Go报告“未定义”的外部包导出常量

Here's the code:

package main

import (
    "log"
    "github.com/google/gopacket"
    "github.com/google/gopacket/pcap"
)

func main() {
    log.Print(gopacket.MaxEndpointSize)
    log.Print(pcap.MaxBpfInstructions)
}

When I run go build I get this:

./main.go:11: undefined: pcap.MaxBpfInstructions

But you can see MaxBpfInstructions right here: https://godoc.org/github.com/google/gopacket/pcap#pkg-constants

I feel this must be a stupid mistake, but I can't find it. Help?

It seems I was missing libpcap-dev. Now why Go or the package didn't throw a proper error message is beyond me.