Rebase gzip patch on top of master

hashicorp#3858

config/interpolate_funcs.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"compress/gzip"
 	"crypto/md5"
 	"crypto/sha1"
 	"crypto/sha256"
@@ -67,6 +68,7 @@ func Funcs() map[string]ast.Function {
 		"floor":        interpolationFuncFloor(),
 		"format":       interpolationFuncFormat(),
 		"formatlist":   interpolationFuncFormatList(),
+		"gzip":         interpolationFuncGzip(),
 		"index":        interpolationFuncIndex(),
 		"join":         interpolationFuncJoin(),
 		"jsonencode":   interpolationFuncJSONEncode(),
@@ -565,6 +567,32 @@ func interpolationFuncFormatList() ast.Function {
 	}
 }
 
+// interpolationFuncGzip implements the "gzip" function that allows gzip compression.
+func interpolationFuncGzip() ast.Function {
+	return ast.Function{
+		ArgTypes:   []ast.Type{ast.TypeString},
+		ReturnType: ast.TypeString,
+		Callback: func(args []interface{}) (interface{}, error) {
+			s := args[0].(string)
+
+			var b bytes.Buffer
+			gz := gzip.NewWriter(&b)
+			if _, err := gz.Write([]byte(s)); err != nil {
+				return "", fmt.Errorf("failed to gzip raw data: '%s'", s)
+			}
+			if err := gz.Flush(); err != nil {
+				return "", fmt.Errorf("failed to gzip raw data: '%s'", s)
+			}
+			if err := gz.Close(); err != nil {
+				return "", fmt.Errorf("failed to gzip raw data: '%s'", s)
+			}
+
+			return b.String(), nil
+		},
+	}
+}
+
+
 // interpolationFuncIndex implements the "index" function that allows one to
 // find the index of a specific element in a list
 func interpolationFuncIndex() ast.Function {

config/interpolate_funcs_test.go

@@ -1010,6 +1010,18 @@ func TestInterpolateFuncFormatList(t *testing.T) {
 	})
 }
 
+func TestInterpolateFuncGzip(t *testing.T) {
+	testFunction(t, testFunctionConfig{
+		Cases: []testFunctionCase{
+			{
+				`${base64encode(gzip("test"))}`,
+				"H4sIAAAJbogA/ypJLS4BAAAA//8BAAD//wx+f9gEAAAA",
+				false,
+			},
+		},
+	})
+}
+
 func TestInterpolateFuncIndex(t *testing.T) {
 	testFunction(t, testFunctionConfig{
 		Vars: map[string]ast.Variable{