Add function to list datasources (#1287)

* Add function to list datasources

* Sort datasources in ascending order and return in listDatasources

* Fix lint error

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

Co-authored-by: Dave Henderson <dhenderson@gmail.com>

5 files changed, 49 insertions, 0 deletions

diff --git a/data/datasource.go b/data/datasource.go
index 5f684a4c..79c29e5f 100644
--- a/data/datasource.go
+++ b/data/datasource.go
@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/url"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"github.com/spf13/afero"
@@ -382,3 +383,13 @@ func (d *Data) readSource(ctx context.Context, source *Source, args ...string) (
 	d.cache[cacheKey] = data
 	return data, nil
 }
+
+// Show all datasources  -
+func (d *Data) ListDatasources() []string {
+	datasources := make([]string, 0, len(d.Sources))
+	for source := range d.Sources {
+		datasources = append(datasources, source)
+	}
+	sort.Strings(datasources)
+	return datasources
+}
diff --git a/data/datasource_test.go b/data/datasource_test.go
index 4cffc763..aadcef0e 100644
--- a/data/datasource_test.go
+++ b/data/datasource_test.go
@@ -412,3 +412,13 @@ func TestFromConfig(t *testing.T) {
 	}
 	assert.EqualValues(t, expected, FromConfig(ctx, cfg))
 }
+
+func TestListDatasources(t *testing.T) {
+	sources := map[string]*Source{
+		"foo": {Alias: "foo"},
+		"bar": {Alias: "bar"},
+	}
+	data := &Data{Sources: sources}
+
+	assert.Equal(t, []string{"bar", "foo"}, data.ListDatasources())
+}
diff --git a/docs-src/content/functions/data.yml b/docs-src/content/functions/data.yml
index 15106372..8fa47736 100644
--- a/docs-src/content/functions/data.yml
+++ b/docs-src/content/functions/data.yml
@@ -62,6 +62,15 @@ funcs:
       - |
         $ gomplate -i '{{if (datasourceReachable "test")}}{{datasource "test"}}{{else}}no worries{{end}}' -d test=https://bogus.example.com/wontwork.json
         no worries
+  - name: listDatasources
+    description: |
+      Lists all the datasources defined, list returned will be sorted in ascending order.
+    pipeline: false
+    examples:
+      - |
+        $ gomplate -d person=env:///FOO -d bar=env:///BAR -i '{{range (listDatasources)}} Datasource-{{.}} {{end}}'
+        Datasource-bar
+        Datasource-person
   - name: defineDatasource
     description: |
       Define a datasource alias with target URL inside the template. Overridden by the [`--datasource/-d`](../../usage/#datasource-d) flag.
diff --git a/docs/content/functions/data.md b/docs/content/functions/data.md
index 4845de60..31d2b27c 100644
--- a/docs/content/functions/data.md
+++ b/docs/content/functions/data.md
@@ -97,6 +97,24 @@ $ gomplate -i '{{if (datasourceReachable "test")}}{{datasource "test"}}{{else}}n
 no worries
 ```
 
+## `listDatasources`
+
+Lists all the datasources defined, list returned will be sorted in ascending order.
+
+### Usage
+
+```go
+listDatasources
+```
+
+### Examples
+
+```console
+$ gomplate -d person=env:///FOO -d bar=env:///BAR -i '{{range (listDatasources)}} Datasource-{{.}} {{end}}'
+Datasource-bar
+Datasource-person
+```
+
 ## `defineDatasource`
 
 Define a datasource alias with target URL inside the template. Overridden by the [`--datasource/-d`](../../usage/#datasource-d) flag.
diff --git a/funcs/data.go b/funcs/data.go
index a6e48ba3..f4ae7b32 100644
--- a/funcs/data.go
+++ b/funcs/data.go
@@ -30,6 +30,7 @@ func CreateDataFuncs(ctx context.Context, d *data.Data) map[string]interface{} {
 	f["datasourceReachable"] = d.DatasourceReachable
 	f["defineDatasource"] = d.DefineDatasource
 	f["include"] = d.Include
+	f["listDatasources"] = d.ListDatasources
 
 	ns := &DataFuncs{ctx}