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fix: chunk large Docker container lists to prevent WebSocket message loss #304

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fix: chunk large Docker container lists to prevent WebSocket message loss #304

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cf853b1
fix: chunk large Docker container lists to prevent WebSocket message …
jaydeep-pipaliya Apr 9, 2026
82523a0
fix: add batchId to chunked container messages for concurrency safety
jaydeep-pipaliya Apr 9, 2026
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63 changes: 49 additions & 14 deletions main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -177,6 +177,51 @@ var (
configFile string
)

// maxContainersPerChunk is the maximum number of containers per WebSocket message.
// Each container with full metadata (labels, ports, networks) can be 1-5KB of JSON.
// 15 containers ≈ 15-75KB which is well within typical proxy frame limits.
const maxContainersPerChunk = 15

// sendContainerList sends a list of Docker containers to the server, chunking if necessary
// to avoid exceeding WebSocket message size limits that can cause data loss through proxies.
// Each chunked batch includes a unique batchId so the server can distinguish interleaved sends
// (e.g., a manual fetch and a Docker event firing concurrently).
func sendContainerList(client *websocket.Client, containers []docker.Container) error {
if len(containers) <= maxContainersPerChunk {
// Small list — send in a single non-chunked message (backward compatible)
return client.SendMessage("newt/socket/containers", map[string]interface{}{
"containers": containers,
})
}

// Generate a unique batch ID so the server can handle concurrent chunk streams
batchId := generateChainId()

totalChunks := (len(containers) + maxContainersPerChunk - 1) / maxContainersPerChunk
logger.Info("Sending %d containers in %d chunks (batch=%s)", len(containers), totalChunks, batchId)

for i := 0; i < len(containers); i += maxContainersPerChunk {
end := i + maxContainersPerChunk
if end > len(containers) {
end = len(containers)
}
chunkIndex := i / maxContainersPerChunk

err := client.SendMessage("newt/socket/containers", map[string]interface{}{
"containers": containers[i:end],
"chunkIndex": chunkIndex,
"totalChunks": totalChunks,
"batchId": batchId,
})
if err != nil {
return fmt.Errorf("failed to send chunk %d/%d (batch=%s): %w", chunkIndex+1, totalChunks, batchId, err)
}
logger.Debug("Sent chunk %d/%d (%d containers, batch=%s)", chunkIndex+1, totalChunks, end-i, batchId)
}

return nil
}

// generateChainId generates a random chain ID for deduplicating round-trip messages.
func generateChainId() string {
b := make([]byte, 8)
Expand Down Expand Up @@ -1462,15 +1507,8 @@ persistent_keepalive_interval=5`, util.FixKey(privateKey.String()), util.FixKey(
return
}

// Send container list back to server
err = client.SendMessage("newt/socket/containers", map[string]interface{}{
"containers": containers,
})
if err != nil {
logger.Error("Failed to send registration message: %v", err)
}

if err != nil {
// Send container list back to server (chunked for large lists)
if err := sendContainerList(client, containers); err != nil {
logger.Error("Failed to send Docker container list: %v", err)
} else {
logger.Debug("Docker container list sent, count: %d", len(containers))
Expand Down Expand Up @@ -1883,12 +1921,9 @@ persistent_keepalive_interval=5`, util.FixKey(privateKey.String()), util.FixKey(
if dockerSocket != "" {
logger.Debug("Initializing Docker event monitoring")
dockerEventMonitor, err = docker.NewEventMonitor(dockerSocket, dockerEnforceNetworkValidationBool, func(containers []docker.Container) {
// Send updated container list via websocket when Docker events occur
// Send updated container list via websocket when Docker events occur (chunked for large lists)
logger.Debug("Docker event detected, sending updated container list (%d containers)", len(containers))
err := client.SendMessage("newt/socket/containers", map[string]interface{}{
"containers": containers,
})
if err != nil {
if err := sendContainerList(client, containers); err != nil {
logger.Error("Failed to send updated container list after Docker event: %v", err)
} else {
logger.Debug("Updated container list sent successfully")
Expand Down