app-MAIL-temp/app/dns_utils.py

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from typing import Optional
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import dns.resolver
def _get_dns_resolver():
my_resolver = dns.resolver.Resolver()
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# 1.1.1.1 is CloudFlare's public DNS server
my_resolver.nameservers = ["1.1.1.1"]
return my_resolver
def get_cname_record(hostname) -> Optional[str]:
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"""Return the CNAME record if exists for a domain, WITHOUT the trailing period at the end"""
try:
answers = _get_dns_resolver().query(hostname, "CNAME")
except Exception:
return None
for a in answers:
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ret = a.to_text()
return ret[:-1]
return None
def get_mx_domains(hostname) -> [(int, str)]:
"""return list of (priority, domain name).
domain name ends with a "." at the end.
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"""
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try:
answers = _get_dns_resolver().query(hostname, "MX")
except Exception:
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return []
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ret = []
for a in answers:
record = a.to_text() # for ex '20 alt2.aspmx.l.google.com.'
parts = record.split(" ")
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ret.append((int(parts[0]), parts[1]))
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return ret
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_include_spf = "include:"
def get_spf_domain(hostname) -> [str]:
"""return all domains listed in *include:*"""
try:
answers = _get_dns_resolver().query(hostname, "TXT")
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except Exception:
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return []
ret = []
for a in answers: # type: dns.rdtypes.ANY.TXT.TXT
for record in a.strings:
record = record.decode() # record is bytes
if record.startswith("v=spf1"):
parts = record.split(" ")
for part in parts:
if part.startswith(_include_spf):
ret.append(part[part.find(_include_spf) + len(_include_spf) :])
return ret
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def get_txt_record(hostname) -> [str]:
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"""return all domains listed in *include:*"""
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try:
answers = _get_dns_resolver().query(hostname, "TXT")
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except Exception:
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return []
ret = []
for a in answers: # type: dns.rdtypes.ANY.TXT.TXT
for record in a.strings:
record = record.decode() # record is bytes
ret.append(record)
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return ret