"""
Compendium of generic DNS utilities
# Examples:
dns.lookup(name, rdtype, ...)
dns.query(name, rdtype, ...)

dns.srv_rec(data)
dns.srv_data('my1.example.com', 389, prio=10, weight=100)
dns.srv_name('ldap/tcp', 'example.com')

"""

import base64
import binascii
import functools
import hashlib
import itertools
import logging
import random
import re
import shlex
import socket
import ssl
import string

import salt.modules.cmdmod
import salt.utils.files
import salt.utils.network
import salt.utils.path
import salt.utils.stringutils
from salt._compat import ipaddress
from salt.ext.six.moves import zip  # pylint: disable=redefined-builtin
from salt.utils.odict import OrderedDict

# Integrations
try:
    import dns.resolver

    HAS_DNSPYTHON = True
except ImportError:
    HAS_DNSPYTHON = False
try:
    import tldextract

    HAS_TLDEXTRACT = True
except ImportError:
    HAS_TLDEXTRACT = False
HAS_DIG = salt.utils.path.which("dig") is not None
DIG_OPTIONS = "+search +fail +noall +answer +nocl +nottl"
HAS_DRILL = salt.utils.path.which("drill") is not None
HAS_HOST = salt.utils.path.which("host") is not None
HAS_NSLOOKUP = salt.utils.path.which("nslookup") is not None

__salt__ = {"cmd.run_all": salt.modules.cmdmod.run_all}
log = logging.getLogger(__name__)


class RFC:
    """
    Simple holding class for all RFC/IANA registered lists & standards
    """

    # https://tools.ietf.org/html/rfc6844#section-3
    CAA_TAGS = ("issue", "issuewild", "iodef")

    # http://www.iana.org/assignments/dns-sshfp-rr-parameters/dns-sshfp-rr-parameters.xhtml
    SSHFP_ALGO = OrderedDict(((1, "rsa"), (2, "dsa"), (3, "ecdsa"), (4, "ed25519"),))

    SSHFP_HASH = OrderedDict(((1, "sha1"), (2, "sha256"),))

    # http://www.iana.org/assignments/dane-parameters/dane-parameters.xhtml
    TLSA_USAGE = OrderedDict(
        ((0, "pkixta"), (1, "pkixee"), (2, "daneta"), (3, "daneee"),)
    )

    TLSA_SELECT = OrderedDict(((0, "cert"), (1, "spki"),))

    TLSA_MATCHING = OrderedDict(((0, "full"), (1, "sha256"), (2, "sha512"),))

    SRV_PROTO = ("tcp", "udp", "sctp")

    @staticmethod
    def validate(lookup, ref, match=None):
        if lookup in ref:
            return lookup
        elif match == "in":
            return [code for code, name in ref.items() if lookup in name][-1]
        else:
            # OrderedDicts only!(?)
            return {name: code for code, name in ref.items()}[lookup]


def _to_port(port):
    try:
        port = int(port)
        assert 1 <= port <= 65535
        return port
    except (ValueError, AssertionError):
        raise ValueError("Invalid port {}".format(port))


def _tree(domain, tld=False):
    """
    Split out a domain in its parents

    Leverages tldextract to take the TLDs from publicsuffix.org
    or makes a valiant approximation of that

    :param domain: dc2.ams2.example.com
    :param tld: Include TLD in list
    :return: [ 'dc2.ams2.example.com', 'ams2.example.com', 'example.com']
    """
    domain = domain.rstrip(".")
    assert "." in domain, "Provide a decent domain"

    if not tld:
        if HAS_TLDEXTRACT:
            tld = tldextract.extract(domain).suffix
        else:
            tld = re.search(
                r"((?:(?:ac|biz|com?|info|edu|gov|mil|name|net|n[oi]m|org)\.)?[^.]+)$",
                domain,
            ).group()
            log.info(
                "Without tldextract, dns.util resolves the TLD of %s to %s", domain, tld
            )

    res = [domain]
    while True:
        idx = domain.find(".")
        if idx < 0:
            break
        domain = domain[idx + 1 :]
        if domain == tld:
            break
        res.append(domain)

    return res


def _weighted_order(recs):
    res = []
    weights = [rec["weight"] for rec in recs]
    while weights:
        rnd = random.random() * sum(weights)
        for i, w in enumerate(weights):
            rnd -= w
            if rnd < 0:
                res.append(recs.pop(i)["name"])
                weights.pop(i)
                break

