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Merged
mikhailm-coder merged 2 commits into from
Jul 29, 2026
+24 −6
Merged

Add exponential backoff on all mesh agent control-channel retry paths #74

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87d0a45
Add exponential backoff on all control-channel retry paths
mikhailm-coder Jul 28, 2026
ada2099
Enforce backoff floor on short sessions and clamp jitter overshoot at…
mikhailm-coder Jul 29, 2026
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26 changes: 21 additions & 5 deletions meshcore/agentcore.c
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,8 @@ int gRemoteMouseRenderDefault = 0;
#define SCRIPT_ENGINE_PIPE_BUFFER_SIZE 65535
#define SERVER_DISCOVERY_BUFFER_SIZE 1024
#define CONTROL_CHANNEL_LOG_THROTTLE_MS 600000 //!< Steady-state control-channel dial/failure logging throttle (10 min); target changes still log immediately
#define MESH_BACKOFF_STABLE_SESSION_MS 60000 //!< An authenticated session must live this long before its drop resets the reconnect backoff
#define MESH_BACKOFF_MIN_RETRY_MS 2000 //!< Floor for the halved backoff after a short-lived authenticated session

#define MESH_AGENT_PORT 16990 //!< Default Mesh Agent Port
#define MESH_MCASTv4_GROUP "239.255.255.235"
Expand Down Expand Up @@ -3020,6 +3022,7 @@ void MeshServer_ServerAuthenticated(ILibWebClient_StateObject WebStateObject, Me
if (agent->serverAuthState == 3)
{
printf("Server fully authenticated (authState=3)\n");
agent->authTick = ILibGetUptime();
ILibDuktape_MeshAgent_PUSH(agent->meshCoreCtx, agent->chain); // [agent]
duk_get_prop_string(agent->meshCoreCtx, -1, "emit"); // [agent][emit]
duk_swap_top(agent->meshCoreCtx, -2); // [emit][this]
Expand Down Expand Up @@ -3101,7 +3104,6 @@ void MeshServer_SendAgentInfo(MeshAgentHostContainer* agent, ILibWebClient_State

// Send mesh agent information to the server
ILibWebClient_WebSocket_Send(WebStateObject, ILibWebClient_WebSocket_DataType_BINARY, (char*)info, sizeof(MeshCommand_BinaryPacket_AuthInfo) + hostnamelen, ILibAsyncSocket_MemoryOwnership_USER, ILibWebClient_WebSocket_FragmentFlag_Complete);
agent->retryTime = 0;

if ((agent->capabilities & MeshCommand_AuthInfo_CapabilitiesMask_RECOVERY) == MeshCommand_AuthInfo_CapabilitiesMask_RECOVERY)
{
Expand Down Expand Up @@ -4128,6 +4130,9 @@ void MeshServer_OnResponse(ILibWebClient_StateObject WebStateObject, int Interru
}

agent->controlChannel = WebStateObject; // Set the agent MeshCentral server control channel
// A live connection makes any pending retry/lockout timer stale; drop it so a later disconnect schedules against fresh backoff state.
ILibLifeTime_Remove(ILibGetBaseTimer(agent->chain), agent);
agent->retryTimerPending = 0;
printf("Control channel established [fd=%d]\n", ILibWebClient_GetDescriptorValue_FromStateObject(WebStateObject));
printf("Connection: WebSocket upgrade successful (fd=%d), starting handshake authentication\n", ILibWebClient_GetDescriptorValue_FromStateObject(WebStateObject));
ILibRemoteLogging_printf(ILibChainGetLogger(agent->chain), ILibRemoteLogging_Modules_Agent_GuardPost | ILibRemoteLogging_Modules_ConsolePrint, ILibRemoteLogging_Flags_VerbosityLevel_1, "Control Channel Idle Timeout = %d seconds", agent->controlChannel_idleTimeout_seconds);
Expand Down Expand Up @@ -4223,6 +4228,10 @@ void MeshServer_OnResponse(ILibWebClient_StateObject WebStateObject, int Interru
// Post-auth drop is a rare, meaningful state change (a healthy session closing) - always log it.
printf("Connection LOST: Disconnected after authentication (fd=%d) - server closed connection\n",
ILibWebClient_GetDescriptorValue_FromStateObject(WebStateObject));
// Only a session that stayed authenticated for a while proves the server healthy enough to reset backoff; a short-lived one halves it, never below the floor.
if (agent->authTick != 0 && (ILibGetUptime() - agent->authTick) >= MESH_BACKOFF_STABLE_SESSION_MS) { agent->retryTime = 0; }
else { agent->retryTime = (agent->retryTime > 2 * MESH_BACKOFF_MIN_RETRY_MS) ? (agent->retryTime / 2) : MESH_BACKOFF_MIN_RETRY_MS; }
agent->authTick = 0;
}
if (agent->controlChannelDebug != 0)
{
Expand Down Expand Up @@ -4368,7 +4377,8 @@ void MeshServer_ConnectEx_NetworkError(void *j)
agent->serverConnectionState = 0;

