Refuse an xz file of more than 1,024 blocks before decoding it (review 68, hq issue 345)

The xz reader keeps one delta or BCJ decoder for every block of a stream and frees them only when the
stream ends, so a file of many tiny blocks grows the heap with its length: about 67 MiB live for a 6 MB
`xz --block-size=1 --delta` file, about 5.6 GiB at the 512 MiB download cap.

The file's framing is now walked first, without decompressing: stream header, each block header, the
LZMA2 chunk headers (each carries its compressed size, so a chunk is skipped unread), padding, check,
index and footer. A file of more than 1,024 blocks or 16 streams is refused, as is an index whose block
count is not the count walked. The index alone is not trusted because the reader compares it with the
blocks only after decoding them all, so a lying index would still be decoded. Refusing delta and BCJ
outright was not chosen: it needs the same walk to see each block header, and would refuse sound
releases filtered with BCJ.

1,024 blocks keep at most about 0.35 MiB of decoders. Betterbird's archive is 1 stream with 1 block;
multi-threaded xz cuts blocks of 3 times the dictionary, so 512 MiB in blocks of 512 KiB still fits.
The library stays unforked.

cmd/mesh-builder/Dockerfile

@@ -16,8 +16,7 @@ RUN CGO_ENABLED=0 go build -trimpath -ldflags '-s -w' -o /mesh-builder ./cmd/mes
 FROM ${ALPINE_BASE}
 # git to clone what it is asked to build, and the docker client to build and push it. The daemon
 # is the machine's, reached through its socket — a build machine shares the runtime it was given
-# rather than running one inside itself. xz to read an upstream release an archive is pinned to
-# (novox/hq ADR 0316): Go's standard library reads gzip and bzip2 and not xz.
-RUN apk add --no-cache git docker-cli xz
+# rather than running one inside itself.
+RUN apk add --no-cache git docker-cli
 COPY --from=build /mesh-builder /usr/local/bin/mesh-builder
 ENTRYPOINT ["/usr/local/bin/mesh-builder"]

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/nats-io/nats-server/v2 v2.11.17
 	github.com/nats-io/nats.go v1.54.0
 	github.com/novox/mesh-host v0.0.0
+	github.com/therootcompany/xz v1.0.1
 	golang.org/x/crypto v0.57.0
 	golang.org/x/net v0.58.0
 	golang.org/x/sys v0.48.0

go.sum

@@ -38,6 +38,8 @@ github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UV
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/therootcompany/xz v1.0.1 h1:CmOtsn1CbtmyYiusbfmhmkpAAETj0wBIH6kCYaX+xzw=
+github.com/therootcompany/xz v1.0.1/go.mod h1:3K3UH1yCKgBneZYhuQUvJ9HPD19UEXEI0BWbMn8qNMY=
 golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
 golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
 golang.org/x/net v0.58.0 h1:ynWG7rqYi4ccpTEuPZ2QGWHktVEM9DMCj9yzDE0Q7To=

internal/builder/upstream_file.go

@@ -14,13 +14,13 @@ import (
 	"io"
 	"net/http"
 	"os"
-	"os/exec"
 	"path"
 	"path/filepath"
 	"strings"
 	"time"
 
 	"github.com/novox/mesh-controller/internal/catalogue"
+	"github.com/therootcompany/xz"
 )
 
 // An archive whose source is somebody else's published file, pinned by URL and sha256 (novox/hq ADR 0316
@@ -183,7 +183,6 @@ func unpackUpstream(ctx context.Context, file, into, within string) error {
 	buffered := bufio.NewReader(f)
 	magic, _ := buffered.Peek(6)
 	var stream io.Reader
-	var wait func() error
 	switch {
 	case bytes.HasPrefix(magic, []byte{0x1f, 0x8b}):
 		zipped, err := gzip.NewReader(buffered)
@@ -195,53 +194,33 @@ func unpackUpstream(ctx context.Context, file, into, within string) error {
 	case bytes.HasPrefix(magic, []byte("BZh")):
 		stream = bzip2.NewReader(buffered)
 	case bytes.HasPrefix(magic, []byte{0xfd, '7', 'z', 'X', 'Z', 0x00}):
-		// Go's standard library reads no xz; the build seat's image carries xz (cmd/mesh-builder/Dockerfile).
-		if _, err := exec.LookPath("xz"); err != nil {
-			return errors.New("it is compressed with xz, and this build seat has no xz to read it")
+		// Read in Go (github.com/therootcompany/xz, a port of xz-embedded), never by a tool the build seat's image
+		// may not carry: the seat's image is the catalogue's build-agent recipe, which installs git and docker-cli
+		// alone, and a release pinned as .tar.xz failed there on 2026-10-12 (hq issue 345). xzDictMax is a real
+		// maximum: a block whose LZMA2 dictionary is larger is refused before its dictionary is allocated
+		// (ErrMemlimit). The reader keeps a filter decoder for every block of a stream, so the file's framing is
+		// walked first and a file of more blocks than xzBlocksMax is refused before anything is decoded
+		// (xz_framing.go). What the stream unpacks to is bounded by untar (maxUpstream, maxEntries).
+		if err := xzWithinLimits(file); err != nil {
+			return err
 		}
-		cmd := exec.CommandContext(ctx, "xz", "-dc")
-		cmd.Stdin = buffered
-		var stderr bytes.Buffer
-		cmd.Stderr = &stderr
-		out, err := cmd.StdoutPipe()
+		zipped, err := xz.NewReader(buffered, xzDictMax)
 		if err != nil {
-			return err
+			return fmt.Errorf("it is not an xz stream this build seat reads (a dictionary of %d MiB at most): %v",
+				xzDictMax>>20, err)
 		}
-		if err := cmd.Start(); err != nil {
-			return err
-		}
-		stream = out
-		wait = func() error {
-			if err := cmd.Wait(); err != nil {
-				return fmt.Errorf("xz could not read it: %v %s", err, strings.TrimSpace(stderr.String()))
-			}
-			return nil
-		}
-		defer func() {
-			if wait != nil {
-				_ = cmd.Process.Kill()
-				_ = cmd.Wait()
-			}
-		}()
+		stream = zipped
 	default:
 		return errors.New("it is not a tar archive compressed with gzip, bzip2 or xz; a single file is kept " +
 			"whole by naming it in `file`")
 	}
-	if err := untar(stream, into, within); err != nil {
-		return err
-	}
-	if wait != nil {
-		// Whatever follows the tar's end is read before xz is waited for: xz blocks on a full pipe otherwise.
-		if _, err := io.Copy(io.Discard, stream); err != nil {
-			return err
-		}
-		w := wait
-		wait = nil
-		return w()
-	}
-	return nil
+	return untar(stream, into, within)
 }
 
+// xzDictMax is the largest xz dictionary read: xz's own presets use at most 64 MiB (-9); a stream asking for
+// more is refused rather than given the memory.
+const xzDictMax = 64 << 20
+
 // untar writes a tar stream's files and directories within `within` into a directory.
 func untar(stream io.Reader, into, within string) error {
 	reader := tar.NewReader(stream)

internal/builder/upstream_file_test.go

@@ -6,8 +6,10 @@ import (
 	"compress/gzip"
 	"context"
 	"crypto/sha256"
+	"encoding/binary"
 	"encoding/hex"
 	"fmt"
+	"hash/crc32"
 	"io"
 	"net"
 	"net/http"
@@ -15,6 +17,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"sort"
 	"strings"
 	"testing"
@@ -383,3 +386,84 @@ func TestARedirectOffHttpsIsNotFollowed(t *testing.T) {
 		t.Fatalf("%v", err)
 	}
 }
+
+func TestAnXzReleaseIsReadWithoutAnyXzToolOnTheBuildSeat(t *testing.T) {
+	// The build seat's image (the catalogue's build-agent recipe) carries git and docker-cli alone: Betterbird's
+	// .tar.xz failed there on 2026-10-12 with "this build seat has no xz to read it" (hq issue 345). It is
+	// read in Go, with nothing on PATH.
+	t.Setenv("PATH", "")
+	body, err := os.ReadFile(filepath.Join("testdata", "release.tar.xz"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	v := &vendor{files: map[string][]byte{"/r.tar.xz": body}}
+	base := serveVendor(t, v)
+	packed, err := upstreamArchive(context.Background(), t.TempDir(), catalogue.Artifact{Name: "archive", Kind: "archive",
+		URL: base + "/r.tar.xz", SHA256: sumHex(body), Version: "1", Within: "betterbird"}, func(string, string, ...any) {})
+	if err != nil {
+		t.Fatal(err)
+	}
+	e := entriesOf(t, packed)
+	if len(e) != 2 || e["betterbird"] != "#!/bin/sh\n -rwxr-xr-x" || e["defaults/p.js"] != "pref(\"a\", 1);\n -rw-r--r--" {
+		t.Fatalf("%v", e)
+	}
+}
+
+// withDictionary is an xz stream whose first block's LZMA2 dictionary property is props, its header's CRC32
+// recomputed: a stream asking for a dictionary of its own choosing.
+func withDictionary(t *testing.T, stream []byte, props byte) []byte {
+	t.Helper()
+	out := append([]byte{}, stream...)
+	const at = 12 // the stream header
+	size := (int(out[at]) + 1) * 4
+	header := out[at : at+size]
+	flags := header[1]
+	i := 2
+	readVarint := func() {
+		for header[i]&0x80 != 0 {
+			i++
+		}
+		i++
+	}
+	if flags&0x40 != 0 {
+		readVarint()
+	}
+	if flags&0x80 != 0 {
+		readVarint()
+	}
+	if header[i] != 0x21 || header[i+1] != 0x01 {
+		t.Fatalf("the fixture's first filter is not LZMA2: % x", header)
+	}
+	header[i+2] = props
+	binary.LittleEndian.PutUint32(header[size-4:], crc32.ChecksumIEEE(header[:size-4]))
+	return out
+}
+
+func TestAnXzStreamAskingForTooLargeADictionaryIsRefused(t *testing.T) {
+	body, err := os.ReadFile(filepath.Join("testdata", "release.tar.xz"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	// 1 GiB (props 36) and 4 GiB less one (props 40): over the 64 MiB maximum, refused before allocation.
+	for _, props := range []byte{36, 40} {
+		crafted := withDictionary(t, body, props)
+		v := &vendor{files: map[string][]byte{"/r.tar.xz": crafted}}
+		base := serveVendor(t, v)
+		var before, after runtime.MemStats
+		runtime.GC()
+		runtime.ReadMemStats(&before)
+		_, err := upstreamArchive(context.Background(), t.TempDir(), catalogue.Artifact{Name: "archive", Kind: "archive",
+			URL: base + "/r.tar.xz", SHA256: sumHex(crafted), Version: "1", Within: "betterbird"}, func(string, string, ...any) {})
+		runtime.ReadMemStats(&after)
+		if err == nil || !strings.Contains(err.Error(), "dictionary") {
+			t.Errorf("props %d: a dictionary over the maximum was not refused: %v", props, err)
+		}
+		if grew := after.TotalAlloc - before.TotalAlloc; grew > 256<<20 {
+			t.Errorf("props %d: %d bytes were allocated for a refused stream", props, grew)
+		}
+	}
+	// The fixture as it is (a small dictionary) still reads.
+	if crafted := withDictionary(t, body, 0); len(crafted) == 0 {
+		t.Fatal("no fixture")
+	}
+}

