Added env variable support for himl (#55)

* Added env variable support for himl

Author: ecojan

README.md

@@ -267,6 +267,11 @@ remote_states:
 endpoint: "{{outputs.cluster_composition.output.value.redis_endpoint}}"
 ```
 
+### Merge with env variables
+```yaml
+kubeconfig_location: {{env(KUBECONFIG)}}
+```
+
 
 ## himl config merger
 

examples/complex/env=dev/region=us-west-2/cluster=cluster1/cluster.yaml

@@ -1 +1,2 @@
 cluster: cluster1
+home: {{env(HOME)}}

himl/config_generator.py

@@ -17,7 +17,8 @@
 import yaml
 from deepmerge import Merger
 
-from .interpolation import InterpolationResolver, EscapingResolver, InterpolationValidator, SecretResolver, DictIterator, replace_parent_working_directory
+from .interpolation import InterpolationResolver, EscapingResolver, InterpolationValidator, SecretResolver, \
+    DictIterator, replace_parent_working_directory, EnvVarResolver
 from .python_compat import iteritems, primitive_types, PY3
 from .remote_state import S3TerraformRemoteStateRetriever
 
@@ -68,6 +69,9 @@ def process(self, cwd=None, path=None, filters=(), exclude_keys=(), enclosing_ke
             # value2: "something-{{value1}} <--- this will be resolved at this step
             generator.resolve_interpolations()
 
+        generator.resolve_env()
+        generator.resolve_interpolations()
+
         if len(filters) > 0:
             generator.filter_data(filters)
 
@@ -279,6 +283,10 @@ def resolve_secrets(self, default_aws_profile):
         resolver = SecretResolver()
         self.generated_data = resolver.resolve_secrets(self.generated_data, default_aws_profile)
 
+    def resolve_env(self):
+        resolver = EnvVarResolver()
+        self.generated_data = resolver.resolve_env_vars(self.generated_data)
+
     def validate_interpolations(self):
         self.interpolation_validator.check_all_interpolations_resolved(self.generated_data)
 

himl/inject_env.py

@@ -0,0 +1,47 @@
+# Copyright 2021 Adobe. All rights reserved.
+# This file is licensed to you under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License. You may obtain a copy
+# of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software distributed under
+# the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+# OF ANY KIND, either express or implied. See the License for the specific language
+# governing permissions and limitations under the License.
+
+from os import getenv
+
+
+class EnvVarInjector(object):
+    """
+    Resolve variables in the form:
+    {{env(HOME)}}
+    """
+
+    def __init__(self):
+        return
+
+    def is_interpolation(self, value):
+        return value.startswith('{{') and value.endswith('}}')
+
+    def inject_env_var(self, line):
+        """
+        Check if value is an interpolation and try to resolve it.
+        """
+        if not self.is_interpolation(line):
+            return line
+
+        # remove {{ and }}
+        updated_line = line[2:-2]
+
+        # check supported function to ensure the proper format is used
+        if not self.is_env_interpolation(updated_line):
+            return line
+
+        # remove env( and ) to extract the env Variable
+        updated_line = updated_line[4:-1]
+
+        # If env variable is missing or not set, the output will be None
+        return getenv(updated_line)
+
+    def is_env_interpolation(self, value):
+        return value.startswith('env(') and value.endswith(')')

himl/interpolation.py

@@ -10,6 +10,7 @@
 
 import re
 
+from .inject_env import EnvVarInjector
 from .inject_secrets import SecretInjector
 from .python_compat import iteritems, string_types, primitive_types
 
@@ -83,6 +84,14 @@ def resolve_secrets(self, data, default_aws_profile):
         return data
 
 
+class EnvVarResolver(object):
+    def resolve_env_vars(self, data):
+        injector = EnvVarInjector()
+        env_resolver = EnvVarInterpolationsResolver(injector)
+        env_resolver.resolve_interpolations(data)
+        return data
+
+
 class DictIterator(object):
 
     def loop_all_items(self, data, process_func):
@@ -168,6 +177,15 @@ def do_resolve_interpolation(self, line):
         return self.secrets_injector.inject_secret(line)
 
 
+class EnvVarInterpolationsResolver(AbstractInterpolationResolver):
+    def __init__(self, env_vars_injector):
+        AbstractInterpolationResolver.__init__(self)
+        self.env_vars_injector = env_vars_injector
+
+    def do_resolve_interpolation(self, line):
+        return self.env_vars_injector.inject_env_var(line)
+
+
 class InterpolationValidator(DictIterator):
 
     def check_all_interpolations_resolved(self, data):