Method udpPacketLoop

proxy/serverudp.go:85–123

udpPacketLoop listens for incoming UDP packets. See also the comment on Proxy.requestsSema.

(ctx context.Context, conn *net.UDPConn, reqSema syncutil.Semaphore)

//
// See also the comment on Proxy.requestsSema.
func (p *Proxy) udpPacketLoop(ctx context.Context, conn *net.UDPConn, reqSema syncutil.Semaphore) {
	p.logger.InfoContext(ctx, "entering udp listener loop", "addr", conn.LocalAddr())

	b := make([]byte, dns.MaxMsgSize)
	for p.isStarted() {
		n, localIP, remoteAddr, err := proxynetutil.UDPRead(conn, b, p.udpOOBSize)
		// The documentation says to handle the packet even if err occurs.
		if n > 0 {
			// Make a copy of all bytes because ReadFrom() will overwrite the
			// contents of b on the next call.  We need that contents to sustain
			// the call because we're handling them in goroutines.
			packet := make([]byte, n)
			copy(packet, b)

			sErr := reqSema.Acquire(ctx)
			if sErr != nil {
				p.logger.ErrorContext(
					ctx,
					"acquiring semaphore",
					"proto", ProtoUDP,
					slogutil.KeyError, sErr,
				)

				break
			}
			go func() {
				defer reqSema.Release()

				p.udpHandlePacket(ctx, packet, localIP, remoteAddr, conn)
			}()
		}

		if err != nil {
			logUDPConnError(err, conn, p.logger)

			break
		}
	}
}

// logUDPConnError writes suitable log message for given err.
func logUDPConnError(err error, conn *net.UDPConn, l *slog.Logger) {