From ef7873c1b31570fb67bec30a1346b4f136b49a7c Mon Sep 17 00:00:00 2001
From: Matthew Meacham <mmeacham@palantir.com>
Date: Mon, 30 Aug 2021 12:12:31 -0400
Subject: [PATCH] Fix bug that can prevent fast-polling clients from ever
 getting data again

---
 .../main/java/org/opensky/api/OpenSkyApi.java | 11 ++++++--
 java/src/test/java/TestOpenSkyApi.java        | 27 +++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/java/src/main/java/org/opensky/api/OpenSkyApi.java b/java/src/main/java/org/opensky/api/OpenSkyApi.java
index 27fc909..97db652 100644
--- a/java/src/main/java/org/opensky/api/OpenSkyApi.java
+++ b/java/src/main/java/org/opensky/api/OpenSkyApi.java
@@ -136,8 +136,15 @@ private OpenSkyStates getResponse(String baseUri, Collection<AbstractMap.Entry<S
 	private boolean checkRateLimit(REQUEST_TYPE type, long timeDiffAuth, long timeDiffNoAuth) {
 		Long t = lastRequestTime.get(type);
 		long now = System.currentTimeMillis();
-		lastRequestTime.put(type, now);
-		return (t == null || (authenticated && now - t > timeDiffAuth) || (!authenticated && now - t > timeDiffNoAuth));
+		boolean mayIssueRequest = t == null
+				|| (authenticated && now - t > timeDiffAuth)
+				|| (!authenticated && now - t > timeDiffNoAuth);
+		if (mayIssueRequest) {
+			// Optimistically update the last request time if the client can actually issue a request. If the request
+			// fails, we don't want to immediately retry anyway
+			lastRequestTime.put(type, now);
+		}
+		return mayIssueRequest;
 	}
 
 	/**
diff --git a/java/src/test/java/TestOpenSkyApi.java b/java/src/test/java/TestOpenSkyApi.java
index ef4ae86..0b7ba4d 100644
--- a/java/src/test/java/TestOpenSkyApi.java
+++ b/java/src/test/java/TestOpenSkyApi.java
@@ -153,4 +153,31 @@ public void testAuthGetMyStates() throws IOException {
 		}
 	}
 
+	@Test
+	public void testClientSideRateLimitingDoesNotLockClient() throws IOException, InterruptedException {
+		// If the client is requesting too fast, ensure it doesn't prevent requests from occurring after the
+		// rate limiting expires
+		OpenSkyApi api = new OpenSkyApi();
+		OpenSkyStates os = api.getStates(0, null);
+		assertTrue("More than 1 state vector", os.getStates().size() > 1);
+		int initialTime = os.getTime();
+
+		// Simulate frequently-requesting client
+		long startTime = System.currentTimeMillis();
+		while (startTime + 8000L > System.currentTimeMillis()) {
+			OpenSkyStates states = api.getStates(0, null);
+			assertNull("Client-side rate limited, should not receive data", states);
+			Thread.sleep(100L);
+		}
+
+		// Wait a few more seconds (but less than anon rate limit frequency)
+		Thread.sleep(5000L);
+
+		// It's been ~13s since our initial request, we should be able to request again as an anonymous caller
+		os = api.getStates(0, null);
+		assertNotNull(os);
+		assertTrue("More than 1 state vector for second valid request", os.getStates().size() > 1);
+		assertNotEquals("Second request should be different", initialTime, os.getTime());
+	}
+
 }