I am trying to cross compile a simple go program.

package main

import (
	"fmt"
	"github.com/fuzxxl/nfc/2.0/nfc"
)

func main() {
	fmt.Println(nfc.Version())
	devices, err := nfc.ListDevices()
	if err != nil {
		fmt.Print(err)
		return
	}
	for _, d := range devices {
		fmt.Printf("found device %s", d)
	}
}

I am cross compiling it with the following command.

GOOS=linux GOARCH=arm go build -a -v github.com/fuzxxl/nfc/2.0/nfc

I am using the golang:1.7.5 docker image (based on debian wheezy) for compilation. I encounter the following compiler error.

../../fuzxxl/nfc/2.0/nfc/nfc.go:206: undefined: context

It is clear that etc.go has type context struct defined in the nfc package. This error occurs only during cross compilation. Is there something that I am missing?

This is more of a documentation issue than a bug. It's not at all clear how you actually select a target once you've listed them.

I can get a Target enumerated from Device#InitiatorListPassiveTargets(), but how do I select it?

1. There is no Select() method on the Target interface
2. There IS a Device#InitiatorSelectPassiveTarget(), but there is no documentation on what the meaning of the second parameter initData is. What is supposed to be passed there? Simply passing a []byte{0} results in the following error:

error libnfc.driver.acr122_usb Invalid RDR_to_PC_DataBlock frame
panic: input / output error

I've tried a number of approaches, none of which seem to work, and I can't find any documentation or examples for this.

Thanks.

I installed the library using go get

go get github.com/fuzxxl/nfc

I'm receiving a build error that would indicate that I possibly installed the library incorrectly.

../github.com/fuzxxl/nfc/2.0/nfc/nfc.go:206: undefined: context

I tried downloading the root project directly into my GOPATH but am still experiencing the same behavior. Can you advise? I'm sure it's something dumb that I'm overlooking.

Should be wrapped as

func (*Device) InitiatorDeselectTarget() error

Problem

When InfiniteSelect == false, nfc_initiator_select_passive_target return 0 when no tag was found, but Device.InitiatorSelectPassiveTarget always calls unmarshallTarget.

Example in https://github.com/nfc-tools/libnfc/blob/master/utils/nfc-mfclassic.c

  if (nfc_initiator_select_passive_target(pnd, nmMifare, NULL, 0, &nt) <= 0) {
    printf("Error: no tag was found\n");
    nfc_close(pnd);
    nfc_exit(context);
    exit(EXIT_FAILURE);
  }

This code use <= 0 for error checking.

How to reproduce

func main() {
    dev, _ := nfc.Open("")
    defer dev.Close()
    dev.InitiatorInit()
    dev.SetPropertyBool(nfc.InfiniteSelect, false)
    dev.SetPropertyBool(nfc.AutoISO14443_4, false)
    fmt.Printf("NFC reader: %s opened\n", dev)
    dev.InitiatorSelectPassiveTarget(nmMifare, nil) // panic when no tag was present
}

Affected version

all version include latest

• In v2.0, the second parameter of Device.InitiatorSelectPassiveTarget is not used
• In v2.0, the libnfc return code is not considered correctly: if the value if negative, then its an error, else it returns the number of selected tags

Reference: http://www.libnfc.org/api/group__initiator.html#gacbe0fa197206cac99c83ed0152174811

The dev version is not working, but I can purpose a PR for a fix in 2.0 if needed :)

go get github.com/fuzxxl/nfc/1.0/nfc

src/github.com/fuzxxl/nfc/1.0/nfc/nfc.go:205: undefined: context

See https://gist.github.com/messinm/7086bfce591bf6f1d554
Running under Ubuntu 14.04 64-bit, libnfc 1.7.0

mifare target gives the following from printing Target received from InitiatorListPassiveTargets:
ISO/IEC 14443A (106 kbps) target:
ATQA (SENS_RES): 00 04

• UID size: single
• bit frame anticollision supported
  UID (NFCID1): 3c be 90 75
  SAK (SEL_RES): 08
• Not compliant with ISO/IEC 14443-4
• Not compliant with ISO/IEC 18092

Fingerprinting based on MIFARE type Identification Procedure:

• MIFARE Classic 1K
• MIFARE Plus (4 Byte UID or 4 Byte RID) 2K, Security level 1
• SmartMX with MIFARE 1K emulation
  Other possible matches based on ATQA & SAK values:

Then attempting marshalling to ISO14443aTarget, I get the following:

Atqa =[0 4]
Sak =8
UIDLen =33091718999965696
UID =[112 70 188 32 255 0 0 0 0 0]
Note that 33091718999965696 = 0x7590BE3C000000, so it appears that the UIDLen field actually contains the UID.

Am I doing something wrong in the marshalling code? Or is this a bug in Go NFC lib or libnfc?

The current implementations of Target.Marshall() do not check the supplied data for invariants. It won't crash because Go checks boundaries, but the code panics if an array is too long.

This needs to be improved.