Add .Free methods to tables and use

Fixes leaking memory

Author: Josh Gummersall

internal/native/diff.go

@@ -17,6 +17,7 @@ func Diff(oldbytes, newbytes []byte, patch io.Writer) (err error) {
 	newptr, newsize := bytesToUint8PtrAndSize(newbytes)
 
 	bufferIndex := writers.Add(patch)
+	defer writers.Free(bufferIndex)
 
 	errCode := int(C.bsdiff_cgo(oldptr, oldsize, newptr, newsize, C.int(bufferIndex)))
 	if errCode != 0 {

internal/native/patch.go

@@ -18,6 +18,7 @@ func Patch(oldbytes, newbytes []byte, patch io.Reader) (err error) {
 	newptr, newsize := bytesToUint8PtrAndSize(newbytes)
 
 	bufferIndex := readers.Add(patch)
+	defer readers.Free(bufferIndex)
 
 	errCode := int(C.bspatch_cgo(oldptr, oldsize, newptr, newsize, C.int(bufferIndex)))
 	if errCode != 0 {

internal/native/table_reader.go

@@ -35,3 +35,10 @@ func (bt *readerTable) Get(index int) io.Reader {
 
 	return bt.table[index]
 }
+
+func (bt *readerTable) Free(index int) {
+	bt.mutex.Lock()
+	defer bt.mutex.Unlock()
+
+	delete(bt.table, index)
+}

internal/native/table_writer.go

@@ -35,3 +35,10 @@ func (bt *writerTable) Get(index int) io.Writer {
 
 	return bt.table[index]
 }
+
+func (bt *writerTable) Free(index int) {
+	bt.mutex.Lock()
+	defer bt.mutex.Unlock()
+
+	delete(bt.table, index)
+}