🐛 filsystem IsFile should return true for special unix files not just regular files (#666)

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### Description

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IsFile should return true for special unix files not just regular files

### Test Coverage

<!--
Please put an `x` in the correct box e.g. `[x]` to indicate the testing
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- [x]  This change is covered by existing or additional automated tests.
- [ ] Manual testing has been performed (and evidence provided) as
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documentation update).

Author: joshjennings98

changes/20250801151058.bugfix

@@ -0,0 +1 @@
+:bug: `filesystem` IsFile should return true for special unix files not just regular files

utils/filesystem/files.go

@@ -11,6 +11,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
 	"os/user"
 	"path/filepath"
@@ -777,7 +778,7 @@ func (fs *VFS) IsFile(path string) (result bool, err error) {
 	if err != nil {
 		return
 	}
-	result = IsRegularFile(fi)
+	result = IsRegularFile(fi) || IsSpecialFile(fi) // We want to treat special files as files (otherwise the only distinction is a directory which special files are not)
 	return
 }
 
@@ -788,6 +789,18 @@ func IsRegularFile(fi os.FileInfo) bool {
 	return fi.Mode().IsRegular()
 }
 
+// IsSpecialFile returns true for files that are not regular files. This includes: unix socket files, device files, and named pipes
+func IsSpecialFile(fi os.FileInfo) bool {
+	if fi == nil {
+		return false
+	}
+	mode := fi.Mode()
+	isSocket := mode&fs.ModeSocket != 0
+	isDevice := mode&fs.ModeDevice != 0
+	isNamedPipe := mode&fs.ModeNamedPipe != 0
+	return isSocket || isDevice || isNamedPipe
+}
+
 func (fs *VFS) IsLink(path string) (result bool, err error) {
 	err = fs.checkWhetherUnderlyingResourceIsClosed()
 	if err != nil {

utils/filesystem/files_test.go

@@ -9,6 +9,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"net"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -22,6 +23,7 @@ import (
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/unix"
 
 	"github.com/ARM-software/golang-utils/utils/collection"
 	"github.com/ARM-software/golang-utils/utils/commonerrors"
@@ -546,6 +548,61 @@ func TestConvertPaths(t *testing.T) {
 	}
 }
 
+func TestIsFile(t *testing.T) {
+	if platform.IsWindows() {
+		t.Skip("Windows doesn't have features such as named pipes or unix sockets")
+	}
+	for _, fsType := range FileSystemTypes {
+		t.Run(fmt.Sprint(fsType), func(t *testing.T) {
+			fs := NewFs(fsType)
+
+			tmpDir := t.TempDir()
+
+			t.Run("normal file", func(t *testing.T) {
+				filePath := filepath.Join(tmpDir, faker.Word())
+				err := fs.Touch(filePath)
+				require.NoError(t, err)
+				b, err := fs.IsFile(filePath)
+				require.NoError(t, err)
+				assert.True(t, b)
+			})
+
+			t.Run("special file", func(t *testing.T) {
+				if fsType == InMemoryFS {
+					t.Skip("In-memory file system won't have hardware devices or special files")
+				}
+
+				b, err := fs.IsFile("/dev/null")
+				require.NoError(t, err)
+				assert.True(t, b)
+
+				fifoPath := filepath.Join(tmpDir, faker.Word())
+				require.NoError(t, err)
+				defer func() { _ = fs.Rm(fifoPath) }()
+				err = unix.Mkfifo(fifoPath, 0666)
+				require.NoError(t, err)
+				b, err = fs.IsFile(fifoPath)
+				require.NoError(t, err)
+				assert.True(t, b)
+				err = fs.Rm(fifoPath)
+				require.NoError(t, err)
+
+				socketPath := filepath.Join(tmpDir, faker.Word())
+				require.NoError(t, err)
+				defer func() { _ = fs.Rm(socketPath) }()
+				l, err := net.Listen("unix", socketPath)
+				require.NoError(t, err)
+				defer func() { _ = l.Close() }()
+				b, err = fs.IsFile(socketPath)
+				require.NoError(t, err)
+				assert.True(t, b)
+				err = fs.Rm(socketPath)
+				require.NoError(t, err)
+			})
+		})
+	}
+}
+
 func TestLink(t *testing.T) {
 	if platform.IsWindows() {
 		fmt.Println("In order to run TestLink on Windows, Developer mode must be enabled: https://github.com/golang/go/pull/24307")