dingdayu/dnsx

package dns

import (
    "strconv"
    "strings"

    "github.com/miekg/dns"

    "github.com/xyser/dnsx/model/dao"
)

// TypeURI provide a means to resolve hostnames to URIs that can be used by various applications.
// For resolution the application needs to know both the hostname and the protocol that the URI is to be used for.
//
// It is an alternative to the SRV record. Similar to the SRV record,
// it returns both weight and priority values which can be used to select an appropriate URI from multiple results.
// However, unlike the SRV no port number is returned in the URI record since this information
// is contained (if applicable) in the URI string.
//
// So the returned URI strings from a URI record query can be used directly by the requested application,
// while the usable URI has to be assembled from the search and results information of an SRV record query.
//
// _ftp._tcp.example.com. 3600 IN URI 10 1 "ftp://ftp.example.com/public"
func TypeURI(msg *dns.Msg) error {
    domain := msg.Question[0].Name
    rrs, err := dao.GetRecordByNameAndType(domain, msg.Question[0].Qtype)
    if err != nil {
        return err
    }
    for _, rr := range rrs {
        // 优先级 权重 端口 目标地址 1 1 80 www.baidu.com
        vs := strings.Split(rr.Value, " ")
        var priority, weight uint64
        if len(vs) == 3 {
            priority, _ = strconv.ParseUint(vs[0], 16, 16)
            weight, _ = strconv.ParseUint(vs[1], 16, 16)
        } else if len(vs) == 2 {
            priority = uint64(rr.Priority)
            weight, _ = strconv.ParseUint(vs[0], 16, 16)
        }

        // URI 协议解释: https://www.dynu.com/Resources/DNS-Records/URI-Record
        msg.Answer = append(msg.Answer, &dns.URI{
            Hdr:      dns.RR_Header{Name: msg.Question[0].Name, Rrtype: msg.Question[0].Qtype, Class: dns.ClassINET, Ttl: rr.TTL},
            Priority: uint16(priority), // 优先级
            Weight:   uint16(weight),   // 权重
            Target:   vs[len(vs)-1],    // 对应目标地址,可以是域名或IP
        })
    }
    return nil
}