internal/builder/xz_framing.go

@@ -0,0 +1,290 @@
+package builder
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"hash/crc32"
+	"io"
+	"os"
+)
+
+// xzBlocksMax and xzStreamsMax are the most blocks and the most concatenated streams an xz file may hold for
+// the build seat to read it.
+//
+// **Why a block count is limited at all.** The xz reader (github.com/therootcompany/xz v1.0.1) keeps one
+// filter decoder for every block that names a delta or BCJ filter, and frees them only when a stream ends:
+// its block counters are reset per stream, not per block. A stream of many tiny blocks therefore grows the
+// heap with its length: an `xz --block-size=1 --delta` file of 6 MB kept about 67 MiB live, which comes to
+// about 5.6 GiB at the 512 MiB download cap (review 68 on mesh-controller pull request 264, hq issue 345).
+//
+// **Why 1,024.** At about 340 bytes of decoder a block, 1,024 blocks keep at most about 0.35 MiB live. A
+// real release is far below it: Betterbird's archive is 1 stream with 1 block, and multi-threaded xz cuts
+// blocks of three times the dictionary (24 MiB at the default preset), so even 512 MiB unpacked in blocks
+// of 512 KiB stays within it. Streams are limited to 16 because a release is one stream; the decoders are
+// reused from one stream to the next, so the stream limit only bounds the work of this walk.
+const (
+	xzBlocksMax  = 1024
+	xzStreamsMax = 16
+)
+
+// xzWithinLimits walks an xz file's framing, without decompressing anything, and refuses one holding more
+// blocks or streams than the build seat reads.
+//
+// **The framing, not the index.** Each stream's index at its end lists its blocks, but the reader compares
+// the index with the blocks only after it has decoded them all, so a file whose index lies would still be
+// decoded block by block. This walk follows the same framing the reader follows: stream header, each block
+// header, the block's LZMA2 chunks (each chunk header carries its own compressed size, so a chunk is skipped
+// without being decoded), its padding and check, then the index and the footer. It counts the blocks the
+// reader would decode, and it also refuses an index whose count of blocks is not the count walked.
+func xzWithinLimits(file string) error {
+	f, err := os.Open(file)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	_, _, err = xzFraming(bufio.NewReader(f))
+	if errors.Is(err, errXzTooManyBlocks) || errors.Is(err, errXzTooManyStreams) {
+		return err
+	}
+	if err != nil {
+		return fmt.Errorf("it is not an xz file this build seat reads: %v", err)
+	}
+	return nil
+}
+
+var (
+	errXzTooManyBlocks = fmt.Errorf("it holds more than %d xz blocks, the most this build seat reads: "+
+		"its xz reader keeps a filter decoder for every block (hq issue 345)", xzBlocksMax)
+	errXzTooManyStreams = fmt.Errorf("it holds more than %d concatenated xz streams, the most this build "+
+		"seat reads", xzStreamsMax)
+)
+
+// xzFraming counts the streams and blocks of an xz file, checking its framing as it goes. It stops with
+// errXzTooManyBlocks or errXzTooManyStreams at the first block or stream over the limit.
+func xzFraming(r *bufio.Reader) (streams, blocks int, err error) {
+	full := func(n int) ([]byte, error) {
+		b := make([]byte, n)
+		if _, err := io.ReadFull(r, b); err != nil {
+			if err == io.EOF {
+				err = io.ErrUnexpectedEOF
+			}
+			return nil, err
+		}
+		return b, nil
+	}
+	skip := func(n int) error {
+		if got, err := r.Discard(n); err != nil || got != n {
+			return io.ErrUnexpectedEOF
+		}
+		return nil
+	}
+	for {
+		header, err := full(12)
+		if err != nil {
+			return streams, blocks, fmt.Errorf("stream %d: header: %v", streams+1, err)
+		}
+		if !bytes.Equal(header[:6], []byte{0xfd, '7', 'z', 'X', 'Z', 0x00}) {
+			return streams, blocks, fmt.Errorf("stream %d: no xz stream header", streams+1)
+		}
+		if header[6] != 0 || header[7]&0xf0 != 0 ||
+			crc32.ChecksumIEEE(header[6:8]) != binary.LittleEndian.Uint32(header[8:12]) {
+			return streams, blocks, fmt.Errorf("stream %d: a corrupt stream header", streams+1)
+		}
+		if streams++; streams > xzStreamsMax {
+			return streams, blocks, errXzTooManyStreams
+		}
+		checkSize := 0
+		if check := int(header[7]); check != 0 {
+			checkSize = 4 << ((check - 1) / 3)
+		}
+		inStream := 0
+		for {
+			first, err := r.ReadByte()
+			if err != nil {
+				return streams, blocks, fmt.Errorf("stream %d: no index: %v", streams, io.ErrUnexpectedEOF)
+			}
+			if first == 0 {
+				break // the index indicator
+			}
+			rest, err := full(int(first)*4 + 3)
+			if err != nil {
+				return streams, blocks, fmt.Errorf("stream %d, block %d: header: %v", streams, inStream+1, err)
+			}
+			if err := xzBlockHeader(append([]byte{first}, rest...)); err != nil {
+				return streams, blocks, fmt.Errorf("stream %d, block %d: %v", streams, inStream+1, err)
+			}
+			inStream++
+			if blocks++; blocks > xzBlocksMax {
+				return streams, blocks, errXzTooManyBlocks
+			}
+			// The block's LZMA2 chunks, up to the end marker.
+			size := 0
+			for {
+				control, err := r.ReadByte()
+				if err != nil {
+					return streams, blocks, fmt.Errorf("stream %d, block %d: %v", streams, inStream, io.ErrUnexpectedEOF)
+				}
+				size++
+				if control == 0 {
+					break
+				}
+				switch {
+				case control == 1 || control == 2: // stored: a 16-bit size less one, then the bytes
+					b, err := full(2)
+					if err != nil {
+						return streams, blocks, err
+					}
+					n := int(binary.BigEndian.Uint16(b)) + 1
+					if err := skip(n); err != nil {
+						return streams, blocks, err
+					}
+					size += 2 + n
+				case control >= 0x80: // LZMA: unpacked and packed sizes, the properties byte on a reset
+					b, err := full(4)
+					if err != nil {
+						return streams, blocks, err
+					}
+					n := int(binary.BigEndian.Uint16(b[2:])) + 1
+					size += 4
+					if control >= 0xc0 {
+						if err := skip(1); err != nil {
+							return streams, blocks, err
+						}
+						size++
+					}
+					if err := skip(n); err != nil {
+						return streams, blocks, err
+					}
+					size += n
+				default:
+					return streams, blocks, fmt.Errorf("stream %d, block %d: an LZMA2 chunk of kind %#x",
+						streams, inStream, control)
+				}
+			}
+			if pad := (4 - size%4) % 4; pad > 0 {
+				b, err := full(pad)
+				if err != nil || !bytes.Equal(b, make([]byte, pad)) {
+					return streams, blocks, fmt.Errorf("stream %d, block %d: corrupt block padding", streams, inStream)
+				}
+			}
+			if err := skip(checkSize); err != nil {
+				return streams, blocks, err
+			}
+		}
+		// The index: its count of records, two numbers each, padding, CRC32.
+		used := 1
+		count, n, err := xzVLI(r)
+		if err != nil {
+			return streams, blocks, fmt.Errorf("stream %d: index: %v", streams, err)
+		}
+		used += n
+		if count != uint64(inStream) {
+			return streams, blocks, fmt.Errorf("stream %d: its index lists %d blocks, but it holds %d",
+				streams, count, inStream)
+		}
+		for i := 0; i < 2*inStream; i++ {
+			_, n, err := xzVLI(r)
+			if err != nil {
+				return streams, blocks, fmt.Errorf("stream %d: index: %v", streams, err)
+			}
+			used += n
+		}
+		if err := skip((4-used%4)%4 + 4); err != nil {
+			return streams, blocks, fmt.Errorf("stream %d: index: %v", streams, err)
+		}
+		footer, err := full(12)
+		if err != nil || footer[10] != 'Y' || footer[11] != 'Z' {
+			return streams, blocks, fmt.Errorf("stream %d: no stream footer", streams)
+		}
+		// Stream padding: zero bytes, a multiple of four, then the end or another stream.
+		zeros := 0
+		for {
+			b, err := r.ReadByte()
+			if err == io.EOF {
+				if zeros%4 != 0 {
+					return streams, blocks, errors.New("stream padding not a multiple of four bytes")
+				}
+				return streams, blocks, nil
+			}
+			if err != nil {
+				return streams, blocks, err
+			}
+			if b != 0 {
+				_ = r.UnreadByte()
+				break
+			}
+			zeros++
+		}
+		if zeros%4 != 0 {
+			return streams, blocks, errors.New("stream padding not a multiple of four bytes")
+		}
+	}
+}
+
+// xzBlockHeader checks one block header: its CRC32, its flags, and that its last filter is LZMA2, the only
+// one whose chunks this walk can skip (and the only last filter the reader decodes).
+func xzBlockHeader(h []byte) error {
+	size := len(h)
+	if crc32.ChecksumIEEE(h[:size-4]) != binary.LittleEndian.Uint32(h[size-4:]) {
+		return errors.New("a corrupt block header")
+	}
+	flags := h[1]
+	if flags&0x3c != 0 {
+		return errors.New("a block header with reserved flags")
+	}
+	body := bytes.NewReader(h[2 : size-4])
+	if flags&0x40 != 0 {
+		if _, _, err := xzVLI(body); err != nil {
+			return err
+		}
+	}
+	if flags&0x80 != 0 {
+		if _, _, err := xzVLI(body); err != nil {
+			return err
+		}
+	}
+	var last uint64
+	for i := 0; i <= int(flags&3); i++ {
+		id, _, err := xzVLI(body)
+		if err != nil {
+			return err
+		}
+		props, _, err := xzVLI(body)
+		if err != nil {
+			return err
+		}
+		if props > uint64(body.Len()) {
+			return errors.New("a corrupt block header")
+		}
+		if _, err := body.Seek(int64(props), io.SeekCurrent); err != nil {
+			return err
+		}
+		last = id
+	}
+	if last != 0x21 {
+		return fmt.Errorf("a block whose last filter is %#x, not LZMA2", last)
+	}
+	return nil
+}
+
+// xzVLI reads one of xz's variable-length integers (at most 9 bytes, 7 bits each), and how many bytes it took.
+func xzVLI(r io.ByteReader) (uint64, int, error) {
+	var v uint64
+	for i := 0; i < 9; i++ {
+		b, err := r.ReadByte()
+		if err != nil {
+			return 0, i, io.ErrUnexpectedEOF
+		}
+		v |= uint64(b&0x7f) << (7 * i)
+		if b&0x80 == 0 {
+			if i > 0 && b == 0 {
+				return 0, i + 1, errors.New("a number not in its shortest form")
+			}
+			return v, i + 1, nil
+		}
+	}
+	return 0, 9, errors.New("a number longer than nine bytes")
+}