    return res


def _cast(rec_data, rec_cast):
    if isinstance(rec_cast, dict):
        rec_data = type(next(iter(rec_cast.keys())))(rec_data)
        res = rec_cast[rec_data]
        return res
    elif isinstance(rec_cast, (list, tuple)):
        return RFC.validate(rec_data, rec_cast)
    else:
        return rec_cast(rec_data)


def _data2rec(schema, rec_data):
    """
    schema = OrderedDict({
        'prio': int,
        'weight': int,
        'port': to_port,
        'name': str,
    })
    rec_data = '10 20 25 myawesome.nl'

    res = {'prio': 10, 'weight': 20, 'port': 25 'name': 'myawesome.nl'}
    """
    try:
        rec_fields = rec_data.split(" ")
        # spaces in digest fields are allowed
        assert len(rec_fields) >= len(schema)
        if len(rec_fields) > len(schema):
            cutoff = len(schema) - 1
            rec_fields = rec_fields[0:cutoff] + ["".join(rec_fields[cutoff:])]

        if len(schema) == 1:
            res = _cast(rec_fields[0], next(iter(schema.values())))
        else:
            res = {
                field_name: _cast(rec_field, rec_cast)
                for (field_name, rec_cast), rec_field in zip(schema.items(), rec_fields)
            }
        return res
    except (AssertionError, AttributeError, TypeError, ValueError) as e:
        raise ValueError(
            'Unable to cast "{0}" as "{2}": {1}'.format(
                rec_data, e, " ".join(schema.keys())
            )
        )


def _data2rec_group(schema, recs_data, group_key):
    if not isinstance(recs_data, (list, tuple)):
        recs_data = [recs_data]

    res = OrderedDict()

    try:
        for rdata in recs_data:
            rdata = _data2rec(schema, rdata)
            assert rdata and group_key in rdata

            idx = rdata.pop(group_key)
            if idx not in res:
                res[idx] = []

            if len(rdata) == 1:
                rdata = next(iter(rdata.values()))

            res[idx].append(rdata)
        return res
    except (AssertionError, ValueError) as e:
        raise ValueError(
            'Unable to cast "{}" as a group of "{}": {}'.format(
                ",".join(recs_data), " ".join(schema.keys()), e
            )
        )


def _rec2data(*rdata):
    return " ".join(rdata)


def _data_clean(data):
    data = data.strip(string.whitespace)
    if data.startswith(('"', "'")) and data.endswith(('"', "'")):
        return data[1:-1]
    else:
        return data


def _lookup_dig(name, rdtype, timeout=None, servers=None, secure=None):
    """
    Use dig to lookup addresses
    :param name: Name of record to search
    :param rdtype: DNS record type
    :param timeout: server response timeout
    :param servers: [] of servers to use
    :return: [] of records or False if error
    """
    cmd = "dig {} -t {} ".format(DIG_OPTIONS, rdtype)
    if servers:
        cmd += "".join(["@{} ".format(srv) for srv in servers])
    if timeout is not None:
        if servers:
            timeout = int(float(timeout) / len(servers))
        else:
            timeout = int(timeout)
        cmd += "+time={} ".format(timeout)
    if secure:
        cmd += "+dnssec +adflag "

    cmd = __salt__["cmd.run_all"](
        "{} {}".format(cmd, name), python_shell=False, output_loglevel="quiet"
    )

    if "ignoring invalid type" in cmd["stderr"]:
        raise ValueError("Invalid DNS type {}".format(rdtype))
    elif cmd["retcode"] != 0:
        log.warning(
            "dig returned (%s): %s",
            cmd["retcode"],
            cmd["stderr"].strip(string.whitespace + ";"),
        )
        return False
    elif not cmd["stdout"]:
        return []

    validated = False
    res = []
    for line in cmd["stdout"].splitlines():
        _, rtype, rdata = line.split(None, 2)
        if rtype == "CNAME" and rdtype != "CNAME":
            continue
        elif rtype == "RRSIG":
            validated = True
            continue
        res.append(_data_clean(rdata))

    if res and secure and not validated:
        return False
    else:
        return res


