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Rate limiter: add an alternative implementation based on Redis. (obse…
…rvatorium#620) * Add a Redis rate limiter * Add useful comments * Allow Redis rate limiter to be used * Regenerate readme * Fix warning * Fix tests in machine in CircleCI * Tidy up go modules Signed-off-by: Douglas Camata <[email protected]> * Address PR review comments * Regenerate readme * Fix test assertion to account for negative time delta * Fix Redis limiter tests * Adjust test case comment * Fix/improve code comments * Keep Go 1.20 * Tidy with go1.20 Signed-off-by: Douglas Camata <[email protected]> --------- Signed-off-by: Douglas Camata <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,66 @@ | ||
| -- this script has side-effects, so it requires replicate commands mode | ||
| redis.replicate_commands() | ||
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| local rate_limit_key = KEYS[1] -- The key to the rate limit bucket. | ||
| local now = ARGV[1] -- Current time (Unix time in milliseconds). | ||
| local burst = ARGV[2] -- This represents the total capacity of the bucket. | ||
| local rate = ARGV[3] -- This represents the amount that leaks from the bucket. | ||
| local period = ARGV[4] -- This represents how often the "rate" leaks from the bucket (in milliseconds). | ||
| local cost = ARGV[5] -- This represents the cost of the request. Often 1 is used per request. | ||
| -- It allows some requests to be assigned a higher cost. | ||
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| local emission_interval = period / rate | ||
| local increment = emission_interval * cost | ||
| local burst_offset = emission_interval * burst | ||
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| local tat = redis.call("GET", rate_limit_key) | ||
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| if not tat then | ||
| tat = now | ||
| else | ||
| tat = tonumber(tat) | ||
| end | ||
| tat = math.max(tat, now) | ||
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| local new_tat = tat + increment | ||
| local allow_at = new_tat - burst_offset | ||
| local diff = now - allow_at | ||
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| local limited | ||
| local retry_in | ||
| local reset_in | ||
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| local remaining = math.floor(diff / emission_interval) -- poor man's round | ||
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| if remaining < 0 then | ||
| limited = 1 | ||
| -- calculate how many tokens there actually are, since | ||
| -- remaining is how many there would have been if we had been able to limit | ||
| -- and we did not limit | ||
| remaining = math.floor((now - (tat - burst_offset)) / emission_interval) | ||
| reset_in = math.ceil(tat - now) | ||
| retry_in = math.ceil(diff * -1) | ||
| elseif remaining == 0 and increment <= 0 then | ||
| -- request with cost of 0 | ||
| -- cost of 0 with remaining 0 is still limited | ||
| limited = 1 | ||
| remaining = 0 | ||
| reset_in = math.ceil(tat - now) | ||
| retry_in = 0 -- retry in is meaningless when cost is 0 | ||
| else | ||
| limited = 0 | ||
| reset_in = math.ceil(new_tat - now) | ||
| retry_in = 0 | ||
| if increment > 0 then | ||
| redis.call("SET", rate_limit_key, new_tat, "PX", reset_in) | ||
| end | ||
| end | ||
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| -- return values (in order): | ||
| -- limited = integer-encoded boolean, 1 if limited, 0 if not | ||
| -- remaining = number of tokens remaining | ||
| -- retry_in = milliseconds until the next request will be allowed | ||
| -- reset_in = milliseconds until the rate limit window resets | ||
| -- diff = milliseconds since the last request | ||
| -- emission_interval = milliseconds between token emissions | ||
| return {limited, remaining, retry_in, reset_in, tostring(diff), tostring(emission_interval)} |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,82 @@ | ||
| package ratelimit | ||
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| import ( | ||
| "context" | ||
| _ "embed" | ||
| "strconv" | ||
| "time" | ||
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| "github.com/redis/rueidis" | ||
| ) | ||
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| //go:embed gcra_rate_limit.lua | ||
| var gcraRateLimitScript string | ||
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| // RedisRateLimiter is a type that represents a rate limiter that uses Redis as its backend. | ||
| // The rate limiting is a leaky bucket implementation using the generic cell rate algorithm. | ||
| // See https://en.wikipedia.org/wiki/Generic_cell_rate_algorithm for details on how this algorithm works. | ||
| type RedisRateLimiter struct { | ||
| client rueidis.Client | ||
| } | ||
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| // Ensure RedisRateLimiter implements the SharedRateLimiter interface. | ||
| var _ SharedRateLimiter = (*RedisRateLimiter)(nil) | ||
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| // NewRedisRateLimiter creates a new instance of RedisRateLimiter. | ||
| func NewRedisRateLimiter(addresses []string) (*RedisRateLimiter, error) { | ||
| client, err := rueidis.NewClient(rueidis.ClientOption{InitAddress: addresses}) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| return &RedisRateLimiter{client: client}, nil | ||
| } | ||
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| // GetRateLimits retrieves the rate limits for a given request using a Redis Rate Limiter. | ||
| // It returns the amount of remaining requests, the reset time in milliseconds, and any error that occurred. | ||
| func (r *RedisRateLimiter) GetRateLimits(ctx context.Context, req *request) (remaining, resetTime int64, err error) { | ||
| inspectScript := rueidis.NewLuaScript(gcraRateLimitScript) | ||
| rateLimitParameters := []string{ | ||
| strconv.FormatInt(time.Now().UnixMilli(), 10), // now | ||
| strconv.FormatInt(req.limit, 10), // burst | ||
| strconv.FormatInt(req.limit, 10), // rate | ||
| strconv.FormatInt(req.duration, 10), // period | ||
| "1", // cost | ||
| } | ||
| result := inspectScript.Exec(ctx, r.client, []string{req.key}, rateLimitParameters) | ||
| limited, remaining, resetIn, err := r.parseRateLimitResult(&result) | ||
| if err != nil { | ||
| return 0, 0, err | ||
| } | ||
| resetTime = time.Now().Add(time.Duration(resetIn) * time.Millisecond).UnixMilli() | ||
| if limited { | ||
| return remaining, resetTime, errOverLimit | ||
| } | ||
| return remaining, resetTime, nil | ||
| } | ||
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| // parseRateLimitResult parses the result of a rate limit check from Redis. | ||
| // It takes a RedisResult as input and returns the parsed rate limit values: whether the request is limited, | ||
| // the number of remaining requests, the reset time in milliseconds, and any error that occurred during parsing. | ||
| func (r *RedisRateLimiter) parseRateLimitResult(result *rueidis.RedisResult) (limited bool, remaining, resetIn int64, err error) { | ||
| values, err := result.ToArray() | ||
| if err != nil { | ||
| return false, 0, 0, err | ||
| } | ||
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| limited, err = values[0].AsBool() | ||
| if err != nil { | ||
| return false, 0, 0, err | ||
| } | ||
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| remaining, err = values[1].AsInt64() | ||
| if err != nil { | ||
| return false, 0, 0, err | ||
| } | ||
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| resetIn, err = values[3].AsInt64() | ||
| if err != nil { | ||
| return false, 0, 0, err | ||
| } | ||
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| return limited, remaining, resetIn, nil | ||
| } |
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