2 files changed, 57 insertions, 2 deletions

diff --git a/internal/file/file.go b/internal/file/file.go
index b95d40b..8510b61 100644
--- a/internal/file/file.go
+++ b/internal/file/file.go
@@ -56,7 +56,12 @@ func NewFdWithPid(fd int32, pid uint32) *FdFile {
 		return f
 	}
 
-	f.flags, _ = readFlagsFromFdInfo(fd, pid)
+	flags, err := readFlagsFromFdInfo(fd, pid)
+	if err != nil {
+		f.flags = unknownFlag
+	} else {
+		f.flags = flags
+	}
 	f.flagsFromProcFS = true
 
 	return f
@@ -73,6 +78,10 @@ func readFlagsFromFdInfo(fd int32, pid uint32) (Flags, error) {
 	if err != nil {
 		return unknownFlag, err
 	}
+	return parseFlagsFromFdInfo(data)
+}
+
+func parseFlagsFromFdInfo(data []byte) (Flags, error) {
 	scanner := bufio.NewScanner(bytes.NewReader(data))
 	for scanner.Scan() {
 		line := scanner.Text()
@@ -82,7 +91,10 @@ func readFlagsFromFdInfo(fd int32, pid uint32) (Flags, error) {
 			return Flags(flags), err
 		}
 	}
-	return unknownFlag, scanner.Err()
+	if err := scanner.Err(); err != nil {
+		return unknownFlag, err
+	}
+	return unknownFlag, fmt.Errorf("flags field not found in fdinfo")
 }
 
 func (f *FdFile) Name() string {
diff --git a/internal/file/file_test.go b/internal/file/file_test.go
index f9025fe..744f37e 100644
--- a/internal/file/file_test.go
+++ b/internal/file/file_test.go
@@ -1,6 +1,7 @@
 package file
 
 import (
+	"bytes"
 	"strings"
 	"syscall"
 	"testing"
@@ -107,3 +108,45 @@ func TestFdFileDup(t *testing.T) {
 		t.Errorf("expected duped String() to NOT contain old fd 1, got '%s'", duped.String())
 	}
 }
+
+func TestParseFlagsFromFdInfo(t *testing.T) {
+	t.Run("valid flags", func(t *testing.T) {
+		flags, err := parseFlagsFromFdInfo([]byte("pos:\t0\nflags:\t0100002\nmnt_id:\t24\n"))
+		if err != nil {
+			t.Fatalf("parseFlagsFromFdInfo valid err = %v", err)
+		}
+		if flags != Flags(0o100002) {
+			t.Fatalf("parseFlagsFromFdInfo valid flags = %v, want %v", flags, Flags(0o100002))
+		}
+	})
+
+	t.Run("invalid octal", func(t *testing.T) {
+		flags, err := parseFlagsFromFdInfo([]byte("flags:\tnot-octal\n"))
+		if err == nil {
+			t.Fatalf("parseFlagsFromFdInfo invalid octal expected error")
+		}
+		if flags != 0 {
+			t.Fatalf("parseFlagsFromFdInfo invalid octal flags = %v, want 0", flags)
+		}
+	})
+
+	t.Run("missing flags", func(t *testing.T) {
+		flags, err := parseFlagsFromFdInfo([]byte("pos:\t0\nmnt_id:\t24\n"))
+		if err == nil {
+			t.Fatalf("parseFlagsFromFdInfo missing flags expected error")
+		}
+		if flags != unknownFlag {
+			t.Fatalf("parseFlagsFromFdInfo missing flags = %v, want %v", flags, unknownFlag)
+		}
+	})
+
+	t.Run("scanner error", func(t *testing.T) {
+		flags, err := parseFlagsFromFdInfo(bytes.Repeat([]byte("x"), 128*1024))
+		if err == nil {
+			t.Fatalf("parseFlagsFromFdInfo scanner error expected error")
+		}
+		if flags != unknownFlag {
+			t.Fatalf("parseFlagsFromFdInfo scanner error flags = %v, want %v", flags, unknownFlag)
+		}
+	})
+}