98 lines
2.9 KiB
Go
98 lines
2.9 KiB
Go
// Copyright 2022 Google LLC All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package compression abstracts over gzip and zstd.
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package compression
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import (
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"bufio"
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"bytes"
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"io"
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"github.com/google/go-containerregistry/internal/gzip"
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"github.com/google/go-containerregistry/internal/zstd"
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"github.com/google/go-containerregistry/pkg/compression"
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)
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// Opener represents e.g. opening a file.
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type Opener = func() (io.ReadCloser, error)
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// GetCompression detects whether an Opener is compressed and which algorithm is used.
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func GetCompression(opener Opener) (compression.Compression, error) {
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rc, err := opener()
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if err != nil {
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return compression.None, err
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}
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defer rc.Close()
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cp, _, err := PeekCompression(rc)
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if err != nil {
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return compression.None, err
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}
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return cp, nil
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}
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// PeekCompression detects whether the input stream is compressed and which algorithm is used.
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//
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// If r implements Peek, we will use that directly, otherwise a small number
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// of bytes are buffered to Peek at the gzip/zstd header, and the returned
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// PeekReader can be used as a replacement for the consumed input io.Reader.
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func PeekCompression(r io.Reader) (compression.Compression, PeekReader, error) {
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pr := intoPeekReader(r)
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if isGZip, _, err := checkHeader(pr, gzip.MagicHeader); err != nil {
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return compression.None, pr, err
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} else if isGZip {
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return compression.GZip, pr, nil
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}
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if isZStd, _, err := checkHeader(pr, zstd.MagicHeader); err != nil {
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return compression.None, pr, err
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} else if isZStd {
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return compression.ZStd, pr, nil
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}
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return compression.None, pr, nil
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}
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// PeekReader is an io.Reader that also implements Peek a la bufio.Reader.
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type PeekReader interface {
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io.Reader
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Peek(n int) ([]byte, error)
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}
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// IntoPeekReader creates a PeekReader from an io.Reader.
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// If the reader already has a Peek method, it will just return the passed reader.
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func intoPeekReader(r io.Reader) PeekReader {
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if p, ok := r.(PeekReader); ok {
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return p
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}
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return bufio.NewReader(r)
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}
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// CheckHeader checks whether the first bytes from a PeekReader match an expected header
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func checkHeader(pr PeekReader, expectedHeader []byte) (bool, PeekReader, error) {
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header, err := pr.Peek(len(expectedHeader))
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if err != nil {
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// https://github.com/google/go-containerregistry/issues/367
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if err == io.EOF {
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return false, pr, nil
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}
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return false, pr, err
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}
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return bytes.Equal(header, expectedHeader), pr, nil
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}
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