[pkg/compression] Support zlib

zlib compression is used in some AMI-based firmwares for AMD CPUs.
Implement the Compressor interface and unit-tests for it.

Information about the ZLIB section header taken from UEFITool which
added support in the A63 release.[^1][^2]

[^1]: https://github.com/LongSoft/UEFITool/releases/tag/A63
[^2]: LongSoft/UEFITool@8d5659c92b08

Signed-off-by: Julian Prein <[email protected]>

pkg/compression/compression.go

@@ -31,6 +31,7 @@ type Compressor interface {
 var (
  LZMAGUID = *guid.MustParse("EE4E5898-3914-4259-9D6E-DC7BD79403CF")
  LZMAX86GUID = *guid.MustParse("D42AE6BD-1352-4BFB-909A-CA72A6EAE889")
+ ZLIBGUID = *guid.MustParse("CE3233F5-2CD6-4D87-9152-4A238BB6D1C4")
 )
 
 // CompressorFromGUID returns a Compressor for the corresponding GUIDed Section.
@@ -51,6 +52,8 @@ func CompressorFromGUID(guid *guid.GUID) Compressor {
  // into xz. It does not make much difference because
  // the x86 filter is not the bottleneck.
  return &LZMAX86{lzma}
+ case ZLIBGUID:
+ return &ZLIB{}
  }
  return nil
 }

pkg/compression/compression_test.go

@@ -48,6 +48,12 @@ var tests = []struct {
  decodedFilename: "testdata/random.bin",
  compressor: &LZMAX86{&SystemLZMA{"xz"}},
  },
+ {
+ name: "random data ZLIB",
+ encodedFilename: "testdata/random.bin.zlib",
+ decodedFilename: "testdata/random.bin",
+ compressor: &ZLIB{},
+ },
 }
 
 func TestEncodeDecode(t *testing.T) {
@@ -122,6 +128,13 @@ func TestCompressorFromGUID(t *testing.T) {
  encodedFilename: "testdata/random.bin.lzma86",
  decodedFilename: "testdata/random.bin",
  },
+ {
+ name: "zlib",
+ guid: &ZLIBGUID,
+ expected: &ZLIB{},
+ encodedFilename: "testdata/random.bin.zlib",
+ decodedFilename: "testdata/random.bin",
+ },
  }
  for _, tt := range compressors {
  t.Run(tt.name, func(t *testing.T) {

pkg/compression/zlib.go

@@ -0,0 +1,83 @@
+// Copyright 2023 the LinuxBoot Authors. All rights reserved
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package compression
+
+import (
+ "bytes"
+ "compress/zlib"
+ "encoding/binary"
+ "errors"
+ "io"
+)
+
+const (
+ zlibCompressionLevel = 9
+ zlibSectionHeaderSize = 256
+ zlibSizeOffset = 20
+)
+
+// ZLIB implements Compressor and uses the zlib package from the standard
+// library
+type ZLIB struct{}
+
+// Name returns the type of compression employed.
+func (c *ZLIB) Name() string {
+ return "ZLIB"
+}
+
+// Decode decodes a byte slice of ZLIB data.
+func (c *ZLIB) Decode(encodedData []byte) ([]byte, error) {
+ if len(encodedData) < 256 {
+ return nil, errors.New("Zlib.Decode: missing section header")
+ }
+
+ // Check size in ZLIB section header
+ size := binary.LittleEndian.Uint32(
+ encodedData[zlibSizeOffset : zlibSizeOffset+4],
+ )
+ if size != uint32(len(encodedData)-zlibSectionHeaderSize) {
+ return nil, errors.New("ZLIB.Decode: size mismatch")
+ }
+
+ // Remove section header
+ r, err := zlib.NewReader(
+ bytes.NewBuffer(encodedData[zlibSectionHeaderSize:]),
+ )
+ if err != nil {
+ return nil, err
+ }
+
+ decodedData, err := io.ReadAll(r)
+ r.Close()
+ if err != nil {
+ return nil, err
+ }
+
+ return decodedData, nil
+}
+
+// Encode encodes a byte slice with ZLIB.
+func (c *ZLIB) Encode(decodedData []byte) ([]byte, error) {
+ var encodedData bytes.Buffer
+
+ w, err := zlib.NewWriterLevel(&encodedData, zlibCompressionLevel)
+ if err != nil {
+ return nil, err
+ }
+
+ _, err = w.Write(decodedData)
+ w.Close()
+ if err != nil {
+ return nil, err
+ }
+
+ // Add ZLIB section header containing the compressed size and zero padding.
+ zlib_header := make([]byte, zlibSectionHeaderSize)
+ binary.LittleEndian.PutUint32(
+ zlib_header[zlibSizeOffset:],
+ uint32(len(encodedData.Bytes())),
+ )
+ return append(zlib_header, encodedData.Bytes()[:]...), nil
+}