def _lookup_drill(name, rdtype, timeout=None, servers=None, secure=None):
    """
    Use drill to lookup addresses
    :param name: Name of record to search
    :param rdtype: DNS record type
    :param timeout: command return timeout
    :param servers: [] of servers to use
    :return: [] of records or False if error
    """
    cmd = "drill "
    if secure:
        cmd += "-D -o ad "
    cmd += "{} {} ".format(rdtype, name)
    if servers:
        cmd += "".join(["@{} ".format(srv) for srv in servers])
    cmd = __salt__["cmd.run_all"](
        cmd, timeout=timeout, python_shell=False, output_loglevel="quiet"
    )

    if cmd["retcode"] != 0:
        log.warning("drill returned (%s): %s", cmd["retcode"], cmd["stderr"])
        return False

    lookup_res = iter(cmd["stdout"].splitlines())
    validated = False
    res = []
    try:
        line = ""
        while "ANSWER SECTION" not in line:
            line = next(lookup_res)
        while True:
            line = next(lookup_res)
            line = line.strip()
            if not line or line.startswith(";;"):
                break

            l_type, l_rec = line.split(None, 4)[-2:]
            if l_type == "CNAME" and rdtype != "CNAME":
                continue
            elif l_type == "RRSIG":
                validated = True
                continue
            elif l_type != rdtype:
                raise ValueError("Invalid DNS type {}".format(rdtype))

            res.append(_data_clean(l_rec))

    except StopIteration:
        pass

    if res and secure and not validated:
        return False
    else:
        return res


def _lookup_gai(name, rdtype, timeout=None):
    """
    Use Python's socket interface to lookup addresses
    :param name: Name of record to search
    :param rdtype: A or AAAA
    :param timeout: ignored
    :return: [] of addresses or False if error
    """
    try:
        sock_t = {"A": socket.AF_INET, "AAAA": socket.AF_INET6}[rdtype]
    except KeyError:
        raise ValueError("Invalid DNS type {} for gai lookup".format(rdtype))

    if timeout:
        log.info("Ignoring timeout on gai resolver; fix resolv.conf to do that")

    try:
        addresses = [
            sock[4][0]
            for sock in socket.getaddrinfo(name, None, sock_t, 0, socket.SOCK_RAW)
        ]
        return addresses
    except socket.gaierror:
        return False


def _lookup_host(name, rdtype, timeout=None, server=None):
    """
    Use host to lookup addresses
    :param name: Name of record to search
    :param server: Server to query
    :param rdtype: DNS record type
    :param timeout: server response wait
    :return: [] of records or False if error
    """
    cmd = "host -t {} ".format(rdtype)

    if timeout:
        cmd += "-W {} ".format(int(timeout))
    cmd += name
    if server is not None:
        cmd += " {}".format(server)

    cmd = __salt__["cmd.run_all"](cmd, python_shell=False, output_loglevel="quiet")

    if "invalid type" in cmd["stderr"]:
        raise ValueError("Invalid DNS type {}".format(rdtype))
    elif cmd["retcode"] != 0:
        log.warning("host returned (%s): %s", cmd["retcode"], cmd["stderr"])
        return False
    elif "has no" in cmd["stdout"]:
        return []

    res = []
    _stdout = cmd["stdout"] if server is None else cmd["stdout"].split("\n\n")[-1]
    for line in _stdout.splitlines():
        if rdtype != "CNAME" and "is an alias" in line:
            continue
        line = line.split(" ", 3)[-1]
        for prefix in ("record", "address", "handled by", "alias for"):
            if line.startswith(prefix):
                line = line[len(prefix) + 1 :]
                break
        res.append(_data_clean(line))

    return res


def _lookup_dnspython(name, rdtype, timeout=None, servers=None, secure=None):
    """
    Use dnspython to lookup addresses
    :param name: Name of record to search
    :param rdtype: DNS record type
    :param timeout: query timeout
    :param server: [] of server(s) to try in order
    :return: [] of records or False if error
    """
    resolver = dns.resolver.Resolver()

    if timeout is not None:
        resolver.lifetime = float(timeout)
    if servers:
        resolver.nameservers = servers
    if secure:
        resolver.ednsflags += dns.flags.DO