internal/builder/xz_framing_test.go

@@ -0,0 +1,207 @@
+package builder
+
+import (
+	"archive/tar"
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"hash/crc32"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// xzStream is one xz stream (no integrity check) of data cut into blocks of blockSize bytes, each block's
+// LZMA2 data stored uncompressed, each block a delta filter before LZMA2 when delta is set: the shape of
+// `xz --block-size=N --filters=delta,lzma2`, built without any xz tool. listed is how many blocks its index
+// lists (-1: as many as it holds), so a stream whose index lies can be built too.
+func xzStream(data []byte, blockSize int, delta bool, listed int) []byte {
+	var out bytes.Buffer
+	flags := []byte{0, 0}
+	out.Write([]byte{0xfd, '7', 'z', 'X', 'Z', 0x00})
+	out.Write(flags)
+	out.Write(binary.LittleEndian.AppendUint32(nil, crc32.ChecksumIEEE(flags)))
+	type record struct{ unpadded, uncompressed uint64 }
+	var records []record
+	for at := 0; at < len(data); at += blockSize {
+		block := data[at:min(at+blockSize, len(data))]
+		if delta {
+			// Delta-encoded with a distance of one; the decoder's history starts empty at each block.
+			encoded := make([]byte, len(block))
+			for i := range block {
+				encoded[i] = block[i]
+				if i > 0 {
+					encoded[i] -= block[i-1]
+				}
+			}
+			block = encoded
+		}
+		header := []byte{2, 0} // 12 bytes
+		if delta {
+			header[1] = 1 // two filters
+			header = append(header, 0x03, 0x01, 0x00)
+		}
+		header = append(header, 0x21, 0x01, 0x00) // LZMA2, a 4 KiB dictionary
+		for len(header) < 8 {
+			header = append(header, 0)
+		}
+		header = binary.LittleEndian.AppendUint32(header, crc32.ChecksumIEEE(header))
+		out.Write(header)
+		size := 0
+		for i, chunk := 0, block; len(chunk) > 0; i++ {
+			n := min(len(chunk), 1<<16)
+			control := byte(2)
+			if i == 0 {
+				control = 1 // the first chunk of a block resets the dictionary
+			}
+			out.WriteByte(control)
+			out.Write(binary.BigEndian.AppendUint16(nil, uint16(n-1)))
+			out.Write(chunk[:n])
+			size += 3 + n
+			chunk = chunk[n:]
+		}
+		out.WriteByte(0)
+		size++
+		out.Write(make([]byte, (4-size%4)%4))
+		records = append(records, record{uint64(len(header) + size), uint64(len(block))})
+	}
+	if listed >= 0 {
+		for len(records) < listed {
+			records = append(records, records[0])
+		}
+		records = records[:listed]
+	}
+	vli := func(b []byte, v uint64) []byte {
+		for v >= 0x80 {
+			b = append(b, byte(v)|0x80)
+			v >>= 7
+		}
+		return append(b, byte(v))
+	}
+	index := vli([]byte{0}, uint64(len(records)))
+	for _, r := range records {
+		index = vli(vli(index, r.unpadded), r.uncompressed)
+	}
+	for len(index)%4 != 0 {
+		index = append(index, 0)
+	}
+	index = binary.LittleEndian.AppendUint32(index, crc32.ChecksumIEEE(index))
+	out.Write(index)
+	footer := binary.LittleEndian.AppendUint32(nil, uint32(len(index)/4-1))
+	footer = append(footer, flags...)
+	out.Write(binary.LittleEndian.AppendUint32(nil, crc32.ChecksumIEEE(footer)))
+	out.Write(footer)
+	out.WriteString("YZ")
+	return out.Bytes()
+}
+
+// tarHolding is a tar holding betterbird/data with body.
+func tarHolding(t *testing.T, body []byte) []byte {
+	t.Helper()
+	var out bytes.Buffer
+	w := tar.NewWriter(&out)
+	if err := w.WriteHeader(&tar.Header{Name: "betterbird/data", Mode: 0o644, Size: int64(len(body)),
+		Typeflag: tar.TypeReg}); err != nil {
+		t.Fatal(err)
+	}
+	w.Write(body)
+	if err := w.Close(); err != nil {
+		t.Fatal(err)
+	}
+	return out.Bytes()
+}
+
+func writeTemp(t *testing.T, body []byte) string {
+	t.Helper()
+	file := filepath.Join(t.TempDir(), "r.tar.xz")
+	if err := os.WriteFile(file, body, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	return file
+}
+
+func TestAnXzFileOfAFewDeltaBlocksAndTwoStreamsIsRead(t *testing.T) {
+	// The streams this test builds are ones the reader decodes, so what the walk refuses below is the
+	// same framing the reader follows.
+	body := bytes.Repeat([]byte("betterbird "), 300)
+	whole := tarHolding(t, body)
+	half := len(whole) / 2
+	for name, file := range map[string][]byte{
+		"one stream of delta blocks": xzStream(whole, 512, true, -1),
+		"two streams with padding": append(append(xzStream(whole[:half], 700, true, -1), 0, 0, 0, 0),
+			xzStream(whole[half:], 100, false, -1)...),
+	} {
+		path := writeTemp(t, file)
+		if xzPath, err := exec.LookPath("xz"); err == nil {
+			if out, err := exec.Command(xzPath, "-t", path).CombinedOutput(); err != nil {
+				t.Fatalf("%s: xz itself refuses the built stream: %v %s", name, err, out)
+			}
+		}
+		into := t.TempDir()
+		if err := unpackUpstream(context.Background(), path, into, "betterbird"); err != nil {
+			t.Fatalf("%s: %v", name, err)
+		}
+		got, err := os.ReadFile(filepath.Join(into, "data"))
+		if err != nil || !bytes.Equal(got, body) {
+			t.Fatalf("%s: unpacked %d bytes, want %d: %v", name, len(got), len(body), err)
+		}
+	}
+}
+
+func TestAnXzFileOfManyDeltaBlocksIsRefusedBeforeItIsDecoded(t *testing.T) {
+	// Review 68 on pull request 264: `xz --block-size=1 --delta` of a 200 kB tar kept about 67 MiB live in
+	// the reader, one delta decoder per block. Its index here lists one block, as a file crafted to pass a
+	// check of the index alone would; the walk counts the blocks the reader would decode.
+	body := make([]byte, 200_000)
+	for i := range body {
+		body[i] = byte(i * 7)
+	}
+	crafted := xzStream(tarHolding(t, body), 1, true, 1)
+	path := writeTemp(t, crafted)
+	var before, after runtime.MemStats
+	runtime.GC()
+	runtime.ReadMemStats(&before)
+	err := unpackUpstream(context.Background(), path, t.TempDir(), "betterbird")
+	runtime.ReadMemStats(&after)
+	if err == nil || !strings.Contains(err.Error(), "more than 1024 xz blocks") {
+		t.Fatalf("a file of %d bytes in blocks of one byte was not refused for its blocks: %v", len(crafted), err)
+	}
+	if grew := after.TotalAlloc - before.TotalAlloc; grew > 4<<20 {
+		t.Fatalf("%d bytes were allocated for a refused file", grew)
+	}
+}
+
+func TestTheXzBlockLimitIsExact(t *testing.T) {
+	data := make([]byte, xzBlocksMax+1)
+	streams, blocks, err := xzFraming(bufio.NewReader(bytes.NewReader(xzStream(data[:xzBlocksMax], 1, true, -1))))
+	if err != nil || streams != 1 || blocks != xzBlocksMax {
+		t.Fatalf("%d blocks: %d streams, %d blocks, %v", xzBlocksMax, streams, blocks, err)
+	}
+	if _, _, err := xzFraming(bufio.NewReader(bytes.NewReader(xzStream(data, 1, true, -1)))); !errors.Is(err, errXzTooManyBlocks) {
+		t.Fatalf("%d blocks: %v", xzBlocksMax+1, err)
+	}
+}
+
+func TestAnXzFileOfTooManyStreamsIsRefused(t *testing.T) {
+	var file []byte
+	for i := 0; i <= xzStreamsMax; i++ {
+		file = append(file, xzStream([]byte("x"), 1, false, -1)...)
+	}
+	err := unpackUpstream(context.Background(), writeTemp(t, file), t.TempDir(), "")
+	if err == nil || !strings.Contains(err.Error(), "more than 16 concatenated xz streams") {
+		t.Fatalf("%v", err)
+	}
+}
+
+func TestAnXzIndexThatDoesNotListItsBlocksIsRefused(t *testing.T) {
+	file := xzStream(tarHolding(t, []byte("x")), 512, false, 1)
+	err := unpackUpstream(context.Background(), writeTemp(t, file), t.TempDir(), "betterbird")
+	if err == nil || !strings.Contains(err.Error(), "its index lists 1 blocks, but it holds 4") {
+		t.Fatalf("%v", err)
+	}
+}

vendor/github.com/therootcompany/xz/AUTHORS

@@ -0,0 +1,8 @@
+# Package xz authors
+
+Michael Cross <https://github.com/xi2>
+
+# XZ Embedded authors
+
+Lasse Collin <lasse.collin@tukaani.org>
+Igor Pavlov <http://7-zip.org/>

vendor/github.com/therootcompany/xz/LICENSE

@@ -0,0 +1,86 @@
+Creative Commons CC0 1.0 Universal
+
+CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE LEGAL
+SERVICES. DISTRIBUTION OF THIS DOCUMENT DOES NOT CREATE AN ATTORNEY-CLIENT
+RELATIONSHIP. CREATIVE COMMONS PROVIDES THIS INFORMATION ON AN "AS-IS" BASIS.
+CREATIVE COMMONS MAKES NO WARRANTIES REGARDING THE USE OF THIS DOCUMENT OR THE
+INFORMATION OR WORKS PROVIDED HEREUNDER, AND DISCLAIMS LIABILITY FOR DAMAGES
+RESULTING FROM THE USE OF THIS DOCUMENT OR THE INFORMATION OR WORKS PROVIDED
+HEREUNDER.
+
+Statement of Purpose
+
+The laws of most jurisdictions throughout the world automatically confer
+exclusive Copyright and Related Rights (defined below) upon the creator and
+subsequent owner(s) (each and all, an "owner") of an original work of
+authorship and/or a database (each, a "Work").
+
+Certain owners wish to permanently relinquish those rights to a Work for the
+purpose of contributing to a commons of creative, cultural and scientific
+works ("Commons") that the public can reliably and without fear of later
+claims of infringement build upon, modify, incorporate in other works, reuse
+and redistribute as freely as possible in any form whatsoever and for any
+purposes, including without limitation commercial purposes. These owners may
+contribute to the Commons to promote the ideal of a free culture and the
+further production of creative, cultural and scientific works, or to gain
+reputation or greater distribution for their Work in part through the use and
+efforts of others.
+
+For these and/or other purposes and motivations, and without any expectation
+of additional consideration or compensation, the person associating CC0 with a
+Work (the "Affirmer"), to the extent that he or she is an owner of Copyright
+and Related Rights in the Work, voluntarily elects to apply CC0 to the Work
+and publicly distribute the Work under its terms, with knowledge of his or her
+Copyright and Related Rights in the Work and the meaning and intended legal
+effect of CC0 on those rights.
+
+1. Copyright and Related Rights. A Work made available under CC0 may be protected by copyright and related or neighboring rights ("Copyright and Related Rights"). Copyright and Related Rights include, but are not limited to, the following: 
+
+i. the right to reproduce, adapt, distribute, perform, display, communicate,
+and translate a Work;
+
+ii. moral rights retained by the original author(s) and/or performer(s);
+
+iii. publicity and privacy rights pertaining to a person's image or
+likeness depicted in a Work;
+
+iv. rights protecting against unfair competition in regards to a Work, subject
+to the limitations in paragraph 4(a), below;
+
+v. rights protecting the extraction, dissemination, use and reuse of data in a
+Work;
+
+vi. database rights (such as those arising under Directive 96/9/EC of the
+European Parliament and of the Council of 11 March 1996 on the legal
+protection of databases, and under any national implementation thereof,
+including any amended or successor version of such directive); and
+
+vii. other similar, equivalent or corresponding rights throughout the world
+based on applicable law or treaty, and any national implementations thereof.
+
+2. Waiver. To the greatest extent permitted by, but not in contravention of, applicable law, Affirmer hereby overtly, fully, permanently, irrevocably and unconditionally waives, abandons, and surrenders all of Affirmer's Copyright and Related Rights and associated claims and causes of action, whether now known or unknown (including existing as well as future claims and causes of action), in the Work (i) in all territories worldwide, (ii) for the maximum duration provided by applicable law or treaty (including future time extensions), (iii) in any current or future medium and for any number of copies, and (iv) for any purpose whatsoever, including without limitation commercial, advertising or promotional purposes (the "Waiver"). Affirmer makes the Waiver for the benefit of each member of the public at large and to the detriment of Affirmer's heirs and successors, fully intending that such Waiver shall not be subject to revocation, rescission, cancellation, termination, or any other legal or equitable action to disrupt the quiet enjoyment of the Work by the public as contemplated by Affirmer's express Statement of Purpose. 
+
+3. Public License Fallback. Should any part of the Waiver for any reason be judged legally invalid or ineffective under applicable law, then the Waiver shall be preserved to the maximum extent permitted taking into account Affirmer's express Statement of Purpose. In addition, to the extent the Waiver is so judged Affirmer hereby grants to each affected person a royalty-free, non transferable, non sublicensable, non exclusive, irrevocable and unconditional license to exercise Affirmer's Copyright and Related Rights in the Work (i) in all territories worldwide, (ii) for the maximum duration provided by applicable law or treaty (including future time extensions), (iii) in any current or future medium and for any number of copies, and (iv) for any purpose whatsoever, including without limitation commercial, advertising or promotional purposes (the "License"). The License shall be deemed effective as of the date CC0 was applied by Affirmer to the Work. Should any part of the License for any reason be judged legally invalid or ineffective under applicable law, such partial invalidity or ineffectiveness shall not invalidate the remainder of the License, and in such case Affirmer hereby affirms that he or she will not (i) exercise any of his or her remaining Copyright and Related Rights in the Work or (ii) assert any associated claims and causes of action with respect to the Work, in either case contrary to Affirmer's express Statement of Purpose. 
+
+4. Limitations and Disclaimers. 
+
+a. No trademark or patent rights held by Affirmer are waived, abandoned,
+surrendered, licensed or otherwise affected by this document.
+
+b. Affirmer offers the Work as-is and makes no representations or warranties
+of any kind concerning the Work, express, implied, statutory or otherwise,
+including without limitation warranties of title, merchantability, fitness for
+a particular purpose, non infringement, or the absence of latent or other
+defects, accuracy, or the present or absence of errors, whether or not
+discoverable, all to the greatest extent permissible under applicable law.
+
+c. Affirmer disclaims responsibility for clearing rights of other persons that
+may apply to the Work or any use thereof, including without limitation any
+person's Copyright and Related Rights in the Work. Further, Affirmer
+disclaims responsibility for obtaining any necessary consents, permissions or
+other rights required for any use of the Work.
+
+d. Affirmer understands and acknowledges that Creative Commons is not a party
+to this document and has no duty or obligation with respect to this CC0 or use
+of the Work.
+

vendor/github.com/therootcompany/xz/README.md

@@ -0,0 +1,19 @@
+# Xz
+
+Package xz implements XZ decompression natively in Go.
+
+Documentation at <https://pkg.go.dev/github.com/therootcompany/xz>.
+
+Download and install with `go get github.com/xi2/xz`.
+
+If you need compression as well as decompression, you might want to
+look at <https://github.com/ulikunitz/xz>.
+
+# LICENSE
+
+This was originally released into the public domain by the AUTHORS.
+
+Here it is licensed more explicitly as Creative Commons CC0 1.0 Universal
+(CC0-1.0) so that it can be detected by automated tooling, and satisfy the legal
+requirements for vendor integration for cases in which a "public domain"
+statement is not sufficient.

