From e455efbffdcc22c02aaf9cbee37ca3b476a30eeb Mon Sep 17 00:00:00 2001
From: Marko Bencun <marko@shiftcrypto.ch>
Date: Wed, 4 Dec 2019 17:54:37 +0100
Subject: [PATCH] communication/u2fhid: parse frame errors

---
 communication/u2fhid/error.go  | 45 ++++++++++++++++++++++++++++++++++
 communication/u2fhid/u2fhid.go | 18 +++++++++++---
 2 files changed, 60 insertions(+), 3 deletions(-)
 create mode 100644 communication/u2fhid/error.go

diff --git a/communication/u2fhid/error.go b/communication/u2fhid/error.go
new file mode 100644
index 0000000..c99b592
--- /dev/null
+++ b/communication/u2fhid/error.go
@@ -0,0 +1,45 @@
+// Copyright 2018-2019 Shift Cryptosecurity AG
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package u2fhid
+
+import "fmt"
+
+const (
+	errCodeChannelBusy = byte(0x06)
+
+	// errCodeChannelNone         = byte(0x00)
+	// errCodeChannelInvalidCmd   = byte(0x01)
+	// errCodeChannelInvalidPar   = byte(0x02)
+	// errCodeChannelInvalidLen   = byte(0x03)
+	// errCodeChannelInvalidSeq   = byte(0x04)
+	// errCodeChannelMsgTimeout   = byte(0x05)
+	// errCodechannellockRequired = byte(0x0A)
+	// errCodechannelInvalidCid   = byte(0x0B)
+	// errCodechannelOther        = byte(0x7F)
+)
+
+// FrameError is returned when the frame which is read indicates an error.
+// The value within is the error code.
+type FrameError byte
+
+// Error implements error.
+func (e FrameError) Error() string {
+	return fmt.Sprintf("frame error: %d", e)
+}
+
+// IsErrBusy returns true if the error code indicates a busy channel.
+func (e FrameError) IsErrBusy() bool {
+	return byte(e) == errCodeChannelBusy
+}
diff --git a/communication/u2fhid/u2fhid.go b/communication/u2fhid/u2fhid.go
index c676fae..8578cf9 100644
--- a/communication/u2fhid/u2fhid.go
+++ b/communication/u2fhid/u2fhid.go
@@ -27,6 +27,8 @@ import (
 const (
 	writeReportSize = 64
 	readReportSize  = 64
+
+	cmdError = 0x80 | 0x3F
 )
 
 const (
@@ -156,12 +158,22 @@ func (communication *Communication) readFrame() ([]byte, error) {
 	if read[0] != 0xff || read[1] != 0 || read[2] != 0 || read[3] != 0 {
 		return nil, errp.Newf("USB command ID mismatch %d %d %d %d", read[0], read[1], read[2], read[3])
 	}
-	if read[4] != communication.cmd {
-		return nil, errp.Newf("USB command frame mismatch (%d, expected %d)", read[4], communication.cmd)
-	}
+
 	data := newBuffer()
 	dataLen := int(read[5])*256 + int(read[6])
 	data.Write(read[7:readLen])
+
+	cmd := read[4]
+	if cmd == cmdError {
+		errCode := byte(0)
+		if data.Len() > 0 {
+			errCode = data.Bytes()[0]
+		}
+		return nil, errp.WithStack(FrameError(errCode))
+	}
+	if cmd != communication.cmd {
+		return nil, errp.Newf("USB command frame mismatch (%d, expected %d)", cmd, communication.cmd)
+	}
 	idx := len(read) - 7
 	for idx < dataLen {
 		readLen, err = communication.device.Read(read)