Adding json filter function

Signed-off-by: Dave Henderson <[email protected]>

README.md

@@ -73,6 +73,23 @@ $ FOO=true gomplate < input.tmpl
 foo
 ```
 
+#### `json`
+
+Converts a JSON string into an object. Only works for JSON Objects. This can be used to access properties of JSON objects.
+
+##### Example
+
+_`input.tmpl`:_
+```
+Hello {{ (getenv "FOO" | json).hello }}
+```
+
+```console
+$ export FOO='{"hello":"world"}'
+$ gomplate < input.tmpl
+Hello world
+```
+
 ### Some more complex examples
 
 ##### Variable assignment and `if`/`else`

main.go

@@ -63,6 +63,8 @@ func NewGomplate() *Gomplate {
 			"getenv":  env.Getenv,
 			"Bool":    typeconv.Bool,
 			"bool":    typeconv.Bool,
+			"JSON":    typeconv.JSON,
+			"json":    typeconv.JSON,
 			"Ec2meta": ec2meta.Ec2meta,
 			"ec2meta": ec2meta.Ec2meta,
 		},

main_test.go

@@ -59,3 +59,17 @@ func TestEc2MetaTemplates_ValidKey(t *testing.T) {
 	assert.Equal(t, "i-1234", testTemplate(g, `{{ec2meta "instance-id"}}`))
 	assert.Equal(t, "i-1234", testTemplate(g, `{{ec2meta "instance-id" "default"}}`))
 }
+
+func TestEc2MetaTemplates_WithJSON(t *testing.T) {
+	server, ec2meta := aws.MockServer(200, `{"foo":"bar"}`)
+	defer server.Close()
+	ty := new(TypeConv)
+	g := &Gomplate{
+		funcMap: template.FuncMap{
+			"ec2meta": ec2meta.Ec2meta,
+			"json":    ty.JSON,
+		},
+	}
+
+	assert.Equal(t, "bar", testTemplate(g, `{{ (ec2meta "obj" | json).foo }}`))
+}

typeconv.go

@@ -1,6 +1,10 @@
 package main
 
-import "strconv"
+import (
+	"encoding/json"
+	"log"
+	"strconv"
+)
 
 // TypeConv - type conversion function
 type TypeConv struct {
@@ -15,3 +19,13 @@ func (t *TypeConv) Bool(in string) bool {
 	}
 	return false
 }
+
+// JSON - Unmarshal a JSON string
+func (t *TypeConv) JSON(in string) map[string]interface{} {
+	obj := make(map[string]interface{})
+	err := json.Unmarshal([]byte(in), &obj)
+	if err != nil {
+		log.Fatalf("Unable to unmarshal JSON object %s: %v", in, err)
+	}
+	return obj
+}

typeconv_test.go

@@ -22,3 +22,16 @@ func TestBool(t *testing.T) {
 	assert.True(t, ty.Bool("T"))
 	assert.True(t, ty.Bool("1"))
 }
+
+func TestJSON(t *testing.T) {
+	ty := new(TypeConv)
+	expected := make(map[string]interface{})
+	expected["foo"] = "bar"
+	expected["one"] = 1.0
+	expected["true"] = true
+
+	actual := ty.JSON(`{"foo":"bar","one":1.0,"true":true}`)
+	assert.Equal(t, expected["foo"], actual["foo"])
+	assert.Equal(t, expected["one"], actual["one"])
+	assert.Equal(t, expected["true"], actual["true"])
+}