Allocate libusb buffers in C (#11)

* add alloc/free_transfer_and_buffer. Manages the buffer memory on the C
side.

* switch libusb.go to use the new alloc/free_transfer_and_buffer. Add
a new buffer() call to get access to the allocated buffer as a Go slice.

* Fake USB transfer uses the new alloc/free/buffer interface.

* Switch to the new libusb.alloc signature, where libusb owns the buffer.

* newUSBTransfer now allocates a separate buffer, do a copy on
endpoint.transfer.

* newUSBTransfer will now allocate it's own buffer.

* Enable autodetach in rawread.

endpoint.go

@@ -89,17 +89,23 @@ func (e *endpoint) transfer(buf []byte) (int, error) {
 		return 0, nil
 	}
 
-	t, err := newUSBTransfer(e.h, &e.Desc, buf, e.Timeout)
+	t, err := newUSBTransfer(e.h, &e.Desc, len(buf), e.Timeout)
 	if err != nil {
 		return 0, err
 	}
 	defer t.free()
+	if e.Desc.Direction == EndpointDirectionOut {
+		copy(t.data(), buf)
+	}
 
 	if err := t.submit(); err != nil {
 		return 0, err
 	}
 
 	n, err := t.wait()
+	if e.Desc.Direction == EndpointDirectionIn {
+		copy(buf, t.data())
+	}
 	if err != nil {
 		return n, err
 	}

endpoint_stream.go

@@ -17,7 +17,7 @@ package gousb
 func (e *endpoint) newStream(size, count int, submit bool) (*stream, error) {
 	var ts []transferIntf
 	for i := 0; i < count; i++ {
-		t, err := newUSBTransfer(e.h, &e.Desc, make([]byte, size), e.Timeout)
+		t, err := newUSBTransfer(e.h, &e.Desc, size, e.Timeout)
 		if err != nil {
 			for _, t := range ts {
 				t.free()

fakelibusb_test.go

@@ -149,11 +149,11 @@ func (f *fakeLibusb) setAlt(d *libusbDevHandle, intf, alt uint8) error {
 	return nil
 }
 
-func (f *fakeLibusb) alloc(_ *libusbDevHandle, _ *EndpointDesc, _ time.Duration, _ int, buf []byte, done chan struct{}) (*libusbTransfer, error) {
+func (f *fakeLibusb) alloc(_ *libusbDevHandle, _ *EndpointDesc, _ time.Duration, _ int, bufLen int, done chan struct{}) (*libusbTransfer, error) {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 	t := newFakeTransferPointer()
-	f.ts[t] = &fakeTransfer{buf: buf, done: done}
+	f.ts[t] = &fakeTransfer{buf: make([]byte, bufLen), done: done}
 	return t, nil
 }
 func (f *fakeLibusb) cancel(t *libusbTransfer) error { return errors.New("not implemented") }
@@ -164,6 +164,7 @@ func (f *fakeLibusb) submit(t *libusbTransfer) error {
 	f.submitted <- ft
 	return nil
 }
+func (f *fakeLibusb) buffer(t *libusbTransfer) []byte { return f.ts[t].buf }
 func (f *fakeLibusb) data(t *libusbTransfer) (int, TransferStatus) {
 	f.mu.Lock()
 	defer f.mu.Unlock()

libusb.go

@@ -27,7 +27,9 @@ import (
 #cgo pkg-config: libusb-1.0
 #include <libusb.h>
 
-int compact_iso_data(struct libusb_transfer *xfer, unsigned char *status);
+int gousb_compact_iso_data(struct libusb_transfer *xfer, unsigned char *status);
+struct libusb_transfer *gousb_alloc_transfer_and_buffer(int bufLen, int numIsoPackets);
+void gousb_free_transfer_and_buffer(struct libusb_transfer *xfer);
 int submit(struct libusb_transfer *xfer);
 */
 import "C"
@@ -156,9 +158,10 @@ type libusbIntf interface {
 	setAlt(*libusbDevHandle, uint8, uint8) error
 
 	// transfer
-	alloc(*libusbDevHandle, *EndpointDesc, time.Duration, int, []byte, chan struct{}) (*libusbTransfer, error)
+	alloc(*libusbDevHandle, *EndpointDesc, time.Duration, int, int, chan struct{}) (*libusbTransfer, error)
 	cancel(*libusbTransfer) error
 	submit(*libusbTransfer) error
+	buffer(*libusbTransfer) []byte
 	data(*libusbTransfer) (int, TransferStatus)
 	free(*libusbTransfer)
 	setIsoPacketLengths(*libusbTransfer, uint32)
@@ -411,18 +414,19 @@ func (libusbImpl) setAlt(d *libusbDevHandle, iface, setup uint8) error {
 	return fromErrNo(C.libusb_set_interface_alt_setting((*C.libusb_device_handle)(d), C.int(iface), C.int(setup)))
 }
 
