摘要：作者簡介地址地址本章介紹代碼網絡中端口映射作者使用操作系統，其他平臺也大同小異介紹通用即插即用。端口映射將一個外部端口映射到一個內網。

作者：Derek

Github地址：https://github.com/Bytom/bytom

Gitee地址：https://gitee.com/BytomBlockc...

本章介紹bytom代碼P2P網絡中upnp端口映射

作者使用MacOS操作系統，其他平臺也大同小異
Golang Version: 1.8

UPNP（Universal Plug and Play）通用即插即用。UPNP端口映射將一個外部端口映射到一個內網ip:port。從而實現p2p網絡從外網能夠穿透網關訪問到內網的bytomd節點。

SSDP（Simple Service Discovery Protocol 簡單服務發現協議）
GENA（Generic Event Notification Architecture 通用事件通知結構）
SOAP（Simple Object Access Protocol 簡單對象訪問協議）
XML（Extensible Markup Language 可擴張標記語言）

p2p/upnp/upnp.go

從網絡中發現支持UPNP功能的設備，并得到該設備的location和url等相關信息

type upnpNAT struct {
    serviceURL string // 設備的描述文件URL，用于得到該設備的描述信息
    ourIP      string // 節點本地ip地址
    urnDomain  string // 設備類型
}

func Discover() (nat NAT, err error) {
    ssdp, err := net.ResolveUDPAddr("udp4", "239.255.255.250:1900")
    if err != nil {
        return
    }
    conn, err := net.ListenPacket("udp4", ":0")
    if err != nil {
        return
    }
    socket := conn.(*net.UDPConn)
    defer socket.Close()

    err = socket.SetDeadline(time.Now().Add(3 * time.Second))
    if err != nil {
        return
    }

    st := "InternetGatewayDevice:1"

    // 多播請求：M-SEARCH SSDP協議定義的發現請求。
    buf := bytes.NewBufferString(
        "M-SEARCH * HTTP/1.1
" +
            "HOST: 239.255.255.250:1900
" +
            "ST: ssdp:all
" +
            "MAN: "ssdp:discover"
" +
            "MX: 2

")
    message := buf.Bytes()
    answerBytes := make([]byte, 1024)
    for i := 0; i < 3; i++ {
        // 向239.255.255.250:1900發送一條多播請求
        _, err = socket.WriteToUDP(message, ssdp)
        if err != nil {
            return
        }
        // 如果從網絡中發現UPNP設備則會從239.255.255.250:1900收到響應消息
        var n int
        n, _, err = socket.ReadFromUDP(answerBytes)
        for {
            n, _, err = socket.ReadFromUDP(answerBytes)
            if err != nil {
                break
            }
            answer := string(answerBytes[0:n])
            if strings.Index(answer, st) < 0 {
                continue
            }
            // HTTP header field names are case-insensitive.
            // http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2
            // 獲得設備location
            locString := "
location:"
            answer = strings.ToLower(answer)
            locIndex := strings.Index(answer, locString)
            if locIndex < 0 {
                continue
            }
            loc := answer[locIndex+len(locString):]
            endIndex := strings.Index(loc, "
")
            if endIndex < 0 {
                continue
            }
            // 獲得設備的描述url和設備類型
            locURL := strings.TrimSpace(loc[0:endIndex])
            var serviceURL, urnDomain string
            serviceURL, urnDomain, err = getServiceURL(locURL)
            if err != nil {
                return
            }
            var ourIP net.IP
            ourIP, err = localIPv4()
            if err != nil {
                return
            }
            nat = &upnpNAT{serviceURL: serviceURL, ourIP: ourIP.String(), urnDomain: urnDomain}
            return
        }
    }
    err = errors.New("UPnP port discovery failed.")
    return
}

向upnp設備發送一條http post請求，將內部網絡ip:port和外部網絡ip:port做映射

func (n *upnpNAT) AddPortMapping(protocol string, externalPort, internalPort int, description string, timeout int) (mappedExternalPort int, err error) {
    // A single concatenation would break ARM compilation.
    message := "
" +
        "" + strconv.Itoa(externalPort)
    message += "" + protocol + ""
    message += "" + strconv.Itoa(internalPort) + "" +
        "" + n.ourIP + "" +
        "1"
    message += description +
        "" + strconv.Itoa(timeout) +
        ""

    var response *http.Response
    response, err = soapRequest(n.serviceURL, "AddPortMapping", message, n.urnDomain)
    if response != nil {
        defer response.Body.Close()
    }
    if err != nil {
        return
    }

    // TODO: check response to see if the port was forwarded
    // log.Println(message, response)
    // JAE:
    // body, err := ioutil.ReadAll(response.Body)
    // fmt.Println(string(body), err)
    mappedExternalPort = externalPort
    _ = response
    return
}

向upnp設備發送一條http post請求，將內部網絡ip:port和外部網絡ip:port刪除映射關系

func (n *upnpNAT) DeletePortMapping(protocol string, externalPort, internalPort int) (err error) {

    message := "
" +
        "" + strconv.Itoa(externalPort) +
        "" + protocol + "" +
        ""

    var response *http.Response
    response, err = soapRequest(n.serviceURL, "DeletePortMapping", message, n.urnDomain)
    if response != nil {
        defer response.Body.Close()
    }
    if err != nil {
        return
    }

    // TODO: check response to see if the port was deleted
    // log.Println(message, response)
    _ = response
    return
}

func (n *upnpNAT) GetExternalAddress() (addr net.IP, err error) {
    info, err := n.getExternalIPAddress()
    if err != nil {
        return
    }
    addr = net.ParseIP(info.externalIpAddress)
    return
}

func (n *upnpNAT) getExternalIPAddress() (info statusInfo, err error) {

    message := "
" +
        ""

    var response *http.Response
    response, err = soapRequest(n.serviceURL, "GetExternalIPAddress", message, n.urnDomain)
    if response != nil {
        defer response.Body.Close()
    }
    if err != nil {
        return
    }
    var envelope Envelope
    data, err := ioutil.ReadAll(response.Body)
    reader := bytes.NewReader(data)
    xml.NewDecoder(reader).Decode(&envelope)

    info = statusInfo{envelope.Soap.ExternalIP.IPAddress}

    if err != nil {
        return
    }

    return
}