From f1d4bd983a62da2727245a355471fcb17d7115e2 Mon Sep 17 00:00:00 2001
From: Joshua Williams <josh.williams@bluemedora.com>
Date: Fri, 7 Aug 2020 16:59:57 -0400
Subject: [PATCH] Add template functions (#84)

* Added a default function for plugin templates

* Updated changelog
---
 CHANGELOG.md       |  1 +
 operator/plugin.go | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b3d57a886..3855421e7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 ### Fixed
 - Google Cloud Output failure when sent a field of type uint16
+- Added a default function to plugin templates
 
 ## [0.9.7] - 2020-08-05
 ### Changed
diff --git a/operator/plugin.go b/operator/plugin.go
index 4441e7efe..97a2a602f 100644
--- a/operator/plugin.go
+++ b/operator/plugin.go
@@ -127,7 +127,7 @@ func (r PluginRegistry) Add(pluginType string, contents string) error {
 		return fmt.Errorf("plugin type %s already exists as a builtin plugin", pluginType)
 	}
 
-	pluginTemplate, err := template.New(pluginType).Parse(contents)
+	pluginTemplate, err := template.New(pluginType).Funcs(pluginFuncs()).Parse(contents)
 	if err != nil {
 		return fmt.Errorf("failed to parse %s as a plugin template: %s", pluginType, err)
 	}
@@ -144,3 +144,18 @@ func NewPluginRegistry(dir string) (PluginRegistry, error) {
 	}
 	return registry, nil
 }
+
+// pluginFuncs returns a map of custom plugin functions used for templating.
+func pluginFuncs() template.FuncMap {
+	funcs := make(map[string]interface{})
+	funcs["default"] = defaultPluginFunc
+	return funcs
+}
+
+// defaultPluginFunc is a plugin function that returns a default value if the supplied value is nil.
+func defaultPluginFunc(def interface{}, val interface{}) interface{} {
+	if val == nil {
+		return def
+	}
+	return val
+}