I have the code below to write some data to a bulk usb output endpoint using the sync api.

// Find device

// Write data

do {

  r = libusb_bulk_transfer(handle, endpoint_out, wdata, swdata, &size, 1000);
  if (r == LIBUSB_ERROR_PIPE) {
    libusb_clear_halt(handle, endpoint_out);
  }
  i++;
} while ((r == LIBUSB_ERROR_PIPE) && (i<RETRY_MAX));

// Read response
int rsize;
char rdata[srdata] = {0};
r = libusb_bulk_transfer(handle, endpoint_in, &rdata, srdata, &rsize, 1000);
if (r < 0)
{
  printf("libusb_bulk_transfer failed: %s\n", libusb_error_name(r));
}

How could I achieve the same with the async api? I have tried the code below, but I do not seem to get the same data back.

  struct libusb_transfer *transfer = libusb_alloc_transfer(0);
  libusb_fill_bulk_transfer(transfer, handle, endpoint_out, wdata, swdata, cb_write, NULL, 0);
  if (libusb_submit_transfer(transfer) < 0)
        printf("Failed to submit the read command.");
  while (1) {
    r = libusb_handle_events(context);
    if (r < 0)
      printf("Failed to handle events\n");
    }

Then, in the write callback:

static void cb_write(struct libusb_transfer *transfer)
{
    if (transfer->status != LIBUSB_TRANSFER_COMPLETED) {
        fprintf(stderr, "Write transfer status %d?\n", transfer->status);
        libusb_free_transfer(transfer);
        transfer = NULL;
        return;
    }  

struct libusb_transfer *read_transfer = libusb_alloc_transfer(0);
libusb_fill_bulk_transfer(read_transfer, handle, endpoint_in, rdata, srdata, cb_ready, NULL, 0);
if (libusb_submit_transfer(read_transfer) < 0)
   printf("Failed to submit the read operation.\n");
else
  printf("Submitted the read operation.\n");

Then, I was thinking that I would need to do something for a read callback:

static void cb_read(struct libusb_transfer *transfer)
{
    if (transfer->status != LIBUSB_TRANSFER_COMPLETED) {
        fprintf(stderr, "Read transfer status: %d, data length: %d\n", transfer->status, transfer->length);
        libusb_free_transfer(transfer);
        transfer = NULL;
        return;
    }  

    if (libusb_submit_transfer(transfer) < 0)
       printf("Failed to submit the transfer\n");
}

So, I guess the real question is whether I am meant to handle the situation of write a request and then read the response in this way with the async libusb api or somehow different.

Kind regards,

Laszlo Papp

PS.: I got most of this logic from the examples.