cfgparser: add optional splitting of ENV variable values on comma via env_split

Author: rjocoleman

docs/reference/config-syntax.md

@@ -87,6 +87,16 @@ directive0 {env:VAR}
 Parse is forgiving and incomplete variable placeholder (e.g. '{env:VAR') will
 be left as-is. Variables are expanded inside quotes too.
 
+Environment values that are comma separated can optionally be split to space separated strings using {env_split:COMMA_SEPARATED_VARIABLE_NAME}
+
+```
+# SEP_VAR=foo,bar,baz
+
+directive1 {env_split:SEP_VAR}
+```
+
+In this usage the value of `directive1` would be `foo bar baz` (and `{env:SEP_VAR}` would be `foo,bar,baz`)
+
 ## Snippets & imports
 
 You can reuse blocks of configuration by defining them as "snippets". Snippet
@@ -196,5 +206,3 @@ No-op module. It doesn't need to be configured explicitly and can be referenced
 using "dummy" name. It can act as a delivery target or auth.
 provider. In the latter case, it will accept any credentials, allowing any
 client to authenticate using any username and password (use with care!).
-
-

framework/cfgparser/env.go

@@ -46,11 +46,21 @@ func expandEnvironment(nodes []Node) []Node {
 	return newNodes
 }
 
-var unixEnvvarRe = regexp.MustCompile(`{env:([^\$]+)}`)
+var unixEnvvarRe = regexp.MustCompile(`\{(env|env_split):([^\}]+)\}`)
 
 func removeUnexpandedEnvvars(s string) string {
-	s = unixEnvvarRe.ReplaceAllString(s, "")
-	return s
+	return unixEnvvarRe.ReplaceAllStringFunc(s, func(match string) string {
+		matches := unixEnvvarRe.FindStringSubmatch(match)
+		if len(matches) != 3 {
+			return match // Not a valid pattern
+		}
+		key, mode := matches[2], matches[1]
+		value := os.Getenv(key)
+		if mode == "env_split" {
+			value = strings.ReplaceAll(value, ",", " ")
+		}
+		return value
+	})
 }
 
 func buildEnvReplacer() *strings.Replacer {
@@ -61,7 +71,7 @@ func buildEnvReplacer() *strings.Replacer {
 		key := parts[0]
 		value := parts[1]
 
-		pairs = append(pairs, "{env:"+key+"}", value)
+		pairs = append(pairs, "{env:"+key+"}", value, "{envSplit:"+key+"}", value)
 	}
 	return strings.NewReplacer(pairs...)
 }

framework/cfgparser/parse_test.go

@@ -342,6 +342,47 @@ var cases = []struct {
 		},
 		false,
 	},
+	{
+		"environment variable split at comma expansion",
+		`a {env_split:TESTING_VARIABLE_SPLIT}`,
+		[]Node{
+			{
+				Name:     "a",
+				Args:     []string{"value1 value2 value3"},
+				Children: nil,
+				File:     "test",
+				Line:     1,
+			},
+		},
+		false,
+	},
+	{
+		"environment variable mixed usage",
+		`mixed {env:TESTING_VARIABLE} {env_split:TESTING_VARIABLE_SPLIT}`,
+		[]Node{
+			{
+				Name:     "mixed",
+				Args:     []string{"ABCDEF", "value1 value2 value3"},
+				Children: nil,
+				File:     "test",
+				Line:     1,
+			},
+		},
+		false,
+	},
+	{
+		"environment variable not split on comma",
+		`not_split {env:TESTING_VARIABLE_SPLIT}`,
+		[]Node{
+			{
+				Name: "not_split",
+				Args: []string{"value1,value2,value3"},
+				File: "test",
+				Line: 1,
+			},
+		},
+		false,
+	},
 	{
 		"snippet expansion",
 		`(foo) { a }
@@ -581,6 +622,7 @@ func printTree(t *testing.T, root Node, indent int) {
 func TestRead(t *testing.T) {
 	os.Setenv("TESTING_VARIABLE", "ABCDEF")
 	os.Setenv("TESTING_VARIABLE2", "ABC2 DEF2")
+	os.Setenv("TESTING_VARIABLE_SPLIT", "value1,value2,value3")
 
 	for _, case_ := range cases {
 		case_ := case_