feat: add file saving

internal/transport/problem.go

@@ -9,6 +9,7 @@ import (
 	"google.golang.org/grpc/status"
 	"google.golang.org/protobuf/types/known/emptypb"
 	"io"
+	"os"
 )
 
 func (s *TesterServer) CreateProblem(server problemv1.ProblemService_CreateProblemServer) error {
@@ -36,7 +37,12 @@ func (s *TesterServer) CreateProblem(server problemv1.ProblemService_CreateProbl
 
 	ch := readChunks(ctx, server)
 
-	id, err := s.problemService.CreateProblem(ctx, p, ch)
+	err = writeChunks(ctx, ch) // temp stub
+	if err != nil {
+		return err // FIXME
+	}
+
+	id, err := s.problemService.CreateProblem(ctx, p, nil) // FIXME
 	if err != nil {
 		return status.Errorf(codes.Unknown, "") // FIXME
 	}
@@ -51,6 +57,28 @@ func (s *TesterServer) CreateProblem(server problemv1.ProblemService_CreateProbl
 	return nil
 }
 
+func writeChunks(ctx context.Context, chunks <-chan []byte) error {
+	// FIXME: use ctx?
+	f, err := os.Create("out.txt") // FIXME: uuidv4 as initial temp name?
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	var off int64 = 0
+	for chunk := range chunks {
+		_, err = f.WriteAt(chunk, off)
+		if err != nil {
+			return err
+		}
+
+		off += int64(len(chunk))
+	}
+
+	// TODO: rename file to its hash
+	return nil
+}
+
 func readChunks(ctx context.Context, server problemv1.ProblemService_CreateProblemServer) <-chan []byte {
 	ch := make(chan []byte)