate_limit_key = KEYS[1]
+local rate = ARGV[1]
+local period = ARGV[2]
+local cost = tonumber(ARGV[3])
+
+local burst = rate
+
+local emission_interval = period / rate
+local increment = emission_interval * cost
+local burst_offset = emission_interval * burst
+
+-- redis returns time as an array containing two integers: seconds of the epoch
+-- time (10 digits) and microseconds (6 digits). for convenience we need to
+-- convert them to a floating point number. the resulting number is 16 digits,
+-- bordering on the limits of a 64-bit double-precision floating point number.
+-- adjust the epoch to be relative to Jan 1, 2017 00:00:00 GMT to avoid floating
+-- point problems. this approach is good until "now" is 2,483,228,799 (Wed, 09
+-- Sep 2048 01:46:39 GMT), when the adjusted value is 16 digits.
+local jan_1_2017 = 1483228800
+local now = redis.call("TIME")
+now = (now[1] - jan_1_2017) + (now[2] / 1000000)
+
+local tat = redis.call("GET", rate_limit_key)
+
+if not tat then
+    tat = now
+else
+    tat = tonumber(tat)
+end
+
+tat = math.max(tat, now)
+
+local new_tat = tat + increment
+local allow_at = new_tat - burst_offset
+
+local diff = now - allow_at
+local remaining = diff / emission_interval
+
+if remaining < 0 then
+    local reset_after = tat - now
+    local retry_after = diff * -1
+    return {
+        0, -- remaining
+        tostring(retry_after),
+        reset_after,
+    }
+end
+
+local reset_after = new_tat - now
+if reset_after > 0 then
+    redis.call("SET", rate_limit_key, new_tat, "EX", math.ceil(reset_after))
+end
+local retry_after = -1
+return {
+    remaining,
+    tostring(retry_after),
+    reset_after
+}