Precisely catch DNS error with Python requests

问题

I am trying to make a check for expired domain name with python-requests.

import requests

try:
    status = requests.head('http://wowsucherror')
except requests.ConnectionError as exc:
    print(exc)

This code looks too generic. It produces the following output:

HTTPConnectionPool(host='wowsucherror', port=80): Max retries exceeded with url: / (Caused by NewConnectionError(': Failed to establish a new connection: [Errno 11001] getaddrinfo failed',))

What I'd like to do is to catch this DNS error only (like ERR_NAME_NOT_RESOLVED in Chrome). As a last resort I can just do string matching, but maybe there is a better, more structured and forward compatible way of dealing with this error?

Ideally it should be some DNSError extension to requests.

UPDATE: The error on Linux is different.

HTTPConnectionPool(host='wowsucherror', port=80): Max retries exceeded with url: / (Caused by NewConnectionError(': Failed to establish a new connection: [Errno -2] Name or service not known',))

Reported bug to requests -> urllib3 https://github.com/shazow/urllib3/issues/1003

UPDATE2: OS X also reports different error.

requests.exceptions.ConnectionError: HTTPConnectionPool(host='wowsucherror', port=80): Max retries exceeded with url: / (Caused by NewConnectionError(': Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known',))

回答1:

Done this with this hack, but please monitor https://github.com/kennethreitz/requests/issues/3630 for a proper way to appear.

import requests

def sitecheck(url):
    status = None
    message = ''
    try:
        resp = requests.head('http://' + url)
        status = str(resp.status_code)
    except requests.ConnectionError as exc:
        # filtering DNS lookup error from other connection errors
        # (until https://github.com/shazow/urllib3/issues/1003 is resolved)
        if type(exc.message) != requests.packages.urllib3.exceptions.MaxRetryError:
            raise
        reason = exc.message.reason    
        if type(reason) != requests.packages.urllib3.exceptions.NewConnectionError:
            raise
        if type(reason.message) != str:
            raise
        if ("[Errno 11001] getaddrinfo failed" in reason.message or     # Windows
            "[Errno -2] Name or service not known" in reason.message or # Linux
            "[Errno 8] nodename nor servname " in reason.message):      # OS X
            message = 'DNSLookupError'
        else:
            raise

    return url, status, message

print sitecheck('wowsucherror')
print sitecheck('google.com')

回答2:

You could use lower-level network interface, socket.getaddrinfo https://docs.python.org/3/library/socket.html#socket.getaddrinfo

import socket


def dns_lookup(host):
    try:
        socket.getaddrinfo(host, 80)
    except socket.gaierror:
        return False
    return True


print(dns_lookup('wowsucherror'))
print(dns_lookup('google.com'))

来源：https://stackoverflow.com/questions/40145631/precisely-catch-dns-error-with-python-requests

标签

dns

python-requests