probelabs/goreplay · error

handle buffer size error: %q, interface: %q

Error message

handle buffer size error: %q, interface: %q

What it means

When config.BufferSize > 0, PcapHandle calls inactive.SetBufferSize to size the kernel ring buffer; failure is wrapped as "handle buffer size error: <err>, interface: <name>". It indicates libpcap/the kernel rejected the requested buffer size for this capture handle.

Source

Thrown at internal/capture/capture.go:453

		for _, i := range infs {
			if i.Name == ifi.Name {
				snap = i.MTU + 200
			}
		}
	}

	if snap == 0 {
		snap = 64<<10 + 200
	}

	err = inactive.SetSnapLen(snap)
	if err != nil {
		return nil, fmt.Errorf("snapshot length error: %q, interface: %q", err, ifi.Name)
	}
	if l.config.BufferSize > 0 {
		err = inactive.SetBufferSize(int(l.config.BufferSize))
		if err != nil {
			return nil, fmt.Errorf("handle buffer size error: %q, interface: %q", err, ifi.Name)
		}
	}
	if l.config.BufferTimeout == 0 {
		l.config.BufferTimeout = 2000 * time.Millisecond
	}
	err = inactive.SetTimeout(l.config.BufferTimeout)
	if err != nil {
		return nil, fmt.Errorf("handle buffer timeout error: %q, interface: %q", err, ifi.Name)
	}
	handle, err = inactive.Activate()
	if err != nil {
		return nil, fmt.Errorf("PCAP Activate device error: %q, interface: %q", err, ifi.Name)
	}

	bpfFilter := l.config.BPFFilter
	if bpfFilter == "" {
		bpfFilter = l.Filter(ifi)
	}

View on GitHub (pinned to 251e45abd2)

Solutions

1. Raise kernel limits: sysctl -w net.core.rmem_max=<bytes> and net.core.rmem_default=<bytes>, then retry
2. Lower config.BufferSize to a value within kernel limits (e.g. 2-32 MB)
3. Verify units are bytes and the value fits in int on the target architecture
4. Only set BufferSize when you have a specific need; leave it 0 for defaults

Example fix

// before
cfg.BufferSize = 1 << 30 // 1GB, rmem_max too small
// after
// sysctl -w net.core.rmem_max=268435456
cfg.BufferSize = 32 << 20 // 32MB

max, err := sysctlRead("net/core/rmem_max")
if err == nil {
    if v, _ := strconv.Atoi(max); cfg.BufferSize > int(v) {
        return fmt.Errorf("BufferSize %d exceeds rmem_max %d", cfg.BufferSize, v)
    }
}

if err != nil && strings.Contains(err.Error(), "handle buffer size error") {
    log.Warnf("buffer size rejected, retrying with 8MB: %v", err)
    cfg.BufferSize = 8 << 20
    handle, err = l.PcapHandle(ifi)
}

When it happens

Trigger: Setting l.config.BufferSize to a value the platform cannot honor (e.g. larger than net.core.rmem_max allows after doubling, non-page-aligned, or overflowing int on 32-bit) so SetBufferSize fails.

Common situations: Very large buffer sizes on hosts without raised net.core.rmem_max/net.core.rmem_default sysctls; 32-bit builds where the size overflows; buffer sizes below the kernel minimum; copying af_packet MB-sized values to a pcap listener expecting different units.

Related errors

• inactive handle error: %q, interface: %q
• %q: supported timestamps: %q, interface: %q
• promiscuous mode error: %q, interface: %q
• monitor mode error: %q, interface: %q
• snapshot length error: %q, interface: %q

AI-assisted analysis of probelabs/goreplay@251e45abd2 (2026-09-02). Data as JSON: /api/errors/2506f703090f0d83. Report an issue: GitHub.