Add basic implementation

The 'setup-postgres' action has been developed by me for
xsnippet/xsnippet-api [1] purpose where we want to run our tests on all
major operating systems. Existing actions are built around Docker
containers, and hence are available for Linux only.

I figured that the work I have done there might be useful for someone
else, and so I decided to create a standalone reusable action and
publish it on GitHub Marketplace.

[1] https://github.com/xsnippet/xsnippet-api/blob/40953d18b70e19d8535bf3aee88f28fe1407b36a/.github/actions/setup-postgres/action.yml

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+  schedule:
+    - cron: "0 8 * * *"
+
+jobs:
+  default:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
+          - macos-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Run setup-postgres
+        uses: ./
+        id: postgres
+
+      - name: Run tests
+        run: |
+          python3 -m pip install --upgrade pip pytest psycopg
+          python3 -m pytest -vv test_action.py
+        env:
+          CONNECTION_URI: ${{ steps.postgres.outputs.connection-uri }}
+          EXPECTED_CONNECTION_URI: postgresql://postgres:postgres@localhost/postgres
+        shell: bash
+
+  parametrized:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
+          - macos-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Run setup-postgres
+        uses: ./
+        with:
+          username: yoda
+          password: GrandMaster
+          database: jedi_order
+        id: postgres
+
+      - name: Run tests
+        run: |
+          python3 -m pip install --upgrade pip pytest psycopg
+          python3 -m pytest -vv test_action.py
+        env:
+          CONNECTION_URI: ${{ steps.postgres.outputs.connection-uri }}
+          EXPECTED_CONNECTION_URI: postgresql://yoda:GrandMaster@localhost/jedi_order
+        shell: bash

LICENSE

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+MIT License
+
+Copyright (c) 2021 Ihor Kalnytskyi
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# setup-postgres
+
+This action sets up a PostgreSQL server for the rest of the job. Here are some
+key features:
+
+* Runs on Linux, macOS and Windows runners.
+* Adds PostgreSQL [binaries][1] (e.g. `psql`) to `PATH`.
+* Uses PostgreSQL installed in [GitHub Actions Virtual Environments][2].
+* [Easy to check][3] that IT DOES NOT contain malicious code.
+
+[1]: https://www.postgresql.org/docs/current/reference-client.html
+[2]: https://github.com/actions/virtual-environments
+[3]: action.yml
+
+## Usage
+
+| Key      | Value                                               |
+|----------|-----------------------------------------------------|
+| URI      | `postgresql://postgres:postgres@localhost/postgres` |
+| Host     | `localhost`                                         |
+| Port     | `5432`                                              |
+| Username | `postgres`                                          |
+| Password | `postgres`                                          |
+| Database | `postgres`                                          |
+
+#### Basic
+
+```yaml
+steps:
+  - uses: ikalnytskyi/action-setup-postgres@v1
+```
+
+#### Advanced
+
+```yaml
+steps:
+  - uses: ikalnytskyi/action-setup-postgres@v1
+    with:
+      username: ci
+      password: sw0rdfish
+      database: test
+    id: postgres
+
+  - run: pytest -vv tests/
+    env:
+      DATABASE_URI: ${{ steps.postgres.outputs.connection-uri }}
+```
+
+## License
+
+The scripts and documentation in this project are released under the
+[MIT License](LICENSE).