    try:
        res = [
            _data_clean(rr.to_text())
            for rr in resolver.query(name, rdtype, raise_on_no_answer=False)
        ]
        return res
    except dns.rdatatype.UnknownRdatatype:
        raise ValueError("Invalid DNS type {}".format(rdtype))
    except (
        dns.resolver.NXDOMAIN,
        dns.resolver.YXDOMAIN,
        dns.resolver.NoNameservers,
        dns.exception.Timeout,
    ):
        return False


def _lookup_nslookup(name, rdtype, timeout=None, server=None):
    """
    Use nslookup to lookup addresses
    :param name: Name of record to search
    :param rdtype: DNS record type
    :param timeout: server response timeout
    :param server: server to query
    :return: [] of records or False if error
    """
    cmd = "nslookup -query={} {}".format(rdtype, name)

    if timeout is not None:
        cmd += " -timeout={}".format(int(timeout))
    if server is not None:
        cmd += " {}".format(server)

    cmd = __salt__["cmd.run_all"](cmd, python_shell=False, output_loglevel="quiet")

    if cmd["retcode"] != 0:
        log.warning(
            "nslookup returned (%s): %s",
            cmd["retcode"],
            cmd["stdout"].splitlines()[-1].strip(string.whitespace + ";"),
        )
        return False

    lookup_res = iter(cmd["stdout"].splitlines())
    res = []
    try:
        line = next(lookup_res)
        if "unknown query type" in line:
            raise ValueError("Invalid DNS type {}".format(rdtype))

        while True:
            if name in line:
                break
            line = next(lookup_res)

        while True:
            line = line.strip()
            if not line or line.startswith("*"):
                break
            elif rdtype != "CNAME" and "canonical name" in line:
                name = line.split()[-1][:-1]
                line = next(lookup_res)
                continue
            elif rdtype == "SOA":
                line = line.split("=")
            elif line.startswith("Name:"):
                line = next(lookup_res)
                line = line.split(":", 1)
            elif line.startswith(name):
                if "=" in line:
                    line = line.split("=", 1)
                else:
                    line = line.split(" ")

            res.append(_data_clean(line[-1]))
            line = next(lookup_res)

    except StopIteration:
        pass

    if rdtype == "SOA":
        return [" ".join(res[1:])]
    else:
        return res


def lookup(
    name,
    rdtype,
    method=None,
    servers=None,
    timeout=None,
    walk=False,
    walk_tld=False,
    secure=None,
):
    """
    Lookup DNS records and return their data

    :param name: name to lookup
    :param rdtype: DNS record type
    :param method: gai (getaddrinfo()), dnspython, dig, drill, host, nslookup or auto (default)
    :param servers: (list of) server(s) to try in-order
    :param timeout: query timeout or a valiant approximation of that
    :param walk: Walk the DNS upwards looking for the record type or name/recordtype if walk='name'.
    :param walk_tld: Include the final domain in the walk
    :param secure: return only DNSSEC secured responses
    :return: [] of record data
    """
    # opts = __opts__.get('dns', {})
    opts = {}
    method = method or opts.get("method", "auto")
    secure = secure or opts.get("secure", None)
    servers = servers or opts.get("servers", None)
    timeout = timeout or opts.get("timeout", False)

    rdtype = rdtype.upper()

    # pylint: disable=bad-whitespace,multiple-spaces-before-keyword
    query_methods = (
        ("gai", _lookup_gai, not any((rdtype not in ("A", "AAAA"), servers, secure))),
        ("dnspython", _lookup_dnspython, HAS_DNSPYTHON),
        ("dig", _lookup_dig, HAS_DIG),
        ("drill", _lookup_drill, HAS_DRILL),
        ("host", _lookup_host, HAS_HOST and not secure),
        ("nslookup", _lookup_nslookup, HAS_NSLOOKUP and not secure),
    )
    # pylint: enable=bad-whitespace,multiple-spaces-before-keyword

    try:
        if method == "auto":
            # The first one not to bork on the conditions becomes the function
            method, resolver = next(
                ((rname, rcb) for rname, rcb, rtest in query_methods if rtest)
            )
        else:
            # The first one not to bork on the conditions becomes the function. And the name must match.
            resolver = next(
                (
                    rcb
                    for rname, rcb, rtest in query_methods
                    if rname == method and rtest
                )
            )
    except StopIteration:
        log.error(
            "Unable to lookup %s/%s: Resolver method %s invalid, unsupported "
            "or unable to perform query",
            method,
            rdtype,
            name,
        )
        return False

    res_kwargs = {
        "rdtype": rdtype,
    }

    if servers:
        if not isinstance(servers, (list, tuple)):
            servers = [servers]
        if method in ("dnspython", "dig", "drill"):
            res_kwargs["servers"] = servers
        else:
            if timeout:
                timeout /= len(servers)

