PYTHON-6080 Introduce Custom Callback logic in Configurable DNS by sleepyStick · Pull Request #3051 · mongodb/mongo-python-driver

sleepyStick · 2026-09-11T03:23:06Z

PYTHON-6080

Changes in this PR

add srvHostValidator
some modifications to srvAllowedHostsSuffix (allowing things like localhost to be considered valid)
found a bug in SRV polling where the topology wouldn't change (new hosts wouldn't be added and hosts no longer in DNS wouldn't be removed) if one returned host was invalid

Test Plan

prose tests
added a new test for the srv bug too

Checklist

Checklist for Author

Did you update the changelog (if necessary)?
Is there test coverage?
Is any followup work tracked in a JIRA ticket? If so, add link(s).

Checklist for Reviewer

Does the title of the PR reference a JIRA Ticket?
Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
Is all relevant documentation (README or docstring) updated?

…was only here for the initial delivery of the project, removing now

…run a resync

…ver into PYTHON-5814

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codecov · 2026-09-11T04:31:25Z

Codecov Report

❌ Patch coverage is 85.82677% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pymongo/synchronous/srv_resolver.py	78.00%	6 Missing and 5 partials ⚠️
pymongo/asynchronous/srv_resolver.py	90.00%	3 Missing and 2 partials ⚠️
pymongo/_telemetry.py	33.33%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

…olling

…ver into PYTHON-5814

Copilot

Copilot review overview

🟡 Changes recommended

Direct non-SRV URI parsing can silently ignore the validator, and polling behavior documentation needs clarification.

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Review effort: Lite
Findings: 1

Open (1)

Clarify polling error handling versus initial SRV discovery · New

What changed in this PR

Introduces configurable SRV host validation and improves polling behavior for invalid DNS records.

Changes:

Adds srv_host_validator to synchronous and asynchronous clients.
Skips invalid hosts during SRV polling and logs them.
Updates suffix handling, tests, telemetry, and changelog documentation.

File	Summary
`test/unified_format.py`	Updates synchronous test coverage and cleanup.
`test/test_srv_polling.py`	Tests synchronous SRV polling validation.
`test/test_dns.py`	Tests synchronous DNS validation and suffix behavior.
`test/asynchronous/unified_format.py`	Updates asynchronous test coverage and cleanup.
`test/asynchronous/test_srv_polling.py`	Tests asynchronous SRV polling validation.
`test/asynchronous/test_dns.py`	Tests callback and suffix behavior; prose test naming needs correction.
`pymongo/synchronous/uri_parser.py`	Synchronous URI parsing and validator propagation.
`pymongo/synchronous/srv_resolver.py`	Synchronous SRV validation and polling filtering.
`pymongo/synchronous/settings.py`	Stores synchronous validator configuration.
`pymongo/synchronous/monitor.py`	Applies validation during synchronous polling.
`pymongo/synchronous/mongo_client.py`	Exposes the synchronous validator option.
`pymongo/settings_shared.py`	Adds shared callback configuration.
`pymongo/public_suffix_list.dat`	Updates bundled suffix data.
`pymongo/common.py`	Validates callback options.
`pymongo/asynchronous/uri_parser.py`	Propagates the validator; non-SRV direct parsing must reject it.
`pymongo/asynchronous/srv_resolver.py`	Implements asynchronous validation and polling filtering.
`pymongo/asynchronous/settings.py`	Stores asynchronous validator configuration.
`pymongo/asynchronous/monitor.py`	Applies validation during asynchronous polling.
`pymongo/asynchronous/mongo_client.py`	Exposes and documents the asynchronous validator option.
`pymongo/_telemetry.py`	Logs skipped invalid SRV hosts.
`pymongo/_psl.py`	Adds special-use suffix handling.
`doc/changelog.rst`	Documents the new functionality.

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sleepyStick · 2026-09-25T17:41:32Z

+            reject it. Rejecting a host raises
+            :exc:`~pymongo.errors.ConfigurationError`, as does an exception raised by
+            the callback itself. Use this when the set of acceptable hosts cannot be
+            expressed as a single suffix::


I don't think users need to know the difference between initial discovery and polling so I believe this suggestion should be ignored.

True but probably doesn't hurt to clarify "During initial discovery" …

done in 07df266

aclark4life · 2026-09-25T20:46:03Z

        elif self.__srv_allowed_hosts_suffix is not None:
            if not srv_host.endswith(self.__srv_allowed_hosts_suffix):
                raise ConfigurationError(f"Invalid SRV host: {srv_host}")
        else:


I think we miss this branch if the conditional on line 155 is True.

sorry i'm not sure i understand what you mean by this comment -- it is possible to enter the else conditional and there is test coverage for all three branches. If we're referring to the identical hostname check, that's intentional per the spec. Can you clarify what you mean?

aclark4life · 2026-09-25T20:47:24Z

+  connection string. See the
+  :class:`~pymongo.synchronous.mongo_client.MongoClient` and
+  :class:`~pymongo.asynchronous.mongo_client.AsyncMongoClient` documentation for
+  security considerations (`PYTHON-5814`_).