ILibWebClient_CancelRequest(request);
MeshServer_ConnectEx(agent);
// CancelRequest normally fired OnResponse->MeshServer_Connect synchronously; this fallback coalesces to a no-op but guarantees forward progress.
MeshServer_Connect(agent);
}
void MeshServer_ConnectEx_NetworkError_Cleanup(void *j)
{
Expand Down Expand Up @@ -4437,6 +4447,8 @@ void MeshServer_ConnectEx(MeshAgentHostContainer *agent)


memset(&meshServer, 0, sizeof(struct sockaddr_in6));
// Must clear before the re-entry guard, or a guard-blocked stale timer would strand the flag and block all future retry scheduling.
agent->retryTimerPending = 0;
if (agent->timerLogging != 0 && agent->retryTimerSet != 0)
{
agent->retryTimerSet = 0;
Expand Down Expand Up @@ -5010,18 +5022,22 @@ void MeshServer_Connect(MeshAgentHostContainer *agent)
else
{
int delay;
if (agent->retryTime >= 240000)
// A retry timer is already scheduled (e.g. by the cancel-induced OnResponse); coalesce instead of double-scheduling.
if (agent->retryTimerPending != 0) { return; }
if (agent->retryTime >= 480000)
{
// Cap at around 4 minutes
delay = 240000 + (timeout % 120000); // Random value between 4 and 6 minutes
// Cap at around 8 minutes
delay = 480000 + (timeout % 120000); // Random value between 8 and 10 minutes
}
else
{
delay = agent->retryTime + (timeout % agent->retryTime); // Random value between current value and double the current value
if (delay >= 480000) { delay = 480000 + (timeout % 120000); } // Never let the last doubling overshoot the 8-10 minute cap
}
// Throttle the offline-retry-loop spam: only log the retry schedule on cycles the throttle decided to log.
if (agent->controlChannelLogThisAttempt != 0) { printf("AutoRetry Connect in %d milliseconds\n", delay); }
if (agent->timerLogging != 0) { agent->retryTimerSet = 1; }
agent->retryTimerPending = 1;
ILibLifeTime_AddEx(ILibGetBaseTimer(agent->chain), agent, delay, (ILibLifeTime_OnCallback)MeshServer_ConnectEx, NULL);
agent->retryTime = delay;
}
Expand Down
4 changes: 3 additions & 1 deletion meshcore/agentcore.h
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Original file line number Diff line number Diff line change
Expand Up @@ -253,7 +253,9 @@ typedef struct MeshAgentHostContainer
int serverAuthState;

int timerLogging;
int retryTimerSet;
int retryTimerSet; // timerLogging diagnostic only
int retryTimerPending; // a scheduled ConnectEx retry timer is pending; coalesces MeshServer_Connect calls
long long authTick; // uptime (ms) when full server auth completed; 0 when not authenticated
int controlChannel_idleTimeout_seconds;
int controlChannel_idleTimeout_dataMode;
char g_selfid[UTIL_SHA384_HASHSIZE];
Expand Down
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