            # Inject a wrapper for multi-server behaviour
            def _multi_srvr(resolv_func):
                @functools.wraps(resolv_func)
                def _wrapper(**res_kwargs):
                    for server in servers:
                        s_res = resolv_func(server=server, **res_kwargs)
                        if s_res:
                            return s_res

                return _wrapper

            resolver = _multi_srvr(resolver)

    if not walk:
        name = [name]
    else:
        idx = 0
        if rdtype in ("SRV", "TLSA"):  # The only RRs I know that have 2 name components
            idx = name.find(".") + 1
        idx = name.find(".", idx) + 1
        domain = name[idx:]
        rname = name[0:idx]

        name = _tree(domain, walk_tld)
        if walk == "name":
            name = [rname + domain for domain in name]

        if timeout:
            timeout /= len(name)

    if secure:
        res_kwargs["secure"] = secure
    if timeout:
        res_kwargs["timeout"] = timeout

    for rname in name:
        res = resolver(name=rname, **res_kwargs)
        if res:
            return res

    return res


def query(
    name,
    rdtype,
    method=None,
    servers=None,
    timeout=None,
    walk=False,
    walk_tld=False,
    secure=None,
):
    """
    Query DNS for information.
    Where `lookup()` returns record data, `query()` tries to interpret the data and return its results

    :param name: name to lookup
    :param rdtype: DNS record type
    :param method: gai (getaddrinfo()), pydns, dig, drill, host, nslookup or auto (default)
    :param servers: (list of) server(s) to try in-order
    :param timeout: query timeout or a valiant approximation of that
    :param secure: return only DNSSEC secured response
    :param walk: Walk the DNS upwards looking for the record type or name/recordtype if walk='name'.
    :param walk_tld: Include the top-level domain in the walk
    :return: [] of records
    """
    rdtype = rdtype.upper()
    qargs = {
        "method": method,
        "servers": servers,
        "timeout": timeout,
        "walk": walk,
        "walk_tld": walk_tld,
        "secure": secure,
    }

    if rdtype == "PTR" and not name.endswith("arpa"):
        name = ptr_name(name)

    if rdtype == "SPF":
        # 'SPF' has become a regular 'TXT' again
        qres = [
            answer
            for answer in lookup(name, "TXT", **qargs)
            if answer.startswith("v=spf")
        ]
        if not qres:
            qres = lookup(name, rdtype, **qargs)
    else:
        qres = lookup(name, rdtype, **qargs)

    rec_map = {
        "A": a_rec,
        "AAAA": aaaa_rec,
        "CAA": caa_rec,
        "MX": mx_rec,
        "SOA": soa_rec,
        "SPF": spf_rec,
        "SRV": srv_rec,
        "SSHFP": sshfp_rec,
        "TLSA": tlsa_rec,
    }

    if not qres or rdtype not in rec_map:
        return qres
    elif rdtype in ("A", "AAAA", "SSHFP", "TLSA"):
        res = [rec_map[rdtype](res) for res in qres]
    elif rdtype in ("SOA", "SPF"):
        res = rec_map[rdtype](qres[0])
    else:
        res = rec_map[rdtype](qres)

    return res


def host(name, ip4=True, ip6=True, **kwargs):
    """
    Return a list of addresses for name

    ip6:
        Return IPv6 addresses
    ip4:
        Return IPv4 addresses

    the rest is passed on to lookup()
    """
    res = {}
    if ip6:
        ip6 = lookup(name, "AAAA", **kwargs)
        if ip6:
            res["ip6"] = ip6
    if ip4:
        ip4 = lookup(name, "A", **kwargs)
        if ip4:
            res["ip4"] = ip4

    return res


def a_rec(rdata):
    """
    Validate and parse DNS record data for an A record
    :param rdata: DNS record data
    :return: { 'address': ip }
    """
    rschema = OrderedDict((("address", ipaddress.IPv4Address),))
    return _data2rec(rschema, rdata)


