Add env variables support in .toml config

data_diff/config.py

@@ -1,3 +1,5 @@
+import re
+import os
 from typing import Any, Dict
 import toml
 
@@ -11,6 +13,8 @@ def is_uri(s: str) -> bool:
 
 
 def _apply_config(config: Dict[str, Any], run_name: str, kw: Dict[str, Any]):
+    _resolve_env(config)
+
     # Load config
     databases = config.pop("database", {})
     runs = config.pop("run", {})
@@ -77,6 +81,32 @@ def _apply_config(config: Dict[str, Any], run_name: str, kw: Dict[str, Any]):
     return new_kw
 
 
+# There are no strict requirements for the environment variable name format.
+# But most shells only allow alphanumeric characters and underscores.
+# https://pubs.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap08.html
+# "Environment variable names (...) consist solely of uppercase letters, digits, and the '_' (underscore)"
+_ENV_VAR_PATTERN = r"\$\{([A-Za-z0-9_]+)\}"
+
+
+def _resolve_env(config: Dict[str, Any]):
+    """
+    Resolve environment variables referenced as ${ENV_VAR_NAME}.
+    Missing environment variables are replaced with an empty string.
+    """
+    for key, value in config.items():
+        if isinstance(value, dict):
+            _resolve_env(value)
+        elif isinstance(value, str):
+            config[key] = re.sub(_ENV_VAR_PATTERN, _replace_match, value)
+
+
+def _replace_match(match: re.Match) -> str:
+    # Lookup referenced variable in environment.
+    # Replace with empty string if not found
+    referenced_var = match.group(1)  # group(0) is the whole string
+    return os.environ.get(referenced_var, "")
+
+
 def apply_config_from_file(path: str, run_name: str, kw: Dict[str, Any]):
     with open(path) as f:
         return _apply_config(toml.load(f), run_name, kw)

tests/test_config.py

@@ -1,3 +1,4 @@
+import os
 import unittest
 
 from data_diff.config import apply_config_from_string, ConfigParseError
@@ -59,3 +60,46 @@ def test_remove_password(self):
             expected = url.replace("PASS", replace_with)
             removed = remove_password_from_url(url, replace_with)
             self.assertEqual(removed, expected)
+
+    def test_embed_env(self):
+        env = {
+            "DRIVER": "postgresql",
+            "USER": "postgres",
+            "PASSWORD": "Password1",
+            "RUN_PG_1_DATABASE": "test_postgresql",
+            "RUN_PG_1_TABLE": "rating",
+            "RUN_PG_2_DATABASE": "postgresql://postgres:Password1@/",
+            "RUN_PG_2_TABLE": "rating_del1",
+        }
+        config = r"""
+            [database.test_postgresql]
+            driver = "${DRIVER}"
+            user = "${USER}"
+            password = "${PASSWORD}"
+
+            [run.default]
+            update_column = "${UPDATE_COLUMN}"
+            verbose = true
+            threads = 2
+
+            [run.pg_pg]
+            threads = 4
+            1.database = "${RUN_PG_1_DATABASE}"
+            1.table = "${RUN_PG_1_TABLE}"
+            1.threads = 11
+            2.database = "${RUN_PG_2_DATABASE}"
+            2.table = "${RUN_PG_2_TABLE}"
+            2.threads = 22
+        """
+
+        os.environ.update(env)
+        res = apply_config_from_string(config, "pg_pg", {})
+        assert res["update_column"] == ""  # missing env var
+        assert res["verbose"] is True
+        assert res["threads"] == 4  # overwritten by pg_pg
+        assert res["database1"] == {"driver": "postgresql", "user": "postgres", "password": "Password1"}
+        assert res["database2"] == "postgresql://postgres:Password1@/"
+        assert res["table1"] == "rating"
+        assert res["table2"] == "rating_del1"
+        assert res["threads1"] == 11
+        assert res["threads2"] == 22