From 495059b92e393d2e7a2910ac5bf1660b308487a3 Mon Sep 17 00:00:00 2001
From: Mikhail <misha_mst@mail.ru>
Date: Fri, 15 May 2026 00:49:28 +0300
Subject: [PATCH] Harden Android VPN uplink transient retries

---
 clients/android/app/build.gradle              |  4 +-
 .../java/su/cin/rapvpn/RapVpnService.java     | 42 +++++++++++++++----
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/clients/android/app/build.gradle b/clients/android/app/build.gradle
index 73ca0bf..23d3402 100644
--- a/clients/android/app/build.gradle
+++ b/clients/android/app/build.gradle
@@ -30,8 +30,8 @@ android {
         applicationId "su.cin.rapvpn"
         minSdk 26
         targetSdk 35
-        versionCode 183
-        versionName "0.2.183"
+        versionCode 184
+        versionName "0.2.184"
         buildConfigField "String", "DEFAULT_BACKEND_URL", "\"${normalizeGradleString(defaultBackendUrl)}\""
         buildConfigField "String", "DEFAULT_CLUSTER_ID", "\"${normalizeGradleString(defaultClusterId)}\""
         buildConfigField "String", "DEFAULT_ORGANIZATION_ID", "\"${normalizeGradleString(defaultOrganizationId)}\""
diff --git a/clients/android/app/src/main/java/su/cin/rapvpn/RapVpnService.java b/clients/android/app/src/main/java/su/cin/rapvpn/RapVpnService.java
index 400a489..67eec8b 100644
--- a/clients/android/app/src/main/java/su/cin/rapvpn/RapVpnService.java
+++ b/clients/android/app/src/main/java/su/cin/rapvpn/RapVpnService.java
@@ -33,6 +33,7 @@ import java.util.ArrayList;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ArrayBlockingQueue;
@@ -60,6 +61,9 @@ public class RapVpnService extends VpnService {
     private static final int PRIORITY_QUEUE_CAPACITY = 4096;
     private static final int UPLINK_SEND_RETRY_COUNT = 2;
     private static final int UPLINK_SEND_RETRY_SLEEP_MS = 80;
+    private static final int UPLINK_TRANSIENT_RETRY_COUNT = 10;
+    private static final int UPLINK_TRANSIENT_RETRY_SLEEP_MS = 250;
+    private static final int UPLINK_TRANSIENT_RETRY_MAX_SLEEP_MS = 1500;
     private static final int DOWNLINK_QUEUE_CAPACITY = 8192;
     private static final int DOWNLINK_FLOW_QUEUE_MAX_COUNT = 8;
     private static final int DOWNLINK_QUEUE_OFFER_MS = 50;
@@ -2475,18 +2479,28 @@ public class RapVpnService extends VpnService {
                 return true;
             }
             RapApiClient client = packetRelayClientForUrl(relayUrl);
-            for (int attempt = 0; attempt <= UPLINK_SEND_RETRY_COUNT && running; attempt++) {
+            int attempt = 0;
+            while (running) {
                 try {
-                client.sendClientPacketBatch(clusterId, vpnConnectionId, batch);
-                if (attempt > 0) {
-                    writeRuntimeDetail("retry_ok", "uplink retry ok worker=" + workerIndex + " relay=" + relayUrl + " attempt=" + attempt + " batch=" + batch.size(), "uplink_sender", -1, -1, "", workerIndex);
-                }
-                return true;
+                    client.sendClientPacketBatch(clusterId, vpnConnectionId, batch);
+                    if (attempt > 0) {
+                        writeRuntimeDetail("retry_ok", "uplink retry ok worker=" + workerIndex + " relay=" + relayUrl + " attempt=" + attempt + " batch=" + batch.size(), "uplink_sender", -1, -1, "", workerIndex);
+                    }
+                    return true;
                 } catch (Exception e) {
                     lastError = e;
                     lastUplinkSendErrorMessage = compactException(e);
                     writeRuntimeDetail("retry", "uplink send retry worker=" + workerIndex + " relay=" + relayUrl + " attempt=" + attempt + " error=" + lastUplinkSendErrorMessage, "uplink_sender", -1, -1, e.getClass().getSimpleName(), workerIndex);
-                    sleepQuietly(UPLINK_SEND_RETRY_SLEEP_MS * (attempt + 1L));
+                    boolean transientError = isTransientUplinkSendError(e);
+                    int retryLimit = transientError ? UPLINK_TRANSIENT_RETRY_COUNT : UPLINK_SEND_RETRY_COUNT;
+                    if (attempt >= retryLimit) {
+                        break;
+                    }
+                    int baseSleepMs = transientError ? UPLINK_TRANSIENT_RETRY_SLEEP_MS : UPLINK_SEND_RETRY_SLEEP_MS;
+                    int maxSleepMs = transientError ? UPLINK_TRANSIENT_RETRY_MAX_SLEEP_MS : UPLINK_SEND_RETRY_SLEEP_MS * (UPLINK_SEND_RETRY_COUNT + 1);
+                    long sleepMs = Math.min(maxSleepMs, baseSleepMs * (attempt + 1L));
+                    sleepQuietly(sleepMs);
+                    attempt++;
                 }
             }
             if (!switchPacketRelayUrl(relayUrl, lastError == null ? "send_failed" : lastError.getClass().getSimpleName())) {
@@ -2499,6 +2513,20 @@ public class RapVpnService extends VpnService {
         return false;
     }
 
+    private boolean isTransientUplinkSendError(Exception e) {
+        String message = e == null ? null : e.getMessage();
+        if (message == null) {
+            return false;
+        }
+        String lower = message.toLowerCase(Locale.ROOT);
+        return lower.contains("http 502")
+                || lower.contains("http 503")
+                || lower.contains("http 504")
+                || lower.contains("mesh synthetic route not found")
+                || lower.contains("forward runtime unavailable")
+                || lower.contains("forward peer unavailable");
+    }
+
     private boolean sendUplinkBatchOverWebSocket(String relayUrl, String clusterId, String vpnConnectionId, List<byte[]> batch, int workerIndex) {
         if (!PACKET_WEBSOCKET_DATAPLANE_ENABLED) {
             return false;