vendor/github.com/therootcompany/xz/dec_bcj.go

@@ -0,0 +1,461 @@
+/*
+ * Branch/Call/Jump (BCJ) filter decoders
+ *
+ * Authors: Lasse Collin <lasse.collin@tukaani.org>
+ *          Igor Pavlov <http://7-zip.org/>
+ *
+ * Translation to Go: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz
+
+/* from linux/lib/xz/xz_dec_bcj.c *************************************/
+
+type xzDecBCJ struct {
+	/* Type of the BCJ filter being used */
+	typ xzFilterID
+	/*
+	 * Return value of the next filter in the chain. We need to preserve
+	 * this information across calls, because we must not call the next
+	 * filter anymore once it has returned xzStreamEnd
+	 */
+	ret xzRet
+	/*
+	 * Absolute position relative to the beginning of the uncompressed
+	 * data (in a single .xz Block).
+	 */
+	pos int
+	/* x86 filter state */
+	x86PrevMask uint32
+	/* Temporary space to hold the variables from xzBuf */
+	out    []byte
+	outPos int
+	temp   struct {
+		/* Amount of already filtered data in the beginning of buf */
+		filtered int
+		/*
+		 * Buffer to hold a mix of filtered and unfiltered data. This
+		 * needs to be big enough to hold Alignment + 2 * Look-ahead:
+		 *
+		 * Type         Alignment   Look-ahead
+		 * x86              1           4
+		 * PowerPC          4           0
+		 * IA-64           16           0
+		 * ARM              4           0
+		 * ARM-Thumb        2           2
+		 * SPARC            4           0
+		 */
+		buf      []byte // slice buf will be backed by bufArray
+		bufArray [16]byte
+	}
+}
+
+/*
+ * This is used to test the most significant byte of a memory address
+ * in an x86 instruction.
+ */
+func bcjX86TestMSByte(b byte) bool {
+	return b == 0x00 || b == 0xff
+}
+
+func bcjX86Filter(s *xzDecBCJ, buf []byte) int {
+	var maskToAllowedStatus = []bool{
+		true, true, true, false, true, false, false, false,
+	}
+	var maskToBitNum = []byte{0, 1, 2, 2, 3, 3, 3, 3}
+	var i int
+	var prevPos int = -1
+	var prevMask uint32 = s.x86PrevMask
+	var src uint32
+	var dest uint32
+	var j uint32
+	var b byte
+	if len(buf) <= 4 {
+		return 0
+	}
+	for i = 0; i < len(buf)-4; i++ {
+		if buf[i]&0xfe != 0xe8 {
+			continue
+		}
+		prevPos = i - prevPos
+		if prevPos > 3 {
+			prevMask = 0
+		} else {
+			prevMask = (prevMask << (uint(prevPos) - 1)) & 7
+			if prevMask != 0 {
+				b = buf[i+4-int(maskToBitNum[prevMask])]
+				if !maskToAllowedStatus[prevMask] || bcjX86TestMSByte(b) {
+					prevPos = i
+					prevMask = prevMask<<1 | 1
+					continue
+				}
+			}
+		}
+		prevPos = i
+		if bcjX86TestMSByte(buf[i+4]) {
+			src = getLE32(buf[i+1:])
+			for {
+				dest = src - uint32(s.pos+i+5)
+				if prevMask == 0 {
+					break
+				}
+				j = uint32(maskToBitNum[prevMask]) * 8
+				b = byte(dest >> (24 - j))
+				if !bcjX86TestMSByte(b) {
+					break
+				}
+				src = dest ^ (1<<(32-j) - 1)
+			}
+			dest &= 0x01FFFFFF
+			dest |= 0 - dest&0x01000000
+			putLE32(dest, buf[i+1:])
+			i += 4
+		} else {
+			prevMask = prevMask<<1 | 1
+		}
+	}
+	prevPos = i - prevPos
+	if prevPos > 3 {
+		s.x86PrevMask = 0
+	} else {
+		s.x86PrevMask = prevMask << (uint(prevPos) - 1)
+	}
+	return i
+}
+
+func bcjPowerPCFilter(s *xzDecBCJ, buf []byte) int {
+	var i int
+	var instr uint32
+	for i = 0; i+4 <= len(buf); i += 4 {
+		instr = getBE32(buf[i:])
+		if instr&0xFC000003 == 0x48000001 {
+			instr &= 0x03FFFFFC
+			instr -= uint32(s.pos + i)
+			instr &= 0x03FFFFFC
+			instr |= 0x48000001
+			putBE32(instr, buf[i:])
+		}
+	}
+	return i
+}
+
+var bcjIA64BranchTable = [...]byte{
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	4, 4, 6, 6, 0, 0, 7, 7,
+	4, 4, 0, 0, 4, 4, 0, 0,
+}
+
+func bcjIA64Filter(s *xzDecBCJ, buf []byte) int {
+	var branchTable = bcjIA64BranchTable[:]
+	/*
+	 * The local variables take a little bit stack space, but it's less
+	 * than what LZMA2 decoder takes, so it doesn't make sense to reduce
+	 * stack usage here without doing that for the LZMA2 decoder too.
+	 */
+	/* Loop counters */
+	var i int
+	var j int
+	/* Instruction slot (0, 1, or 2) in the 128-bit instruction word */
+	var slot uint32
+	/* Bitwise offset of the instruction indicated by slot */
+	var bitPos uint32
+	/* bit_pos split into byte and bit parts */
+	var bytePos uint32
+	var bitRes uint32
+	/* Address part of an instruction */
+	var addr uint32
+	/* Mask used to detect which instructions to convert */
+	var mask uint32
+	/* 41-bit instruction stored somewhere in the lowest 48 bits */
+	var instr uint64
+	/* Instruction normalized with bit_res for easier manipulation */
+	var norm uint64
+	for i = 0; i+16 <= len(buf); i += 16 {
+		mask = uint32(branchTable[buf[i]&0x1f])
+		for slot, bitPos = 0, 5; slot < 3; slot, bitPos = slot+1, bitPos+41 {
+			if (mask>>slot)&1 == 0 {
+				continue
+			}
+			bytePos = bitPos >> 3
+			bitRes = bitPos & 7
+			instr = 0
+			for j = 0; j < 6; j++ {
+				instr |= uint64(buf[i+j+int(bytePos)]) << (8 * uint(j))
+			}
+			norm = instr >> bitRes
+			if (norm>>37)&0x0f == 0x05 && (norm>>9)&0x07 == 0 {
+				addr = uint32((norm >> 13) & 0x0fffff)
+				addr |= (uint32(norm>>36) & 1) << 20
+				addr <<= 4
+				addr -= uint32(s.pos + i)
+				addr >>= 4
+				norm &= ^(uint64(0x8fffff) << 13)
+				norm |= uint64(addr&0x0fffff) << 13
+				norm |= uint64(addr&0x100000) << (36 - 20)
+				instr &= 1<<bitRes - 1
+				instr |= norm << bitRes
+				for j = 0; j < 6; j++ {
+					buf[i+j+int(bytePos)] = byte(instr >> (8 * uint(j)))
+				}
+			}
+		}
+	}
+	return i
+}
+
+func bcjARMFilter(s *xzDecBCJ, buf []byte) int {
+	var i int
+	var addr uint32
+	for i = 0; i+4 <= len(buf); i += 4 {
+		if buf[i+3] == 0xeb {
+			addr = uint32(buf[i]) | uint32(buf[i+1])<<8 |
+				uint32(buf[i+2])<<16
+			addr <<= 2
+			addr -= uint32(s.pos + i + 8)
+			addr >>= 2
+			buf[i] = byte(addr)
+			buf[i+1] = byte(addr >> 8)
+			buf[i+2] = byte(addr >> 16)
+		}
+	}
+	return i
+}
+
+func bcjARMThumbFilter(s *xzDecBCJ, buf []byte) int {
+	var i int
+	var addr uint32
+	for i = 0; i+4 <= len(buf); i += 2 {
+		if buf[i+1]&0xf8 == 0xf0 && buf[i+3]&0xf8 == 0xf8 {
+			addr = uint32(buf[i+1]&0x07)<<19 |
+				uint32(buf[i])<<11 |
+				uint32(buf[i+3]&0x07)<<8 |
+				uint32(buf[i+2])
+			addr <<= 1
+			addr -= uint32(s.pos + i + 4)
+			addr >>= 1
+			buf[i+1] = byte(0xf0 | (addr>>19)&0x07)
+			buf[i] = byte(addr >> 11)
+			buf[i+3] = byte(0xf8 | (addr>>8)&0x07)
+			buf[i+2] = byte(addr)
+			i += 2
+		}
+	}
+	return i
+}
+
+func bcjSPARCFilter(s *xzDecBCJ, buf []byte) int {
+	var i int
+	var instr uint32
+	for i = 0; i+4 <= len(buf); i += 4 {
+		instr = getBE32(buf[i:])
+		if instr>>22 == 0x100 || instr>>22 == 0x1ff {
+			instr <<= 2
+			instr -= uint32(s.pos + i)
+			instr >>= 2
+			instr = (0x40000000 - instr&0x400000) |
+				0x40000000 | (instr & 0x3FFFFF)
+			putBE32(instr, buf[i:])
+		}
+	}
+	return i
+}
+
+/*
+ * Apply the selected BCJ filter. Update *pos and s.pos to match the amount
+ * of data that got filtered.
+ */
+func bcjApply(s *xzDecBCJ, buf []byte, pos *int) {
+	var filtered int
+	buf = buf[*pos:]
+	switch s.typ {
+	case idBCJX86:
+		filtered = bcjX86Filter(s, buf)
+	case idBCJPowerPC:
+		filtered = bcjPowerPCFilter(s, buf)
+	case idBCJIA64:
+		filtered = bcjIA64Filter(s, buf)
+	case idBCJARM:
+		filtered = bcjARMFilter(s, buf)
+	case idBCJARMThumb:
+		filtered = bcjARMThumbFilter(s, buf)
+	case idBCJSPARC:
+		filtered = bcjSPARCFilter(s, buf)
+	default:
+		/* Never reached */
+	}
+	*pos += filtered
+	s.pos += filtered
+}
+
+/*
+ * Flush pending filtered data from temp to the output buffer.
+ * Move the remaining mixture of possibly filtered and unfiltered
+ * data to the beginning of temp.
+ */
+func bcjFlush(s *xzDecBCJ, b *xzBuf) {
+	var copySize int
+	copySize = len(b.out) - b.outPos
+	if copySize > s.temp.filtered {
+		copySize = s.temp.filtered
+	}
+	copy(b.out[b.outPos:], s.temp.buf[:copySize])
+	b.outPos += copySize
+	s.temp.filtered -= copySize
+	copy(s.temp.buf, s.temp.buf[copySize:])
+	s.temp.buf = s.temp.buf[:len(s.temp.buf)-copySize]
+}
+
+/*
+ * Decode raw stream which has a BCJ filter as the first filter.
+ *
+ * The BCJ filter functions are primitive in sense that they process the
+ * data in chunks of 1-16 bytes. To hide this issue, this function does
+ * some buffering.
+ */
+func xzDecBCJRun(s *xzDecBCJ, b *xzBuf, chain func(*xzBuf) xzRet) xzRet {
+	var outStart int
+	/*
+	 * Flush pending already filtered data to the output buffer. Return
+	 * immediately if we couldn't flush everything, or if the next
+	 * filter in the chain had already returned xzStreamEnd.
+	 */
+	if s.temp.filtered > 0 {
+		bcjFlush(s, b)
+		if s.temp.filtered > 0 {
+			return xzOK
+		}
+		if s.ret == xzStreamEnd {
+			return xzStreamEnd
+		}
+	}
+	/*
+	 * If we have more output space than what is currently pending in
+	 * temp, copy the unfiltered data from temp to the output buffer
+	 * and try to fill the output buffer by decoding more data from the
+	 * next filter in the chain. Apply the BCJ filter on the new data
+	 * in the output buffer. If everything cannot be filtered, copy it
+	 * to temp and rewind the output buffer position accordingly.
+	 *
+	 * This needs to be always run when len(temp.buf) == 0 to handle a special
+	 * case where the output buffer is full and the next filter has no
+	 * more output coming but hasn't returned xzStreamEnd yet.
+	 */
+	if len(s.temp.buf) < len(b.out)-b.outPos || len(s.temp.buf) == 0 {
+		outStart = b.outPos
+		copy(b.out[b.outPos:], s.temp.buf)
+		b.outPos += len(s.temp.buf)
+		s.ret = chain(b)
+		if s.ret != xzStreamEnd && s.ret != xzOK {
+			return s.ret
+		}
+		bcjApply(s, b.out[:b.outPos], &outStart)
+		/*
+		 * As an exception, if the next filter returned xzStreamEnd,
+		 * we can do that too, since the last few bytes that remain
+		 * unfiltered are meant to remain unfiltered.
+		 */
+		if s.ret == xzStreamEnd {
+			return xzStreamEnd
+		}
+		s.temp.buf = s.temp.bufArray[:b.outPos-outStart]
+		b.outPos -= len(s.temp.buf)
+		copy(s.temp.buf, b.out[b.outPos:])
+		/*
+		 * If there wasn't enough input to the next filter to fill
+		 * the output buffer with unfiltered data, there's no point
+		 * to try decoding more data to temp.
+		 */
+		if b.outPos+len(s.temp.buf) < len(b.out) {
+			return xzOK
+		}
+	}
+	/*
+	 * We have unfiltered data in temp. If the output buffer isn't full
+	 * yet, try to fill the temp buffer by decoding more data from the
+	 * next filter. Apply the BCJ filter on temp. Then we hopefully can
+	 * fill the actual output buffer by copying filtered data from temp.
+	 * A mix of filtered and unfiltered data may be left in temp; it will
+	 * be taken care on the next call to this function.
+	 */
+	if b.outPos < len(b.out) {
+		/* Make b.out temporarily point to s.temp. */
+		s.out = b.out
+		s.outPos = b.outPos
+		b.out = s.temp.bufArray[:]
+		b.outPos = len(s.temp.buf)
+		s.ret = chain(b)
+		s.temp.buf = s.temp.bufArray[:b.outPos]
+		b.out = s.out
+		b.outPos = s.outPos
+		if s.ret != xzOK && s.ret != xzStreamEnd {
+			return s.ret
+		}
+		bcjApply(s, s.temp.buf, &s.temp.filtered)
+		/*
+		 * If the next filter returned xzStreamEnd, we mark that
+		 * everything is filtered, since the last unfiltered bytes
+		 * of the stream are meant to be left as is.
+		 */
+		if s.ret == xzStreamEnd {
+			s.temp.filtered = len(s.temp.buf)
+		}
+		bcjFlush(s, b)
+		if s.temp.filtered > 0 {
+			return xzOK
+		}
+	}
+	return s.ret
+}
+
+/*
+ * Allocate memory for BCJ decoders. xzDecBCJReset must be used before
+ * calling xzDecBCJRun.
+ */
+func xzDecBCJCreate() *xzDecBCJ {
+	return new(xzDecBCJ)
+}
+
+/*
+ * Decode the Filter ID of a BCJ filter and check the start offset is
+ * valid. Returns xzOK if the given Filter ID and offset is
+ * supported. Otherwise xzOptionsError is returned.
+ */
+func xzDecBCJReset(s *xzDecBCJ, id xzFilterID, offset int) xzRet {
+	switch id {
+	case idBCJX86:
+	case idBCJPowerPC:
+	case idBCJIA64:
+	case idBCJARM:
+	case idBCJARMThumb:
+	case idBCJSPARC:
+	default:
+		/* Unsupported Filter ID */
+		return xzOptionsError
+	}
+	// check offset is a multiple of alignment
+	switch id {
+	case idBCJPowerPC, idBCJARM, idBCJSPARC:
+		if offset%4 != 0 {
+			return xzOptionsError
+		}
+	case idBCJIA64:
+		if offset%16 != 0 {
+			return xzOptionsError
+		}
+	case idBCJARMThumb:
+		if offset%2 != 0 {
+			return xzOptionsError
+		}
+	}
+	s.typ = id
+	s.ret = xzOK
+	s.pos = offset
+	s.x86PrevMask = 0
+	s.temp.filtered = 0
+	s.temp.buf = nil
+	return xzOK
+}

