fix: don't crash when mariadb connection string doesn't include port or user [backport 1.18] (#6689)

Backport 6a6e688 from #6682 to 1.18.

This change fixes #6203 by
supplying defaults for the accesses of `port` and `user` fields from the
MariaDB connection info object.

## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed. If no release note is required, add label
`changelog/no-changelog`.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer has explicitly acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment.
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Emmett Butler <[email protected]>

Author: github-actions[bot]

ddtrace/contrib/mariadb/patch.py

@@ -39,10 +39,10 @@ def unpatch():
 def _connect(func, instance, args, kwargs):
     conn = func(*args, **kwargs)
     tags = {
-        net.TARGET_HOST: kwargs["host"],
-        net.TARGET_PORT: kwargs["port"],
-        db.USER: kwargs["user"],
-        db.NAME: kwargs["database"],
+        net.TARGET_HOST: kwargs.get("host", "127.0.0.1"),
+        net.TARGET_PORT: kwargs.get("port", 3306),
+        db.USER: kwargs.get("user", "test"),
+        db.NAME: kwargs.get("database", "test"),
         db.SYSTEM: "mariadb",
     }
 

releasenotes/notes/maria-missing-port-e30630b4f5a5ee33.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    mariadb: This fix resolves an issue where MariaDB connection information objects not including the user
+    or port caused exceptions to be raised.

tests/contrib/mariadb/test_mariadb.py

@@ -51,6 +51,18 @@ def connection(tracer):
         yield connection
 
 
+def test_connection_no_port_or_user_does_not_raise():
+    conf = MARIADB_CONFIG.copy()
+    del conf["port"]
+    del conf["user"]
+    try:
+        mariadb.connect(**conf)
+    except mariadb.OperationalError as exc:
+        # this error is expected because mariadb defaults user to root when not given
+        if "Access denied for user 'root'" not in str(exc):
+            raise exc
+
+
 def test_simple_query(connection, tracer):
     cursor = connection.cursor()
     cursor.execute("SELECT 1")