def aaaa_rec(rdata):
    """
    Validate and parse DNS record data for an AAAA record
    :param rdata: DNS record data
    :return: { 'address': ip }
    """
    rschema = OrderedDict((("address", ipaddress.IPv6Address),))
    return _data2rec(rschema, rdata)


def caa_rec(rdatas):
    """
    Validate and parse DNS record data for a CAA record
    :param rdata: DNS record data
    :return: dict w/fields
    """
    rschema = OrderedDict(
        (
            ("flags", lambda flag: ["critical"] if int(flag) > 0 else []),
            ("tag", RFC.CAA_TAGS),
            ("value", lambda val: val.strip("',\"")),
        )
    )

    res = _data2rec_group(rschema, rdatas, "tag")

    for tag in ("issue", "issuewild"):
        tag_res = res.get(tag, False)
        if not tag_res:
            continue
        for idx, val in enumerate(tag_res):
            if ";" not in val:
                continue
            val, params = val.split(";", 1)
            params = dict(param.split("=") for param in shlex.split(params))
            tag_res[idx] = {val: params}

    return res


def mx_data(target, preference=10):
    """
    Generate MX record data
    :param target: server
    :param preference: preference number
    :return: DNS record data
    """
    return _rec2data(int(preference), target)


def mx_rec(rdatas):
    """
    Validate and parse DNS record data for MX record(s)
    :param rdata: DNS record data
    :return: dict w/fields
    """
    rschema = OrderedDict((("preference", int), ("name", str),))
    return _data2rec_group(rschema, rdatas, "preference")


def ptr_name(rdata):
    """
    Return PTR name of given IP
    :param rdata: IP address
    :return: PTR record name
    """
    try:
        return ipaddress.ip_address(rdata).reverse_pointer
    except ValueError:
        log.error("Unable to generate PTR record; %s is not a valid IP address", rdata)
        return False


def soa_rec(rdata):
    """
    Validate and parse DNS record data for SOA record(s)
    :param rdata: DNS record data
    :return: dict w/fields
    """
    rschema = OrderedDict(
        (
            ("mname", str),
            ("rname", str),
            ("serial", int),
            ("refresh", int),
            ("retry", int),
            ("expire", int),
            ("minimum", int),
        )
    )
    return _data2rec(rschema, rdata)


def spf_rec(rdata):
    """
    Validate and parse DNS record data for SPF record(s)
    :param rdata: DNS record data
    :return: dict w/fields
    """
    spf_fields = rdata.split(" ")
    if not spf_fields.pop(0).startswith("v=spf"):
        raise ValueError("Not an SPF record")

    res = OrderedDict()
    mods = set()
    for mech_spec in spf_fields:
        if mech_spec.startswith(("exp", "redirect")):
            # It's a modifier
            mod, val = mech_spec.split("=", 1)
            if mod in mods:
                raise KeyError("Modifier {} can only appear once".format(mod))

            mods.add(mod)
            continue

            # TODO: Should be in something intelligent like an SPF_get
            # if mod == 'exp':
            #     res[mod] = lookup(val, 'TXT', **qargs)
            #     continue
            # elif mod == 'redirect':
            #     return query(val, 'SPF', **qargs)

        mech = {}
        if mech_spec[0] in ("+", "-", "~", "?"):
            mech["qualifier"] = mech_spec[0]
            mech_spec = mech_spec[1:]

        if ":" in mech_spec:
            mech_spec, val = mech_spec.split(":", 1)
        elif "/" in mech_spec:
            idx = mech_spec.find("/")
            mech_spec = mech_spec[0:idx]
            val = mech_spec[idx:]
        else:
            val = None

        res[mech_spec] = mech
        if not val:
            continue
        elif mech_spec in ("ip4", "ip6"):
            val = ipaddress.ip_interface(val)
            assert val.version == int(mech_spec[-1])

        mech["value"] = val

    return res


def srv_data(target, port, prio=10, weight=10):
    """
    Generate SRV record data
    :param target:
    :param port:
    :param prio:
    :param weight:
    :return:
    """
    return _rec2data(prio, weight, port, target)


def srv_name(svc, proto="tcp", domain=None):
    """
    Generate SRV record name
    :param svc: ldap, 389 etc
    :param proto: tcp, udp, sctp etc.
    :param domain: name to append
    :return:
    """
    proto = RFC.validate(proto, RFC.SRV_PROTO)
    if isinstance(svc, int) or svc.isdigit():
        svc = _to_port(svc)