vendor/github.com/therootcompany/xz/dec_delta.go

@@ -0,0 +1,55 @@
+/*
+ * Delta decoder
+ *
+ * Author: Lasse Collin <lasse.collin@tukaani.org>
+ *
+ * Translation to Go: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz
+
+type xzDecDelta struct {
+	delta    [256]byte
+	pos      byte
+	distance int // in range [1, 256]
+}
+
+/*
+ * Decode raw stream which has a delta filter as the first filter.
+ */
+func xzDecDeltaRun(s *xzDecDelta, b *xzBuf, chain func(*xzBuf) xzRet) xzRet {
+	outStart := b.outPos
+	ret := chain(b)
+	for i := outStart; i < b.outPos; i++ {
+		tmp := b.out[i] + s.delta[byte(s.distance+int(s.pos))]
+		s.delta[s.pos] = tmp
+		b.out[i] = tmp
+		s.pos--
+	}
+	return ret
+}
+
+/*
+ * Allocate memory for a delta decoder. xzDecDeltaReset must be used
+ * before calling xzDecDeltaRun.
+ */
+func xzDecDeltaCreate() *xzDecDelta {
+	return new(xzDecDelta)
+}
+
+/*
+ * Returns xzOK if the given distance is valid. Otherwise
+ * xzOptionsError is returned.
+ */
+func xzDecDeltaReset(s *xzDecDelta, distance int) xzRet {
+	if distance < 1 || distance > 256 {
+		return xzOptionsError
+	}
+	s.delta = [256]byte{}
+	s.pos = 0
+	s.distance = distance
+	return xzOK
+}

