fix(flags): retry DNS, TLS, and connection-refused failures on /flags

.changeset/flags-retry-transport-errors.md

@@ -0,0 +1,7 @@
+---
+'posthog': patch
+'posthog-android': patch
+'posthog-server': patch
+---
+
+Retry feature flag requests that fail with a DNS, TLS, or connection-refused transport error, instead of only timeouts, EOF, and connection resets

posthog/src/main/java/com/posthog/internal/PostHogApi.kt

@@ -22,8 +22,11 @@ import okio.BufferedSink
 import java.io.EOFException
 import java.io.IOException
 import java.io.OutputStream
+import java.net.ConnectException
 import java.net.SocketException
 import java.net.SocketTimeoutException
+import java.net.UnknownHostException
+import javax.net.ssl.SSLException
 
 /**
  * The class that calls the PostHog API
@@ -306,6 +309,9 @@ public class PostHogApi(
             is IOException ->
                 error is SocketTimeoutException ||
                     error is EOFException ||
+                    error is UnknownHostException ||
+                    error is SSLException ||
+                    error is ConnectException ||
                     (error is SocketException && error.message?.contains("reset", ignoreCase = true) == true)
             else -> false
         }

posthog/src/test/java/com/posthog/internal/PostHogApiTest.kt

@@ -20,11 +20,14 @@ import org.junit.runner.RunWith
 import org.junit.runners.Parameterized
 import java.io.File
 import java.io.IOException
+import java.net.ConnectException
 import java.net.InetSocketAddress
 import java.net.Proxy
 import java.net.SocketException
+import java.net.UnknownHostException
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicInteger
+import javax.net.ssl.SSLException
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
@@ -401,14 +404,16 @@ internal class PostHogApiTest {
         }
     }
 
-    @Test
-    fun `flags does not retry connection refused`() {
+    private fun assertFlagsRetries(
+        error: IOException,
+        expectedAttempts: Int,
+    ) {
         val attempts = AtomicInteger(0)
         val client =
             OkHttpClient.Builder()
                 .addInterceptor {
                     attempts.incrementAndGet()
-                    throw SocketException("Connection refused")
+                    throw error
                 }
                 .build()
         val http = mockHttp(response = MockResponse().setBody("{}"))
@@ -421,13 +426,33 @@ internal class PostHogApiTest {
                 sut.flags("distinctId", anonymousId = "anonId", groups = emptyMap())
             }
 
-            assertEquals(1, attempts.get())
+            assertEquals(expectedAttempts, attempts.get())
             assertEquals(0, http.requestCount)
         } finally {
             http.shutdown()
         }
     }
 
+    @Test
+    fun `flags retries connection refused`() {
+        assertFlagsRetries(ConnectException("Connection refused"), expectedAttempts = 2)
+    }
+
+    @Test
+    fun `flags retries dns resolution failures`() {
+        assertFlagsRetries(UnknownHostException("app.posthog.com"), expectedAttempts = 2)
+    }
+
+    @Test
+    fun `flags retries tls transport failures`() {
+        assertFlagsRetries(SSLException("handshake aborted"), expectedAttempts = 2)
+    }
+
+    @Test
+    fun `flags does not retry non transport IO failures`() {
+        assertFlagsRetries(IOException("unexpected end of stream"), expectedAttempts = 1)
+    }
+
     @Test
     fun `remote config returns successful response`() {
         val file = File("src/test/resources/json/basic-remote-config.json")