From a0cbc0cb65ae601270bdbe3f5313e2dfd49c80e4 Mon Sep 17 00:00:00 2001
From: Marin Bezhanov <marin.bezhanov@gmail.com>
Date: Wed, 19 Jun 2024 18:55:47 +0300
Subject: [PATCH 1/2] feat: support environment variable substitution in config
 files (#3195)

Signed-off-by: Marin Bezhanov <marin.bezhanov@gmail.com>
---
 internal/config/config.go             | 24 +++++++++++++++++++++++-
 internal/config/config_test.go        | 14 ++++++++++++++
 internal/config/testdata/envsubst.yml |  4 ++++
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 internal/config/testdata/envsubst.yml

diff --git a/internal/config/config.go b/internal/config/config.go
index 1e67dde43e..bdd916220f 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -10,6 +10,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"regexp"
 	"slices"
 	"strings"
 	"time"
@@ -27,10 +28,12 @@ const (
 )
 
 var (
-	_ validator = (*Config)(nil)
+	_        validator = (*Config)(nil)
+	envsubst           = regexp.MustCompile(`^\${([a-zA-Z_]+[a-zA-Z0-9_]*)}$`)
 )
 
 var DecodeHooks = []mapstructure.DecodeHookFunc{
+	stringToEnvsubstHookFunc(),
 	mapstructure.StringToTimeDurationHookFunc(),
 	stringToSliceHookFunc(),
 	stringToEnumHookFunc(stringToCacheBackend),
@@ -475,6 +478,25 @@ func experimentalFieldSkipHookFunc(types ...reflect.Type) mapstructure.DecodeHoo
 	}
 }
 
+// stringToEnvsubstHookFunc returns a DecodeHookFunc that substitutes
+// `${VARIABLE}` strings with their matching environment variables.
+func stringToEnvsubstHookFunc() mapstructure.DecodeHookFunc {
+	return func(
+		f reflect.Type,
+		t reflect.Type,
+		data interface{}) (interface{}, error) {
+		if f.Kind() != reflect.String || f != reflect.TypeOf("") {
+			return data, nil
+		}
+		str := data.(string)
+		if !envsubst.MatchString(str) {
+			return data, nil
+		}
+		key := envsubst.ReplaceAllString(str, `$1`)
+		return os.Getenv(key), nil
+	}
+}
+
 // stringToSliceHookFunc returns a DecodeHookFunc that converts
 // string to []string by splitting using strings.Fields().
 func stringToSliceHookFunc() mapstructure.DecodeHookFunc {
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 271a8690d7..8541d8803e 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -243,6 +243,20 @@ func TestLoad(t *testing.T) {
 				return cfg
 			},
 		},
+		{
+			name: "environment variable substitution",
+			path: "./testdata/envsubst.yml",
+			envOverrides: map[string]string{
+				"HTTP_PORT":  "18080",
+				"LOG_FORMAT": "json",
+			},
+			expected: func() *Config {
+				cfg := Default()
+				cfg.Log.Encoding = "json"
+				cfg.Server.HTTPPort = 18080
+				return cfg
+			},
+		},
 		{
 			name: "deprecated tracing jaeger",
 			path: "./testdata/deprecated/tracing_jaeger.yml",
diff --git a/internal/config/testdata/envsubst.yml b/internal/config/testdata/envsubst.yml
new file mode 100644
index 0000000000..d8f80984fd
--- /dev/null
+++ b/internal/config/testdata/envsubst.yml
@@ -0,0 +1,4 @@
+server:
+  http_port: ${HTTP_PORT}
+log:
+  encoding: ${LOG_FORMAT}

From 1804b130916779a241eaef105c952a3380707c95 Mon Sep 17 00:00:00 2001
From: "allcontributors[bot]"
 <46447321+allcontributors[bot]@users.noreply.github.com>
Date: Wed, 19 Jun 2024 12:39:17 -0400
Subject: [PATCH 2/2] docs: add mbezhanov as a contributor for code (#3197)

* docs: update README.md [skip ci]

* docs: update .all-contributorsrc [skip ci]

---------

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>
---
 .all-contributorsrc | 9 +++++++++
 README.md           | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/.all-contributorsrc b/.all-contributorsrc
index 7440bdad5e..0ea4338739 100644
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@@ -448,6 +448,15 @@
       "contributions": [
         "code"
       ]
+    },
+    {
+      "login": "mbezhanov",
+      "name": "Marin Bezhanov",
+      "avatar_url": "https://avatars.githubusercontent.com/u/785542?v=4",
+      "profile": "https://www.linkedin.com/in/mbezhanov",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "contributorsPerLine": 7,
diff --git a/README.md b/README.md
index 2a7fb61d21..f700c24930 100644
--- a/README.md
+++ b/README.md
@@ -397,6 +397,9 @@ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/d
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/kyryl-perepelytsia"><img src="https://avatars.githubusercontent.com/u/46731109?v=4?s=100" width="100px;" alt="Kyryl Perepelytsia"/><br /><sub><b>Kyryl Perepelytsia</b></sub></a><br /><a href="https://github.com/flipt-io/flipt/commits?author=kyryl-perepelytsia" title="Code">💻</a></td>
       <td align="center" valign="top" width="14.28%"><a href="http://pythonhacker24.github.io"><img src="https://avatars.githubusercontent.com/u/72488360?v=4?s=100" width="100px;" alt="Aditya Patil"/><br /><sub><b>Aditya Patil</b></sub></a><br /><a href="https://github.com/flipt-io/flipt/commits?author=PythonHacker24" title="Code">💻</a></td>
     </tr>
+    <tr>
+      <td align="center" valign="top" width="14.28%"><a href="https://www.linkedin.com/in/mbezhanov"><img src="https://avatars.githubusercontent.com/u/785542?v=4?s=100" width="100px;" alt="Marin Bezhanov"/><br /><sub><b>Marin Bezhanov</b></sub></a><br /><a href="https://github.com/flipt-io/flipt/commits?author=mbezhanov" title="Code">💻</a></td>
+    </tr>
   </tbody>
 </table>