vendor/github.com/therootcompany/xz/dec_stream.go

@@ -0,0 +1,932 @@
+/*
+ * .xz Stream decoder
+ *
+ * Author: Lasse Collin <lasse.collin@tukaani.org>
+ *
+ * Translation to Go: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"hash"
+	"hash/crc32"
+	"hash/crc64"
+)
+
+/* from linux/lib/xz/xz_stream.h **************************************/
+
+/*
+ * See the .xz file format specification at
+ * http://tukaani.org/xz/xz-file-format.txt
+ * to understand the container format.
+ */
+const (
+	streamHeaderSize = 12
+	headerMagic      = "\xfd7zXZ\x00"
+	footerMagic      = "YZ"
+)
+
+/*
+ * Variable-length integer can hold a 63-bit unsigned integer or a special
+ * value indicating that the value is unknown.
+ */
+type vliType uint64
+
+const (
+	vliUnknown vliType = ^vliType(0)
+	/* Maximum encoded size of a VLI */
+	vliBytesMax = 8 * 8 / 7 // (Sizeof(vliType) * 8 / 7)
+)
+
+/* from linux/lib/xz/xz_dec_stream.c **********************************/
+
+/* Hash used to validate the Index field */
+type xzDecHash struct {
+	unpadded     vliType
+	uncompressed vliType
+	sha256       hash.Hash
+}
+
+// type of xzDec.sequence
+type xzDecSeq int
+
+const (
+	seqStreamHeader xzDecSeq = iota
+	seqBlockStart
+	seqBlockHeader
+	seqBlockUncompress
+	seqBlockPadding
+	seqBlockCheck
+	seqIndex
+	seqIndexPadding
+	seqIndexCRC32
+	seqStreamFooter
+)
+
+// type of xzDec.index.sequence
+type xzDecIndexSeq int
+
+const (
+	seqIndexCount xzDecIndexSeq = iota
+	seqIndexUnpadded
+	seqIndexUncompressed
+)
+
+/**
+ * xzDec - Opaque type to hold the XZ decoder state
+ */
+type xzDec struct {
+	/* Position in decMain */
+	sequence xzDecSeq
+	/* Position in variable-length integers and Check fields */
+	pos int
+	/* Variable-length integer decoded by decVLI */
+	vli vliType
+	/* Saved inPos and outPos */
+	inStart  int
+	outStart int
+	/* CRC32 checksum hash used in Index */
+	crc32 hash.Hash
+	/* Hashes used in Blocks */
+	checkCRC32  hash.Hash
+	checkCRC64  hash.Hash
+	checkSHA256 hash.Hash
+	/* for checkTypes CRC32/CRC64/SHA256, check is one of the above 3 hashes */
+	check hash.Hash
+	/* Embedded stream header struct containing CheckType */
+	*Header
+	/*
+	 * True if the next call to xzDecRun is allowed to return
+	 * xzBufError.
+	 */
+	allowBufError bool
+	/* Information stored in Block Header */
+	blockHeader struct {
+		/*
+		 * Value stored in the Compressed Size field, or
+		 * vliUnknown if Compressed Size is not present.
+		 */
+		compressed vliType
+		/*
+		 * Value stored in the Uncompressed Size field, or
+		 * vliUnknown if Uncompressed Size is not present.
+		 */
+		uncompressed vliType
+		/* Size of the Block Header field */
+		size int
+	}
+	/* Information collected when decoding Blocks */
+	block struct {
+		/* Observed compressed size of the current Block */
+		compressed vliType
+		/* Observed uncompressed size of the current Block */
+		uncompressed vliType
+		/* Number of Blocks decoded so far */
+		count vliType
+		/*
+		 * Hash calculated from the Block sizes. This is used to
+		 * validate the Index field.
+		 */
+		hash xzDecHash
+	}
+	/* Variables needed when verifying the Index field */
+	index struct {
+		/* Position in decIndex */
+		sequence xzDecIndexSeq
+		/* Size of the Index in bytes */
+		size vliType
+		/* Number of Records (matches block.count in valid files) */
+		count vliType
+		/*
+		 * Hash calculated from the Records (matches block.hash in
+		 * valid files).
+		 */
+		hash xzDecHash
+	}
+	/*
+	 * Temporary buffer needed to hold Stream Header, Block Header,
+	 * and Stream Footer. The Block Header is the biggest (1 KiB)
+	 * so we reserve space according to that. bufArray has to be aligned
+	 * to a multiple of four bytes; the variables before it
+	 * should guarantee this.
+	 */
+	temp struct {
+		pos      int
+		buf      []byte // slice buf will be backed by bufArray
+		bufArray [1024]byte
+	}
+	// chain is the function (or to be more precise, closure) which
+	// does the decompression and will call into the lzma2 and other
+	// filter code as needed. It is constructed by decBlockHeader
+	chain func(b *xzBuf) xzRet
+	// lzma2 holds the state of the last filter (which must be LZMA2)
+	lzma2 *xzDecLZMA2
+	// pointers to allocated BCJ/Delta filters
+	bcjs   []*xzDecBCJ
+	deltas []*xzDecDelta
+	// number of currently in use BCJ/Delta filters from the above
+	bcjsUsed   int
+	deltasUsed int
+}
+
+/* Sizes of the Check field with different Check IDs */
+var checkSizes = [...]byte{
+	0,
+	4, 4, 4,
+	8, 8, 8,
+	16, 16, 16,
+	32, 32, 32,
+	64, 64, 64,
+}
+
+/*
+ * Fill s.temp by copying data starting from b.in[b.inPos]. Caller
+ * must have set s.temp.pos to indicate how much data we are supposed
+ * to copy into s.temp.buf. Return true once s.temp.pos has reached
+ * len(s.temp.buf).
+ */
+func fillTemp(s *xzDec, b *xzBuf) bool {
+	copySize := len(b.in) - b.inPos
+	tempRemaining := len(s.temp.buf) - s.temp.pos
+	if copySize > tempRemaining {
+		copySize = tempRemaining
+	}
+	copy(s.temp.buf[s.temp.pos:], b.in[b.inPos:])
+	b.inPos += copySize
+	s.temp.pos += copySize
+	if s.temp.pos == len(s.temp.buf) {
+		s.temp.pos = 0
+		return true
+	}
+	return false
+}
+
+/* Decode a variable-length integer (little-endian base-128 encoding) */
+func decVLI(s *xzDec, in []byte, inPos *int) xzRet {
+	var byte byte
+	if s.pos == 0 {
+		s.vli = 0
+	}
+	for *inPos < len(in) {
+		byte = in[*inPos]
+		*inPos++
+		s.vli |= vliType(byte&0x7f) << uint(s.pos)
+		if byte&0x80 == 0 {
+			/* Don't allow non-minimal encodings. */
+			if byte == 0 && s.pos != 0 {
+				return xzDataError
+			}
+			s.pos = 0
+			return xzStreamEnd
+		}
+		s.pos += 7
+		if s.pos == 7*vliBytesMax {
+			return xzDataError
+		}
+	}
+	return xzOK
+}
+
+/*
+ * Decode the Compressed Data field from a Block. Update and validate
+ * the observed compressed and uncompressed sizes of the Block so that
+ * they don't exceed the values possibly stored in the Block Header
+ * (validation assumes that no integer overflow occurs, since vliType
+ * is uint64). Update s.check if presence of the CRC32/CRC64/SHA256
+ * field was indicated in Stream Header.
+ *
+ * Once the decoding is finished, validate that the observed sizes match
+ * the sizes possibly stored in the Block Header. Update the hash and
+ * Block count, which are later used to validate the Index field.
+ */
+func decBlock(s *xzDec, b *xzBuf) xzRet {
+	var ret xzRet
+	s.inStart = b.inPos
+	s.outStart = b.outPos
+	ret = s.chain(b)
+	s.block.compressed += vliType(b.inPos - s.inStart)
+	s.block.uncompressed += vliType(b.outPos - s.outStart)
+	/*
+	 * There is no need to separately check for vliUnknown since
+	 * the observed sizes are always smaller than vliUnknown.
+	 */
+	if s.block.compressed > s.blockHeader.compressed ||
+		s.block.uncompressed > s.blockHeader.uncompressed {
+		return xzDataError
+	}
+	switch s.CheckType {
+	case CheckCRC32, CheckCRC64, CheckSHA256:
+		_, _ = s.check.Write(b.out[s.outStart:b.outPos])
+	}
+	if ret == xzStreamEnd {
+		if s.blockHeader.compressed != vliUnknown &&
+			s.blockHeader.compressed != s.block.compressed {
+			return xzDataError
+		}
+		if s.blockHeader.uncompressed != vliUnknown &&
+			s.blockHeader.uncompressed != s.block.uncompressed {
+			return xzDataError
+		}
+		s.block.hash.unpadded +=
+			vliType(s.blockHeader.size) + s.block.compressed
+		s.block.hash.unpadded += vliType(checkSizes[s.CheckType])
+		s.block.hash.uncompressed += s.block.uncompressed
+		var buf [2 * 8]byte // 2*Sizeof(vliType)
+		putLE64(uint64(s.block.hash.unpadded), buf[:])
+		putLE64(uint64(s.block.hash.uncompressed), buf[8:])
+		_, _ = s.block.hash.sha256.Write(buf[:])
+		s.block.count++
+	}
+	return ret
+}
+
+/* Update the Index size and the CRC32 hash. */
+func indexUpdate(s *xzDec, b *xzBuf) {
+	inUsed := b.inPos - s.inStart
+	s.index.size += vliType(inUsed)
+	_, _ = s.crc32.Write(b.in[s.inStart : s.inStart+inUsed])
+}
+
+/*
+ * Decode the Number of Records, Unpadded Size, and Uncompressed Size
+ * fields from the Index field. That is, Index Padding and CRC32 are not
+ * decoded by this function.
+ *
+ * This can return xzOK (more input needed), xzStreamEnd (everything
+ * successfully decoded), or xzDataError (input is corrupt).
+ */
+func decIndex(s *xzDec, b *xzBuf) xzRet {
+	var ret xzRet
+	for {
+		ret = decVLI(s, b.in, &b.inPos)
+		if ret != xzStreamEnd {
+			indexUpdate(s, b)
+			return ret
+		}
+		switch s.index.sequence {
+		case seqIndexCount:
+			s.index.count = s.vli
+			/*
+			 * Validate that the Number of Records field
+			 * indicates the same number of Records as
+			 * there were Blocks in the Stream.
+			 */
+			if s.index.count != s.block.count {
+				return xzDataError
+			}
+			s.index.sequence = seqIndexUnpadded
+		case seqIndexUnpadded:
+			s.index.hash.unpadded += s.vli
+			s.index.sequence = seqIndexUncompressed
+		case seqIndexUncompressed:
+			s.index.hash.uncompressed += s.vli
+			var buf [2 * 8]byte // 2*Sizeof(vliType)
+			putLE64(uint64(s.index.hash.unpadded), buf[:])
+			putLE64(uint64(s.index.hash.uncompressed), buf[8:])
+			_, _ = s.index.hash.sha256.Write(buf[:])
+			s.index.count--
+			s.index.sequence = seqIndexUnpadded
+		}
+		if !(s.index.count > 0) {
+			break
+		}
+	}
+	return xzStreamEnd
+}
+
+/*
+ * Validate that the next 4 bytes match s.crc32.Sum(nil). s.pos must
+ * be zero when starting to validate the first byte.
+ */
+func crcValidate(s *xzDec, b *xzBuf) xzRet {
+	sum := s.crc32.Sum(nil)
+	// CRC32 - reverse slice
+	sum[0], sum[1], sum[2], sum[3] = sum[3], sum[2], sum[1], sum[0]
+	for {
+		if b.inPos == len(b.in) {
+			return xzOK
+		}
+		if sum[s.pos] != b.in[b.inPos] {
+			return xzDataError
+		}
+		b.inPos++
+		s.pos++
+		if !(s.pos < 4) {
+			break
+		}
+	}
+	s.crc32.Reset()
+	s.pos = 0
+	return xzStreamEnd
+}
+
+/*
+ * Validate that the next 4/8/32 bytes match s.check.Sum(nil). s.pos
+ * must be zero when starting to validate the first byte.
+ */
+func checkValidate(s *xzDec, b *xzBuf) xzRet {
+	sum := s.check.Sum(nil)
+	if s.CheckType == CheckCRC32 || s.CheckType == CheckCRC64 {
+		// CRC32/64 - reverse slice
+		for i, j := 0, len(sum)-1; i < j; i, j = i+1, j-1 {
+			sum[i], sum[j] = sum[j], sum[i]
+		}
+	}
+	for {
+		if b.inPos == len(b.in) {
+			return xzOK
+		}
+		if sum[s.pos] != b.in[b.inPos] {
+			return xzDataError
+		}
+		b.inPos++
+		s.pos++
+		if !(s.pos < len(sum)) {
+			break
+		}
+	}
+	s.check.Reset()
+	s.pos = 0
+	return xzStreamEnd
+}
+
+/*
+ * Skip over the Check field when the Check ID is not supported.
+ * Returns true once the whole Check field has been skipped over.
+ */
+func checkSkip(s *xzDec, b *xzBuf) bool {
+	for s.pos < int(checkSizes[s.CheckType]) {
+		if b.inPos == len(b.in) {
+			return false
+		}
+		b.inPos++
+		s.pos++
+	}
+	s.pos = 0
+	return true
+}
+
+/* polynomial table used in decStreamHeader below */
+var xzCRC64Table = crc64.MakeTable(crc64.ECMA)
+
+/* Decode the Stream Header field (the first 12 bytes of the .xz Stream). */
+func decStreamHeader(s *xzDec) xzRet {
+	if string(s.temp.buf[:len(headerMagic)]) != headerMagic {
+		return xzFormatError
+	}
+	if crc32.ChecksumIEEE(s.temp.buf[len(headerMagic):len(headerMagic)+2]) !=
+		getLE32(s.temp.buf[len(headerMagic)+2:]) {
+		return xzDataError
+	}
+	if s.temp.buf[len(headerMagic)] != 0 {
+		return xzOptionsError
+	}
+	/*
+	 * Of integrity checks, we support none (Check ID = 0),
+	 * CRC32 (Check ID = 1), CRC64 (Check ID = 4) and SHA256 (Check ID = 10)
+	 * However, we will accept other check types too, but then the check
+	 * won't be verified and a warning (xzUnsupportedCheck) will be given.
+	 */
+	s.CheckType = CheckID(s.temp.buf[len(headerMagic)+1])
+	if s.CheckType > checkMax {
+		return xzOptionsError
+	}
+	switch s.CheckType {
+	case CheckNone:
+		// CheckNone: no action needed
+	case CheckCRC32:
+		if s.checkCRC32 == nil {
+			s.checkCRC32 = crc32.NewIEEE()
+		} else {
+			s.checkCRC32.Reset()
+		}
+		s.check = s.checkCRC32
+	case CheckCRC64:
+		if s.checkCRC64 == nil {
+			s.checkCRC64 = crc64.New(xzCRC64Table)
+		} else {
+			s.checkCRC64.Reset()
+		}
+		s.check = s.checkCRC64
+	case CheckSHA256:
+		if s.checkSHA256 == nil {
+			s.checkSHA256 = sha256.New()
+		} else {
+			s.checkSHA256.Reset()
+		}
+		s.check = s.checkSHA256
+	default:
+		return xzUnsupportedCheck
+	}
+	return xzOK
+}
+
+/* Decode the Stream Footer field (the last 12 bytes of the .xz Stream) */
+func decStreamFooter(s *xzDec) xzRet {
+	if string(s.temp.buf[10:10+len(footerMagic)]) != footerMagic {
+		return xzDataError
+	}
+	if crc32.ChecksumIEEE(s.temp.buf[4:10]) != getLE32(s.temp.buf) {
+		return xzDataError
+	}
+	/*
+	 * Validate Backward Size. Note that we never added the size of the
+	 * Index CRC32 field to s->index.size, thus we use s->index.size / 4
+	 * instead of s->index.size / 4 - 1.
+	 */
+	if s.index.size>>2 != vliType(getLE32(s.temp.buf[4:])) {
+		return xzDataError
+	}
+	if s.temp.buf[8] != 0 || CheckID(s.temp.buf[9]) != s.CheckType {
+		return xzDataError
+	}
+	/*
+	 * Use xzStreamEnd instead of xzOK to be more convenient
+	 * for the caller.
+	 */
+	return xzStreamEnd
+}
+
+/* Decode the Block Header and initialize the filter chain. */
+func decBlockHeader(s *xzDec) xzRet {
+	var ret xzRet
+	/*
+	 * Validate the CRC32. We know that the temp buffer is at least
+	 * eight bytes so this is safe.
+	 */
+	crc := getLE32(s.temp.buf[len(s.temp.buf)-4:])
+	s.temp.buf = s.temp.buf[:len(s.temp.buf)-4]
+	if crc32.ChecksumIEEE(s.temp.buf) != crc {
+		return xzDataError
+	}
+	s.temp.pos = 2
+	/*
+	 * Catch unsupported Block Flags.
+	 */
+	if s.temp.buf[1]&0x3C != 0 {
+		return xzOptionsError
+	}
+	/* Compressed Size */
+	if s.temp.buf[1]&0x40 != 0 {
+		if decVLI(s, s.temp.buf, &s.temp.pos) != xzStreamEnd {
+			return xzDataError
+		}
+		if s.vli >= 1<<63-8 {
+			// the whole block must stay smaller than 2^63 bytes
+			// the block header cannot be smaller than 8 bytes
+			return xzDataError
+		}
+		if s.vli == 0 {
+			// compressed size must be non-zero
+			return xzDataError
+		}
+		s.blockHeader.compressed = s.vli
+	} else {
+		s.blockHeader.compressed = vliUnknown
+	}
+	/* Uncompressed Size */
+	if s.temp.buf[1]&0x80 != 0 {
+		if decVLI(s, s.temp.buf, &s.temp.pos) != xzStreamEnd {
+			return xzDataError
+		}
+		s.blockHeader.uncompressed = s.vli
+	} else {
+		s.blockHeader.uncompressed = vliUnknown
+	}
+	// get total number of filters (1-4)
+	filterTotal := int(s.temp.buf[1]&0x03) + 1
+	// slice to hold decoded filters
+	filterList := make([]struct {
+		id    xzFilterID
+		props uint32
+	}, filterTotal)
+	// decode the non-last filters which cannot be LZMA2
+	for i := 0; i < filterTotal-1; i++ {
+		/* Valid Filter Flags always take at least two bytes. */
+		if len(s.temp.buf)-s.temp.pos < 2 {
+			return xzDataError
+		}
+		s.temp.pos += 2
+		switch id := xzFilterID(s.temp.buf[s.temp.pos-2]); id {
+		case idDelta:
+			// delta filter
+			if s.temp.buf[s.temp.pos-1] != 0x01 {
+				return xzOptionsError
+			}
+			/* Filter Properties contains distance - 1 */
+			if len(s.temp.buf)-s.temp.pos < 1 {
+				return xzDataError
+			}
+			props := uint32(s.temp.buf[s.temp.pos])
+			s.temp.pos++
+			filterList[i] = struct {
+				id    xzFilterID
+				props uint32
+			}{id: id, props: props}
+		case idBCJX86, idBCJPowerPC, idBCJIA64,
+			idBCJARM, idBCJARMThumb, idBCJSPARC:
+			// bcj filter
+			var props uint32
+			switch s.temp.buf[s.temp.pos-1] {
+			case 0x00:
+				props = 0
+			case 0x04:
+				if len(s.temp.buf)-s.temp.pos < 4 {
+					return xzDataError
+				}
+				props = getLE32(s.temp.buf[s.temp.pos:])
+				s.temp.pos += 4
+			default:
+				return xzOptionsError
+			}
+			filterList[i] = struct {
+				id    xzFilterID
+				props uint32
+			}{id: id, props: props}
+		default:
+			return xzOptionsError
+		}
+	}
+	/*
+	 * decode the last filter which must be LZMA2
+	 */
+	if len(s.temp.buf)-s.temp.pos < 2 {
+		return xzDataError
+	}
+	/* Filter ID = LZMA2 */
+	if xzFilterID(s.temp.buf[s.temp.pos]) != idLZMA2 {
+		return xzOptionsError
+	}
+	s.temp.pos++
+	/* Size of Properties = 1-byte Filter Properties */
+	if s.temp.buf[s.temp.pos] != 0x01 {
+		return xzOptionsError
+	}
+	s.temp.pos++
+	/* Filter Properties contains LZMA2 dictionary size. */
+	if len(s.temp.buf)-s.temp.pos < 1 {
+		return xzDataError
+	}
+	props := uint32(s.temp.buf[s.temp.pos])
+	s.temp.pos++
+	filterList[filterTotal-1] = struct {
+		id    xzFilterID
+		props uint32
+	}{id: idLZMA2, props: props}
+	/*
+	 * Process the filter list and create s.chain, going from last
+	 * filter (LZMA2) to first filter
+	 *
+	 * First, LZMA2.
+	 */
+	ret = xzDecLZMA2Reset(s.lzma2, byte(filterList[filterTotal-1].props))
+	if ret != xzOK {
+		return ret
+	}
+	s.chain = func(b *xzBuf) xzRet {
+		return xzDecLZMA2Run(s.lzma2, b)
+	}
+	/*
+	 * Now the non-last filters
+	 */
+	for i := filterTotal - 2; i >= 0; i-- {
+		switch id := filterList[i].id; id {
+		case idDelta:
+			// delta filter
+			var delta *xzDecDelta
+			if s.deltasUsed < len(s.deltas) {
+				delta = s.deltas[s.deltasUsed]
+			} else {
+				delta = xzDecDeltaCreate()
+				s.deltas = append(s.deltas, delta)
+			}
+			s.deltasUsed++
+			ret = xzDecDeltaReset(delta, int(filterList[i].props)+1)
+			if ret != xzOK {
+				return ret
+			}
+			chain := s.chain
+			s.chain = func(b *xzBuf) xzRet {
+				return xzDecDeltaRun(delta, b, chain)
+			}
+		case idBCJX86, idBCJPowerPC, idBCJIA64,
+			idBCJARM, idBCJARMThumb, idBCJSPARC:
+			// bcj filter
+			var bcj *xzDecBCJ
+			if s.bcjsUsed < len(s.bcjs) {
+				bcj = s.bcjs[s.bcjsUsed]
+			} else {
+				bcj = xzDecBCJCreate()
+				s.bcjs = append(s.bcjs, bcj)
+			}
+			s.bcjsUsed++
+			ret = xzDecBCJReset(bcj, id, int(filterList[i].props))
+			if ret != xzOK {
+				return ret
+			}
+			chain := s.chain
+			s.chain = func(b *xzBuf) xzRet {
+				return xzDecBCJRun(bcj, b, chain)
+			}
+		}
+	}
+	/* The rest must be Header Padding. */
+	for s.temp.pos < len(s.temp.buf) {
+		if s.temp.buf[s.temp.pos] != 0x00 {
+			return xzOptionsError
+		}
+		s.temp.pos++
+	}
+	s.temp.pos = 0
+	s.block.compressed = 0
+	s.block.uncompressed = 0
+	return xzOK
+}
+
+func decMain(s *xzDec, b *xzBuf) xzRet {
+	var ret xzRet
+	/*
+	 * Store the start position for the case when we are in the middle
+	 * of the Index field.
+	 */
+	s.inStart = b.inPos
+	for {
+		switch s.sequence {
+		case seqStreamHeader:
+			/*
+			 * Stream Header is copied to s.temp, and then
+			 * decoded from there. This way if the caller
+			 * gives us only little input at a time, we can
+			 * still keep the Stream Header decoding code
+			 * simple. Similar approach is used in many places
+			 * in this file.
+			 */
+			if !fillTemp(s, b) {
+				return xzOK
+			}
+			/*
+			 * If decStreamHeader returns
+			 * xzUnsupportedCheck, it is still possible
+			 * to continue decoding. Thus, update s.sequence
+			 * before calling decStreamHeader.
+			 */
+			s.sequence = seqBlockStart
+			ret = decStreamHeader(s)
+			if ret != xzOK {
+				return ret
+			}
+			fallthrough
+		case seqBlockStart:
+			/* We need one byte of input to continue. */
+			if b.inPos == len(b.in) {
+				return xzOK
+			}
+			/* See if this is the beginning of the Index field. */
+			if b.in[b.inPos] == 0 {
+				s.inStart = b.inPos
+				b.inPos++
+				s.sequence = seqIndex
+				break
+			}
+			/*
+			 * Calculate the size of the Block Header and
+			 * prepare to decode it.
+			 */
+			s.blockHeader.size = (int(b.in[b.inPos]) + 1) * 4
+			s.temp.buf = s.temp.bufArray[:s.blockHeader.size]
+			s.temp.pos = 0
+			s.sequence = seqBlockHeader
+			fallthrough
+		case seqBlockHeader:
+			if !fillTemp(s, b) {
+				return xzOK
+			}
+			ret = decBlockHeader(s)
+			if ret != xzOK {
+				return ret
+			}
+			s.sequence = seqBlockUncompress
+			fallthrough
+		case seqBlockUncompress:
+			ret = decBlock(s, b)
+			if ret != xzStreamEnd {
+				return ret
+			}
+			s.sequence = seqBlockPadding
+			fallthrough
+		case seqBlockPadding:
+			/*
+			 * Size of Compressed Data + Block Padding
+			 * must be a multiple of four. We don't need
+			 * s->block.compressed for anything else
+			 * anymore, so we use it here to test the size
+			 * of the Block Padding field.
+			 */
+			for s.block.compressed&3 != 0 {
+				if b.inPos == len(b.in) {
+					return xzOK
+				}
+				if b.in[b.inPos] != 0 {
+					return xzDataError
+				}
+				b.inPos++
+				s.block.compressed++
+			}
+			s.sequence = seqBlockCheck
+			fallthrough
+		case seqBlockCheck:
+			switch s.CheckType {
+			case CheckCRC32, CheckCRC64, CheckSHA256:
+				ret = checkValidate(s, b)
+				if ret != xzStreamEnd {
+					return ret
+				}
+			default:
+				if !checkSkip(s, b) {
+					return xzOK
+				}
+			}
+			s.sequence = seqBlockStart
+		case seqIndex:
+			ret = decIndex(s, b)
+			if ret != xzStreamEnd {
+				return ret
+			}
+			s.sequence = seqIndexPadding
+			fallthrough
+		case seqIndexPadding:
+			for (s.index.size+vliType(b.inPos-s.inStart))&3 != 0 {
+				if b.inPos == len(b.in) {
+					indexUpdate(s, b)
+					return xzOK
+				}
+				if b.in[b.inPos] != 0 {
+					return xzDataError
+				}
+				b.inPos++
+			}
+			/* Finish the CRC32 value and Index size. */
+			indexUpdate(s, b)
+			/* Compare the hashes to validate the Index field. */
+			if !bytes.Equal(
+				s.block.hash.sha256.Sum(nil), s.index.hash.sha256.Sum(nil)) {
+				return xzDataError
+			}
+			s.sequence = seqIndexCRC32
+			fallthrough
+		case seqIndexCRC32:
+			ret = crcValidate(s, b)
+			if ret != xzStreamEnd {
+				return ret
+			}
+			s.temp.buf = s.temp.bufArray[:streamHeaderSize]
+			s.sequence = seqStreamFooter
+			fallthrough
+		case seqStreamFooter:
+			if !fillTemp(s, b) {
+				return xzOK
+			}
+			return decStreamFooter(s)
+		}
+	}
+	/* Never reached */
+}
+
+/**
+ * xzDecRun - Run the XZ decoder
+ * @s:         Decoder state allocated using xzDecInit
+ * @b:         Input and output buffers
+ *
+ * See xzRet for details of return values.
+ *
+ * xzDecRun is a wrapper for decMain to handle some special cases.
+ *
+ * We must return xzBufError when it seems clear that we are not
+ * going to make any progress anymore. This is to prevent the caller
+ * from calling us infinitely when the input file is truncated or
+ * otherwise corrupt. Since zlib-style API allows that the caller
+ * fills the input buffer only when the decoder doesn't produce any
+ * new output, we have to be careful to avoid returning xzBufError
+ * too easily: xzBufError is returned only after the second
+ * consecutive call to xzDecRun that makes no progress.
+ */
+func xzDecRun(s *xzDec, b *xzBuf) xzRet {
+	inStart := b.inPos
+	outStart := b.outPos
+	ret := decMain(s, b)
+	if ret == xzOK && inStart == b.inPos && outStart == b.outPos {
+		if s.allowBufError {
+			ret = xzBufError
+		}
+		s.allowBufError = true
+	} else {
+		s.allowBufError = false
+	}
+	return ret
+}
+
+/**
+ * xzDecInit - Allocate and initialize a XZ decoder state
+ * @dictMax:    Maximum size of the LZMA2 dictionary (history buffer) for
+ *              decoding. LZMA2 dictionary is always 2^n bytes
+ *              or 2^n + 2^(n-1) bytes (the latter sizes are less common
+ *              in practice), so other values for dictMax don't make sense.
+ *
+ * dictMax specifies the maximum allowed dictionary size that xzDecRun
+ * may allocate once it has parsed the dictionary size from the stream
+ * headers. This way excessive allocations can be avoided while still
+ * limiting the maximum memory usage to a sane value to prevent running the
+ * system out of memory when decompressing streams from untrusted sources.
+ *
+ * xzDecInit returns a pointer to an xzDec, which is ready to be used with
+ * xzDecRun.
+ */
+func xzDecInit(dictMax uint32, header *Header) *xzDec {
+	s := new(xzDec)
+	s.crc32 = crc32.NewIEEE()
+	s.Header = header
+	s.block.hash.sha256 = sha256.New()
+	s.index.hash.sha256 = sha256.New()
+	s.lzma2 = xzDecLZMA2Create(dictMax)
+	xzDecReset(s)
+	return s
+}
+
+/**
+ * xzDecReset - Reset an already allocated decoder state
+ * @s:          Decoder state allocated using xzDecInit
+ *
+ * This function can be used to reset the decoder state without
+ * reallocating memory with xzDecInit.
+ */
+func xzDecReset(s *xzDec) {
+	s.sequence = seqStreamHeader
+	s.allowBufError = false
+	s.pos = 0
+	s.crc32.Reset()
+	s.check = nil
+	s.CheckType = checkUnset
+	s.block.compressed = 0
+	s.block.uncompressed = 0
+	s.block.count = 0
+	s.block.hash.unpadded = 0
+	s.block.hash.uncompressed = 0
+	s.block.hash.sha256.Reset()
+	s.index.sequence = seqIndexCount
+	s.index.size = 0
+	s.index.count = 0
+	s.index.hash.unpadded = 0
+	s.index.hash.uncompressed = 0
+	s.index.hash.sha256.Reset()
+	s.temp.pos = 0
+	s.temp.buf = s.temp.bufArray[:streamHeaderSize]
+	s.chain = nil
+	s.bcjsUsed = 0
+	s.deltasUsed = 0
+}

