Retry connection when initial attempt fails. Close #90

When connecting to a reader fails, we retry connecting later.
This is done by showing another Bus number for the device.
We need to fake Bus numbers anyway as chrome.usb does not let us retrieve them.
PCSC then views it as a different device from the previous one and attempts
to connect to it once a smartcard reader needs to be accessed.

third_party/libusb/naclport/src/libusb_over_chrome_usb.cc

@@ -23,6 +23,7 @@
 #include <cstring>
 #include <functional>
 #include <limits>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -32,9 +33,15 @@
 #include <google_smart_card_common/pp_var_utils/construction.h>
 #include <google_smart_card_common/pp_var_utils/extraction.h>
 
-// This arbitrary chosen constant is used as a stub for the device bus number
-// (as the chrome.usb API does not provide means of retrieving this).
-const uint8_t kFakeDeviceBusNumber = 42;
+//
+// We use stubs for the device bus number (as the chrome.usb API does not provide means of 
+// retrieving it). We modify this for a device when opening the device fails.
+// This makes PCSC recognize it as a new device which causes PCSC to retry opening it.
+//
+
+std::unordered_map<int64_t, uint8_t> kBusNumbers;
+const uint8_t kDefaultBusNumber = 1;
+const uint8_t kMaximumReconnectAttempts = 64;
 
 //
 // Bit mask values for the bmAttributes field of the libusb_config_descriptor
@@ -498,8 +505,11 @@ int LibusbOverChromeUsb::LibusbGetDeviceDescriptor(
   return LIBUSB_SUCCESS;
 }
 
-uint8_t LibusbOverChromeUsb::LibusbGetBusNumber(libusb_device* /*dev*/) {
-  return kFakeDeviceBusNumber;
+uint8_t LibusbOverChromeUsb::LibusbGetBusNumber(libusb_device* dev) {
+  if (kBusNumbers.find(dev->chrome_usb_device().device) != kBusNumbers.end()) {
+    return kBusNumbers[dev->chrome_usb_device().device];
+  }
+  return kDefaultBusNumber;
 }
 
 uint8_t LibusbOverChromeUsb::LibusbGetDeviceAddress(libusb_device* dev) {
@@ -523,6 +533,17 @@ int LibusbOverChromeUsb::LibusbOpen(
   if (!result.is_successful()) {
     GOOGLE_SMART_CARD_LOG_WARNING << "LibusbOverChromeUsb::LibusbOpen " <<
         "request failed: " << result.error_message();
+    // modify the devices (fake) bus number that we report so that PCSC will 
+    // retry to connect to the device once it updates the device list
+    if (kBusNumbers.find(dev->chrome_usb_device().device) != 
+        kBusNumbers.end()) {
+      kBusNumbers[dev->chrome_usb_device().device] = std::min(
+          static_cast<uint8_t>(
+          kBusNumbers[dev->chrome_usb_device().device] + 1),
+          kMaximumReconnectAttempts);
+    } else {
+      kBusNumbers[dev->chrome_usb_device().device] = kDefaultBusNumber + 1;
+    }
     return LIBUSB_ERROR_OTHER;
   }
   const chrome_usb::ConnectionHandle chrome_usb_connection_handle =