Add Pydantic types for Postgres and Redis DSNs

Add new types `safir.pydantic.EnvAsyncPostgresDsn` and
`safir.pydantic.EnvRedisDsn`, which validate PostgreSQL and Redis
DSNs but rewrite them based on the environment variables set by
tox-docker. Programs using these types for their configuration will
therefore automatically honor tox-docker environment variables when
running the test suite. `EnvAsyncPostgresDsn` also enforces that the
scheme of the DSN is compatible with asyncpg and the Safir database
support.

changelog.d/20240717_101902_rra_DM_45281_queue.md

@@ -0,0 +1,3 @@
+### New features
+
+- Add new types `safir.pydantic.EnvAsyncPostgresDsn` and `safir.pydantic.EnvRedisDsn`, which validate PostgreSQL and Redis DSNs but rewrite them based on the environment variables set by tox-docker. Programs using these types for their configuration will therefore automatically honor tox-docker environment variables when running the test suite. `EnvAsyncPostgresDsn` also enforces that the scheme of the DSN is compatible with asyncpg and the Safir database support.

docs/_rst_epilog.rst

@@ -23,4 +23,5 @@
 .. _structlog: https://www.structlog.org/en/stable/
 .. _templatekit: https://templatekit.lsst.io
 .. _tox: https://tox.wiki/en/latest/
+.. _tox-docker: https://tox-docker.readthedocs.io/en/latest/
 .. _Uvicorn: https://www.uvicorn.org/

docs/documenteer.toml

@@ -25,6 +25,8 @@ nitpick_ignore = [
     ["py:class", "BaseModel"],
     # sphinx-automodapi apparently doesn't recognize TypeAlias as an object
     # that should have generated documentation, even with include-all-objects.
+    ["py:obj", "safir.pydantic.EnvAsyncPostgresDsn"],
+    ["py:obj", "safir.pydantic.EnvRedisDsn"],
     ["py:obj", "safir.pydantic.HumanTimedelta"],
     ["py:obj", "safir.pydantic.SecondsTimedelta"],
 ]

docs/user-guide/database.rst

@@ -13,6 +13,8 @@ Safir uses the `asyncpg`_ PostgreSQL database driver.
 Database support in Safir is optional.
 To use it, depend on ``safir[db]`` in your pip requirements.
 
+Also see :ref:`pydantic-dsns` for Pydantic types that help with configuring the PostgreSQL DSN.
+
 Initializing a database
 =======================
 

docs/user-guide/pydantic.rst

@@ -5,6 +5,55 @@ Utilities for Pydantic models
 Several validation and configuration problems arise frequently with Pydantic models.
 Safir offers some utility functions to assist in solving them.
 
+.. _pydantic-dsns:
+
+Configuring PostgreSQL and Redis DSNs
+=====================================
+
+Databases and other storage services often use a :abbr:`DSN (Data Source Name)` to specify how to connect to the service.
+Pydantic provides multiple pre-defined types to parse and validate those DSNs, including ones for PostgreSQL and Redis.
+
+Safir applications often use tox-docker_ to start local PostgreSQL and Redis servers before running tests.
+tox-docker starts services on random loopback IP addresses and ports, and stores the hostname and IP address in standard environment variables.
+
+Safir provides alternative data types for PostgreSQL and Redis DSNs that behave largely the same as the Pydantic data types if the tox-docker environment variables aren't set.
+If the tox-docker variables are set, their contents are used to override the hostname and port of any provided DSN with the values provided by tox-docker.
+This allows the application to get all of its configuration from environment variables at module load time without needing special code in every application to handle the tox-docker environment variables.
+
+For PostgreSQL DSNs, use the data type `safir.pydantic.EnvAsyncPostgresDsn` instead of `pydantic.PostgresDsn`.
+This type additionally forces the scheme of the PostgreSQL DSN to either not specify the underying library or to specify asyncpg, allowing it to work correctly with the :doc:`Safir database API <database>`.
+Unlike the Pydantic type, `~safir.pydantic.EnvAsyncPostgresDsn` only supports a single host.
+
+For Redis DSNs, use the data type `safir.pydantic.EnvRedisDsn` instead of `pydantic.RedisDsn`.
+
+For example:
+
+.. code-block:: python
+
+   from pydantic_settings import BaseSettings, SettingsConfigDict
+   from safir.pydantic import EnvAsyncPostgresDsn, EnvRedisDsn
+
+
+   class Config(BaseSettings):
+       database_url: EnvAsyncPostgresDsn
+       redis_url: EnvRedisDsn
+
+       model_config = SettingsConfigDict(
+           env_prefix="EXAMPLE_", case_sensitive=False
+       )
+
+These types only adjust DSNs initialized as normal.
+They do not synthesize DSNs if none are set.
+Therefore, the application will still need to set the corresponding environment variables in :file:`tox.ini` for testing purposes, although the hostname and port can be dummy values.
+In this case, that would look something like:
+
+.. code-block:: ini
+
+   [testenv:py]
+   setenv =
+       EXAMPLE_DATABASE_URL = postgresql://example@localhost/example
+       EXAMPLE_REDIS_URL = redis://localhost/0
+
 .. _pydantic-datetime:
 
