From a47809fda80200bc054fd30011b41fded2c9994c Mon Sep 17 00:00:00 2001
From: Sebastian Zagrodzki <sebek@zagrodzki.net>
Date: Mon, 13 Feb 2017 02:50:47 +0100
Subject: [PATCH] Simplify the C part even more - the buffer that xfer uses for
 transferring data is the same as the one that was created in newUSBTransfer.

---
 usb/transfer.c  | 53 ++++++++++++-------------------------------------
 usb/transfer.go | 14 ++++++-------
 2 files changed, 20 insertions(+), 47 deletions(-)

diff --git a/usb/transfer.c b/usb/transfer.c
index 14585e6..2fa3497 100644
--- a/usb/transfer.c
+++ b/usb/transfer.c
@@ -54,54 +54,27 @@ void print_xfer(struct libusb_transfer *xfer) {
 	}
 }
 
-// extract data from a non-isochronous transfer.
-int extract_data(struct libusb_transfer *xfer, void *raw, int max, unsigned char *status) {
+// 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 i;
+	int sum = 0;
 	unsigned char *in = xfer->buffer;
-	unsigned char *out = raw;
-
-    int len = xfer->actual_length;
-    if (len > max) {
-            len = max;
-    }
-    memcpy(out, in, len);
-   	if (xfer->status != 0 && *status == 0) {
-            *status = xfer->status;
-   	}
-    return len;
-}
-
-// extract data from an isochronous transfer. Very similar to extract_data, but
-// acquires data from xfer->iso_packet_desc array instead of xfer attributes.
-int extract_iso_data(struct libusb_transfer *xfer, void *raw, int max, unsigned char *status) {
-	int i;
-	int copied = 0;
-	unsigned char *in = xfer->buffer;
-	unsigned char *out = raw;
+	unsigned char *out = xfer->buffer;
 	for (i = 0; i < xfer->num_iso_packets; i++) {
 		struct libusb_iso_packet_descriptor pkt = xfer->iso_packet_desc[i];
-
+		if (pkt.status != 0) {
+		    *status = pkt.status;
+			break;
+		}
 		// Copy the data
 		int len = pkt.actual_length;
-		if (copied + len > max) {
-			len = max - copied;
-		}
-		memcpy(out, in, len);
-		copied += len;
-
+		memmove(out, in, len);
 		// Increment offsets
+		sum += len;
 		in += pkt.length;
 		out += len;
-
-        if (copied == max) {
-                break;
-        }
-
-		// Extract first error
-		if (pkt.status == 0 || *status != 0) {
-			continue;
-		}
-		*status = pkt.status;
 	}
-	return copied;
+	return sum;
 }
diff --git a/usb/transfer.go b/usb/transfer.go
index 0e22080..f5c9129 100644
--- a/usb/transfer.go
+++ b/usb/transfer.go
@@ -17,8 +17,7 @@ package usb
 /*
 #include <libusb-1.0/libusb.h>
 
-int extract_data(struct libusb_transfer *xfer, void *data, int max, unsigned char *status);
-int extract_iso_data(struct libusb_transfer *xfer, void *data, int max, unsigned char *status);
+int compact_iso_data(struct libusb_transfer *xfer, unsigned char *status);
 int submit(struct libusb_transfer *xfer);
 */
 import "C"
@@ -56,15 +55,16 @@ func (t *usbTransfer) wait() (n int, err error) {
 		return 0, fmt.Errorf("wait timed out after 10s")
 	case <-t.done:
 	}
-	var status uint8
+	var status TransferStatus
 	switch TransferType(t.xfer._type) {
 	case TRANSFER_TYPE_ISOCHRONOUS:
-		n = int(C.extract_iso_data(t.xfer, unsafe.Pointer(&t.buf[0]), C.int(len(t.buf)), (*C.uchar)(unsafe.Pointer(&status))))
+		n = int(C.compact_iso_data(t.xfer, (*C.uchar)(unsafe.Pointer(&status))))
 	default:
-		n = int(C.extract_data(t.xfer, unsafe.Pointer(&t.buf[0]), C.int(len(t.buf)), (*C.uchar)(unsafe.Pointer(&status))))
+		n = int(t.xfer.length)
+		status = TransferStatus(t.xfer.status)
 	}
-	if status != 0 {
-		err = TransferStatus(status)
+	if status != LIBUSB_TRANSFER_COMPLETED {
+		return 0, status
 	}
 	return n, err
 }