From 753de35ee0bf7f86e380f015c135264b5bcd44a7 Mon Sep 17 00:00:00 2001
From: Nils <9465658+nlueb@users.noreply.github.com>
Date: Mon, 10 Jan 2022 08:22:24 +0000
Subject: [PATCH] Add readDir as a templating function (#1934)

Adds a new templating function called `readDir`. With `readDir` users can read the contents of a specified directory and get a list of all contained files. This is useful when reading a bunch of files from a directory. The following example shows a snippet of a values file for configuring a Logstash deployment. Using only `readFile`, a user must specify each file by hand and adjust this list as the number of files to be read grows.
```yaml
logstash:
  configs:
    logstash.yml: |
      {{- tpl (readFile "config/logstash.yml.gotmpl") . | nindent 6 }}
    jvm.options: |
      {{- readFile "config/jvm.options" | nindent 6 }}
    pipelines.yml: |
      {{- readFile "config/pipelines.yml" | nindent 6 }}
  pipelines:
    beats-log4j.conf: |
      {{- readFile "config/pipelines/beats-log4j.conf" | nindent 6 }}
    nginx-access.conf: |
      {{- readFile "config/pipelines/nginx-access.conf" | nindent 6 }}
    nginx-error.conf: |
      {{- readFile "config/pipelines/nginx-error.conf" | nindent 6 }}
    syslog-logs.conf: |
      {{- readFile "config/pipelines/syslog-logs.conf" | nindent 6 }}
    tcp-logs.conf: |
      {{- readFile "config/pipelines/tcp-logs.conf" | nindent 6 }}
    udp-debug.conf: |
      {{- readFile "config/pipelines/udp-debug.conf" | nindent 6 }}
    udp-logs.conf: |
      {{- readFile "config/pipelines/udp-logs.conf" | nindent 6 }}
  certificates:
    ca.crt: |
      {{- readFile "config/certificates/ca.crt" | nindent 6 }}
    logstash.crt: |
      {{- readFile "config/certificates/logstash.crt" | nindent 6 }}
    logstash.key: |
      {{- readFile "config/certificates/logstash.key" | nindent 6 }}
```
With `readDir` the above snippet can be rewritten as follows:
```yaml
logstash:
  configs:
  {{- range readDir "config" }}
    {{ base . }}: |
      {{- if hasSuffix "gotmpl" . }}
          {{- tpl (readFile .) $ | nindent 6 }}
      {{- else }}
          {{- readFile . | nindent 6 }}
      {{- end }}
  {{- end }}
  pipelines:
  {{- range readDir "config/pipelines" }}
    {{ base . }}: |
      {{- readFile . | nindent 6 }}
  {{- end }}
  certificates:
  {{- range readDir "config/certificates" }}
    {{ base . }}: |
      {{- readFile . | nindent 6 }}
  {{- end }}
```
---
 pkg/tmpl/context_funcs.go | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/pkg/tmpl/context_funcs.go b/pkg/tmpl/context_funcs.go
index 7e64aa5d..85e7e849 100644
--- a/pkg/tmpl/context_funcs.go
+++ b/pkg/tmpl/context_funcs.go
@@ -20,6 +20,7 @@ func (c *Context) createFuncMap() template.FuncMap {
 	funcMap := template.FuncMap{
 		"exec":             c.Exec,
 		"readFile":         c.ReadFile,
+		"readDir":          ReadDir,
 		"toYaml":           ToYaml,
 		"fromYaml":         FromYaml,
 		"setValueAtPath":   SetValueAtPath,
@@ -130,6 +131,21 @@ func (c *Context) ReadFile(filename string) (string, error) {
 	return string(bytes), nil
 }
 
+func ReadDir(path string) ([]string, error) {
+	entries, err := os.ReadDir(path)
+	if err != nil {
+		return nil, err
+	}
+	var filenames []string
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		filenames = append(filenames, filepath.Join(path, entry.Name()))
+	}
+	return filenames, nil
+}
+
 func (c *Context) Tpl(text string, data interface{}) (string, error) {
 	buf, err := c.RenderTemplateToBuffer(text, data)
 	if err != nil {