Mailman 3 April 2013 - Twisted

[Twisted-Python] twisted.cred interface deficiences
by Shell April 3, 2013

April 3, 2013

The twisted.cred.IUsernamePassword interface declares: * IUsernamePassword.username - "The username associated with these credentials." * IUsernamePassword.password - "The password associated with these credentials." * IUsernamePassword.checkPassword(password) - "Validate these credentials against the correct password." The issue is that the interface (according to exarkun) allows you to implement checkPassword() to do things other than the obvious "password == self.password". Now, this is an issue because Twisted then explicitly supports (again, according to exarkun) two different uses of this interface by the credentials checker: * Call the checkPassword() method, passing it the correct password * Just take the password out and do whatever you want with it (which is necessary in any secure system) Now, imagine I write a version of checkPassword() in a library which does something security-centric (what would this be? shouldn't it be part of the checker?), assuming that it'll be used by a credentials checker which calls checkPassword(). Except... then, a library user uses it with a credentials checker which checks the password itself. Now they're skipping over my security-centric code! So I have to tell my library users that they have to use my library with a credentials checker which makes sure to call checkPassword(), not just one which accepts the correct interface. IUsernamePassword's docstring claims that the stored password must be reversible to plaintext to be compared with the password, which implies that taking the password out and doing other things is incorrect, unlike what exarkun suggests. In this case, exposing password in the interface makes little sense. In addition, twisted.cred.checkers.FilePasswordDB apparently ignores this docstring entirely already (http://twistedmatrix.com/trac/browser/tags/releases/twisted-12.3.0/twisted/…). I propose that IUsernamePassword should be split into at least two interfaces: * IUsernamePassword, with only username and password, no methods, which allows password to be used in any way * Another interface, which only defines username and checkPassword() - possibly just a rename of IUsernameHashedPassword, which declares a similar interface However, this has the issue that any credential checker which can use the second interface would also be able to use an IUsernamePassword here if there were an adapter between the two, but support for this would have to go into every credential checker which supports the second interface at present. Maybe the Portal could automatically search for adapters if it can't find a direct match? Thanks, Cameron

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[Twisted-Python] How to determine whether transport.write() succeed?
by Todong Ma April 3, 2013

April 3, 2013

Hi, everyone How could I dertermine ITransport.write() succeed? In windows socket API, I can check send()'s return value to dertermine whether send() succeed. Any suggestion is appreciated.

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[Twisted-Python] t.n.c.lookupAddress returns DNSNameError for hostnames w/ no A record
by byr sa April 2, 2013

April 2, 2013

Hi all, I saw in previous posts that DNSNameError signifies an 'NXDOMAIN' status and DNSServerError signifies 'SERVFAIL'. However, I am getting a DNSNameError from twisted.names.client.lookupAddress() when I query a hostname that has no A records, but *does have* other records (NS, SOA, etc). An example: ; <<>> DiG 9.8.3-P1 <<>> megaupload.com ANY ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19402 ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;megaupload.com. IN ANY ;; ANSWER SECTION: megaupload.com. 21600 IN SOA ns5.cirfu.net. ipr.ic.fbi.gov. 2013022001 3600 900 604800 900 megaupload.com. 21600 IN NS ns5.cirfu.net. megaupload.com. 21600 IN NS ns6.cirfu.net. dig is telling me 'status: NOERROR'. Is there an easy way to determine the status of a DNS query from a twisted.names.dns.Message ? I checked the source and it wasn't readily apparent (to me). In my code I'm checking the value of failure.value.__class__.__name__ to determine if an answer is NX or SERVFAIL. Seems like there should be a better way... Here's the code if anybody wants to take a look: http://paste.ubuntu.com/5669612/ Thanks to the Twisted devs and maintainers for all your hard work! byrsa

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