cfgparser: add env_split for splitting of ENV variable values on comma

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

@@ -31,13 +31,19 @@ func expandEnvironment(nodes []Node) []Node {
 		return nil
 	}
 
-	replacer := buildEnvReplacer()
+	envMap := buildEnvMap()
+	replacer := buildEnvReplacerFromMap(envMap)
 	newNodes := make([]Node, 0, len(nodes))
 	for _, node := range nodes {
 		node.Name = removeUnexpandedEnvvars(replacer.Replace(node.Name))
 		newArgs := make([]string, 0, len(node.Args))
 		for _, arg := range node.Args {
-			newArgs = append(newArgs, removeUnexpandedEnvvars(replacer.Replace(arg)))
+			expArg := replacer.Replace(arg)
+			if splitArgs, ok := handleEnvSplitWithMap(expArg, envMap); ok {
+				newArgs = append(newArgs, splitArgs...)
+			} else {
+				newArgs = append(newArgs, removeUnexpandedEnvvars(expArg))
+			}
 		}
 		node.Args = newArgs
 		node.Children = expandEnvironment(node.Children)
@@ -47,21 +53,42 @@ func expandEnvironment(nodes []Node) []Node {
 }
 
 var unixEnvvarRe = regexp.MustCompile(`{env:([^\$]+)}`)
+var unixEnvSplitRe = regexp.MustCompile(`{env_split:([^\$]+)}`)
 
 func removeUnexpandedEnvvars(s string) string {
 	s = unixEnvvarRe.ReplaceAllString(s, "")
 	return s
 }
 
-func buildEnvReplacer() *strings.Replacer {
+func buildEnvMap() map[string]string {
 	env := os.Environ()
-	pairs := make([]string, 0, len(env)*4)
+	envMap := make(map[string]string, len(env))
 	for _, entry := range env {
 		parts := strings.SplitN(entry, "=", 2)
-		key := parts[0]
-		value := parts[1]
+		if len(parts) == 2 {
+			envMap[parts[0]] = parts[1]
+		}
+	}
+	return envMap
+}
 
+func buildEnvReplacerFromMap(envMap map[string]string) *strings.Replacer {
+	pairs := make([]string, 0, len(envMap)*4)
+	for key, value := range envMap {
 		pairs = append(pairs, "{env:"+key+"}", value)
 	}
 	return strings.NewReplacer(pairs...)
 }
+
+func handleEnvSplitWithMap(arg string, envMap map[string]string) ([]string, bool) {
+	matches := unixEnvSplitRe.FindStringSubmatch(arg)
+	if len(matches) == 2 {
+		value, exists := envMap[matches[1]]
+		if !exists {
+			return nil, false
+		}
+		splitValues := strings.Split(value, ",")
+		return splitValues, true
+	}
+	return nil, false
+}

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_