Should this be PYTHON-6080 ?

yes, but also current iris isn't sure why past iris put a ticket there so i'm going to just remove the ticket reference entirely.

aclark4life · 2026-09-25T20:48:25Z

-            self.__srv_allowed_hosts_suffix
-        ):
+        self.__srv_host_validator = srv_host_validator
+        # parse_uri() can this constructor independently of AsyncMongoClient.


"can … this constructor"?

ah, oops, fixed in 07df266. thanks!

aclark4life · 2026-09-25T20:48:33Z

-            self.__srv_allowed_hosts_suffix
-        ):
+        self.__srv_host_validator = srv_host_validator
+        # parse_uri() can this constructor independently of MongoClient.


"can … this constructor"?

aclark4life · 2026-09-25T20:56:44Z

Does the caller reject it? Looks like a..b becomes .a..b

sorry I think this was a case of bad comment -- realistically DNS won't return an SRV target with an empty label, so even if a user passes it in, it would fail verification. I've updated the comment appropriately in 07df266. Thanks!

aclark4life · 2026-09-25T21:01:12Z

+                nodes = []
+                for node in self.nodelist_callback():
+                    try:
+                        resolver._validate_host(node[0].rstrip(".").lower())


Since the mock calls _validate_host and drops rejected hosts here, tests 14 and 15 would still pass if _get_srv_response_and_hosts stopped filtering for some reason.

ah good catch -- i've reworked this in 07df266 to only mock the DNS answer so the real filtering happens now!

sleepyStick and others added 30 commits June 11, 2026 13:53

add srvAllowedHostsSuffix option to srv uri

2cd02da

Merge branch 'master' into PYTHON-5814

499a3ec

sync unified tests

3423d39

Merge branch 'master' into PYTHON-5814

3e30434

add unified test (forgot to commit this previously oops)

1ac4967

Merge branch 'master' into PYTHON-5814

a8a3b4e

Merge branch 'master' into PYTHON-5814

9663485

Merge branch 'master' into PYTHON-5814

a71dd7a

add more tests and edit docstring

4a6ba01

edit changelog

466a47e

cache public suffix list after first load

7902127

add example to docstring

c8f8c9f

Merge branch 'main' into PYTHON-5814

2c8ad29

add psl tests

14ae604

remove two label minimum

1fc7fe2

add test

fa34923

Merge branch 'main' into PYTHON-5814

aaad72f

lower the srv response

a2c5cbd

replaced this test with a different one in the spec repo -- this one …

071a285

…was only here for the initial delivery of the project, removing now

add psl to resync spec script so it can be synced regularly and sync …

63d57ca

…run a resync

Merge branch 'main' into PYTHON-5814

7c4e57a

update changelog

ae72df1

Merge branch 'PYTHON-5814' of github.com:sleepyStick/mongo-python-dri…

c950d35

…ver into PYTHON-5814

NS feedback

8f58480

Merge branch 'main' into PYTHON-5814

820c648

sort the list alphabetically

d99b4e9

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

add test and convert all strings to punycode

684f31b

pre-convert to punycode

44283f2

Merge branch 'main' into PYTHON-5814

7a6c2e8

fix srv_allow_hosts_suffix in settings shared

46efa90

sleepyStick added 2 commits September 2, 2026 15:48

resync specs

c949f54

PYTHON-5814 add srvHostValidator

8fb7ded

sleepyStick mentioned this pull request Sep 11, 2026

DRIVERS-3632 Introduce Custom Callback logic in Configurable DNS mongodb/specifications#1980

Merged

4 tasks

Merge branch 'main' into PYTHON-5814

46f8c83

sleepyStick and others added 8 commits September 15, 2026 08:17

add tests

1fba850

failed hosts shouldn't cause valid hosts to not be added during SRV p…

b745c3b

…olling

Merge branch 'main' into PYTHON-5814

461ef6f

Merge branch 'main' into PYTHON-5814

23d664a

i think this should fix the failing tests...

886172f

Merge branch 'PYTHON-5814' of github.com:sleepyStick/mongo-python-dri…

c7f1de3

…ver into PYTHON-5814

Merge branch 'main' into PYTHON-5814

9c94fbd

run pre-commit locally after merge

26512c7

sleepyStick marked this pull request as ready for review September 24, 2026 21:54

sleepyStick requested a review from a team as a code owner September 24, 2026 21:54

sleepyStick requested review from aclark4life and a lite review from Copilot and removed request for Copilot September 24, 2026 21:54

Copilot started reviewing on behalf of sleepyStick September 25, 2026 16:24 View session

Copilot AI reviewed Sep 25, 2026

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sleepyStick and others added 2 commits September 25, 2026 10:42

clean up code comments

abb1550

Merge branch 'main' into PYTHON-5814

46de8d4

aclark4life requested changes Sep 25, 2026

View reviewed changes

AC feedback

07df266

sleepyStick requested a review from aclark4life September 25, 2026 23:35

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sleepyStick commented Sep 11, 2026 • edited by aclark4life Loading Uh oh! There was an error while loading. Please reload this page.

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sleepyStick commented Sep 11, 2026 •

edited by aclark4life

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