debug: add an mtree.Debugf and -debug flag

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

cmd/gomtree/main.go

@@ -23,6 +23,8 @@ var (
 	flListKeywords = flag.Bool("list-keywords", false, "List the keywords available")
 	flResultFormat = flag.String("result-format", "bsd", "output the validation results using the given format (bsd, json, path)")
 	flTar          = flag.String("T", "", "use tar archive to create or validate a directory hierarchy spec")
+
+	flDebug = flag.Bool("debug", false, "output debug info to STDERR")
 )
 
 var formats = map[string]func(*mtree.Result) string{
@@ -57,6 +59,10 @@ var formats = map[string]func(*mtree.Result) string{
 func main() {
 	flag.Parse()
 
+	if *flDebug {
+		os.Setenv("DEBUG", "1")
+	}
+
 	// so that defers cleanly exec
 	var isErr bool
 	defer func() {

debug.go

@@ -0,0 +1,18 @@
+package mtree
+
+import (
+	"fmt"
+	"os"
+	"time"
+)
+
+// DebugOutput is the where DEBUG output is written
+var DebugOutput = os.Stderr
+
+// Debugf does formatted output to DebugOutput, only if DEBUG environment variable is set
+func Debugf(format string, a ...interface{}) (n int, err error) {
+	if os.Getenv("DEBUG") != "" {
+		return fmt.Fprintf(DebugOutput, "[%d] [DEBUG] %s\n", time.Now().UnixNano(), fmt.Sprintf(format, a...))
+	}
+	return 0, nil
+}

keywords.go

@@ -185,7 +185,8 @@ var (
 		// The pattern for this keyword key is prefixed by "xattr." followed by the extended attribute "namespace.key".
 		// The keyword value is the SHA1 digest of the extended attribute's value.
 		// In this way, the order of the keys does not matter, and the contents of the value is not revealed.
-		"xattr": xattrKeywordFunc,
+		"xattr":  xattrKeywordFunc,
+		"xattrs": xattrKeywordFunc,
 	}
 )
 

keywords_linux.go

@@ -1,5 +1,3 @@
-// +build linux
-
 package mtree
 
 import (