Hi,
Hope everyone is well.
We encountered a situation where uuids generated by tcllib's uuid::uuid
generate can repeat sequences under naviserver which has caused some issues
in our codebase with collisions.
We wondered if you would expect this behaviour?
Using Debian 9.7 with Naviserver 4.99.19 tarball.
We have a /usr/local/ns/tcl/test.tcl file:
proc uuid_test {} {
ns_return 200 text/plain [uuid::uuid generate]
}
package require uuid
ns_register_proc GET /test.tcl uuid_test
Then we start naviserver with:
sudo /usr/local/ns/bin/nsd -u nsadmin -t /usr/local/ns/conf/nsd-config.tcl
Each request starts off with unique uuids:
$ curl http://127.0.0.1:8080/test.tcl
94648710-5503-4ecb-8853-7acd68fe289c
$ curl http://127.0.0.1:8080/test.tcl
de3a7eee-8b4d-45b9-b80c-71985b2b6346
$ curl http://127.0.0.1:8080/test.tcl
efec82f4-2e0f-43ff-a951-6abb0a9a61a9
Then if we do a ns_eval -sync source of any file:
$ nc 127.0.0.1 4080
Welcome to default running at /usr/local/ns/bin/nsd (pid 12248)
NaviServer/4.99.19 for linux built on Apr 6 2020 at 14:27:50
Tag: tar-4.99.19
default:nscp 1> ns_eval -sync source /usr/local/ns/tcl/file.tcl
We are given the same sequence of uuids again:
$ curl http://127.0.0.1:8080/test.tcl
94648710-5503-4ecb-8853-7acd68fe289c
$ curl http://127.0.0.1:8080/test.tcl
de3a7eee-8b4d-45b9-b80c-71985b2b6346
$ curl http://127.0.0.1:8080/test.tcl
efec82f4-2e0f-43ff-a951-6abb0a9a61a9
The same issue does *not* happen with your ns_uuid implementation.
We dug into the implementation details of the tcllib version. I'm not
familiar with the uuid algorithm particularly, but it seems when initially
called, the code generates some random data to use when making the uuid
which it calls machinfo. This is then cached and will not change as long as
the variable exists in memory. The only thing making each subsequent
request different is an incrementing counter (called uid) which is used in
the MD5 hash.
What happens with ns_eval, is that this counter (uid) is reset, the machinfo
stays the same, so the same sequence of uuids begins again.
https://github.com/tcltk/tcllib/blob/master/modules/uuid/uuid.tcl#L37
What's your take on this behaviour?
Thanks,
--
David
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