action.yml

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+name: Setup PostgreSQL for Linux/macOS/Windows
+author: Ihor Kalnytskyi
+description: Setup a preinstalled PostgreSQL server.
+branding:
+  icon: database
+  color: purple
+inputs:
+  username:
+    description: The username of the user to setup.
+    default: postgres
+    required: false
+  password:
+    description: The password of the user to setup.
+    default: postgres
+    required: false
+  database:
+    description: The database name to setup and grant permissions to created user.
+    default: postgres
+    required: false
+outputs:
+  connection-uri:
+    description: The connection URI to connect to PostgreSQL.
+    value: ${{ steps.connection-uri.outputs.value }}
+runs:
+  using: composite
+  steps:
+    - name: Prerequisites
+      run: |
+        if [ "$RUNNER_OS" == "Linux" ]; then
+          echo "$(pg_config --bindir)" >> $GITHUB_PATH
+        elif [ "$RUNNER_OS" == "Windows" ]; then
+          echo "$PGBIN" >> $GITHUB_PATH
+          echo "PQ_LIB_DIR=$PGROOT\lib" >> $GITHUB_ENV
+        fi
+      shell: bash
+
+
+    - name: Setup and start PostgreSQL
+      run: |
+        export PGDATA="$RUNNER_TEMP/pgdata"
+        pg_ctl init
+
+        # Forbid creating unix sockets since they are created by default in the
+        # directory we don't have permissions to.
+        echo "unix_socket_directories = ''" >> "$PGDATA/postgresql.conf"
+        pg_ctl start
+
+        # Both PGHOST and PGUSER are used by PostgreSQL tooling such as 'psql'
+        # or 'createuser'. Since PostgreSQL data has been resetup, we cannot
+        # rely on defaults anymore.
+        #
+        # PGHOST is required for Linux and macOS since they default to unix
+        # sockets, and we have turned them off.
+        #
+        # PGUSER is required for Windows since default the tooling's default
+        # user is 'postgres', while 'pg_ctl init' creates one with the name of
+        # the current user.
+        echo "PGHOST=localhost" >> $GITHUB_ENV
+        echo "PGUSER=${USER:-$USERNAME}" >> $GITHUB_ENV
+      shell: bash
+
+    - name: Setup PostgreSQL user and database
+      run: |
+        createuser --createdb ${{ inputs.username }}
+
+        if [ "${{ inputs.database}}" != "postgres" ]; then
+          createdb -O ${{ inputs.username }} ${{ inputs.database }}
+        fi
+
+        psql -c "ALTER USER ${{ inputs.username }} PASSWORD '${{ inputs.password }}';" ${{ inputs.database }}
+      shell: bash
+
+    - name: Expose connection URI
+      run: |
+        CONNECTION_URI="postgresql://${{ inputs.username }}:${{ inputs.password }}@localhost/${{ inputs.database }}"
+        echo ::set-output name=value::$CONNECTION_URI
+      shell: bash
+      id: connection-uri

test_action.py

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+import typing as t
+import os
+
+import psycopg
+import pytest
+
+
+@pytest.fixture(scope="function")
+def connection_factory() -> t.Callable[[str], psycopg.Connection]:
+    def factory(connection_uri: str) -> psycopg.Connection:
+        return psycopg.connect(connection_uri)
+    return factory
+
+
+@pytest.fixture(scope="function")
+def connection(connection_factory) -> psycopg.Connection:
+    return connection_factory(os.getenv("CONNECTION_URI"))
+
+
+def test_connection_uri():
+    """Test that CONNECTION_URI matches EXPECTED_CONNECTION_URI."""
+
+    connection_uri = os.getenv("CONNECTION_URI")
+    expected_connection_uri = os.getenv("EXPECTED_CONNECTION_URI")
+    assert connection_uri == expected_connection_uri
+
+
+def test_user_permissions(connection: psycopg.Connection):
+    """Test that a user can create databases but is not a superuser."""
+
+    with connection:
+        record = connection \
+            .execute("SELECT usecreatedb, usesuper FROM pg_user WHERE usename = CURRENT_USER") \
+            .fetchone()
+        assert record
+
+        usecreatedb, usesuper = record
+        assert usecreatedb
+        assert not usesuper
+
+
+def test_user_create_insert_select(connection: psycopg.Connection):
+    """Test that a user has CRUD permissions in a database."""
+
+    table_name = "test_setup_postgres"
+
+    with connection, connection.transaction(force_rollback=True):
+        records = connection \
+            .execute(f"CREATE TABLE {table_name}(eggs INTEGER, rice VARCHAR)") \
+            .execute(f"INSERT INTO {table_name}(eggs, rice) VALUES (1, '42')") \
+            .execute(f"SELECT * FROM {table_name}") \
+            .fetchall()
+        assert records == [(1, "42")]
+
+
+def test_user_create_drop_database(connection: psycopg.Connection):
+    """Test that a user has no permissions to create databases."""
+
+    # CREATE/DROP DATABASE statements don't work within transactions, and with
+    # autocommit disabled transactions are created by psycopg automatically.
+    connection.autocommit = True
+
+    database_name = "foobar42"
+    connection.execute(f"CREATE DATABASE {database_name}")
+    connection.execute(f"DROP DATABASE {database_name}")