    if domain:
        domain = "." + domain
    return "_{}._{}{}".format(svc, proto, domain)


def srv_rec(rdatas):
    """
    Validate and parse DNS record data for SRV record(s)
    :param rdata: DNS record data
    :return: dict w/fields
    """
    rschema = OrderedDict(
        (("prio", int), ("weight", int), ("port", _to_port), ("name", str),)
    )
    return _data2rec_group(rschema, rdatas, "prio")


def sshfp_data(key_t, hash_t, pub):
    """
    Generate an SSHFP record
    :param key_t: rsa/dsa/ecdsa/ed25519
    :param hash_t: sha1/sha256
    :param pub: the SSH public key
    """
    key_t = RFC.validate(key_t, RFC.SSHFP_ALGO, "in")
    hash_t = RFC.validate(hash_t, RFC.SSHFP_HASH)

    hasher = hashlib.new(hash_t)
    hasher.update(base64.b64decode(pub))
    ssh_fp = hasher.hexdigest()

    return _rec2data(key_t, hash_t, ssh_fp)


def sshfp_rec(rdata):
    """
    Validate and parse DNS record data for TLSA record(s)
    :param rdata: DNS record data
    :return: dict w/fields
    """
    rschema = OrderedDict(
        (
            ("algorithm", RFC.SSHFP_ALGO),
            ("fp_hash", RFC.SSHFP_HASH),
            (
                "fingerprint",
                lambda val: val.lower(),
            ),  # resolvers are inconsistent on this one
        )
    )

    return _data2rec(rschema, rdata)


def tlsa_data(pub, usage, selector, matching):
    """
    Generate a TLSA rec
    :param pub: Pub key in PEM format
    :param usage:
    :param selector:
    :param matching:
    :return: TLSA data portion
    """
    usage = RFC.validate(usage, RFC.TLSA_USAGE)
    selector = RFC.validate(selector, RFC.TLSA_SELECT)
    matching = RFC.validate(matching, RFC.TLSA_MATCHING)

    pub = ssl.PEM_cert_to_DER_cert(pub.strip())
    if matching == 0:
        cert_fp = binascii.b2a_hex(pub)
    else:
        hasher = hashlib.new(RFC.TLSA_MATCHING[matching])
        hasher.update(pub)
        cert_fp = hasher.hexdigest()

    return _rec2data(usage, selector, matching, cert_fp)


def tlsa_rec(rdata):
    """
    Validate and parse DNS record data for TLSA record(s)
    :param rdata: DNS record data
    :return: dict w/fields
    """
    rschema = OrderedDict(
        (
            ("usage", RFC.TLSA_USAGE),
            ("selector", RFC.TLSA_SELECT),
            ("matching", RFC.TLSA_MATCHING),
            ("pub", str),
        )
    )

    return _data2rec(rschema, rdata)


def service(svc, proto="tcp", domain=None, walk=False, secure=None):
    """
    Find an SRV service in a domain or its parents
    :param svc: service to find (ldap, 389, etc)
    :param proto: protocol the service talks (tcp, udp, etc)
    :param domain: domain to start search in
    :param walk: walk the parents if domain doesn't provide the service
    :param secure: only return DNSSEC-validated results
    :return: [
        [ prio1server1, prio1server2 ],
        [ prio2server1, prio2server2 ],
    ] (the servers will already be weighted according to the SRV rules)
    """
    qres = query(srv_name(svc, proto, domain), "SRV", walk=walk, secure=secure)
    if not qres:
        return False

    res = []
    for _, recs in qres.items():
        res.append(_weighted_order(recs))

    return res


def services(services_file="/etc/services"):
    """
    Parse through system-known services
    :return: {
        'svc': [
          {  'port': port
             'proto': proto,
             'desc': comment
          },
        ],
    }
    """
    res = {}
    with salt.utils.files.fopen(services_file, "r") as svc_defs:
        for svc_def in svc_defs.readlines():
            svc_def = salt.utils.stringutils.to_unicode(svc_def.strip())
            if not svc_def or svc_def.startswith("#"):
                continue
            elif "#" in svc_def:
                svc_def, comment = svc_def.split("#", 1)
                comment = comment.strip()
            else:
                comment = None
            svc_def = svc_def.split()

