feat(config): add configurable packet channel buffer size

- Add PacketBufferSize field to api.Config struct
- Add DefaultPacketBuffer constant (1000 packets)
- Add JA4SENTINEL_PACKET_BUFFER_SIZE environment variable support
- Update mergeConfigs to handle PacketBufferSize override
- Update main.go to use configurable buffer size with fallback
- Update config.yml.example with packet_buffer_size option

Allows tuning for high-traffic environments by increasing buffer size
via config file or environment variable

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

api/types.go

@@ -13,10 +13,11 @@ type ServiceLog struct {
 
 // Config holds basic network and TLS configuration
 type Config struct {
-	Interface      string   `json:"interface"`
-	ListenPorts    []uint16 `json:"listen_ports"`
-	BPFFilter      string   `json:"bpf_filter,omitempty"`
-	FlowTimeoutSec int      `json:"flow_timeout_sec,omitempty"` // Timeout for TLS handshake extraction (default: 30)
+	Interface        string   `json:"interface"`
+	ListenPorts      []uint16 `json:"listen_ports"`
+	BPFFilter        string   `json:"bpf_filter,omitempty"`
+	FlowTimeoutSec   int      `json:"flow_timeout_sec,omitempty"` // Timeout for TLS handshake extraction (default: 30)
+	PacketBufferSize int      `json:"packet_buffer_size,omitempty"` // Buffer size for packet channel (default: 1000)
 }
 
 // IPMeta contains IP metadata for stack fingerprinting
@@ -238,10 +239,11 @@ func joinStringSlice(slice []string, sep string) string {
 // Default values and constants
 
 const (
-	DefaultInterface   = "eth0"
-	DefaultPort        = 443
-	DefaultBPFFilter   = ""
-	DefaultFlowTimeout = 30 // seconds
+	DefaultInterface     = "eth0"
+	DefaultPort          = 443
+	DefaultBPFFilter     = ""
+	DefaultFlowTimeout   = 30 // seconds
+	DefaultPacketBuffer  = 1000 // packet channel buffer size
 
 	// Logging levels
 	LogLevelDebug = "DEBUG"
@@ -252,15 +254,17 @@ const (
 
 // DefaultConfig returns an AppConfig with sensible default values.
 // Uses eth0 as the default interface, port 443 for monitoring,
-// no BPF filter, and a 30-second flow timeout. Returns an empty
-// outputs slice (caller must configure outputs explicitly).
+// no BPF filter, a 30-second flow timeout, and a 1000-packet
+// channel buffer. Returns an empty outputs slice (caller must
+// configure outputs explicitly).
 func DefaultConfig() AppConfig {
 	return AppConfig{
 		Core: Config{
-			Interface:      DefaultInterface,
-			ListenPorts:    []uint16{DefaultPort},
-			BPFFilter:      DefaultBPFFilter,
-			FlowTimeoutSec: DefaultFlowTimeout,
+			Interface:        DefaultInterface,
+			ListenPorts:      []uint16{DefaultPort},
+			BPFFilter:        DefaultBPFFilter,
+			FlowTimeoutSec:   DefaultFlowTimeout,
+			PacketBufferSize: DefaultPacketBuffer,
 		},
 		Outputs: []OutputConfig{},
 	}