[#73] Uploader, downloader structures refactoring

Signed-off-by: Marina Biryukova <m.biryukova@yadro.com>

internal/handler/reader_test.go

@@ -0,0 +1,48 @@
+//go:build !integration
+
+package handler
+
+import (
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDetector(t *testing.T) {
+	txtContentType := "text/plain; charset=utf-8"
+	sb := strings.Builder{}
+	for i := 0; i < 10; i++ {
+		sb.WriteString("Some txt content. Content-Type must be detected properly by detector.")
+	}
+
+	for _, tc := range []struct {
+		Name        string
+		ContentType string
+		Expected    string
+	}{
+		{
+			Name:        "less than 512b",
+			ContentType: txtContentType,
+			Expected:    sb.String()[:256],
+		},
+		{
+			Name:        "more than 512b",
+			ContentType: txtContentType,
+			Expected:    sb.String(),
+		},
+	} {
+		t.Run(tc.Name, func(t *testing.T) {
+			contentType, data, err := readContentType(uint64(len(tc.Expected)),
+				func(sz uint64) (io.Reader, error) {
+					return strings.NewReader(tc.Expected), nil
+				},
+			)
+
+			require.NoError(t, err)
+			require.Equal(t, tc.ContentType, contentType)
+			require.True(t, strings.HasPrefix(tc.Expected, string(data)))
+		})
+	}
+}