 Normalizing datetime fields

src/safir/pydantic.py

@@ -2,11 +2,19 @@
 
 from __future__ import annotations
 
+import os
 from collections.abc import Callable
 from datetime import UTC, datetime, timedelta
 from typing import Annotated, Any, ParamSpec, TypeAlias, TypeVar
 
-from pydantic import BaseModel, BeforeValidator, ConfigDict
+from pydantic import (
+    AfterValidator,
+    BaseModel,
+    BeforeValidator,
+    ConfigDict,
+    UrlConstraints,
+)
+from pydantic_core import Url
 
 from .datetime import parse_timedelta
 
@@ -15,6 +23,8 @@
 
 __all__ = [
     "CamelCaseModel",
+    "EnvAsyncPostgresDsn",
+    "EnvRedisDsn",
     "HumanTimedelta",
     "SecondsTimedelta",
     "normalize_datetime",
@@ -24,6 +34,87 @@
 ]
 
 
+def _validate_env_async_postgres_dsn(v: Url) -> Url:
+    """Possibly adjust a PostgreSQL DSN based on environment variables.
+
+    When run via tox and tox-docker, the PostgreSQL hostname and port will be
+    randomly selected and exposed only in environment variables. We have to
+    patch that into the database URL at runtime since `tox doesn't have a way
+    of substituting it into the environment
+    <https://github.com/tox-dev/tox-docker/issues/55>`__.
+    """
+    if port := os.getenv("POSTGRES_5432_TCP_PORT"):
+        return Url.build(
+            scheme=v.scheme,
+            username=v.username,
+            password=v.password,
+            host=os.getenv("POSTGRES_HOST", v.unicode_host() or "localhost"),
+            port=int(port),
+            path=v.path.lstrip("/") if v.path else v.path,
+            query=v.query,
+            fragment=v.fragment,
+        )
+    else:
+        return v
+
+
+EnvAsyncPostgresDsn: TypeAlias = Annotated[
+    Url,
+    UrlConstraints(
+        host_required=True,
+        allowed_schemes=["postgresql", "postgresql+asyncpg"],
+    ),
+    AfterValidator(_validate_env_async_postgres_dsn),
+]
+"""Async PostgreSQL data source URL honoring Docker environment variables.
+
+Unlike the standard Pydantic ``PostgresDsn`` type, this type does not support
+multiple hostnames because Safir's database library does not support multiple
+hostnames.
+"""
+
+
+def _validate_env_redis_dsn(v: Url) -> Url:
+    """Possibly adjust a Redis DSN based on environment variables.
+
+    When run via tox and tox-docker, the Redis hostname and port will be
+    randomly selected and exposed only in environment variables. We have to
+    patch that into the Redis URL at runtime since `tox doesn't have a way of
+    substituting it into the environment
+    <https://github.com/tox-dev/tox-docker/issues/55>`__.
+    """
+    if port := os.getenv("REDIS_6379_TCP_PORT"):
+        return Url.build(
+            scheme=v.scheme,
+            username=v.username,
+            password=v.password,
+            host=os.getenv("REDIS_HOST", v.unicode_host() or "localhost"),
+            port=int(port),
+            path=v.path.lstrip("/") if v.path else v.path,
+            query=v.query,
+            fragment=v.fragment,
+        )
+    else:
+        return v
+
+
+EnvRedisDsn: TypeAlias = Annotated[
+    Url,
+    UrlConstraints(
+        allowed_schemes=["redis"],
+        default_host="localhost",
+        default_port=6379,
+        default_path="/0",
+    ),
+    AfterValidator(_validate_env_redis_dsn),
+]
+"""Redis data source URL honoring Docker environment variables.
+
+Unlike the standard Pydantic ``RedisDsn`` type, this does not support the
+``rediss`` scheme, which indicates the use of TLS.
+"""
+
+
 def _validate_human_timedelta(v: str | float | timedelta) -> float | timedelta:
     if not isinstance(v, str):
         return v

tests/pydantic_test.py

@@ -15,6 +15,8 @@
 
 from safir.pydantic import (
     CamelCaseModel,
+    EnvAsyncPostgresDsn,
+    EnvRedisDsn,
     HumanTimedelta,
     SecondsTimedelta,
     normalize_datetime,
@@ -24,6 +26,119 @@
 )
 
