1 files changed, 171 insertions, 0 deletions
diff --git a/ws_utils.go b/ws_utils.go
new file mode 100644
index 0000000..949863f
--- /dev/null
+++ b/ws_utils.go
@@ -0,0 +1,171 @@
+/*
+ * WebSocket auxiliary functions
+ *
+ * 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"
+	"fmt"
+	"log"
+	"sync/atomic"
+
+	"github.com/coder/websocket"
+)
+
+/*
+ * The message format is a WebSocket message separated with spaces.
+ * The contents of each field could contain anything other than spaces,
+ * The first character of each argument cannot be a colon. As an exception, the
+ * last argument may contain spaces and the first character thereof may be a
+ * colon, if the argument is prefixed with a colon. The colon used for the
+ * prefix is not considered part of the content of the message. For example, in
+ *
+ *    SQUISH POP :cat purr!!
+ *
+ * the first field is "SQUISH", the second field is "POP", and the third
+ * field is "cat purr!!".
+ *
+ * It is essentially an RFC 1459 IRC message without trailing CR-LF and
+ * without prefixes. See section 2.3.1 of RFC 1459 for an approximate
+ * BNF representation.
+ *
+ * The reason this was chosen instead of using protobuf etc. is that it
+ * is simple to parse without external libraries, and it also happens to
+ * be a format I'm very familiar with, having extensively worked with the
+ * IRC protocol.
+ */
+
+/*
+ * Split an IRC-style message of type []byte into type []string where each
+ * element is a complete argument. Generally, arguments are separated by
+ * spaces, and an argument that begins with a ':' causes the rest of the
+ * line to be treated as a single argument.
+ */
+func splitMsg(b *[]byte) []string {
+	mar := make([]string, 0, config.Perf.MessageArgumentsCap)
+	elem := make([]byte, 0, config.Perf.MessageBytesCap)
+	for i, c := range *b {
+		switch c {
+		case ' ':
+			if (*b)[i+1] == ':' {
+				mar = append(mar, string(elem))
+				mar = append(mar, string((*b)[i+2:]))
+				goto endl
+			}
+			mar = append(mar, string(elem))
+			elem = make([]byte, 0, config.Perf.MessageBytesCap)
+		default:
+			elem = append(elem, c)
+		}
+	}
+	mar = append(mar, string(elem))
+endl:
+	return mar
+}
+
+func baseReportError(
+	ctx context.Context,
+	conn *websocket.Conn,
+	e string,
+) error {
+	err := writeText(ctx, conn, "E :"+e)
+	if err != nil {
+		return fmt.Errorf("error reporting protocol violation: %w", err)
+	}
+	err = conn.Close(websocket.StatusProtocolError, e)
+	if err != nil {
+		return fmt.Errorf("error closing websocket: %w", err)
+	}
+	return nil
+}
+
+type reportErrorT func(e string) error
+
+func makeReportError(ctx context.Context, conn *websocket.Conn) reportErrorT {
+	return func(e string) error {
+		return baseReportError(ctx, conn, e)
+	}
+}
+
+func propagateSelectedUpdate(course *courseT) {
+	course.Usems.Range(func(key, value interface{}) bool {
+		_ = key
+		usem, ok := value.(*usemT)
+		if !ok {
+			panic("Usems contains non-\"*usemT\" value")
+		}
+		usem.set()
+		return true
+	})
+}
+
+func sendSelectedUpdate(
+	ctx context.Context,
+	conn *websocket.Conn,
+	courseID int,
+) error {
+	_course, ok := courses.Load(courseID)
+	if !ok {
+		return fmt.Errorf("%w: %d", errNoSuchCourse, courseID)
+	}
+	course, ok := _course.(*courseT)
+	if !ok {
+		panic("courses map has non-\"*courseT\" items")
+	}
+	if course == nil {
+		return fmt.Errorf("%w: %d", errNoSuchCourse, courseID)
+	}
+	selected := atomic.LoadUint32(&course.Selected)
+	err := writeText(ctx, conn, fmt.Sprintf("M %d %d", courseID, selected))
+	if err != nil {
+		return fmt.Errorf(
+			"error sending to websocket for course selected update: %w",
+			err,
+		)
+	}
+	return nil
+}
+
+func propagate(msg string) {
+	chanPool.Range(func(_userID, _ch interface{}) bool {
+		ch, ok := _ch.(*chan string)
+		if !ok {
+			panic("chanPool has non-\"*chan string\" key")
+		}
+		select {
+		case *ch <- msg:
+		default:
+			userID, ok := _userID.(string)
+			if !ok {
+				panic("chanPool has non-string key")
+			}
+			log.Println("WARNING: SendQ exceeded for " + userID)
+		}
+		return true
+	})
+}
+
+func writeText(ctx context.Context, c *websocket.Conn, msg string) error {
+	err := c.Write(ctx, websocket.MessageText, []byte(msg))
+	if err != nil {
+		return fmt.Errorf("%w: %w", errWebSocketWrite, err)
+	}
+	return nil
+}