1 files changed, 118 insertions, 0 deletions
diff --git a/internal/gzip/zip.go b/internal/gzip/zip.go
new file mode 100644
index 0000000..018c0f8
--- /dev/null
+++ b/internal/gzip/zip.go
@@ -0,0 +1,118 @@
+// Copyright 2020 Google LLC All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package gzip provides helper functions for interacting with gzipped streams.
+package gzip
+
+import (
+	"bufio"
+	"bytes"
+	"compress/gzip"
+	"io"
+
+	"github.com/google/go-containerregistry/internal/and"
+)
+
+// MagicHeader is the start of gzip files.
+var MagicHeader = []byte{'\x1f', '\x8b'}
+
+// ReadCloser reads uncompressed input data from the io.ReadCloser and
+// returns an io.ReadCloser from which compressed data may be read.
+// This uses gzip.BestSpeed for the compression level.
+func ReadCloser(r io.ReadCloser) io.ReadCloser {
+	return ReadCloserLevel(r, gzip.BestSpeed)
+}
+
+// ReadCloserLevel reads uncompressed input data from the io.ReadCloser and
+// returns an io.ReadCloser from which compressed data may be read.
+// Refer to compress/gzip for the level:
+// https://golang.org/pkg/compress/gzip/#pkg-constants
+func ReadCloserLevel(r io.ReadCloser, level int) io.ReadCloser {
+	pr, pw := io.Pipe()
+
+	// For highly compressible layers, gzip.Writer will output a very small
+	// number of bytes per Write(). This is normally fine, but when pushing
+	// to a registry, we want to ensure that we're taking full advantage of
+	// the available bandwidth instead of sending tons of tiny writes over
+	// the wire.
+	// 64K ought to be small enough for anybody.
+	bw := bufio.NewWriterSize(pw, 2<<16)
+
+	// Returns err so we can pw.CloseWithError(err)
+	go func() error {
+		// TODO(go1.14): Just defer {pw,gw,r}.Close like you'd expect.
+		// Context: https://golang.org/issue/24283
+		gw, err := gzip.NewWriterLevel(bw, level)
+		if err != nil {
+			return pw.CloseWithError(err)
+		}
+
+		if _, err := io.Copy(gw, r); err != nil {
+			defer r.Close()
+			defer gw.Close()
+			return pw.CloseWithError(err)
+		}
+
+		// Close gzip writer to Flush it and write gzip trailers.
+		if err := gw.Close(); err != nil {
+			return pw.CloseWithError(err)
+		}
+
+		// Flush bufio writer to ensure we write out everything.
+		if err := bw.Flush(); err != nil {
+			return pw.CloseWithError(err)
+		}
+
+		// We don't really care if these fail.
+		defer pw.Close()
+		defer r.Close()
+
+		return nil
+	}()
+
+	return pr
+}
+
+// UnzipReadCloser reads compressed input data from the io.ReadCloser and
+// returns an io.ReadCloser from which uncompressed data may be read.
+func UnzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
+	gr, err := gzip.NewReader(r)
+	if err != nil {
+		return nil, err
+	}
+	return &and.ReadCloser{
+		Reader: gr,
+		CloseFunc: func() error {
+			// If the unzip fails, then this seems to return the same
+			// error as the read.  We don't want this to interfere with
+			// us closing the main ReadCloser, since this could leave
+			// an open file descriptor (fails on Windows).
+			gr.Close()
+			return r.Close()
+		},
+	}, nil
+}
+
+// Is detects whether the input stream is compressed.
+func Is(r io.Reader) (bool, error) {
+	magicHeader := make([]byte, 2)
+	n, err := r.Read(magicHeader)
+	if n == 0 && err == io.EOF {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+	return bytes.Equal(magicHeader, MagicHeader), nil
+}