-func (libusbImpl) alloc(d *libusbDevHandle, ep *EndpointDesc, timeout time.Duration, isoPackets int, buf []byte, done chan struct{}) (*libusbTransfer, error) {
-	xfer := C.libusb_alloc_transfer(C.int(isoPackets))
+func (libusbImpl) alloc(d *libusbDevHandle, ep *EndpointDesc, timeout time.Duration, isoPackets int, bufLen int, done chan struct{}) (*libusbTransfer, error) {
+	xfer := C.gousb_alloc_transfer_and_buffer(C.int(bufLen), C.int(isoPackets))
 	if xfer == nil {
-		return nil, fmt.Errorf("libusb_alloc_transfer(%d) failed", isoPackets)
+		return nil, fmt.Errorf("gousb_alloc_transfer_and_buffer(%d, %d) failed", bufLen, isoPackets)
+	}
+	if int(xfer.length) != bufLen {
+		return nil, fmt.Errorf("gousb_alloc_transfer_and_buffer(%d, %d): length = %d, want %d", bufLen, isoPackets, xfer.length, bufLen)
 	}
 	xfer.dev_handle = (*C.libusb_device_handle)(d)
 	xfer.endpoint = C.uchar(ep.Address)
 	xfer.timeout = C.uint(timeout / time.Millisecond)
 	xfer._type = C.uchar(ep.TransferType)
 	xfer.num_iso_packets = C.int(isoPackets)
-	xfer.buffer = (*C.uchar)(unsafe.Pointer(&buf[0]))
-	xfer.length = C.int(len(buf))
 	ret := (*libusbTransfer)(xfer)
 	xferDoneMap.Lock()
 	xferDoneMap.m[ret] = done
@@ -438,17 +442,29 @@ func (libusbImpl) submit(t *libusbTransfer) error {
 	return fromErrNo(C.submit((*C.struct_libusb_transfer)(t)))
 }
 
+func (libusbImpl) buffer(t *libusbTransfer) []byte {
+	// TODO(go1.10?): replace with more user-friendly construct once
+	// one exists. https://github.com/golang/go/issues/13656
+	var ret []byte
+	*(*reflect.SliceHeader)(unsafe.Pointer(&ret)) = reflect.SliceHeader{
+		Data: uintptr(unsafe.Pointer(t.buffer)),
+		Len:  int(t.length),
+		Cap:  int(t.length),
+	}
+	return ret
+}
+
 func (libusbImpl) data(t *libusbTransfer) (int, TransferStatus) {
 	if TransferType(t._type) == TransferTypeIsochronous {
 		var status TransferStatus
-		n := int(C.compact_iso_data((*C.struct_libusb_transfer)(t), (*C.uchar)(unsafe.Pointer(&status))))
+		n := int(C.gousb_compact_iso_data((*C.struct_libusb_transfer)(t), (*C.uchar)(unsafe.Pointer(&status))))
 		return n, status
 	}
 	return int(t.actual_length), TransferStatus(t.status)
 }
 
 func (libusbImpl) free(t *libusbTransfer) {
-	C.libusb_free_transfer((*C.struct_libusb_transfer)(t))
+	C.gousb_free_transfer_and_buffer((*C.struct_libusb_transfer)(t))
 	xferDoneMap.Lock()
 	delete(xferDoneMap.m, t)
 	xferDoneMap.Unlock()

rawread/main.go

@@ -140,6 +140,9 @@ func main() {
 	}
 	dev := devs[0]
 
+	log.Print("Enabling autodetach")
+	dev.SetAutoDetach(true)
+
 	log.Printf("Setting configuration %d...", *config)
 	cfg, err := dev.Config(*config)
 	if err != nil {

