fix: Handle small reads in branch converters (#144)

* fix: Handle reads into small slices

Handle the case for `Read(p)` where `len(p)` is smaller than the minimum
length required by the branch converter.

* test: Make use of `iotest.OneByteReader()`

This now exposes a bug in all of the branch converters.

* fix: Handle small reads in branch converters

Add missing benchmarks also.

internal/bra/bra.go

@@ -12,3 +12,11 @@ func max(x, y int) int {
 
 	return y
 }
+
+func min(x, y int) int {
+	if x < y {
+		return x
+	}
+
+	return y
+}

internal/bra/reader.go

@@ -9,6 +9,7 @@ import (
 type readCloser struct {
 	rc   io.ReadCloser
 	buf  bytes.Buffer
+	n    int
 	conv converter
 }
 
@@ -30,13 +31,19 @@ func (rc *readCloser) Read(p []byte) (int, error) {
 		if !errors.Is(err, io.EOF) {
 			return 0, err
 		}
-	}
 
-	if n := rc.conv.Convert(rc.buf.Bytes(), false); n > 0 {
-		return rc.buf.Read(p[:n])
+		if rc.buf.Len() < rc.conv.Size() {
+			rc.n = rc.buf.Len()
+		}
 	}
 
-	return rc.buf.Read(p)
+	rc.n += rc.conv.Convert(rc.buf.Bytes()[rc.n:], false)
+
+	n, err := rc.buf.Read(p[:min(rc.n, len(p))])
+
+	rc.n -= n
+
+	return n, err
 }
 
 func newReader(readers []io.ReadCloser, conv converter) (io.ReadCloser, error) {

reader_test.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"testing"
 	"testing/fstest"
+	"testing/iotest"
 
 	"github.com/bodgit/sevenzip"
 	"github.com/bodgit/sevenzip/internal/util"
@@ -28,7 +29,7 @@ func readArchive(t *testing.T, r *sevenzip.ReadCloser) {
 
 		h.Reset()
 
-		if _, err := io.Copy(h, rc); err != nil {
+		if _, err := io.Copy(h, iotest.OneByteReader(rc)); err != nil {
 			t.Fatal(err)
 		}
 
@@ -332,3 +333,19 @@ func BenchmarkBrotli(b *testing.B) {
 func BenchmarkZstandard(b *testing.B) {
 	benchmarkArchive(b, "zstd.7z")
 }
+
+func BenchmarkBCJ(b *testing.B) {
+	benchmarkArchive(b, "bcj.7z")
+}
+
+func BenchmarkPPC(b *testing.B) {
+	benchmarkArchive(b, "ppc.7z")
+}
+
+func BenchmarkARM(b *testing.B) {
+	benchmarkArchive(b, "arm.7z")
+}
+
+func BenchmarkSPARC(b *testing.B) {
+	benchmarkArchive(b, "sparc.7z")
+}