1 files changed, 113 insertions, 0 deletions
diff --git a/pkg/flipcall/io.go b/pkg/flipcall/io.go
new file mode 100644
index 000000000..85e40b932
--- /dev/null
+++ b/pkg/flipcall/io.go
@@ -0,0 +1,113 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package flipcall
+
+import (
+	"fmt"
+	"io"
+)
+
+// DatagramReader implements io.Reader by reading a datagram from an Endpoint's
+// packet window. Its use is optional; users that can use Endpoint.Data() more
+// efficiently are advised to do so.
+type DatagramReader struct {
+	ep  *Endpoint
+	off uint32
+	end uint32
+}
+
+// Init must be called on zero-value DatagramReaders before first use.
+//
+// Preconditions: dataLen is 0, or was returned by a previous call to
+// ep.RecvFirst() or ep.SendRecv().
+func (r *DatagramReader) Init(ep *Endpoint, dataLen uint32) {
+	r.ep = ep
+	r.Reset(dataLen)
+}
+
+// Reset causes r to begin reading a new datagram of the given length from the
+// associated Endpoint.
+//
+// Preconditions: dataLen is 0, or was returned by a previous call to the
+// associated Endpoint's RecvFirst() or SendRecv() methods.
+func (r *DatagramReader) Reset(dataLen uint32) {
+	if dataLen > r.ep.dataCap {
+		panic(fmt.Sprintf("invalid dataLen (%d) > ep.dataCap (%d)", dataLen, r.ep.dataCap))
+	}
+	r.off = 0
+	r.end = dataLen
+}
+
+// NewReader is a convenience function that returns an initialized
+// DatagramReader allocated on the heap.
+//
+// Preconditions: dataLen was returned by a previous call to ep.RecvFirst() or
+// ep.SendRecv().
+func (ep *Endpoint) NewReader(dataLen uint32) *DatagramReader {
+	r := &DatagramReader{}
+	r.Init(ep, dataLen)
+	return r
+}
+
+// Read implements io.Reader.Read.
+func (r *DatagramReader) Read(dst []byte) (int, error) {
+	n := copy(dst, r.ep.Data()[r.off:r.end])
+	r.off += uint32(n)
+	if r.off == r.end {
+		return n, io.EOF
+	}
+	return n, nil
+}
+
+// DatagramWriter implements io.Writer by writing a datagram to an Endpoint's
+// packet window. Its use is optional; users that can use Endpoint.Data() more
+// efficiently are advised to do so.
+type DatagramWriter struct {
+	ep  *Endpoint
+	off uint32
+}
+
+// Init must be called on zero-value DatagramWriters before first use.
+func (w *DatagramWriter) Init(ep *Endpoint) {
+	w.ep = ep
+}
+
+// Reset causes w to begin writing a new datagram to the associated Endpoint.
+func (w *DatagramWriter) Reset() {
+	w.off = 0
+}
+
+// NewWriter is a convenience function that returns an initialized
+// DatagramWriter allocated on the heap.
+func (ep *Endpoint) NewWriter() *DatagramWriter {
+	w := &DatagramWriter{}
+	w.Init(ep)
+	return w
+}
+
+// Write implements io.Writer.Write.
+func (w *DatagramWriter) Write(src []byte) (int, error) {
+	n := copy(w.ep.Data()[w.off:w.ep.dataCap], src)
+	w.off += uint32(n)
+	if n != len(src) {
+		return n, fmt.Errorf("datagram would exceed maximum size of %d bytes", w.ep.dataCap)
+	}
+	return n, nil
+}
+
+// Len returns the length of the written datagram.
+func (w *DatagramWriter) Len() uint32 {
+	return w.off
+}