add gzip api

pkg/yttlibrary/all.go

@@ -59,6 +59,9 @@ func NewAPI(
 		"url":    URLAPI,
 		"ip":     IPAPI,
 
+		// Compression
+		"gzip": GzipAPI,
+
 		// Templating
 		"template": NewTemplateModule(replaceNodeFunc).AsModule(),
 		"data":     dataMod.AsModule(),

pkg/yttlibrary/gzip.go

@@ -0,0 +1,81 @@
+// Copyright 2020 VMware, Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+package yttlibrary
+
+import (
+	"bytes"
+	"compress/gzip"
+	"fmt"
+
+	"github.com/k14s/starlark-go/starlark"
+	"github.com/k14s/starlark-go/starlarkstruct"
+	"github.com/vmware-tanzu/carvel-ytt/pkg/template/core"
+)
+
+var (
+	GzipAPI = starlark.StringDict{
+		"gzip": &starlarkstruct.Module{
+			Name: "gzip",
+			Members: starlark.StringDict{
+				"compress":   starlark.NewBuiltin("gzip.compress", core.ErrWrapper(gzipModule{}.Compress)),
+				"decompress": starlark.NewBuiltin("gzip.decompress", core.ErrWrapper(gzipModule{}.Decompress)),
+			},
+		},
+	}
+)
+
+type gzipModule struct{}
+
+func (b gzipModule) Compress(thread *starlark.Thread, f *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	if args.Len() != 1 {
+		return starlark.None, fmt.Errorf("expected exactly one argument")
+	}
+
+	val, err := core.NewStarlarkValue(args.Index(0)).AsString()
+	if err != nil {
+		return starlark.None, err
+	}
+
+	var buf bytes.Buffer
+	gz := gzip.NewWriter(&buf)
+
+	if _, err := gz.Write([]byte(val)); err != nil {
+		return nil, err
+	}
+
+	if err := gz.Close(); err != nil {
+		return nil, err
+	}
+
+	return starlark.String(buf.String()), nil
+}
+
+func (b gzipModule) Decompress(thread *starlark.Thread, f *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	if args.Len() != 1 {
+		return starlark.None, fmt.Errorf("expected exactly one argument")
+	}
+
+	val, err := core.NewStarlarkValue(args.Index(0)).AsString()
+	if err != nil {
+		return starlark.None, err
+	}
+
+	buf := bytes.NewBufferString(val)
+
+	gz, err := gzip.NewReader(buf)
+	if err != nil {
+		return nil, err
+	}
+
+	var out bytes.Buffer
+	if _, err := out.ReadFrom(gz); err != nil {
+		return nil, err
+	}
+
+	if err := gz.Close(); err != nil {
+		return nil, err
+	}
+
+	return starlark.String(out.String()), nil
+}