Create envutil package and refactor duplicate environment variable getters

- Created internal/envutil package with GetEnvString, GetEnvInt, and GetEnvBool utilities
- Added comprehensive test coverage for envutil package (46 test cases)
- Refactored flags_logging.go to use envutil (reduced from ~35 lines to ~12 lines)
- Refactored flags_difc.go to use envutil (reduced from ~9 lines to ~2 lines)
- All existing tests pass

Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Author: Copilot

internal/cmd/flags_difc.go

@@ -3,9 +3,7 @@ package cmd
 // DIFC (Decentralized Information Flow Control) related flags
 
 import (
-	"os"
-	"strings"
-
+	"github.com/github/gh-aw-mcpg/internal/envutil"
 	"github.com/spf13/cobra"
 )
 
@@ -28,11 +26,5 @@ func init() {
 // getDefaultEnableDIFC returns the default DIFC setting, checking MCP_GATEWAY_ENABLE_DIFC
 // environment variable first, then falling back to the hardcoded default (false)
 func getDefaultEnableDIFC() bool {
-	if envDIFC := os.Getenv("MCP_GATEWAY_ENABLE_DIFC"); envDIFC != "" {
-		switch strings.ToLower(envDIFC) {
-		case "1", "true", "yes", "on":
-			return true
-		}
-	}
-	return defaultEnableDIFC
+	return envutil.GetEnvBool("MCP_GATEWAY_ENABLE_DIFC", defaultEnableDIFC)
 }

internal/cmd/flags_logging.go

@@ -3,9 +3,7 @@ package cmd
 // Logging-related flags
 
 import (
-	"fmt"
-	"os"
-
+	"github.com/github/gh-aw-mcpg/internal/envutil"
 	"github.com/spf13/cobra"
 )
 
@@ -34,31 +32,17 @@ func init() {
 // getDefaultLogDir returns the default log directory, checking MCP_GATEWAY_LOG_DIR
 // environment variable first, then falling back to the hardcoded default
 func getDefaultLogDir() string {
-	if envLogDir := os.Getenv("MCP_GATEWAY_LOG_DIR"); envLogDir != "" {
-		return envLogDir
-	}
-	return defaultLogDir
+	return envutil.GetEnvString("MCP_GATEWAY_LOG_DIR", defaultLogDir)
 }
 
 // getDefaultPayloadDir returns the default payload directory, checking MCP_GATEWAY_PAYLOAD_DIR
 // environment variable first, then falling back to the hardcoded default
 func getDefaultPayloadDir() string {
-	if envPayloadDir := os.Getenv("MCP_GATEWAY_PAYLOAD_DIR"); envPayloadDir != "" {
-		return envPayloadDir
-	}
-	return defaultPayloadDir
+	return envutil.GetEnvString("MCP_GATEWAY_PAYLOAD_DIR", defaultPayloadDir)
 }
 
 // getDefaultPayloadSizeThreshold returns the default payload size threshold, checking
 // MCP_GATEWAY_PAYLOAD_SIZE_THRESHOLD environment variable first, then falling back to the hardcoded default
 func getDefaultPayloadSizeThreshold() int {
-	if envThreshold := os.Getenv("MCP_GATEWAY_PAYLOAD_SIZE_THRESHOLD"); envThreshold != "" {
-		// Try to parse as integer
-		var threshold int
-		if _, err := fmt.Sscanf(envThreshold, "%d", &threshold); err == nil && threshold > 0 {
-			return threshold
-		}
-		// Invalid value, use default
-	}
-	return defaultPayloadSizeThreshold
+	return envutil.GetEnvInt("MCP_GATEWAY_PAYLOAD_SIZE_THRESHOLD", defaultPayloadSizeThreshold)
 }

internal/envutil/envutil.go

@@ -0,0 +1,46 @@
+package envutil
+
+import (
+"os"
+"strconv"
+"strings"
+)
+
+// GetEnvString returns the value of the environment variable specified by envKey.
+// If the environment variable is not set or is empty, it returns the defaultValue.
+func GetEnvString(envKey, defaultValue string) string {
+if value := os.Getenv(envKey); value != "" {
+return value
+}
+return defaultValue
+}
+
+// GetEnvInt returns the integer value of the environment variable specified by envKey.
+// If the environment variable is not set, is empty, cannot be parsed as an integer,
+// or is not positive (> 0), it returns the defaultValue.
+// This function validates that the value is a positive integer.
+func GetEnvInt(envKey string, defaultValue int) int {
+if envValue := os.Getenv(envKey); envValue != "" {
+if value, err := strconv.Atoi(envValue); err == nil && value > 0 {
+return value
+}
+}
+return defaultValue
+}
+
+// GetEnvBool returns the boolean value of the environment variable specified by envKey.
+// If the environment variable is not set or is empty, it returns the defaultValue.
+// Truthy values (case-insensitive): "1", "true", "yes", "on"
+// Falsy values (case-insensitive): "0", "false", "no", "off"
+// Any other value returns the defaultValue.
+func GetEnvBool(envKey string, defaultValue bool) bool {
+if envValue := os.Getenv(envKey); envValue != "" {
+switch strings.ToLower(envValue) {
+case "1", "true", "yes", "on":
+return true
+case "0", "false", "no", "off":
+return false
+}
+}
+return defaultValue
+}