From 1d4667aa28062ade38eb9326ea1190de0a97c8a0 Mon Sep 17 00:00:00 2001
From: Joachim Bauch <bauch@struktur.de>
Date: Tue, 30 Apr 2024 11:41:50 +0200
Subject: [PATCH] Add function to resolve environment variables in config
 values.

---
 config.go      | 32 +++++++++++++++++++++++++++++++-
 config_test.go | 41 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/config.go b/config.go
index c7d316c..a1964f4 100644
--- a/config.go
+++ b/config.go
@@ -23,10 +23,40 @@ package signaling
 
 import (
 	"errors"
+	"os"
+	"regexp"
 
 	"github.com/dlintw/goconf"
 )
 
+var (
+	searchVarsRegexp = regexp.MustCompile(`\$\([A-Za-z][A-Za-z0-9]*\)`)
+)
+
+func replaceEnvVars(s string) string {
+	return searchVarsRegexp.ReplaceAllStringFunc(s, func(name string) string {
+		name = name[2 : len(name)-1]
+		value, found := os.LookupEnv(name)
+		if !found {
+			return name
+		}
+
+		return value
+	})
+}
+
+// GetStringOptionWithEnv will get the string option and resolve any environment
+// variable references in the form "$(VAR)".
+func GetStringOptionWithEnv(config *goconf.ConfigFile, section string, option string) (string, error) {
+	value, err := config.GetString(section, option)
+	if err != nil {
+		return "", err
+	}
+
+	value = replaceEnvVars(value)
+	return value, nil
+}
+
 func GetStringOptions(config *goconf.ConfigFile, section string, ignoreErrors bool) (map[string]string, error) {
 	options, _ := config.GetOptions(section)
 	if len(options) == 0 {
@@ -35,7 +65,7 @@ func GetStringOptions(config *goconf.ConfigFile, section string, ignoreErrors bo
 
 	result := make(map[string]string)
 	for _, option := range options {
-		value, err := config.GetString(section, option)
+		value, err := GetStringOptionWithEnv(config, section, option)
 		if err != nil {
 			if ignoreErrors {
 				continue
diff --git a/config_test.go b/config_test.go
index d14ba94..ed83823 100644
--- a/config_test.go
+++ b/config_test.go
@@ -29,13 +29,19 @@ import (
 )
 
 func TestStringOptions(t *testing.T) {
+	t.Setenv("FOO", "foo")
 	expected := map[string]string{
 		"one": "1",
 		"two": "2",
+		"foo": "http://foo/1",
 	}
 	config := goconf.NewConfigFile()
 	for k, v := range expected {
-		config.AddOption("foo", k, v)
+		if k == "foo" {
+			config.AddOption("foo", k, "http://$(FOO)/1")
+		} else {
+			config.AddOption("foo", k, v)
+		}
 	}
 	config.AddOption("default", "three", "3")
 
@@ -48,3 +54,36 @@ func TestStringOptions(t *testing.T) {
 		t.Errorf("expected %+v, got %+v", expected, options)
 	}
 }
+
+func TestStringOptionWithEnv(t *testing.T) {
+	t.Setenv("FOO", "foo")
+	t.Setenv("BAR", "")
+
+	config := goconf.NewConfigFile()
+	config.AddOption("test", "foo", "http://$(FOO)/1")
+	config.AddOption("test", "bar", "http://$(BAR)/2")
+	config.AddOption("test", "baz", "http://$(BAZ)/3")
+	config.AddOption("test", "inv1", "http://$(FOO")
+	config.AddOption("test", "inv2", "http://$FOO)")
+	config.AddOption("test", "inv3", "http://$((FOO)")
+	config.AddOption("test", "inv4", "http://$(F.OO)")
+
+	expected := map[string]string{
+		"foo":  "http://foo/1",
+		"bar":  "http:///2",
+		"baz":  "http://BAZ/3",
+		"inv1": "http://$(FOO",
+		"inv2": "http://$FOO)",
+		"inv3": "http://$((FOO)",
+		"inv4": "http://$(F.OO)",
+	}
+	for k, v := range expected {
+		value, err := GetStringOptionWithEnv(config, "test", k)
+		if err != nil {
+			t.Errorf("expected value for %s, got %s", k, err)
+		} else if value != v {
+			t.Errorf("expected value %s for %s, got %s", v, k, value)
+		}
+	}
+
+}