Cache empty results on the failure schedule.

okhttp/src/commonJvmAndroid/kotlin/okhttp3/internal/dns/RealDnsCache.kt

@@ -205,9 +205,18 @@ class RealDnsCache(
         val previous = entry.state.get()
         val sentAt = previous.inFlightCall!!.sentAt
         val timeToLive =
-          (dnsResponse.answers.minOfOrNull { it.timeToLive } ?: 0)
-            .seconds
-            .coerceIn(minimumTimeToLive, maximumTimeToLive)
+          when {
+            dnsResponse.answers.isEmpty() -> {
+              failureTimeToLive
+            }
+
+            else -> {
+              dnsResponse.answers
+                .minOf { it.timeToLive }
+                .seconds
+                .coerceIn(minimumTimeToLive, maximumTimeToLive)
+            }
+          }
         val revalidateDelay = (timeToLive - revalidateBeforeExpire).coerceAtLeast(0.seconds)
 
         val next =

okhttp/src/commonTest/kotlin/okhttp3/internal/dns/StateMachineDnsCallTest.kt

@@ -738,6 +738,67 @@ class StateMachineDnsCallTest {
       assertThat(cache.hitCount).isEqualTo(0)
     }
 
+  @Test
+  fun `empty result expires on the same schedule as failure`() =
+    testStateMachineDnsCall {
+      val call0 =
+        newCall(
+          request = Dns.Request(hostname = "lysine.dev"),
+          caching = true,
+          includeIPv6 = false,
+          includeServiceMetadata = false,
+        )
+      call0.enqueue()
+      queryFactory.respondToQuery(
+        hostname = "lysine.dev",
+        type = TYPE_A,
+        addresses = listOf(),
+      )
+      call0.takeOnRecordsIpAddresses(
+        last = true,
+        addresses = listOf(),
+      )
+
+      // The empty result is still cached.
+      val call1 =
+        newCall(
+          request = Dns.Request(hostname = "lysine.dev"),
+          caching = true,
+          includeIPv6 = false,
+          includeServiceMetadata = false,
+        )
+      call1.enqueue()
+      call1.takeOnRecordsIpAddresses(
+        last = true,
+        addresses = listOf(),
+      )
+
+      // The empty result expires after 5 seconds.
+      sleep(5.seconds)
+      val call2 =
+        newCall(
+          request = Dns.Request(hostname = "lysine.dev"),
+          caching = true,
+          includeIPv6 = false,
+          includeServiceMetadata = false,
+        )
+      call2.enqueue()
+      queryFactory.respondToQuery(
+        hostname = "lysine.dev",
+        type = TYPE_A,
+        addresses = blueIpv4s,
+      )
+      call2.takeOnRecordsIpAddresses(
+        last = true,
+        addresses = blueIpv4s,
+      )
+
+      assertThat(cache.size).isEqualTo(1)
+      assertThat(cache.requestCount).isEqualTo(3)
+      assertThat(cache.networkCount).isEqualTo(2)
+      assertThat(cache.hitCount).isEqualTo(1)
+    }
+
   @Test
   fun `failure is revalidated`() =
     testStateMachineDnsCall {