From 2821def4fdfdf2fa405311fbb1030f7300e0e6ee Mon Sep 17 00:00:00 2001
From: Spencer Gibb <spencer@gibb.us>
Date: Wed, 8 Apr 2020 22:49:04 -0400
Subject: [PATCH] Allows 0 burstCapacity.

Fixes gh-1312
---
 .../filter/ratelimit/RedisRateLimiter.java    | 34 +++++++++++--------
 .../META-INF/scripts/request_rate_limiter.lua |  7 ++--
 .../ratelimit/RedisRateLimiterTests.java      | 18 ++++++++++
 3 files changed, 42 insertions(+), 17 deletions(-)

diff --git a/spring-cloud-gateway-core/src/main/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiter.java b/spring-cloud-gateway-core/src/main/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiter.java
index 85b4a623..2ab47e11 100644
--- a/spring-cloud-gateway-core/src/main/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiter.java
+++ b/spring-cloud-gateway-core/src/main/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiter.java
@@ -282,22 +282,26 @@ public class RedisRateLimiter extends AbstractRateLimiter<RedisRateLimiter.Confi
 			Flux<List<Long>> flux = this.redisTemplate.execute(this.script, keys,
 					scriptArgs);
 			// .log("redisratelimiter", Level.FINER);
-			return flux.onErrorResume(throwable -> Flux.just(Arrays.asList(1L, -1L)))
-					.reduce(new ArrayList<Long>(), (longs, l) -> {
-						longs.addAll(l);
-						return longs;
-					}).map(results -> {
-						boolean allowed = results.get(0) == 1L;
-						Long tokensLeft = results.get(1);
+			return flux.onErrorResume(throwable -> {
+				if (log.isDebugEnabled()) {
+					log.debug("Error calling rate limiter lua", throwable);
+				}
+				return Flux.just(Arrays.asList(1L, -1L));
+			}).reduce(new ArrayList<Long>(), (longs, l) -> {
+				longs.addAll(l);
+				return longs;
+			}).map(results -> {
+				boolean allowed = results.get(0) == 1L;
+				Long tokensLeft = results.get(1);
 
-						Response response = new Response(allowed,
-								getHeaders(routeConfig, tokensLeft));
+				Response response = new Response(allowed,
+						getHeaders(routeConfig, tokensLeft));
 
-						if (log.isDebugEnabled()) {
-							log.debug("response: " + response);
-						}
-						return response;
-					});
+				if (log.isDebugEnabled()) {
+					log.debug("response: " + response);
+				}
+				return response;
+			});
 		}
 		catch (Exception e) {
 			/*
@@ -345,7 +349,7 @@ public class RedisRateLimiter extends AbstractRateLimiter<RedisRateLimiter.Confi
 		@Min(1)
 		private int replenishRate;
 
-		@Min(1)
+		@Min(0)
 		private int burstCapacity = 1;
 
 		@Min(1)
diff --git a/spring-cloud-gateway-core/src/main/resources/META-INF/scripts/request_rate_limiter.lua b/spring-cloud-gateway-core/src/main/resources/META-INF/scripts/request_rate_limiter.lua
index ee7a7334..de316dd2 100644
--- a/spring-cloud-gateway-core/src/main/resources/META-INF/scripts/request_rate_limiter.lua
+++ b/spring-cloud-gateway-core/src/main/resources/META-INF/scripts/request_rate_limiter.lua
@@ -44,7 +44,10 @@ end
 --redis.log(redis.LOG_WARNING, "allowed_num " .. allowed_num)
 --redis.log(redis.LOG_WARNING, "new_tokens " .. new_tokens)
 
-redis.call("setex", tokens_key, ttl, new_tokens)
-redis.call("setex", timestamp_key, ttl, now)
+if ttl > 0 then
+  redis.call("setex", tokens_key, ttl, new_tokens)
+  redis.call("setex", timestamp_key, ttl, now)
+end
 
+-- return { allowed_num, new_tokens, capacity, filled_tokens, requested, new_tokens }
 return { allowed_num, new_tokens }
diff --git a/spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiterTests.java b/spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiterTests.java
index 7636a858..9c2eb087 100644
--- a/spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiterTests.java
+++ b/spring-cloud-gateway-core/src/test/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiterTests.java
@@ -104,6 +104,24 @@ public class RedisRateLimiterTests extends BaseWebClientTests {
 		checkLimitEnforced(id, replenishRate, burstCapacity, requestedTokens, routeId);
 	}
 
+	@Test
+	public void redisRateLimiterWorksForZeroBurstCapacity() throws Exception {
+		String id = UUID.randomUUID().toString();
+
+		int replenishRate = 1;
+		int burstCapacity = 0;
+		int requestedTokens = 1;
+
+		String routeId = "zero_burst_capacity_route";
+		rateLimiter.getConfig().put(routeId,
+				new RedisRateLimiter.Config().setBurstCapacity(burstCapacity)
+						.setReplenishRate(replenishRate)
+						.setRequestedTokens(requestedTokens));
+
+		Response response = rateLimiter.isAllowed(routeId, id).block();
+		assertThat(response.isAllowed()).isFalse();
+	}
+
 	@Test
 	public void keysUseRedisKeyHashTags() {
 		assertThat(RedisRateLimiter.getKeys("1")).containsExactly(