Set the right content type for files in multipart requests

file.go

@@ -2,9 +2,12 @@ package httptest
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"mime/multipart"
 	"net/http"
+	"net/textproto"
+	"strings"
 )
 
 type File struct {
@@ -29,19 +32,35 @@ func (r *Request) MultiPartPut(body interface{}, files ...File) (*Response, erro
 	return r.Perform(req), nil
 }
 
+var quoteEscaper = strings.NewReplacer("\\", "\\\\", `"`, "\\\"")
+
+func escapeQuotes(s string) string {
+	return quoteEscaper.Replace(s)
+}
+
 // this helper method was inspired by this blog post by Matt Aimonetti:
 // https://matt.aimonetti.net/posts/2013/07/01/golang-multipart-file-upload-example/
 func newMultipart(url string, method string, body interface{}, files ...File) (*http.Request, error) {
-
 	bb := &bytes.Buffer{}
 	writer := multipart.NewWriter(bb)
 	defer writer.Close()
 	for _, f := range files {
-		part, err := writer.CreateFormFile(f.ParamName, f.FileName)
+		fBuffer, err := io.ReadAll(f)
+		if err != nil {
+			return nil, err
+		}
+
+		h := make(textproto.MIMEHeader)
+		h.Set("Content-Disposition",
+			fmt.Sprintf(`form-data; name="%s"; filename="%s"`,
+				escapeQuotes(f.ParamName), escapeQuotes(f.FileName)))
+		h.Set("Content-Type", http.DetectContentType(fBuffer))
+		part, err := writer.CreatePart(h)
 		if err != nil {
 			return nil, err
 		}
-		_, err = io.Copy(part, f)
+		fReader := bytes.NewReader(fBuffer)
+		_, err = io.Copy(part, fReader)
 		if err != nil {
 			return nil, err
 		}

file_test.go

@@ -1,7 +1,8 @@
 package httptest
 
 import (
-	"os"
+	"fmt"
+	"github.com/gobuffalo/httptest/testassets"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -11,20 +12,27 @@ func Test_FileUpload(t *testing.T) {
 	r := require.New(t)
 	w := New(App())
 
-	f := struct {
-		Name string
-	}{"Foo"}
+	foo := func(filename, expectedType string) {
+		f := struct {
+			Name string
+		}{"Foo"}
 
-	rr, err := os.Open("./file_test.go")
-	r.NoError(err)
-	wf := File{
-		ParamName: "MyFile",
-		FileName:  "foo.go",
-		Reader:    rr,
+		rr, err := testassets.FS.Open(filename)
+		r.NoError(err)
+		wf := File{
+			ParamName: "MyFile",
+			FileName:  filename,
+			Reader:    rr,
+		}
+		res, err := w.HTML("/up").MultiPartPost(f, wf)
+		r.NoError(err)
+		r.Equal(200, res.Code)
+		r.Equal(fmt.Sprintf("Foo\n%s\n%s\n", filename, expectedType), res.Body.String())
 	}
 
-	res, err := w.HTML("/up").MultiPartPost(f, wf)
-	r.NoError(err)
-	r.Equal(200, res.Code)
-	r.Equal("Foo\nfoo.go\n", res.Body.String())
+	foo("test.jpg", "image/jpeg")
+	foo("test.png", "image/png")
+	foo("test.pdf", "application/pdf")
+	foo("embed.go", "text/plain; charset=utf-8")
+	foo("random.bin", "application/octet-stream")
 }

httptest_test.go

@@ -95,6 +95,7 @@ func App() http.Handler {
 		}
 		fmt.Fprintln(res, req.FormValue("Name"))
 		fmt.Fprintln(res, h.Filename)
+		fmt.Fprintln(res, h.Header.Get("Content-Type"))
 	})
 	return p
 }

testassets/embed.go

@@ -0,0 +1,8 @@
+package testassets
+
+import (
+	"embed"
+)
+
+//go:embed *
+var FS embed.FS

testassets/random.bin

@@ -0,0 +1 @@
+�>#�n���-p8