Make uploads content seekable

docs/content/reference/scalars.md

@@ -35,7 +35,7 @@ Maps a `Upload` GraphQL scalar to a `graphql.Upload` struct, defined as follows:
 
 ```go
 type Upload struct {
-	File        io.Reader
+	File        io.ReadSeeker
 	Filename    string
 	Size        int64
 	ContentType string

graphql/handler/transport/http_form.go

@@ -132,7 +132,7 @@ func (f MultipartForm) Do(w http.ResponseWriter, r *http.Request, exec graphql.G
 			}
 			for _, path := range paths {
 				upload = graphql.Upload{
-					File:        &bytesReader{s: &fileBytes, i: 0, prevRune: -1},
+					File:        &bytesReader{s: &fileBytes, i: 0},
 					Size:        int64(len(fileBytes)),
 					Filename:    filename,
 					ContentType: contentType,

graphql/handler/transport/reader.go

@@ -6,9 +6,8 @@ import (
 )
 
 type bytesReader struct {
-	s        *[]byte
-	i        int64 // current reading index
-	prevRune int   // index of previous rune; or < 0
+	s *[]byte
+	i int64 // current reading index
 }
 
 func (r *bytesReader) Read(b []byte) (n int, err error) {
@@ -18,8 +17,29 @@ func (r *bytesReader) Read(b []byte) (n int, err error) {
 	if r.i >= int64(len(*r.s)) {
 		return 0, io.EOF
 	}
-	r.prevRune = -1
 	n = copy(b, (*r.s)[r.i:])
 	r.i += int64(n)
 	return
 }
+
+func (r *bytesReader) Seek(offset int64, whence int) (int64, error) {
+	if r.s == nil {
+		return 0, errors.New("byte slice pointer is nil")
+	}
+	var abs int64
+	switch whence {
+	case io.SeekStart:
+		abs = offset
+	case io.SeekCurrent:
+		abs = r.i + offset
+	case io.SeekEnd:
+		abs = int64(len(*r.s)) + offset
+	default:
+		return 0, errors.New("invalid whence")
+	}
+	if abs < 0 {
+		return 0, errors.New("negative position")
+	}
+	r.i = abs
+	return abs, nil
+}

graphql/handler/transport/reader_test.go

@@ -82,4 +82,46 @@ func TestBytesRead(t *testing.T) {
 		}
 		require.Equal(t, "0193456789", string(got))
 	})
+
+	t.Run("read using buffer multiple times", func(t *testing.T) {
+		data := []byte("0123456789")
+		r := bytesReader{s: &data}
+
+		got := make([]byte, 0, 11)
+		buf := make([]byte, 1)
+		for {
+			n, err := r.Read(buf)
+			if n < 0 {
+				require.Fail(t, "unexpected bytes read size")
+			}
+			got = append(got, buf[:n]...)
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				require.Fail(t, "unexpected error while reading", err.Error())
+			}
+		}
+		require.Equal(t, "0123456789", string(got))
+
+		pos, err := r.Seek(0, io.SeekStart)
+		require.NoError(t, err)
+		require.Equal(t, int64(0), pos)
+
+		got = make([]byte, 0, 11)
+		for {
+			n, err := r.Read(buf)
+			if n < 0 {
+				require.Fail(t, "unexpected bytes read size")
+			}
+			got = append(got, buf[:n]...)
+			if err != nil {
+				if err == io.EOF {
+					break
+				}
+				require.Fail(t, "unexpected error while reading", err.Error())
+			}
+		}
+		require.Equal(t, "0123456789", string(got))
+	})
 }

graphql/upload.go

@@ -6,7 +6,7 @@ import (
 )
 
 type Upload struct {
-	File        io.Reader
+	File        io.ReadSeeker
 	Filename    string
 	Size        int64
 	ContentType string