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// Copyright 2016 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 gousb
import (
"context"
"errors"
"runtime"
"sync"
)
type usbTransfer struct {
// mu protects the transfer state.
mu sync.Mutex
// xfer is the allocated libusb_transfer.
xfer *libusbTransfer
// buf is the buffer allocated for the transfer. The underlying memory
// is allocated by the C code, both buf and xfer.buffer point to the same
// memory.
buf []byte
// done is blocking until the transfer is complete and data and transfer
// status are available.
done chan struct{}
// submitted is true if submit() was called on this transfer.
submitted bool
// ctx is the Context that created this transfer.
ctx *Context
}
// submits the transfer. After submit() the transfer is in flight and is owned by libusb.
// It's not safe to access the contents of the transfer until wait() returns.
// Once wait() returns, it's ok to re-use the same transfer structure by calling submit() again.
func (t *usbTransfer) submit() error {
t.mu.Lock()
defer t.mu.Unlock()
if t.submitted {
return errors.New("transfer was already submitted and is not finished yet")
}
if err := t.ctx.libusb.submit(t.xfer); err != nil {
return err
}
t.submitted = true
return nil
}
// waits for libusb to signal the release of transfer data.
// After wait returns, the transfer contents are safe to access
// via t.buf. The number returned by wait indicates how many bytes
// of the buffer were read or written by libusb, and it can be
// smaller than the length of t.buf.
func (t *usbTransfer) wait(ctx context.Context) (n int, err error) {
t.mu.Lock()
defer t.mu.Unlock()
if !t.submitted {
return 0, nil
}
select {
case <-ctx.Done():
t.ctx.libusb.cancel(t.xfer)
// after the transfer is cancelled, it will run a callback
// that triggers the activation of t.done.
<-t.done
case <-t.done:
}
t.submitted = false
n, status := t.ctx.libusb.data(t.xfer)
if status != TransferCompleted {
return n, status
}
return n, err
}
// cancel aborts a submitted transfer. The transfer is cancelled
// asynchronously and the user still needs to wait() to return.
func (t *usbTransfer) cancel() error {
t.mu.Lock()
defer t.mu.Unlock()
if !t.submitted {
return nil
}
err := t.ctx.libusb.cancel(t.xfer)
if err == ErrorNotFound {
// transfer already completed
return nil
}
return err
}
// free releases the memory allocated for the transfer.
// free should be called only if the transfer is not used by libusb,
// i.e. it should not be called after submit() and before wait() returns.
func (t *usbTransfer) free() error {
t.mu.Lock()
defer t.mu.Unlock()
if t.submitted {
return errors.New("free() cannot be called on a submitted transfer until wait() returns")
}
if t.xfer == nil {
return nil
}
t.ctx.libusb.free(t.xfer)
t.xfer = nil
t.buf = nil
t.done = nil
return nil
}
// data returns the slice containing transfer buffer.
func (t *usbTransfer) data() []byte {
return t.buf
}
// newUSBTransfer allocates a new transfer structure and a new buffer for
// communication with a given device/endpoint.
func newUSBTransfer(ctx *Context, dev *libusbDevHandle, ei *EndpointDesc, bufLen int) (*usbTransfer, error) {
var isoPackets, isoPktSize int
if ei.TransferType == TransferTypeIsochronous {
isoPktSize = ei.MaxPacketSize
if bufLen < isoPktSize {
isoPktSize = bufLen
}
if isoPktSize > 0 {
isoPackets = bufLen / isoPktSize
} else {
isoPackets = 1
}
debug.Printf("New isochronous transfer - buffer length %d, using %d packets of %d bytes each", bufLen, isoPackets, isoPktSize)
}
done := make(chan struct{}, 1)
xfer, err := ctx.libusb.alloc(dev, ei, isoPackets, bufLen, done)
if err != nil {
return nil, err
}
if ei.TransferType == TransferTypeIsochronous {
ctx.libusb.setIsoPacketLengths(xfer, uint32(isoPktSize))
}
t := &usbTransfer{
xfer: xfer,
buf: ctx.libusb.buffer(xfer),
done: done,
ctx: ctx,
}
runtime.SetFinalizer(t, func(t *usbTransfer) {
t.cancel()
t.wait(context.Background())
t.free()
})
return t, nil
}
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