First version of streaming transfers.

usb/endpoint_stream.go

@@ -0,0 +1,44 @@
+// Copyright 2017 the gousb Authors.  All rights reserved.
+//
+// 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 usb
+
+func (e *endpoint) newStream(size, count uint, submit bool) (*stream, error) {
+	var ts []transferIntf
+	for i := uint(0); i < count; i++ {
+		t, err := newUSBTransfer(e.h, &e.Info, make([]byte, size), e.timeout)
+		if err != nil {
+			for _, t := range ts {
+				t.free()
+			}
+			return nil, err
+		}
+		ts = append(ts, t)
+	}
+	return newStream(ts, submit), nil
+}
+
+// NewStream prepares a new read stream that will keep reading data from the
+// endpoint until closed.
+// Size defines a buffer size for a single read transaction and count
+// defines how many transactions should be active at any time.
+// By keeping multiple transfers active at the same time, a Stream reduces
+// the latency between subsequent transfers and increases reading throughput.
+func (e *InEndpoint) NewStream(size, count uint) (ReadStream, error) {
+	s, err := e.newStream(size, count, true)
+	if err != nil {
+		return ReadStream{}, err
+	}
+	return ReadStream{s}, nil
+}