[#128] downloader: Simplify detecting the Content-Type from payload

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

downloader/reader_test.go

@@ -1,8 +1,6 @@
 package downloader
 
 import (
-	"bytes"
-	"fmt"
 	"io"
 	"strings"
 	"testing"
@@ -10,40 +8,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestReader(t *testing.T) {
-	data := []byte("test string")
-	err := fmt.Errorf("something wrong")
-
-	for _, tc := range []struct {
-		err  error
-		buff []byte
-	}{
-		{err: nil, buff: make([]byte, len(data)+1)},
-		{err: nil, buff: make([]byte, len(data))},
-		{err: nil, buff: make([]byte, len(data)-1)},
-		{err: err, buff: make([]byte, len(data)+1)},
-		{err: err, buff: make([]byte, len(data))},
-		{err: err, buff: make([]byte, len(data)-1)},
-	} {
-		var res []byte
-		var err error
-		var n int
-
-		r := newReader(data, tc.err)
-		for err == nil {
-			n, err = r.Read(tc.buff)
-			res = append(res, tc.buff[:n]...)
-		}
-
-		if tc.err == nil {
-			require.Equal(t, io.EOF, err)
-		} else {
-			require.Equal(t, tc.err, err)
-		}
-		require.Equal(t, data, res)
-	}
-}
-
 func TestDetector(t *testing.T) {
 	txtContentType := "text/plain; charset=utf-8"
 	sb := strings.Builder{}
@@ -68,19 +32,15 @@ func TestDetector(t *testing.T) {
 		},
 	} {
 		t.Run(tc.Name, func(t *testing.T) {
-			detector := newDetector()
+			contentType, data, err := readContentType(uint64(len(tc.Expected)),
+				func(sz uint64) (io.Reader, error) {
+					return strings.NewReader(tc.Expected), nil
+				},
+			)
 
-			go func() {
-				detector.SetReader(bytes.NewBufferString(tc.Expected))
-				detector.Detect()
-			}()
-
-			detector.Wait()
-			require.Equal(t, tc.ContentType, detector.contentType)
-
-			data, err := io.ReadAll(detector.MultiReader())
 			require.NoError(t, err)
-			require.Equal(t, tc.Expected, string(data))
+			require.Equal(t, tc.ContentType, contentType)
+			require.True(t, strings.HasPrefix(tc.Expected, string(data)))
 		})
 	}
 }