ignore irregular files while indexing directory (#616)

* stop hidding  command from help doc

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* do not index irregular files

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* fix fixture dir and err name

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* improve the description of irregular files

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* explicitly check indexed file name

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

syft/source/directory_resolver_test.go

@@ -1,10 +1,13 @@
 package source
 
 import (
+	"io/ioutil"
 	"os"
 	"path"
+	"path/filepath"
 	"reflect"
 	"strings"
+	"syscall"
 	"testing"
 
 	"github.com/scylladb/go-set/strset"
@@ -459,3 +462,29 @@ func Test_directoryResolver_FilesByMIMEType(t *testing.T) {
 		})
 	}
 }
+
+func Test_ignoreIrregularFiles(t *testing.T) {
+	// NOTE: craeting a pipe/fifo file on demand since git doesn't let me
+	// commit one. The directory resolver should ignore it (and any other
+	// file that is neither regular, a symlink or directory) when indexing a directory
+	dir := "./test-fixtures/irregular-files"
+	f := "f.fifo"
+
+	err := syscall.Mknod(filepath.Join(dir, f), syscall.S_IFIFO|0666, 0)
+	assert.NoError(t, err)
+	defer func() {
+		err := os.Remove(filepath.Join(dir, f))
+		assert.NoError(t, err)
+	}()
+
+	fileRefs, err := ioutil.ReadDir(dir)
+	assert.NoError(t, err)
+	assert.Len(t, fileRefs, 2) // two files (f.fifo and readme)
+
+	resolver, err := newDirectoryResolver(dir)
+	assert.NoError(t, err)
+
+	assert.Len(t, resolver.fileTree.AllFiles(), 1)
+	rp := resolver.fileTree.AllFiles()[0].RealPath
+	assert.True(t, strings.Contains(string(rp), filepath.Join(dir, "readme")))
+}