helper/schema: Add helper function JsonEnvDefaultFunc

Author: gw0

Diff for: helper/schema/schema.go

@@ -13,6 +13,7 @@ package schema
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"log"
 	"os"
@@ -296,6 +297,23 @@ func MultiEnvDefaultFunc(ks []string, dv interface{}) SchemaDefaultFunc {
 	}
 }
 
+// JsonEnvDefaultFunc is a helper function that parses the given environment
+// variable as a JSON object, or returns the default value otherwise.
+func JsonEnvDefaultFunc(k string, dv interface{}) SchemaDefaultFunc {
+	return func() (interface{}, error) {
+		if valStr := os.Getenv(k); valStr != "" {
+			var valObj map[string]interface{}
+			err := json.Unmarshal([]byte(valStr), &valObj)
+			if err != nil {
+				return nil, err
+			}
+			return valObj, nil
+		}
+
+		return dv, nil
+	}
+}
+
 // SchemaSetFunc is a function that must return a unique ID for the given
 // element. This unique ID is used to store the element in a hash.
 type SchemaSetFunc func(interface{}) int

Diff for: helper/schema/schema_test.go

@@ -107,6 +107,45 @@ func TestMultiEnvDefaultFunc(t *testing.T) {
 	}
 }
 
+func TestJsonEnvDefaultFunc(t *testing.T) {
+	key := "TF_TEST_JSON_ENV_DEFAULT_FUNC"
+	defer os.Unsetenv(key)
+
+	def := map[string]interface{}{"foo": "default"}
+	f := JsonEnvDefaultFunc(key, def)
+	if err := os.Setenv(key, "{\"foo\":\"bar\"}"); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actualAbs, err := f()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	actual, ok := actualAbs.(map[string]interface{})
+	if !ok {
+		t.Fatalf("bad: %#v", actualAbs)
+	}
+	if actual["foo"] != "bar" {
+		t.Fatalf("bad: %#v", actual)
+	}
+
+	if err := os.Unsetenv(key); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actualAbs, err = f()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	actual, ok = actualAbs.(map[string]interface{})
+	if !ok {
+		t.Fatalf("bad: %#v", actualAbs)
+	}
+	if actual["foo"] != "default" {
+		t.Fatalf("bad: %#v", actual)
+	}
+}
+
 func TestValueType_Zero(t *testing.T) {
 	cases := []struct {
 		Type  ValueType