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Allow braces to appear in dhclient output #911

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Merged
blackboxsw merged 3 commits into from
Jun 1, 2021
Merged

Allow braces to appear in dhclient output #911

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a74f1dd
Allow braces to appear in dhclient output
May 26, 2021
48d06c5
Merge branch 'master' into regex-fix
eb3095 May 27, 2021
1484f2d
Add unit test for this use case
May 27, 2021
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2 changes: 1 addition & 1 deletion cloudinit/net/dhcp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -173,7 +173,7 @@ def parse_dhcp_lease_file(lease_file):
@raises: InvalidDHCPLeaseFileError on empty of unparseable leasefile
content.
"""
lease_regex = re.compile(r"lease {(?P<lease>[^}]*)}\n")
lease_regex = re.compile(r"lease {(?P<lease>.*?)}\n", re.DOTALL)
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@blackboxsw blackboxsw Jun 1, 2021

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From man dchp.client I see now that lease declarations such as filename, server-name, script-name can all contain arbitrary "string" values, so trying to limit our regex and stop matching at the first the "}" it encounters will cause some significant issue, as you mentioned.

The description of a lease declaration from man dhclient.conf is

       A  lease  statement  consists  of the lease keyword, followed by a left
       curly brace, followed by one or more lease declaration statements, fol‐
       lowed  by  a  right  curly brace.  The following lease declarations are
       possible:

I can see by the vague text it could be possible that a multiple DHCP lease declarations could be emitted all on one line as in lease { ... } lease { ... }, in that case our regex ending with a curly brace newline "}\n" would continue to break there,... But, I'd say since we have gotten this far on multiple distributions we probably don't need to solve that issue in this PR. We can deal with that if it comes up.

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@eb3095 eb3095 Jun 7, 2021

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Just adding to this for future reference when/if it comes up. I saw that also but I have never personally seen it resolve like that, might need a special set of very intentional circumstances. However if it ever does come up I do not think regex is the correct answer. It took me quite some time and fiddling to get this to work, and that would be excessively difficult. I would sooner take a customized algorithmic approach to handling this if it comes up by counting the brackets. Every { adds 1 to a var, every } reduces by one, concluding the parsing only when that var == 0. Again just adding this for the next unfortunate sap left to stare this issue down! If anyone wants me to implement this now however I wouldnt mind doing so and adding the test case for it.

dhcp_leases = []
lease_content = util.load_file(lease_file)
if len(lease_content) == 0:
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6 changes: 5 additions & 1 deletion cloudinit/net/tests/test_dhcp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@ def test_parse_multiple_leases(self):
lease {
interface "wlp3s0";
fixed-address 192.168.2.74;
filename "http://192.168.2.50/boot.php?mac=${netX}";
option subnet-mask 255.255.255.0;
option routers 192.168.2.1;
renew 4 2017/07/27 18:02:30;
Expand All @@ -50,6 +51,7 @@ def test_parse_multiple_leases(self):
lease {
interface "wlp3s0";
fixed-address 192.168.2.74;
filename "http://192.168.2.50/boot.php?mac=${netX}";
option subnet-mask 255.255.255.0;
option routers 192.168.2.1;
}
Expand All @@ -58,8 +60,10 @@ def test_parse_multiple_leases(self):
{'interface': 'wlp3s0', 'fixed-address': '192.168.2.74',
'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1',
'renew': '4 2017/07/27 18:02:30',
'expire': '5 2017/07/28 07:08:15'},
'expire': '5 2017/07/28 07:08:15',
'filename': 'http://192.168.2.50/boot.php?mac=${netX}'},
{'interface': 'wlp3s0', 'fixed-address': '192.168.2.74',
'filename': 'http://192.168.2.50/boot.php?mac=${netX}',
'subnet-mask': '255.255.255.0', 'routers': '192.168.2.1'}]
write_file(lease_file, content)
self.assertCountEqual(expected, parse_dhcp_lease_file(lease_file))
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