diff options
Diffstat (limited to 'ws.go')
| -rw-r--r-- | ws.go | 106 |
1 files changed, 64 insertions, 42 deletions
@@ -125,7 +125,7 @@ func handleWs(w http.ResponseWriter, req *http.Request) { } return } else if err != nil { - err := writeText(req.Context(), c, "E :Database error") + err := writeText(req.Context(), c, "E :Database error while selecting session") if err != nil { log.Println(err) } @@ -327,60 +327,82 @@ func handleConn( } courseID := int(_courseID) course := courses[courseID] - /* - * TODO: Ensure that the user is not already enrolled in this course - * and pay attention to relevant race conditions. It might be useful - * to restructure this part, to begin a transaction that adds the user - * to the database (and check the (currently not existing) uniqueness) - * constraint at that exact moment, and abort the transaction if the - * course limit is exceeded. - * Or perhaps choices should be also stored in an internal data - * structure, though that requires extra attention on consistency - * issues between the internal data structure and the database. - * (Sometime I should really go fix the LMDB bindings...) - */ - ok := false - func() { - course.SelectedLock.Lock() - defer course.SelectedLock.Unlock() - if course.Selected < course.Max { - course.Selected++ - go propagateCouldFail(fmt.Sprintf("N %d %d", courseID, course.Selected)) - ok = true - return + + err = func() error { + tx, err := db.Begin(ctx) + if err != nil { + err := writeText(ctx, c, "R "+mar[1]+" :Database error while beginning transaction") + if err != nil { + return fmt.Errorf("error rejecting based on database error: %w", err) + } + return nil } - ok = false - }() - if ok { - _, err = db.Exec( + defer func() { + err := tx.Rollback(ctx) + if err != nil && (!errors.Is(err, pgx.ErrTxClosed)) { + err := writeText(ctx, c, "R "+mar[1]+" :Database error while rolling back transaction due to deferred return") + if err != nil { + log.Printf("error fejecting based on database error: %v", err) /* TODO: Handle this better */ + } + } + }() + + _, err = tx.Exec( ctx, /* TODO: Do we really want this to be in a request context? */ "INSERT INTO choices (seltime, userid, courseid) VALUES ($1, $2, $3)", time.Now().UnixMicro(), userID, courseID, - /* TODO: Set uniqueness constraint for each (userid, courseid) pair */ ) if err != nil { - go func() { /* Separate goroutine because we don't need a response from this operation */ - course.SelectedLock.Lock() - defer course.SelectedLock.Unlock() - course.Selected-- - propagateCouldFail(fmt.Sprintf("N %d %d", courseID, course.Selected)) - }() - err := writeText(ctx, c, "R "+mar[1]+" :Database error") /* TODO: Handle this better */ + /* TODO: Handle uniqueness constraint as a special case */ + err := writeText(ctx, c, "R "+mar[1]+" :Database error while inserting course choice") if err != nil { return fmt.Errorf("error rejecting course choice: %w", err) } + return nil } - err := writeText(ctx, c, "Y "+mar[1]) - if err != nil { - return fmt.Errorf("error affirming course choice: %w", err) - } - } else { - err := writeText(ctx, c, "R "+mar[1]+" :Full") - if err != nil { - return fmt.Errorf("error rejecting course choice: %w", err) + + ok := func() bool { + course.SelectedLock.Lock() + defer course.SelectedLock.Unlock() + if course.Selected < course.Max { + course.Selected++ + go propagateCouldFail(fmt.Sprintf("N %d %d", courseID, course.Selected)) + return true + } + return false + }() + + if ok { + err := tx.Commit(ctx) + if err != nil { + err := writeText(ctx, c, "R "+mar[1]+" :Database error while committing transaction") + if err != nil { + return fmt.Errorf("error fejecting based on database error: %w", err) + } + } + err = writeText(ctx, c, "Y "+mar[1]) + if err != nil { + return fmt.Errorf("error affirming course choice: %w", err) + } + } else { + err := tx.Rollback(ctx) + if err != nil { + err := writeText(ctx, c, "R "+mar[1]+" :Database error while rolling back transaction due to course limit") + if err != nil { + return fmt.Errorf("error fejecting based on database error: %w", err) + } + } + err = writeText(ctx, c, "R "+mar[1]+" :Full") + if err != nil { + return fmt.Errorf("error rejecting course choice: %w", err) + } } + return nil + }() + if err != nil { + return err } case "N": if len(mar) != 2 { |