cspot: delayed Pong (like librespot) stops the 6-minute connection resets

The Spotify AP reset the connection (recv -1, errno 104 ECONNRESET) on the third Ping, every 6 minutes, like clockwork. cspot answered each Ping at once; librespot (core/src/session.rs) waits 60 s: Ping -> 60 s -> Pong -> PongAck -> 60 s -> Ping. - 0003-delayed-pong: record the Ping, send the Pong 60 s later from triggerTimeout() (called on every 3 s receive timeout), through the PR #3 connection snapshot; dropped on reconnect. - 0002-diag-log-recv-errors: log recv's return value/errno before "Error in read" (error path only); this is what showed the RST. Verified: over 8+ minutes Ping/delayed Pong/PongAck every 2 min, no reset at the 6-minute mark. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-09-25 20:47:27 +10:00
parent 8008aa175f
commit 5ce4588c80
2 changed files with 89 additions and 0 deletions
@@ -0,0 +1,15 @@
+diff --git a/cspot/src/PlainConnection.cpp b/cspot/src/PlainConnection.cpp
+index 1bff6cf..b4ee6ff 100644
+--- a/cspot/src/PlainConnection.cpp
+++ b/cspot/src/PlainConnection.cpp
+@@ -150,6 +150,10 @@ void PlainConnection::readBlock(const uint8_t* dst, size_t size) {
+         case EINTR:
+           break;
+         default:
+          // diagnostic (project patch): n == 0 means the peer closed (FIN); n < 0 with errno
+          // e.g. ECONNRESET (RST). Note errno is not updated when n == 0.
+          CSPOT_LOG(error, "recv returned %d, errno %d, %u of %u bytes, retry %d", (int)n,
+                    getErrno(), idx, (unsigned)size, retries);
+           if (retries++ > 4)
+             throw std::runtime_error("Error in read");
+           goto READ;
@@ -0,0 +1,74 @@
+Keep-alive like librespot (core/src/session.rs): the server sends a Ping every ~2 min; send
+the Pong 60 s later, not at once. With an immediate Pong the server reset the AP connection
+(ECONNRESET) on the third Ping, i.e. every 6 minutes, and the Spotify app lost the device.
+
+--- a/cspot/include/MercurySession.h
+++ b/cspot/include/MercurySession.h
+@@ -120,6 +120,14 @@
+ 
+   unsigned long long timestampDiff;
+   unsigned long long lastPingTimestamp = -1;
+
+  // Keep-alive as librespot does it: Ping -> wait 60 s -> Pong -> PongAck. Answering at once made
+  // the server reset the connection on the third Ping (every 6 minutes).
+  const int PONG_DELAY_MS = 60 * 1000;
+  bool pongPending = false;
+  unsigned long long pongDueTimestamp = 0;
+  std::vector<uint8_t> pongData;
+  void sendPendingPong();
+   std::string countryCode = "";
+ 
+   std::mutex isRunningMutex;
+--- a/cspot/src/MercurySession.cpp
+++ b/cspot/src/MercurySession.cpp
+@@ -45,7 +45,10 @@
+         timeProvider->syncWithPingPacket(packet.data);
+ 
+         this->lastPingTimestamp = timeProvider->getSyncedTimestamp();
+-        this->shanConn->sendPacket(0x49, packet.data);
+        // Pong 60 s later (sent from triggerTimeout(), called on every 3 s receive timeout)
+        this->pongData = packet.data;
+        this->pongDueTimestamp = this->lastPingTimestamp + PONG_DELAY_MS;
+        this->pongPending = true;
+       } else {
+         this->packetQueue.push(packet);
+       }
+@@ -80,6 +83,7 @@
+     BELL_SLEEP_MS(100);
+ 
+     lastPingTimestamp = timeProvider->getSyncedTimestamp();
+    pongPending = false;    // a Ping on the old connection needs no Pong on the new one
+     isReconnecting = false;
+ 
+     this->executeEstabilishedCallback = true;
+@@ -98,9 +102,30 @@
+   this->connectionReadyCallback = callback;
+ }
+ 
+void MercurySession::sendPendingPong() {
+  if (!pongPending ||
+      timeProvider->getSyncedTimestamp() < pongDueTimestamp)
+    return;
+  pongPending = false;
+  std::shared_ptr<ShannonConnection> shanConn;
+  {
+    std::scoped_lock lock(connMutex);
+    shanConn = this->shanConn;
+  }
+  if (!shanConn)
+    return;
+  try {
+    shanConn->sendPacket(0x49, pongData);
+    CSPOT_LOG(info, "Sent delayed Pong");
+  } catch (...) {
+    CSPOT_LOG(error, "Failed to send Pong");
+  }
+}
+
+ bool MercurySession::triggerTimeout() {
+   if (!isRunning)
+     return true;
+  sendPendingPong();
+   auto currentTimestamp = timeProvider->getSyncedTimestamp();
+ 
+   if (currentTimestamp - this->lastPingTimestamp > PING_TIMEOUT_MS) {