diff options
Diffstat (limited to 'wsmsg_choose.go')
| -rw-r--r-- | wsmsg_choose.go | 223 |
1 files changed, 223 insertions, 0 deletions
diff --git a/wsmsg_choose.go b/wsmsg_choose.go new file mode 100644 index 0000000..92f6453 --- /dev/null +++ b/wsmsg_choose.go @@ -0,0 +1,223 @@ +/* + * Handle the "Y" message for choosing a course + * + * Copyright (C) 2024 Runxi Yu <https://runxiyu.org> + * SPDX-License-Identifier: AGPL-3.0-or-later + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU Affero General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU Affero General Public License for more details. + * + * You should have received a copy of the GNU Affero General Public License + * along with this program. If not, see <https://www.gnu.org/licenses/>. + */ + +package main + +import ( + "context" + "errors" + "fmt" + "strconv" + "sync/atomic" + "time" + + "github.com/coder/websocket" + "github.com/jackc/pgx/v5" + "github.com/jackc/pgx/v5/pgconn" +) + +func messageChooseCourse( + ctx context.Context, + c *websocket.Conn, + reportError reportErrorT, + mar []string, + userID string, + session string, + userCourseGroups *userCourseGroupsT, +) error { + _ = session + + if atomic.LoadUint32(&state) != 2 { + err := writeText(ctx, c, "E :Course selections are not open") + if err != nil { + return fmt.Errorf( + "%w: %w", + errCannotSend, + err, + ) + } + return nil + } + + select { + case <-ctx.Done(): + return fmt.Errorf( + "%w: %w", + errContextCancelled, + ctx.Err(), + ) + default: + } + + if len(mar) != 2 { + return reportError("Invalid number of arguments for Y") + } + _courseID, err := strconv.ParseInt(mar[1], 10, strconv.IntSize) + if err != nil { + return reportError("Course ID must be an integer") + } + courseID := int(_courseID) + + _course, ok := courses.Load(courseID) + if !ok { + return reportError("no such course") + } + course, ok := _course.(*courseT) + if !ok { + panic("courses map has non-\"*courseT\" items") + } + if course == nil { + return reportError("couse is nil") + } + + if _, ok := (*userCourseGroups)[course.Group]; ok { + err := writeText(ctx, c, "R "+mar[1]+" :Group conflict") + if err != nil { + return fmt.Errorf( + "%w: %w", + errCannotSend, + err, + ) + } + return nil + } + + err = func() (returnedError error) { + tx, err := db.Begin(ctx) + if err != nil { + return reportError( + "Database error while beginning transaction", + ) + } + defer func() { + err := tx.Rollback(ctx) + if err != nil && (!errors.Is(err, pgx.ErrTxClosed)) { + returnedError = reportError( + "Database error while rolling back transaction in defer block", + ) + return + } + }() + + _, err = tx.Exec( + ctx, + "INSERT INTO choices (seltime, userid, courseid) VALUES ($1, $2, $3)", + time.Now().UnixMicro(), + userID, + courseID, + ) + if err != nil { + var pgErr *pgconn.PgError + if errors.As(err, &pgErr) && + pgErr.Code == pgErrUniqueViolation { + err := writeText(ctx, c, "Y "+mar[1]) + if err != nil { + return fmt.Errorf( + "error reaffirming course choice: %w", + err, + ) + } + return nil + } + return reportError( + "Database error while inserting course choice", + ) + } + + ok := func() bool { + course.SelectedLock.Lock() + defer course.SelectedLock.Unlock() + /* + * The read here doesn't have to be atomic because the + * lock guarantees that no other goroutine is writing to + * it. + */ + if course.Selected < course.Max { + atomic.AddUint32(&course.Selected, 1) + return true + } + return false + }() + + if ok { + go propagateSelectedUpdate(course) + err := tx.Commit(ctx) + if err != nil { + err := course.decrementSelectedAndPropagate(ctx, c) + if err != nil { + return fmt.Errorf( + "%w: %w", + errCannotSend, + err, + ) + } + return reportError( + "Database error while committing transaction", + ) + } + + /* + * This would race if message handlers could run + * concurrently for one connection. + */ + (*userCourseGroups)[course.Group] = struct{}{} + + err = writeText(ctx, c, "Y "+mar[1]) + if err != nil { + return fmt.Errorf( + "%w: %w", + errCannotSend, + err, + ) + } + + if config.Perf.PropagateImmediate { + err = sendSelectedUpdate(ctx, c, courseID) + if err != nil { + return fmt.Errorf( + "%w: %w", + errCannotSend, + err, + ) + } + } + } else { + err := tx.Rollback(ctx) + if err != nil { + return reportError( + "Database error while rolling back transaction due to course limit", + ) + } + err = writeText(ctx, c, "R "+mar[1]+" :Full") + if err != nil { + return fmt.Errorf( + "%w: %w", + errCannotSend, + err, + ) + } + } + return nil + }() + if err != nil { + return err + } + return nil +} |