Workaround for usb communication issue aka 'N*128 problem' or 'N*512 problem'

For some strange reason packets that are N*128 bytes long via USB 1.1,
or N*512 bytes long via USB 2.0, the device will not send an answer and
any following packet will cause a connection reset.
See this as a workaround until the usb issue has been resolved.

1 files changed, 59 insertions, 10 deletions

diff --git a/src/usbmux.c b/src/usbmux.c
index 1d6497e..2157e05 100644
--- a/src/usbmux.c
+++ b/src/usbmux.c
@@ -822,6 +822,7 @@ int usbmux_send(usbmux_client_t client, const char *data, uint32_t datalen,
         pthread_mutex_lock(&client->mutex);
 
         int sendresult = 0;
+        int fullsendresult = 0;
         uint32_t blocksize = 0;
         if (client->wr_window <= 0) {
                 struct timespec ts;
@@ -840,20 +841,67 @@ int usbmux_send(usbmux_client_t client, const char *data, uint32_t datalen,
         // client->scnt and client->ocnt should already be in host notation...
         // we don't need to change them juuuust yet. 
         char *buffer = (char *) malloc(blocksize + 2);  // allow 2 bytes of safety padding
+        const char *dataptr = data;
+        uint32_t curlen = datalen;
+        uint32_t packetsize = blocksize;
+
+        // BEGIN HACK
+        if ((blocksize % 128) == 0) {
+            int cutoff = 28;
+            // HACK: we need to split up the packet because of an unresolved
+            // usb communication issue aka 'N*128 problem' or 'N*512 problem'
+            log_debug_msg("%s: HACK: splitting packet, two send_to_device calls will follow\n");
+            packetsize = blocksize - cutoff;
+            curlen = datalen - cutoff;
+            client->header->length = packetsize;
+            client->header->length16 = packetsize;
+            hton_header(client->header);
+            memcpy(buffer, client->header, sizeof(usbmux_tcp_header));
+            memcpy(buffer + sizeof(usbmux_tcp_header), dataptr, curlen);
+
+            log_debug_msg("%s: send_to_device(%d --> %d) window = %d\n", __func__,
+                                  ntohs(client->header->sport),
+                                  ntohs(client->header->dport),
+                                  ntohs(client->header->window));
+            sendresult = send_to_device(client->device, buffer, packetsize);
+            fullsendresult = sendresult;
+
+            // revert header fields that have been swapped before trying to send
+            ntoh_header(client->header);
+
+            // update counts ONLY if the send succeeded.
+            if ((uint32_t) sendresult == packetsize) {
+                // Re-calculate scnt
+                client->header->scnt += curlen;
+                client->wr_window -= packetsize;
+            } else {
+                goto err_cond;
+            }
+
+            dataptr += curlen;
+            curlen = cutoff;
+            packetsize = sizeof(usbmux_tcp_header) + curlen;
+            // fix fullsendresult to not include the header length to make
+            //  setting *sent_bytes work properly
+            fullsendresult -= sizeof(usbmux_tcp_header);
+        }
+        // END HACK
+
         // Set the length
-        client->header->length = blocksize;
-        client->header->length16 = blocksize;
+        client->header->length = packetsize;
+        client->header->length16 = packetsize;
 
         // Put header into big-endian notation
         hton_header(client->header);
         // Concatenation of stuff in the buffer.
         memcpy(buffer, client->header, sizeof(usbmux_tcp_header));
-        memcpy(buffer + sizeof(usbmux_tcp_header), data, datalen);
+        memcpy(buffer + sizeof(usbmux_tcp_header), dataptr, curlen);
 
         log_debug_msg("%s: send_to_device(%d --> %d)\n", __func__,
                                   ntohs(client->header->sport),
                                   ntohs(client->header->dport));
-        sendresult = send_to_device(client->device, buffer, blocksize);
+        sendresult = send_to_device(client->device, buffer, packetsize);
+        fullsendresult += sendresult;
         // Now that we've sent it off, we can clean up after our sloppy selves.
         if (buffer)
                 free(buffer);
@@ -862,12 +910,13 @@ int usbmux_send(usbmux_client_t client, const char *data, uint32_t datalen,
         ntoh_header(client->header);
 
         // update counts ONLY if the send succeeded.
-        if ((uint32_t) sendresult == blocksize) {
+        if ((uint32_t) sendresult == packetsize) {
                 // Re-calculate scnt
-                client->header->scnt += datalen;
-                client->wr_window -= blocksize;
+                client->header->scnt += curlen;
+                client->wr_window -= packetsize;
         }
 
+err_cond:
         pthread_mutex_unlock(&client->mutex);
 
         if (sendresult == -ETIMEDOUT || sendresult == 0) {
@@ -876,14 +925,14 @@ int usbmux_send(usbmux_client_t client, const char *data, uint32_t datalen,
                 return -ETIMEDOUT;
         } else if (sendresult < 0) {
                 return sendresult;
-        } else if ((uint32_t) sendresult == blocksize) {
+        } else if ((uint32_t) fullsendresult == blocksize) {
                 // actual number of data bytes sent.
-                *sent_bytes = sendresult - sizeof(usbmux_tcp_header);
+                *sent_bytes = fullsendresult - sizeof(usbmux_tcp_header);
                 return 0;
         } else {
                 fprintf(stderr,
                                 "usbsend managed to dump a packet that is not full size. %d of %d\n",
-                                sendresult, blocksize);
+                                sendresult, packetsize);
                 return -EBADMSG;
         }
 }