Avoid write after partial write

redcon.go

@@ -25,6 +25,8 @@ var (
 	errTooMuchData            = errors.New("too much data")
 )
 
+const maxBufferCap = 262144
+
 type errProtocol struct {
 	msg string
 }
@@ -576,8 +578,9 @@ type TLSServer struct {
 
 // Writer allows for writing RESP messages.
 type Writer struct {
-	w io.Writer
-	b []byte
+	w   io.Writer
+	b   []byte
+	err error
 }
 
 // NewWriter creates a new RESP writer.
@@ -589,6 +592,9 @@ func NewWriter(wr io.Writer) *Writer {
 
 // WriteNull writes a null to the client
 func (w *Writer) WriteNull() {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendNull(w.b)
 }
 
@@ -600,67 +606,105 @@ func (w *Writer) WriteNull() {
 //   c.WriteBulkString("item 1")
 //   c.WriteBulkString("item 2")
 func (w *Writer) WriteArray(count int) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendArray(w.b, count)
 }
 
 // WriteBulk writes bulk bytes to the client.
 func (w *Writer) WriteBulk(bulk []byte) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendBulk(w.b, bulk)
 }
 
 // WriteBulkString writes a bulk string to the client.
 func (w *Writer) WriteBulkString(bulk string) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendBulkString(w.b, bulk)
 }
 
 // Buffer returns the unflushed buffer. This is a copy so changes
 // to the resulting []byte will not affect the writer.
 func (w *Writer) Buffer() []byte {
+	if w.err != nil {
+		return nil
+	}
 	return append([]byte(nil), w.b...)
 }
 
 // SetBuffer replaces the unflushed buffer with new bytes.
 func (w *Writer) SetBuffer(raw []byte) {
+	if w.err != nil {
+		return
+	}
 	w.b = w.b[:0]
 	w.b = append(w.b, raw...)
 }
 
 // Flush writes all unflushed Write* calls to the underlying writer.
 func (w *Writer) Flush() error {
-	if _, err := w.w.Write(w.b); err != nil {
-		return err
+	if w.err != nil {
+		return w.err
 	}
-	w.b = w.b[:0]
-	return nil
+	_, w.err = w.w.Write(w.b)
+	if cap(w.b) > maxBufferCap || w.err != nil {
+		w.b = nil
+	} else {
+		w.b = w.b[:0]
+	}
+	return w.err
 }
 
 // WriteError writes an error to the client.
 func (w *Writer) WriteError(msg string) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendError(w.b, msg)
 }
 
 // WriteString writes a string to the client.
 func (w *Writer) WriteString(msg string) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendString(w.b, msg)
 }
 
 // WriteInt writes an integer to the client.
 func (w *Writer) WriteInt(num int) {
+	if w.err != nil {
+		return
+	}
 	w.WriteInt64(int64(num))
 }
 
 // WriteInt64 writes a 64-bit signed integer to the client.
 func (w *Writer) WriteInt64(num int64) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendInt(w.b, num)
 }
 
 // WriteUint64 writes a 64-bit unsigned integer to the client.
 func (w *Writer) WriteUint64(num uint64) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendUint(w.b, num)
 }
 
 // WriteRaw writes raw data to the client.
 func (w *Writer) WriteRaw(data []byte) {
+	if w.err != nil {
+		return
+	}
 	w.b = append(w.b, data...)
 }
 
@@ -677,6 +721,9 @@ func (w *Writer) WriteRaw(data []byte) {
 //   SimpleInt       -> integer
 //   everything-else -> bulk-string representation using fmt.Sprint()
 func (w *Writer) WriteAny(v interface{}) {
+	if w.err != nil {
+		return
+	}
 	w.b = AppendAny(w.b, v)
 }