 
+def test_env_async_postgres_dsn(monkeypatch: pytest.MonkeyPatch) -> None:
+    class TestModel(BaseModel):
+        dsn: EnvAsyncPostgresDsn
+
+    monkeypatch.delenv("POSTGRES_5432_TCP_PORT", raising=False)
+    monkeypatch.delenv("POSTGRES_HOST", raising=False)
+    model = TestModel.model_validate(
+        {"dsn": "postgresql://localhost:7777/some-database"}
+    )
+    assert model.dsn.scheme == "postgresql"
+    assert not model.dsn.username
+    assert not model.dsn.password
+    assert model.dsn.host == "localhost"
+    assert model.dsn.port == 7777
+    assert model.dsn.path == "/some-database"
+    assert not model.dsn.query
+
+    model = TestModel.model_validate(
+        {
+            "dsn": (
+                "postgresql+asyncpg://user:password@localhost/other"
+                "?connect_timeout=10"
+            )
+        }
+    )
+    assert model.dsn.scheme == "postgresql+asyncpg"
+    assert model.dsn.username == "user"
+    assert model.dsn.password == "password"
+    assert model.dsn.host == "localhost"
+    assert not model.dsn.port
+    assert model.dsn.path == "/other"
+    assert model.dsn.query == "connect_timeout=10"
+
+    monkeypatch.setenv("POSTGRES_5432_TCP_PORT", "8999")
+    model = TestModel.model_validate(
+        {
+            "dsn": (
+                "postgresql://user:password@localhost/other?connect_timeout=10"
+            )
+        }
+    )
+    assert model.dsn.scheme == "postgresql"
+    assert model.dsn.username == "user"
+    assert model.dsn.password == "password"
+    assert model.dsn.host == "localhost"
+    assert model.dsn.port == 8999
+    assert model.dsn.path == "/other"
+    assert model.dsn.query == "connect_timeout=10"
+
+    monkeypatch.setenv("POSTGRES_HOST", "example.com")
+    model = TestModel.model_validate({"dsn": "postgresql://localhost/other"})
+    assert model.dsn.scheme == "postgresql"
+    assert not model.dsn.username
+    assert not model.dsn.password
+    assert model.dsn.host == "example.com"
+    assert model.dsn.port == 8999
+    assert model.dsn.path == "/other"
+    assert not model.dsn.query
+
+    with pytest.raises(ValidationError):
+        TestModel.model_validate(
+            {"dsn": "postgresql+psycopg2://localhost/other"}
+        )
+
+
+def test_env_redis_dsn(monkeypatch: pytest.MonkeyPatch) -> None:
+    class TestModel(BaseModel):
+        dsn: EnvRedisDsn
+
+    monkeypatch.delenv("REDIS_6379_TCP_PORT", raising=False)
+    monkeypatch.delenv("REDIS_HOST", raising=False)
+    model = TestModel.model_validate(
+        {"dsn": "redis://user:[email protected]:7777/1"}
+    )
+    assert model.dsn.scheme == "redis"
+    assert model.dsn.username == "user"
+    assert model.dsn.password == "password"
+    assert model.dsn.host == "example.com"
+    assert model.dsn.port == 7777
+    assert model.dsn.path == "/1"
+
+    model = TestModel.model_validate({"dsn": "redis://localhost"})
+    assert model.dsn.scheme == "redis"
+    assert not model.dsn.username
+    assert not model.dsn.password
+    assert model.dsn.host == "localhost"
+    assert model.dsn.port == 6379
+    assert model.dsn.path == "/0"
+
+    monkeypatch.setenv("REDIS_6379_TCP_PORT", "4567")
+    model = TestModel.model_validate(
+        {"dsn": "redis://user:[email protected]:7777/1"}
+    )
+    assert model.dsn.scheme == "redis"
+    assert model.dsn.username == "user"
+    assert model.dsn.password == "password"
+    assert model.dsn.host == "example.com"
+    assert model.dsn.port == 4567
+    assert model.dsn.path == "/1"
+
+    monkeypatch.setenv("REDIS_HOST", "127.12.0.1")
+    model = TestModel.model_validate({"dsn": "redis://localhost"})
+    assert model.dsn.scheme == "redis"
+    assert not model.dsn.username
+    assert not model.dsn.password
+    assert model.dsn.host == "127.12.0.1"
+    assert model.dsn.port == 4567
+    assert model.dsn.path == "/0"
+
+    with pytest.raises(ValidationError):
+        TestModel.model_validate({"dsn": "rediss://example.com/0"})
+
+
 def test_human_timedelta() -> None:
     class TestModel(BaseModel):
         delta: HumanTimedelta