constrain max buffer size

archiver.go

@@ -180,14 +180,14 @@ func (a *Archiver) compress(file *pool.File) error {
 		return nil
 	}
 
-	compressor, err := flate.NewWriter(&file.CompressedData, defaultCompression)
+	compressor, err := flate.NewWriter(file, defaultCompression)
 	if err != nil {
 		return errors.New("ERROR: could not create compressor")
 	}
 	hasher := crc32.NewIEEE()
 	w := io.MultiWriter(compressor, hasher)
 
-	err = a.read(w, file)
+	err = a.copy(w, file)
 	if err != nil {
 		return errors.Wrapf(err, "ERROR: could not read file %s", file.Path)
 	}
@@ -203,11 +203,10 @@ func (a *Archiver) compress(file *pool.File) error {
 	}
 
 	file.Header.CRC32 = hasher.Sum32()
-	file.Status = pool.FileFinished
 	return nil
 }
 
-func (a *Archiver) read(w io.Writer, file *pool.File) error {
+func (a *Archiver) copy(w io.Writer, file *pool.File) error {
 	f, err := os.Open(file.Path)
 	if err != nil {
 		return errors.Errorf("ERROR: could not open file %s", file.Path)

archiver_test.go

@@ -2,6 +2,7 @@ package pzip
 
 import (
 	"archive/zip"
+	"bytes"
 	"encoding/binary"
 	"fmt"
 	"path/filepath"
@@ -142,6 +143,26 @@ func TestCompress(t *testing.T) {
 		assertExtendedTimestamp(t, file.Header.Extra)
 	})
 
+	t.Run("writes a maximum of buffer cap bytes", func(t *testing.T) {
+		archive, cleanup := testutils.CreateTempArchive(t, archivePath)
+		defer cleanup()
+
+		archiver, err := NewArchiver(archive)
+		assert.NoError(t, err)
+
+		info := testutils.GetFileInfo(t, helloTxtFileFixture)
+		file, err := pool.NewFile(helloTxtFileFixture, info, "")
+		assert.NoError(t, err)
+		bufCap := 5
+		file.CompressedData = *bytes.NewBuffer(make([]byte, 0, bufCap))
+
+		err = archiver.compress(&file)
+		assert.NoError(t, err)
+
+		assert.Equal(t, file.CompressedData.Len(), bufCap)
+		assert.Equal(t, pool.FileFull, file.Status)
+	})
+
 	t.Run("for directories", func(t *testing.T) {
 		archive, cleanup := testutils.CreateTempArchive(t, archivePath)
 		defer cleanup()

go.mod

@@ -1,6 +1,6 @@
 module github.com/pzip
 
-go 1.20
+go 1.21
 
 require (
 	github.com/alecthomas/assert/v2 v2.3.0

pool/file.go

@@ -20,7 +20,9 @@ type File struct {
 type Status int
 
 const (
-	FileFinished Status = iota
+	defaultBufferSize        = 1000000
+	FileFinished      Status = iota
+	FileFull
 )
 
 func NewFile(path string, info fs.FileInfo, relativeTo string) (File, error) {
@@ -29,14 +31,24 @@ func NewFile(path string, info fs.FileInfo, relativeTo string) (File, error) {
 		return File{}, errors.Errorf("ERROR: could not get file info header for %s: %v", path, err)
 	}
 
-	f := File{Path: path, Info: info, Header: hdr}
+	f := File{Path: path, Info: info, Header: hdr, CompressedData: *bytes.NewBuffer(make([]byte, 0, defaultBufferSize))}
 	if relativeTo != "" {
 		f.setNameRelativeTo(relativeTo)
 	}
 
 	return f, nil
 }
 
+func (f *File) Write(p []byte) (n int, err error) {
+	if f.CompressedData.Available() != 0 {
+		maxWritable := min(f.CompressedData.Available(), len(p))
+		return f.CompressedData.Write(p[:int(maxWritable)])
+	}
+
+	f.Status = FileFull
+	return len(p), nil
+}
+
 func (f *File) setNameRelativeTo(root string) error {
 	relativeToRoot, err := filepath.Rel(root, f.Path)
 	if err != nil {