Add base64Decode and base64Encode template functions

Fixes #1416

docs/content/templates/functions.md

@@ -650,3 +650,33 @@ In this version, we are now sorting the tags, converting them to links with "pos
     {{ end }}
 
 `apply` does not work when receiving the sequence as an argument through a pipeline.
+
+***
+
+### base64Encode and base64Decode
+
+`base64Encode` and `base64Decode` let you easily decode content with a base64 enconding and vice versa through pipes. Let's take a look at an example:
+
+
+    {{ "Hello world" | base64Encode }}
+    <!-- will output "SGVsbG8gd29ybGQ=" and -->
+
+    {{ "SGVsbG8gd29ybGQ=" | base64Decode }}
+    <!-- becomes "Hello world" again. -->
+
+You can also pass other datatypes as argument to the template function which tries
+to convert them. Now we use an integer instead of a string:
+
+
+    {{ 42 | base64Encode | base64Decode }}
+    <!-- will output "42". Both functions always return a string. -->
+
+**Tip:** Using base64 to decode and encode becomes really powerful if we have to handle
+responses of APIs.
+
+    {{ $resp := getJSON "https://api.github.com/repos/spf13/hugo/readme"  }}
+    {{ $resp.content | base64Decode | markdownify }}
+
+ The response of the Github API contains the base64-encoded version of the [README.md](https://github.com/spf13/hugo/blob/master/README.md) in the Hugo repository.
+Now we can decode it and parse the Markdown. The final output will look similar to the
+rendered version in Github.

tpl/template_funcs.go

@@ -16,6 +16,7 @@ package tpl
 import (
 	"bitbucket.org/pkg/inflect"
 	"bytes"
+	"encoding/base64"
 	"errors"
 	"fmt"
 	"html"
@@ -1318,6 +1319,32 @@ func ModBool(a, b interface{}) (bool, error) {
 	return res == int64(0), nil
 }
 
+func Base64Decode(content interface{}) (string, error) {
+	conv, err := cast.ToStringE(content)
+
+	if err != nil {
+		return "", err
+	}
+
+	dec, err := base64.StdEncoding.DecodeString(conv)
+
+	if err != nil {
+		return "", err
+	}
+
+	return string(dec), nil
+}
+
+func Base64Encode(content interface{}) (string, error) {
+	conv, err := cast.ToStringE(content)
+
+	if err != nil {
+		return "", err
+	}
+
+	return base64.StdEncoding.EncodeToString([]byte(conv)), nil
+}
+
 func init() {
 	funcMap = template.FuncMap{
 		"urlize":       helpers.URLize,
@@ -1372,6 +1399,8 @@ func init() {
 		"readDir":      ReadDir,
 		"seq":          helpers.Seq,
 		"getenv":       func(varName string) string { return os.Getenv(varName) },
+		"base64Decode": Base64Decode,
+		"base64Encode": Base64Encode,
 		"pluralize": func(in interface{}) (string, error) {
 			word, err := cast.ToStringE(in)
 			if err != nil {
@@ -1387,5 +1416,4 @@ func init() {
 			return inflect.Singularize(word), nil
 		},
 	}
-
 }

tpl/template_funcs_test.go

@@ -2,6 +2,7 @@ package tpl
 
 import (
 	"bytes"
+	"encoding/base64"
 	"errors"
 	"fmt"
 	"html/template"
@@ -1581,3 +1582,36 @@ func TestSafeURL(t *testing.T) {
 		}
 	}
 }
+
+func TestBase64Decode(t *testing.T) {
+	testStr := "abc123!?$*&()'-=@~"
+	enc := base64.StdEncoding.EncodeToString([]byte(testStr))
+	result, err := Base64Decode(enc)
+
+	if err != nil {
+		t.Error("Base64Decode:", err)
+	}
+
+	if result != testStr {
+		t.Errorf("Base64Decode: got '%s', expected '%s'", result, testStr)
+	}
+}
+
+func TestBase64Encode(t *testing.T) {
+	testStr := "YWJjMTIzIT8kKiYoKSctPUB+"
+	dec, err := base64.StdEncoding.DecodeString(testStr)
+
+	if err != nil {
+		t.Error("Base64Encode: the DecodeString function of the base64 package returned an error.", err)
+	}
+
+	result, err := Base64Encode(string(dec))
+
+	if err != nil {
+		t.Errorf("Base64Encode: Can't cast arg '%s' into a string.", testStr)
+	}
+
+	if result != testStr {
+		t.Errorf("Base64Encode: got '%s', expected '%s'", result, testStr)
+	}
+}