vendor/github.com/therootcompany/xz/dec_util.go

@@ -0,0 +1,52 @@
+/*
+ * XZ decompressor utility functions
+ *
+ * Author: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz
+
+func getLE32(buf []byte) uint32 {
+	return uint32(buf[0]) |
+		uint32(buf[1])<<8 |
+		uint32(buf[2])<<16 |
+		uint32(buf[3])<<24
+}
+
+func getBE32(buf []byte) uint32 {
+	return uint32(buf[0])<<24 |
+		uint32(buf[1])<<16 |
+		uint32(buf[2])<<8 |
+		uint32(buf[3])
+}
+
+func putLE32(val uint32, buf []byte) {
+	buf[0] = byte(val)
+	buf[1] = byte(val >> 8)
+	buf[2] = byte(val >> 16)
+	buf[3] = byte(val >> 24)
+	return
+}
+
+func putBE32(val uint32, buf []byte) {
+	buf[0] = byte(val >> 24)
+	buf[1] = byte(val >> 16)
+	buf[2] = byte(val >> 8)
+	buf[3] = byte(val)
+	return
+}
+
+func putLE64(val uint64, buf []byte) {
+	buf[0] = byte(val)
+	buf[1] = byte(val >> 8)
+	buf[2] = byte(val >> 16)
+	buf[3] = byte(val >> 24)
+	buf[4] = byte(val >> 32)
+	buf[5] = byte(val >> 40)
+	buf[6] = byte(val >> 48)
+	buf[7] = byte(val >> 56)
+	return
+}

