Bugfixes, add INFO command, graceful shutdown. elimitate dead code

- Remove unsed handleClientKill, handleClientKill
- Fix misleading error message on rate limit
- Eliminated unused channel-to-pattern index that was causing unnecessary work
- Fixed O(n²) duplicate check in PublishToPattern
- Limit total pattern subscriptions to 10,000
- Limit channel subscriptions per client to 10,000
- Added INFO command
- Added graceful shutdown timeout
- Validate that log directory is writable during config load
- Make SELECT properly handle whitespace around DB index like Redis
- Return proper error instead of empty array for unsupported commands on sharded pubsub stubs
- More accurate error messages throughout
- Updated README.md

internal/config/config.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"path/filepath"
 	"strconv"
 	"time"
 
@@ -15,27 +16,29 @@ import (
 
 // Constants for default values - chosen to be production-ready defaults
 const (
-	DefaultBind         = "0.0.0.0"
-	DefaultPort         = 6379
-	DefaultMaxClients   = 10000
-	DefaultReadTimeout  = 0                 // 0 means no timeout (blocking I/O)
-	DefaultWriteTimeout = 0                 // 0 means no timeout
-	DefaultMaxMsgBytes  = 512 * 1024 * 1024 // 512 MB - allows large messages
-	DefaultLogLevel     = "info"
-	DefaultLogFile      = "" // empty = stdout only
-	DefaultPidFile      = "" // empty = no PID file created
+	DefaultBind            = "0.0.0.0"
+	DefaultPort            = 6379
+	DefaultMaxClients      = 10000
+	DefaultReadTimeout     = 0                 // 0 means no timeout (blocking I/O)
+	DefaultWriteTimeout    = 0                 // 0 means no timeout
+	DefaultMaxMsgBytes     = 512 * 1024 * 1024 // 512 MB - allows large messages
+	DefaultLogLevel        = "info"
+	DefaultLogFile         = "" // empty = stdout only
+	DefaultPidFile         = "" // empty = no PID file created
+	DefaultShutdownTimeout = 30 // 30 seconds grace period for shutdown
 )
 
 type Config struct {
-	Bind         string `json:"bind"`
-	Port         int    `json:"port"`
-	MaxClients   int    `json:"max_clients"`
-	ReadTimeout  int    `json:"read_timeout"`  // in seconds, 0 = no timeout
-	WriteTimeout int    `json:"write_timeout"` // in seconds, 0 = no timeout
-	MaxMsgBytes  int    `json:"max_message_bytes"`
-	LogLevel     string `json:"log_level"`
-	LogFile      string `json:"log_file"` // empty = stdout only
-	PidFile      string `json:"pid_file"` // empty = no PID file
+	Bind            string `json:"bind"`
+	Port            int    `json:"port"`
+	MaxClients      int    `json:"max_clients"`
+	ReadTimeout     int    `json:"read_timeout"`  // in seconds, 0 = no timeout
+	WriteTimeout    int    `json:"write_timeout"` // in seconds, 0 = no timeout
+	MaxMsgBytes     int    `json:"max_message_bytes"`
+	LogLevel        string `json:"log_level"`
+	LogFile         string `json:"log_file"`         // empty = stdout only
+	PidFile         string `json:"pid_file"`         // empty = no PID file
+	ShutdownTimeout int    `json:"shutdown_timeout"` // in seconds, 0 = wait forever (not recommended)
 }
 
 // SetDefaults applies sensible defaults when config values are missing or invalid.
@@ -69,6 +72,9 @@ func (c *Config) SetDefaults() {
 	if c.PidFile == "" {
 		c.PidFile = DefaultPidFile
 	}
+	if c.ShutdownTimeout <= 0 {
+		c.ShutdownTimeout = DefaultShutdownTimeout
+	}
 }
 
 // Validate checks that all configuration values are within acceptable bounds.
@@ -99,6 +105,37 @@ func (c *Config) Validate() error {
 	if !validLevels[c.LogLevel] {
 		return fmt.Errorf("invalid log_level: %s (must be debug, info, warn, or error)", c.LogLevel)
 	}
+	// Validate log file directory is writable
+	if c.LogFile != "" {
+		dir := filepath.Dir(c.LogFile)
+		if err := testWriteDir(dir); err != nil {
+			return fmt.Errorf("log_file: %w", err)
+		}
+	}
+	// Validate shutdown timeout is non-negative
+	if c.ShutdownTimeout < 0 {
+		return fmt.Errorf("shutdown_timeout must be non-negative")
+	}
+	return nil
+}
+
+// testWriteDir checks if a directory is writable by trying to create a temp file
+func testWriteDir(dir string) error {
+	// If directory doesn't exist, check parent
+	if _, err := os.Stat(dir); os.IsNotExist(err) {
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			return fmt.Errorf("directory does not exist: %s", dir)
+		}
+		return testWriteDir(parent)
+	}
+	// Directory exists - try to create a temp file
+	tmp, err := os.CreateTemp(dir, ".pekoe_test_")
+	if err != nil {
+		return fmt.Errorf("directory not writable: %s", dir)
+	}
+	_ = tmp.Close()
+	_ = os.Remove(tmp.Name())
 	return nil
 }