From 8825cf0838553fd8ddb14a357d0176e3c2074e2b Mon Sep 17 00:00:00 2001
From: ospab <ospab@ospab.host>
Date: Sat, 30 May 2026 22:21:12 +0300
Subject: [PATCH] fix: resolve deadlock, multiplexing backpressure, and LTE
 fragmentation issues

---
 ostp-client/src/bridge.rs                              |  4 ++--
 ostp-client/src/config.rs                              |  2 +-
 ostp-core/src/protocol.rs                              | 10 +++++-----
 .../kotlin/com/ospab/ostp_client/OstpVpnService.kt     |  2 +-
 4 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/ostp-client/src/bridge.rs b/ostp-client/src/bridge.rs
index 748c586..30c25e9 100644
--- a/ostp-client/src/bridge.rs
+++ b/ostp-client/src/bridge.rs
@@ -617,8 +617,8 @@ impl Bridge {
                     }
                 }
                 proxy_ev = proxy_rx.recv(), if self.running && sessions_opt.as_ref().map(|s| {
-                    // Backpressure: suspend proxy reads when ARQ window is saturated
-                    s.iter().all(|ses| ses.machine.in_flight_count() < ses.machine.cwnd_packets().clamp(16, 16384))
+                    // Backpressure: suspend proxy reads when ARQ window is saturated across ALL sessions
+                    s.iter().any(|ses| ses.machine.in_flight_count() < ses.machine.cwnd_packets().clamp(16, 16384))
                 }).unwrap_or(true) => {
                     if let Some(ev) = proxy_ev {
                         if let Some(sessions) = sessions_opt.as_mut() {
diff --git a/ostp-client/src/config.rs b/ostp-client/src/config.rs
index 3bab864..e9db5df 100644
--- a/ostp-client/src/config.rs
+++ b/ostp-client/src/config.rs
@@ -58,7 +58,7 @@ pub struct OstpConfig {
 
 fn default_keepalive() -> u64 { 5 }
 
-fn default_mtu() -> usize { 1500 }
+fn default_mtu() -> usize { 1140 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct LocalProxyConfig {
diff --git a/ostp-core/src/protocol.rs b/ostp-core/src/protocol.rs
index 463186b..5dc6b0b 100644
--- a/ostp-core/src/protocol.rs
+++ b/ostp-core/src/protocol.rs
@@ -557,9 +557,6 @@ impl ProtocolMachine {
         // Limit retransmits per tick to prevent bandwidth saturation
         let mut retransmit_budget: usize = self.cc.retransmit_budget();
         for frame in self.sent_history.iter_mut() {
-            if retransmit_budget == 0 {
-                break;
-            }
             if !frame.is_retransmittable {
                 continue;
             }
@@ -571,8 +568,11 @@ impl ProtocolMachine {
             if now.duration_since(frame.last_sent) >= effective_rto {
                 frame.last_sent = now;
                 frame.retries = frame.retries.saturating_add(1);
-                actions.push(ProtocolAction::SendDatagram(frame.bytes.clone()));
-                retransmit_budget -= 1;
+                
+                if retransmit_budget > 0 {
+                    actions.push(ProtocolAction::SendDatagram(frame.bytes.clone()));
+                    retransmit_budget -= 1;
+                }
             }
         }
 
diff --git a/ostp-flutter/android/app/src/main/kotlin/com/ospab/ostp_client/OstpVpnService.kt b/ostp-flutter/android/app/src/main/kotlin/com/ospab/ostp_client/OstpVpnService.kt
index 2f774f3..09cbdf1 100644
--- a/ostp-flutter/android/app/src/main/kotlin/com/ospab/ostp_client/OstpVpnService.kt
+++ b/ostp-flutter/android/app/src/main/kotlin/com/ospab/ostp_client/OstpVpnService.kt
@@ -161,7 +161,7 @@ class OstpVpnService : VpnService() {
                 .addRoute("0.0.0.0", 0)
                 .addRoute("::", 0)
                 .addDnsServer(dnsServer)
-                .setMtu(json.optJSONObject("ostp")?.optInt("mtu", 1280) ?: 1280)
+                .setMtu(json.optJSONObject("ostp")?.optInt("mtu", 1140) ?: 1140)
                 
             try { builder.addDnsServer("8.8.8.8") } catch (e: Throwable) {}