transfer.c

@@ -15,6 +15,7 @@
 
 #include <libusb.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 void print_xfer(struct libusb_transfer *xfer);
@@ -53,7 +54,7 @@ void print_xfer(struct libusb_transfer *xfer) {
 // compact the data in an isochronous transfer. The contents of individual
 // iso packets are shifted left, so that no gaps are left between them.
 // Status is set to the first non-zero status of an iso packet.
-int compact_iso_data(struct libusb_transfer *xfer, unsigned char *status) {
+int gousb_compact_iso_data(struct libusb_transfer *xfer, unsigned char *status) {
 	int i;
 	int sum = 0;
 	unsigned char *in = xfer->buffer;
@@ -74,3 +75,26 @@ int compact_iso_data(struct libusb_transfer *xfer, unsigned char *status) {
 	}
 	return sum;
 }
+
+// allocates a libusb transfer and a buffer for packet data.
+struct libusb_transfer *gousb_alloc_transfer_and_buffer(int bufLen, int isoPackets) {
+        struct libusb_transfer *xfer = libusb_alloc_transfer(isoPackets);
+        if (xfer == NULL) {
+                return NULL;
+        }
+        xfer->buffer = (unsigned char*)malloc(bufLen);
+        if (xfer->buffer == NULL) {
+                libusb_free_transfer(xfer);
+                return NULL;
+        }
+        xfer->length = bufLen;
+        return xfer;
+}
+
+// frees a libusb transfer and its buffer. The buffer of the given
+// libusb_transfer must have been allocated with alloc_transfer_and_buffer.
+void gousb_free_transfer_and_buffer(struct libusb_transfer *xfer) {
+        free(xfer->buffer);
+        xfer->length = 0;
+        libusb_free_transfer(xfer);
+}

transfer.go

@@ -26,8 +26,9 @@ type usbTransfer struct {
 	mu sync.Mutex
 	// xfer is the allocated libusb_transfer.
 	xfer *libusbTransfer
-	// buf is the buffer allocated for the transfer. Both buf and xfer.buffer
-	// point to the same piece of memory.
+	// 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.
@@ -97,6 +98,9 @@ func (t *usbTransfer) free() error {
 	if t.submitted {
 		return errors.New("free() cannot be called on a submitted transfer until wait() returns")
 	}
+	if t.xfer == nil {
+		return nil
+	}
 	libusb.free(t.xfer)
 	t.xfer = nil
 	t.buf = nil
@@ -109,21 +113,21 @@ func (t *usbTransfer) data() []byte {
 	return t.buf
 }
 
-// newUSBTransfer allocates a new transfer structure for communication with a
-// given device/endpoint, with buf as the underlying transfer buffer.
-func newUSBTransfer(dev *libusbDevHandle, ei *EndpointDesc, buf []byte, timeout time.Duration) (*usbTransfer, error) {
+// newUSBTransfer allocates a new transfer structure and a new buffer for
+// communication with a given device/endpoint.
+func newUSBTransfer(dev *libusbDevHandle, ei *EndpointDesc, bufLen int, timeout time.Duration) (*usbTransfer, error) {
 	var isoPackets, isoPktSize int
 	if ei.TransferType == TransferTypeIsochronous {
 		isoPktSize = ei.MaxPacketSize
-		if len(buf) < isoPktSize {
-			isoPktSize = len(buf)
+		if bufLen < isoPktSize {
+			isoPktSize = bufLen
 		}
-		isoPackets = len(buf) / isoPktSize
-		debug.Printf("New isochronous transfer - buffer length %d, using %d packets of %d bytes each", len(buf), isoPackets, isoPktSize)
+		isoPackets = bufLen / isoPktSize
+		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 := libusb.alloc(dev, ei, timeout, isoPackets, buf, done)
+	xfer, err := libusb.alloc(dev, ei, timeout, isoPackets, bufLen, done)
 	if err != nil {
 		return nil, err
 	}
@@ -134,7 +138,7 @@ func newUSBTransfer(dev *libusbDevHandle, ei *EndpointDesc, buf []byte, timeout
 
 	t := &usbTransfer{
 		xfer: xfer,
-		buf:  buf,
+		buf:  libusb.buffer(xfer),
 		done: done,
 	}
 	runtime.SetFinalizer(t, func(t *usbTransfer) {

transfer_test.go

@@ -57,13 +57,13 @@ func TestNewTransfer(t *testing.T) {
 			Direction:     tc.dir,
 			TransferType:  tc.tt,
 			MaxPacketSize: tc.maxPkt,
-		}, make([]byte, tc.buf), tc.timeout)
+		}, tc.buf, tc.timeout)
 
 		if err != nil {
 			t.Fatalf("newUSBTransfer(): %v", err)
 		}
 		defer xfer.free()
-		if got, want := len(xfer.buf), tc.wantLength; got != want {
+		if got, want := len(xfer.data()), tc.wantLength; got != want {
 			t.Errorf("xfer.buf: got %d bytes, want %d", got, want)
 		}
 	}
@@ -81,7 +81,7 @@ func TestTransferProtocol(t *testing.T) {
 			Direction:     EndpointDirectionIn,
 			TransferType:  TransferTypeBulk,
 			MaxPacketSize: 512,
-		}, make([]byte, 10240), time.Second)
+		}, 10240, time.Second)
 		if err != nil {
 			t.Fatalf("newUSBTransfer: %v", err)
 		}