From 2b3be217552ff34d0fcd927698785119763345f3 Mon Sep 17 00:00:00 2001
From: Alex Goodman <alex.goodman@anchore.com>
Date: Tue, 15 Feb 2022 18:56:04 -0500
Subject: [PATCH] empty files should have not mimetype

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>
---
 pkg/file/mime_type.go      | 22 +++++++++++++++++++++-
 pkg/file/mime_type_test.go |  6 +++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/pkg/file/mime_type.go b/pkg/file/mime_type.go
index bc308629..797a6fee 100644
--- a/pkg/file/mime_type.go
+++ b/pkg/file/mime_type.go
@@ -14,11 +14,31 @@ func MIMEType(reader io.Reader) string {
 	if reader == nil {
 		return ""
 	}
+
+	s := sizer{reader: reader}
+
 	var mTypeStr string
-	mType, err := mimetype.DetectReader(reader)
+	mType, err := mimetype.DetectReader(&s)
 	if err == nil {
 		// extract the string mimetype and ignore aux information (e.g. 'text/plain; charset=utf-8' -> 'text/plain')
 		mTypeStr = strings.Split(mType.String(), ";")[0]
 	}
+
+	// we may have a reader that is not nil but the observed contents was empty
+	if s.size == 0 {
+		return ""
+	}
+
 	return mTypeStr
 }
+
+type sizer struct {
+	reader io.Reader
+	size   int64
+}
+
+func (s *sizer) Read(p []byte) (int, error) {
+	n, err := s.reader.Read(p)
+	s.size += int64(n)
+	return n, err
+}
diff --git a/pkg/file/mime_type_test.go b/pkg/file/mime_type_test.go
index de313abf..48bbbb9c 100644
--- a/pkg/file/mime_type_test.go
+++ b/pkg/file/mime_type_test.go
@@ -1,7 +1,9 @@
 package file
 
 import (
+	"bytes"
 	"github.com/stretchr/testify/assert"
+	"io"
 	"os"
 	"testing"
 )
@@ -30,11 +32,13 @@ func Test_MIMEType(t *testing.T) {
 	}
 	for _, test := range tests {
 		t.Run(test.fixture, func(t *testing.T) {
-			var f *os.File
+			var f io.Reader
 			var err error
 			if test.fixture != "" {
 				f, err = os.Open(test.fixture)
 				assert.NoError(t, err)
+			} else {
+				f = bytes.NewReader(nil)
 			}
 			assert.Equal(t, test.expected, MIMEType(f))
 		})