            port, proto = svc_def.pop(1).split("/")
            port = int(port)

            for name in svc_def:
                svc_res = res.get(name, {})
                pp_res = svc_res.get(port, False)
                if not pp_res:
                    svc = {
                        "port": port,
                        "proto": proto,
                    }
                    if comment:
                        svc["desc"] = comment
                    svc_res[port] = svc
                else:
                    curr_proto = pp_res["proto"]
                    if isinstance(curr_proto, (list, tuple)):
                        curr_proto.append(proto)
                    else:
                        pp_res["proto"] = [curr_proto, proto]

                    curr_desc = pp_res.get("desc", False)
                    if comment:
                        if not curr_desc:
                            pp_res["desc"] = comment
                        elif comment != curr_desc:
                            pp_res["desc"] = "{}, {}".format(curr_desc, comment)
                res[name] = svc_res

    for svc, data in res.items():
        if len(data) == 1:
            res[svc] = data.values().pop()
            continue
        else:
            res[svc] = list(data.values())

    return res


def parse_resolv(src="/etc/resolv.conf"):
    """
    Parse a resolver configuration file (traditionally /etc/resolv.conf)
    """

    nameservers = []
    ip4_nameservers = []
    ip6_nameservers = []
    search = []
    sortlist = []
    domain = ""
    options = []

    try:
        with salt.utils.files.fopen(src) as src_file:
            # pylint: disable=too-many-nested-blocks
            for line in src_file:
                line = salt.utils.stringutils.to_unicode(line).strip().split()

                try:
                    (directive, arg) = (line[0].lower(), line[1:])
                    # Drop everything after # or ; (comments)
                    arg = list(
                        itertools.takewhile(lambda x: x[0] not in ("#", ";"), arg)
                    )
                    if directive == "nameserver":
                        addr = arg[0]
                        try:
                            ip_addr = ipaddress.ip_address(addr)
                            version = ip_addr.version
                            ip_addr = str(ip_addr)
                            if ip_addr not in nameservers:
                                nameservers.append(ip_addr)
                            if version == 4 and ip_addr not in ip4_nameservers:
                                ip4_nameservers.append(ip_addr)
                            elif version == 6 and ip_addr not in ip6_nameservers:
                                ip6_nameservers.append(ip_addr)
                        except ValueError as exc:
                            log.error("%s: %s", src, exc)
                    elif directive == "domain":
                        domain = arg[0]
                    elif directive == "search":
                        search = arg
                    elif directive == "sortlist":
                        # A sortlist is specified by IP address netmask pairs.
                        # The netmask is optional and defaults to the natural
                        # netmask of the net. The IP address and optional
                        # network pairs are separated by slashes.
                        for ip_raw in arg:
                            try:
                                ip_net = ipaddress.ip_network(ip_raw)
                            except ValueError as exc:
                                log.error("%s: %s", src, exc)
                            else:
                                if "/" not in ip_raw:
                                    # No netmask has been provided, guess
                                    # the "natural" one
                                    if ip_net.version == 4:
                                        ip_addr = str(ip_net.network_address)
                                        # pylint: disable=protected-access
                                        mask = salt.utils.network.natural_ipv4_netmask(
                                            ip_addr
                                        )
                                        ip_net = ipaddress.ip_network(
                                            "{}{}".format(ip_addr, mask), strict=False
                                        )
                                    if ip_net.version == 6:
                                        # TODO
                                        pass

                                if ip_net not in sortlist:
                                    sortlist.append(ip_net)
                    elif directive == "options":
                        # Options allows certain internal resolver variables to
                        # be modified.
                        if arg[0] not in options:
                            options.append(arg[0])
                except IndexError:
                    continue

        if domain and search:
            # The domain and search keywords are mutually exclusive.  If more
            # than one instance of these keywords is present, the last instance
            # will override.
            log.debug("%s: The domain and search keywords are mutually exclusive.", src)

        return {
            "nameservers": nameservers,
            "ip4_nameservers": ip4_nameservers,
            "ip6_nameservers": ip6_nameservers,
            "sortlist": [ip.with_netmask for ip in sortlist],
            "domain": domain,
            "search": search,
            "options": options,
        }
    except OSError:
        return {}
