From bed17bab0bf80f1c78e17f54621640db837b1515 Mon Sep 17 00:00:00 2001
From: Evan Phoenix <evan@phx.io>
Date: Sat, 6 Jan 2024 13:06:00 -0800
Subject: [PATCH] Reverts bc1239ba, no longer needed to conform to legacy

This fixes the tests and verifies that the fix from bc1239ba, which
broke the tests, is no longer needed to conform to legacy compression.
---
 internal/lz4block/blocks.go |  5 +---
 internal/lz4stream/block.go |  4 +--
 writer_test.go              | 57 +++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/internal/lz4block/blocks.go b/internal/lz4block/blocks.go
index a1bfa99e..138083d9 100644
--- a/internal/lz4block/blocks.go
+++ b/internal/lz4block/blocks.go
@@ -8,12 +8,9 @@ const (
 	Block256Kb
 	Block1Mb
 	Block4Mb
+	Block8Mb = 2 * Block4Mb
 )
 
-// In legacy mode all blocks are compressed regardless
-// of the compressed size: use the bound size.
-var Block8Mb = uint32(CompressBlockBound(8 << 20))
-
 var (
 	BlockPool64K  = sync.Pool{New: func() interface{} { return make([]byte, Block64Kb) }}
 	BlockPool256K = sync.Pool{New: func() interface{} { return make([]byte, Block256Kb) }}
diff --git a/internal/lz4stream/block.go b/internal/lz4stream/block.go
index 459086f0..e9646546 100644
--- a/internal/lz4stream/block.go
+++ b/internal/lz4stream/block.go
@@ -224,9 +224,7 @@ func (b *FrameDataBlock) Close(f *Frame) {
 func (b *FrameDataBlock) Compress(f *Frame, src []byte, level lz4block.CompressionLevel) *FrameDataBlock {
 	data := b.data
 	if f.isLegacy() {
-		// In legacy mode, the buffer is sized according to CompressBlockBound,
-		// but only 8Mb is buffered for compression.
-		src = src[:8<<20]
+		data = data[:cap(data)]
 	} else {
 		data = data[:len(src)] // trigger the incompressible flag in CompressBlock
 	}
diff --git a/writer_test.go b/writer_test.go
index 379fb13f..59965358 100644
--- a/writer_test.go
+++ b/writer_test.go
@@ -7,6 +7,7 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
+	"os/exec"
 	"reflect"
 	"strings"
 	"testing"
@@ -285,6 +286,11 @@ func TestWriterLegacy(t *testing.T) {
 			if _, err := io.Copy(out2, zr); err != nil {
 				t.Fatal(err)
 			}
+
+			if len(src) != out2.Len() {
+				t.Fatalf("uncompressed output not correct size. %d != %d", len(src), out2.Len())
+			}
+
 			if !bytes.Equal(out2.Bytes(), src) {
 				t.Fatal("uncompressed compressed output different from source")
 			}
@@ -292,6 +298,57 @@ func TestWriterLegacy(t *testing.T) {
 	}
 }
 
+func TestWriterLegacyCommand(t *testing.T) {
+	_, err := exec.LookPath("lz4")
+	if err != nil {
+		t.Skip("no lz4 binary to test against")
+	}
+
+	goldenFiles := []string{
+		"testdata/vmlinux_LZ4_19377",
+		"testdata/bzImage_lz4_isolated",
+	}
+
+	for _, fname := range goldenFiles {
+		t.Run(fname, func(t *testing.T) {
+			fname := fname
+			t.Parallel()
+
+			src, err := ioutil.ReadFile(fname)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			out := new(bytes.Buffer)
+			zw := lz4.NewWriter(out)
+			if err := zw.Apply(lz4.LegacyOption(true), lz4.CompressionLevelOption(lz4.Fast)); err != nil {
+				t.Fatal(err)
+			}
+			if _, err := io.Copy(zw, bytes.NewReader(src)); err != nil {
+				t.Fatal(err)
+			}
+			if err := zw.Close(); err != nil {
+				t.Fatal(err)
+			}
+
+			// write to filesystem for further checking
+			tmp, err := os.CreateTemp("", "")
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer os.Remove(tmp.Name())
+			if _, err := tmp.Write(out.Bytes()); err != nil {
+				t.Fatal(err)
+			}
+
+			cmd := exec.Command("lz4", "--test", tmp.Name())
+			if _, err := cmd.Output(); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}
+
 func TestWriterConcurrency(t *testing.T) {
 	const someGiantFile = "testdata/vmlinux_LZ4_19377"