see if you got a bad dns server

dns.jl

using Fire
using Dates
using Base64
using Sockets
using OhMyJulia
using Statistics

import Base.adjoint # monky patch
adjoint(x::Unsigned) = ntoh(x)

const list = [
    "www.baidu.com",
    "www.google.com",
    "scholar.google.com.hk",
    "stackoverflow.com",
    "en.wikipedia.org",
    "zh.wikipedia.org",
    "www.sharelatex.com"
]

function pack_dns_query(website, id::u16=rand(u16))
    buf = IOBuffer()
    buf << asbytes(id') << asbytes(0b0_0000_0_0_1_0_000_0000')

    buf << asbytes(0x0001') << asbytes(0x0000) << asbytes(0x0000) << asbytes(0x0000)
    
    qname = mapreduce(++, split(website, '.')) do seg
        l = length(seg)
        (l % u8) ++ Bytes(seg)
    end
    buf << qname << asbytes(0x00) << asbytes(0x0001') << asbytes(0x0001') >> take!
end

function get_default_dns_linux()
    first(cadr(split(line)) for line in eachline("/etc/resolv.conf") if startswith(line, "nameserver"))
end

@main function record_ng(server=get_default_dns_linux())
    server = IPv4(server)
    prt("time", "website", "status", "elapsed(ms)", "info")
    locks = Lock(@fill(UDPSocket(), 4))

    while true
        waitfor(x->!isempty(x), locks)
        socket = pop!(locks[])

        @async let socket = socket
            sleep(2rand())
            website = rand(list)
            msg = pack_dns_query(website)
            starttime = time()
            done = false

            task = @async try
                send(socket, server, 53, msg)
                result = recv(socket)
                prt(Dates.format(Dates.now(), "HH:MM:SS"), website, "succeed", floor(Int, 1000(time() - starttime)), base64encode(result))
            catch e
                print(Dates.format(Dates.now(), "HH:MM:SS\t"), website, "\tfailed\t", floor(Int, 1000(time() - starttime)), '\t')
                show(e)
                println()
            finally
                done = true
                flush(stdout)
                locks[:one] = locks[] ++ socket
            end

            @async begin # timeout
                sleep(5)
                if (!done)
                    close(socket)
                    socket = UDPSocket()
                end
            end

            fetch(task)
        end
    end
end

@main function record()
    prt("time", "website", "status", "elapsed(ms)", "info")
    l = Lock(4)

    while true
        waitfor(x->x>0, l)
        l[] -= 1

        @async let
            sleep(rand())
            starttime = time()
            website = rand(list)
            try
                info = getalladdrinfo(website)
                prt(Dates.format(Dates.now(), "HH:MM:SS"), website, "succeed", floor(Int, 1000(time() - starttime)), join(info, ", "))
            catch e
                print(Dates.format(Dates.now(), "HH:MM:SS\t"), website, "\tfailed\t", floor(Int, 1000(time() - starttime)), '\t')
                show(e)
                println()
            finally
                flush(stdout)
                l[:one] += 1
            end
        end
    end
end

@main function stat(file)
    a = readlines(file)[2:end]
    a = map(x->split(x, '\t'), a)
    a = groupby(x->x[2], (x, y) -> push!(x, (y[3], parse(Int, y[4]))), ()->[], a)
    for (k, v) in a
        s = filter(x->car(x) == "succeed", v)
        r = floor(100(length(s) / length(v)), digits=2)
        println(k, " Success rate: $r%, average time: $(floor(Int, mean(cadr.(s))))ms")
    end
end

@main function cdf(file)
    a = readlines(file)[2:end]
    a = map(x->split(x, '\t'), a)
    a = groupby(x->x[2], (x, y) -> push!(x, parse(Int, y[4])), ()->[], a)
    str = s"""
        \documentclass[tikz]{standalone}
        \usepackage{pgfplots}
        \pgfplotsset{compat=newest}
        \pgfplotsset{every axis legend/.append style={%
        cells={anchor=west}}
        }

        \begin{document}
            \begin{tikzpicture}[]
                \begin{axis}[%
                    grid=both,
                    grid style={line width=.1pt, draw=gray!20},
                    ylabel={CDF},
                    xlabel={Lantency (s)},
                    width=12cm,
                    height=9cm,
                    ymin=0,
                    ymax=1,
                    legend style={
                        at = {(.99,.015)},
                        anchor = south east,
                        font = \fontsize{8pt}{8pt}\selectfont,
                        row sep=-1pt
                    },
                    legend image post style={scale=0.8},
                ]
    """
    for (k, v) in a
        g = level_to_edge(sort(v))
        x = map(cadr, g) ./ 1000
        y = ((map(car, g)[2:end] .- 1) ./ length(v)) ++ 1
        str *= """
        \\addplot+[mark=none] coordinates {
            $(join(zip(x, y), '\n'))
        };
        \\addlegendentry{$k}
        """
    end
    println(str, s"""
        \end{axis}

        \end{tikzpicture}
    \end{document}
    """)
end