vendor/github.com/therootcompany/xz/dec_xz.go

@@ -0,0 +1,124 @@
+/*
+ * XZ decompressor
+ *
+ * Authors: Lasse Collin <lasse.collin@tukaani.org>
+ *          Igor Pavlov <http://7-zip.org/>
+ *
+ * Translation to Go: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz
+
+/* from linux/include/linux/xz.h **************************************/
+
+/**
+ * xzRet - Return codes
+ * @xzOK:                   Everything is OK so far. More input or more
+ *                          output space is required to continue.
+ * @xzStreamEnd:            Operation finished successfully.
+ * @xzUnSupportedCheck:     Integrity check type is not supported. Decoding
+ *                          is still possible by simply calling xzDecRun
+ *                          again.
+ * @xzMemlimitError:        A bigger LZMA2 dictionary would be needed than
+ *                          allowed by the dictMax argument given to
+ *                          xzDecInit.
+ * @xzFormatError:          File format was not recognized (wrong magic
+ *                          bytes).
+ * @xzOptionsError:         This implementation doesn't support the requested
+ *                          compression options. In the decoder this means
+ *                          that the header CRC32 matches, but the header
+ *                          itself specifies something that we don't support.
+ * @xzDataError:            Compressed data is corrupt.
+ * @xzBufError:             Cannot make any progress.
+ *
+ * xzBufError is returned when two consecutive calls to XZ code cannot
+ * consume any input and cannot produce any new output.  This happens
+ * when there is no new input available, or the output buffer is full
+ * while at least one output byte is still pending. Assuming your code
+ * is not buggy, you can get this error only when decoding a
+ * compressed stream that is truncated or otherwise corrupt.
+ */
+type xzRet int
+
+const (
+	xzOK xzRet = iota
+	xzStreamEnd
+	xzUnsupportedCheck
+	xzMemlimitError
+	xzFormatError
+	xzOptionsError
+	xzDataError
+	xzBufError
+)
+
+/**
+ * xzBuf - Passing input and output buffers to XZ code
+ * @in:         Input buffer.
+ * @inPos:      Current position in the input buffer. This must not exceed
+ *              input buffer size.
+ * @out:        Output buffer.
+ * @outPos:     Current position in the output buffer. This must not exceed
+ *              output buffer size.
+ *
+ * Only the contents of the output buffer from out[outPos] onward, and
+ * the variables inPos and outPos are modified by the XZ code.
+ */
+type xzBuf struct {
+	in     []byte
+	inPos  int
+	out    []byte
+	outPos int
+}
+
+/* All XZ filter IDs */
+type xzFilterID int64
+
+const (
+	idDelta       xzFilterID = 0x03
+	idBCJX86      xzFilterID = 0x04
+	idBCJPowerPC  xzFilterID = 0x05
+	idBCJIA64     xzFilterID = 0x06
+	idBCJARM      xzFilterID = 0x07
+	idBCJARMThumb xzFilterID = 0x08
+	idBCJSPARC    xzFilterID = 0x09
+	idLZMA2       xzFilterID = 0x21
+)
+
+// CheckID is the type of the data integrity check in an XZ stream
+// calculated from the uncompressed data.
+type CheckID int
+
+func (id CheckID) String() string {
+	switch id {
+	case CheckNone:
+		return "None"
+	case CheckCRC32:
+		return "CRC32"
+	case CheckCRC64:
+		return "CRC64"
+	case CheckSHA256:
+		return "SHA256"
+	default:
+		return "Unknown"
+	}
+}
+
+const (
+	CheckNone   CheckID = 0x00
+	CheckCRC32  CheckID = 0x01
+	CheckCRC64  CheckID = 0x04
+	CheckSHA256 CheckID = 0x0A
+	checkMax    CheckID = 0x0F
+	checkUnset  CheckID = -1
+)
+
+// An XZ stream contains a stream header which holds information about
+// the stream. That information is exposed as fields of the
+// Reader. Currently it contains only the stream's data integrity
+// check type.
+type Header struct {
+	CheckType CheckID // type of the stream's data integrity check
+}

vendor/github.com/therootcompany/xz/doc.go

@@ -0,0 +1,35 @@
+// Package xz implements XZ decompression natively in Go.
+//
+// Usage
+//
+// For ease of use, this package is designed to have a similar API to
+// compress/gzip. See the examples for further details.
+//
+// Implementation
+//
+// This package is a translation from C to Go of XZ Embedded
+// (http://tukaani.org/xz/embedded.html) with enhancements made so as
+// to implement all mandatory and optional parts of the XZ file format
+// specification v1.0.4. It supports all filters and block check
+// types, supports multiple streams, and performs index verification
+// using SHA-256 as recommended by the specification.
+//
+// Speed
+//
+// On the author's Intel Ivybridge i5, decompression speed is about
+// half that of the standard XZ Utils (tested with a recent linux
+// kernel tarball).
+//
+// Thanks
+//
+// Thanks are due to Lasse Collin and Igor Pavlov, the authors of XZ
+// Embedded, on whose code package xz is based. It would not exist
+// without their decision to allow others to modify and reuse their
+// code.
+//
+// Bug reports
+//
+// For bug reports relating to this package please contact the author
+// through https://github.com/xi2/xz/issues, and not the authors of XZ
+// Embedded.
+package xz

vendor/github.com/therootcompany/xz/reader.go

@@ -0,0 +1,256 @@
+/*
+ * Package xz Go Reader API
+ *
+ * Author: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz
+
+import (
+	"errors"
+	"io"
+)
+
+// Package specific errors.
+var (
+	ErrUnsupportedCheck = errors.New("xz: integrity check type not supported")
+	ErrMemlimit         = errors.New("xz: LZMA2 dictionary size exceeds max")
+	ErrFormat           = errors.New("xz: file format not recognized")
+	ErrOptions          = errors.New("xz: compression options not supported")
+	ErrData             = errors.New("xz: data is corrupt")
+	ErrBuf              = errors.New("xz: data is truncated or corrupt")
+)
+
+// DefaultDictMax is the default maximum dictionary size in bytes used
+// by the decoder. This value is sufficient to decompress files
+// created with XZ Utils "xz -9".
+const DefaultDictMax = 1 << 26 // 64 MiB
+
+// inBufSize is the input buffer size used by the decoder.
+const inBufSize = 1 << 13 // 8 KiB
+
+// A Reader is an io.Reader that can be used to retrieve uncompressed
+// data from an XZ file.
+//
+// In general, an XZ file can be a concatenation of other XZ
+// files. Reads from the Reader return the concatenation of the
+// uncompressed data of each.
+type Reader struct {
+	Header
+	r           io.Reader       // the wrapped io.Reader
+	multistream bool            // true if reader is in multistream mode
+	rEOF        bool            // true after io.EOF received on r
+	dEOF        bool            // true after decoder has completed
+	padding     int             // bytes of stream padding read (or -1)
+	in          [inBufSize]byte // backing array for buf.in
+	buf         *xzBuf          // decoder input/output buffers
+	dec         *xzDec          // decoder state
+	err         error           // the result of the last decoder call
+}
+
+// NewReader creates a new Reader reading from r. The decompressor
+// will use an LZMA2 dictionary size up to dictMax bytes in
+// size. Passing a value of zero sets dictMax to DefaultDictMax.  If
+// an individual XZ stream requires a dictionary size greater than
+// dictMax in order to decompress, Read will return ErrMemlimit.
+//
+// If NewReader is passed a value of nil for r then a Reader is
+// created such that all read attempts will return io.EOF. This is
+// useful if you just want to allocate memory for a Reader which will
+// later be initialized with Reset.
+//
+// Due to internal buffering, the Reader may read more data than
+// necessary from r.
+func NewReader(r io.Reader, dictMax uint32) (*Reader, error) {
+	if dictMax == 0 {
+		dictMax = DefaultDictMax
+	}
+	z := &Reader{
+		r:           r,
+		multistream: true,
+		padding:     -1,
+		buf:         &xzBuf{},
+	}
+	if r == nil {
+		z.rEOF, z.dEOF = true, true
+	}
+	z.dec = xzDecInit(dictMax, &z.Header)
+	var err error
+	if r != nil {
+		_, err = z.Read(nil) // read stream header
+	}
+	return z, err
+}
+
+// decode is a wrapper around xzDecRun that additionally handles
+// stream padding. It treats the padding as a kind of stream that
+// decodes to nothing.
+//
+// When decoding padding, z.padding >= 0
+// When decoding a real stream, z.padding == -1
+func (z *Reader) decode() (ret xzRet) {
+	if z.padding >= 0 {
+		// read all padding in input buffer
+		for z.buf.inPos < len(z.buf.in) &&
+			z.buf.in[z.buf.inPos] == 0 {
+			z.buf.inPos++
+			z.padding++
+		}
+		switch {
+		case z.buf.inPos == len(z.buf.in) && z.rEOF:
+			// case: out of padding. no more input data available
+			if z.padding%4 != 0 {
+				ret = xzDataError
+			} else {
+				ret = xzStreamEnd
+			}
+		case z.buf.inPos == len(z.buf.in):
+			// case: read more padding next loop iteration
+			ret = xzOK
+		default:
+			// case: out of padding. more input data available
+			if z.padding%4 != 0 {
+				ret = xzDataError
+			} else {
+				xzDecReset(z.dec)
+				ret = xzStreamEnd
+			}
+		}
+	} else {
+		ret = xzDecRun(z.dec, z.buf)
+	}
+	return
+}
+
+func (z *Reader) Read(p []byte) (n int, err error) {
+	// restore err
+	err = z.err
+	// set decoder output buffer to p
+	z.buf.out = p
+	z.buf.outPos = 0
+	for {
+		// update n
+		n = z.buf.outPos
+		// if last call to decoder ended with an error, return that error
+		if err != nil {
+			break
+		}
+		// if decoder has finished, return with err == io.EOF
+		if z.dEOF {
+			err = io.EOF
+			break
+		}
+		// if p full, return with err == nil, unless we have not yet
+		// read the stream header with Read(nil)
+		if n == len(p) && z.CheckType != checkUnset {
+			break
+		}
+		// if needed, read more data from z.r
+		if z.buf.inPos == len(z.buf.in) && !z.rEOF {
+			rn, e := z.r.Read(z.in[:])
+			if e != nil && e != io.EOF {
+				// read error
+				err = e
+				break
+			}
+			if e == io.EOF {
+				z.rEOF = true
+			}
+			// set new input buffer in z.buf
+			z.buf.in = z.in[:rn]
+			z.buf.inPos = 0
+		}
+		// decode more data
+		ret := z.decode()
+		switch ret {
+		case xzOK:
+			// no action needed
+		case xzStreamEnd:
+			if z.padding >= 0 {
+				z.padding = -1
+				if !z.multistream || z.rEOF {
+					z.dEOF = true
+				}
+			} else {
+				z.padding = 0
+			}
+		case xzUnsupportedCheck:
+			err = ErrUnsupportedCheck
+		case xzMemlimitError:
+			err = ErrMemlimit
+		case xzFormatError:
+			err = ErrFormat
+		case xzOptionsError:
+			err = ErrOptions
+		case xzDataError:
+			err = ErrData
+		case xzBufError:
+			err = ErrBuf
+		}
+		// save err
+		z.err = err
+	}
+	return
+}
+
+// Multistream controls whether the reader is operating in multistream
+// mode.
+//
+// If enabled (the default), the Reader expects the input to be a
+// sequence of XZ streams, possibly interspersed with stream padding,
+// which it reads one after another. The effect is that the
+// concatenation of a sequence of XZ streams or XZ files is
+// treated as equivalent to the compressed result of the concatenation
+// of the sequence. This is standard behaviour for XZ readers.
+//
+// Calling Multistream(false) disables this behaviour; disabling the
+// behaviour can be useful when reading file formats that distinguish
+// individual XZ streams. In this mode, when the Reader reaches the
+// end of the stream, Read returns io.EOF. To start the next stream,
+// call z.Reset(nil) followed by z.Multistream(false). If there is no
+// next stream, z.Reset(nil) will return io.EOF.
+func (z *Reader) Multistream(ok bool) {
+	z.multistream = ok
+}
+
+// Reset, for non-nil values of io.Reader r, discards the Reader z's
+// state and makes it equivalent to the result of its original state
+// from NewReader, but reading from r instead. This permits reusing a
+// Reader rather than allocating a new one.
+//
+// If you wish to leave r unchanged use z.Reset(nil). This keeps r
+// unchanged and ensures internal buffering is preserved. If the
+// Reader was at the end of a stream it is then ready to read any
+// follow on streams. If there are no follow on streams z.Reset(nil)
+// returns io.EOF. If the Reader was not at the end of a stream then
+// z.Reset(nil) does nothing.
+func (z *Reader) Reset(r io.Reader) error {
+	switch {
+	case r == nil:
+		z.multistream = true
+		if !z.dEOF {
+			return nil
+		}
+		if z.rEOF {
+			return io.EOF
+		}
+		z.dEOF = false
+		_, err := z.Read(nil) // read stream header
+		return err
+	default:
+		z.r = r
+		z.multistream = true
+		z.rEOF = false
+		z.dEOF = false
+		z.padding = -1
+		z.buf.in = nil
+		z.buf.inPos = 0
+		xzDecReset(z.dec)
+		z.err = nil
+		_, err := z.Read(nil) // read stream header
+		return err
+	}
+}

vendor/modules.txt

@@ -83,6 +83,9 @@ github.com/nats-io/nuid
 github.com/novox/mesh-host/internal/declaration
 github.com/novox/mesh-host/rootsearch
 github.com/novox/mesh-host/validate
+# github.com/therootcompany/xz v1.0.1
+## explicit; go 1.15
+github.com/therootcompany/xz
 # golang.org/x/crypto v0.57.0
 ## explicit; go 1.26.0
 golang.org/x/crypto/acme