InitConnectionReceiveWindow must be at least 16384

Error message

InitConnectionReceiveWindow must be at least 16384

What it means

The 16384-byte minimum applied to the connection-level initial receive window (finalMask.quicParams.initConnectionReceiveWindow). Positive values below 16 KiB are rejected; 0 keeps the default. Connection windows must be at least as large as stream windows for QUIC flow control to function.

Source

Thrown at infra/conf/transport_internet.go:267

				if up == 0 {
					return nil, errors.New("force-brutal requires up")
				}
			default:
				return nil, errors.New("unknown congestion control: ", c.FinalMask.QuicParams.Congestion, ", valid values: reno, bbr, brutal, force-brutal")
			}

			if (c.FinalMask.QuicParams.UdpHop.Interval.From != 0 && c.FinalMask.QuicParams.UdpHop.Interval.From < 5) || (c.FinalMask.QuicParams.UdpHop.Interval.To != 0 && c.FinalMask.QuicParams.UdpHop.Interval.To < 5) {
				return nil, errors.New("Interval must be at least 5")
			}

			if c.FinalMask.QuicParams.InitStreamReceiveWindow > 0 && c.FinalMask.QuicParams.InitStreamReceiveWindow < 16384 {
				return nil, errors.New("InitStreamReceiveWindow must be at least 16384")
			}
			if c.FinalMask.QuicParams.MaxStreamReceiveWindow > 0 && c.FinalMask.QuicParams.MaxStreamReceiveWindow < 16384 {
				return nil, errors.New("MaxStreamReceiveWindow must be at least 16384")
			}
			if c.FinalMask.QuicParams.InitConnectionReceiveWindow > 0 && c.FinalMask.QuicParams.InitConnectionReceiveWindow < 16384 {
				return nil, errors.New("InitConnectionReceiveWindow must be at least 16384")
			}
			if c.FinalMask.QuicParams.MaxConnectionReceiveWindow > 0 && c.FinalMask.QuicParams.MaxConnectionReceiveWindow < 16384 {
				return nil, errors.New("MaxConnectionReceiveWindow must be at least 16384")
			}
			if c.FinalMask.QuicParams.MaxIdleTimeout != 0 && (c.FinalMask.QuicParams.MaxIdleTimeout < 4 || c.FinalMask.QuicParams.MaxIdleTimeout > 120) {
				return nil, errors.New("MaxIdleTimeout must be between 4 and 120")
			}
			if c.FinalMask.QuicParams.KeepAlivePeriod != 0 && (c.FinalMask.QuicParams.KeepAlivePeriod < 2 || c.FinalMask.QuicParams.KeepAlivePeriod > 60) {
				return nil, errors.New("KeepAlivePeriod must be between 2 and 60")
			}
			if c.FinalMask.QuicParams.MaxIncomingStreams != 0 && c.FinalMask.QuicParams.MaxIncomingStreams < 8 {
				return nil, errors.New("MaxIncomingStreams must be at least 8")
			}

			if c.FinalMask.QuicParams.Debug {
				os.Setenv("HYSTERIA_BBR_DEBUG", "true")
				os.Setenv("HYSTERIA_BRUTAL_DEBUG", "true")
			}

View on GitHub (pinned to 7d214f8b09)

Solutions

Set initConnectionReceiveWindow >= 16384 bytes (commonly a few MiB, e.g. 8388608).
Or remove the field to accept the default.
Keep it >= initStreamReceiveWindow.

Example fix

// before
"quicParams": { "initConnectionReceiveWindow": 1024 }
// after
"quicParams": { "initConnectionReceiveWindow": 8388608 }

Defensive patterns

Strategy: validation

Validate before calling

func connectionInitWindowOK(qp map[string]any) bool {
    return windowFloorOK(qp["initConnectionReceiveWindow"], 16384)
}

Prevention

Set connection windows >= stream windows, never below 16384 bytes.
Prefer omitting window fields unless profiling shows a need.
Keep a canonical quicParams snippet that already passes all floors.

When it happens

Trigger: "quicParams": { "initConnectionReceiveWindow": 1024 }.

Common situations: Shrinking all window knobs uniformly below the floor; forgetting this field when copying a tuned set of QUIC parameters; unit mistakes.

Related errors

AI-assisted analysis of XTLS/Xray-core@7d214f8b09 (2026-08-15). Data as JSON: /api/errors/925b2a56d4550459. Report an issue: GitHub.