handle zero allocation in buffered writer

readme.md

@@ -2,9 +2,9 @@
 
 Pooled Buffer IO for Go programs.
 
-Package buffer provides a reader implementation similar to bufio.Reader. The underlying memory buffers can be
+Package buffer provides a reader implementation similar to bufio.Reader, and a writer implementation to batch
-used from a synchronized pool. It also supports scenarios similar to io.Pipe, where a content writer process is
+write operations targeting an underlying writer. The used memory buffers can be taken from a synchronized pool.
-wrapped by a buffered reader.
+It also supports scenarios similar to io.Pipe, where a content writer process is wrapped by a buffered reader.
 
 Find the documentation here:
 

writer.go

@@ -28,6 +28,10 @@ func (w *writer) write(p []byte) (int, error) {
 
 		if len(w.buffer) == 0 {
 			w.buffer, w.err = w.options.Pool.Get()
+			if len(w.buffer) == 0 && w.err == nil {
+				w.err = ErrZeroAllocation
+			}
+
 			continue
 		}
 

writer_test.go

@@ -402,4 +402,14 @@ func TestWriter(t *testing.T) {
 			t.Fatal(string(w.written))
 		}
 	})
+
+	t.Run("zero allocation", func(t *testing.T) {
+		w := &writer{}
+		p := &fakePool{}
+		o := buffer.Options{Pool: p}
+		b := buffer.BufferedWriter(w, o)
+		if n, err := b.Write([]byte("123")); n != 0 || !errors.Is(err, buffer.ErrZeroAllocation) {
+			t.Fatal(n, err)
+		}
+	})
 }