gousb-不是OUT端点

Question

I'm new to the go programming language. Trying to use gousb to access an epson receipt printer.

So I took some example code from the repo and repurposed it a bit just to validate that I could access the printer.

I can see the printer and enumerate the endpoints. I receive this output:

Printer found: 020.005 Receipt Printer M129C/TM-T70 (Seiko Epson Corp.)
Length of device array: 1
[0] 020.005 04b8 - 0202
  [0] Config 01 [1]
    [0]--------------[0]
    [0] Interface 00 Setup 00 [0]
      Vendor Specific Class (Vendor Specific Subclass)
      [0] [1] Endpoint #1 OUT bulk - unsynchronized data [64 0] [OUT]
      [1] [130] Endpoint #2 IN  bulk - unsynchronized data [64 0] [IN]

My understanding is that if I want to write something to the printer, I would open the endpoint that corresponds to [OUT]. Aand this is where my trouble begins.

If I use outEP, err := thePrinter.OpenEndpoint(1,0,0,0), I receive a seg fault. If I pass a 1, gousb assumes I'm trying to access endpoint 130 [IN].

So.. What do I pass as the endpoint ID to access the OUT endpoint?

Code:

package main

import (
        "fmt"
        "strings"

        "github.com/kylelemons/gousb/usb"
        "github.com/kylelemons/gousb/usbid"

        "C"
)

func main() {
  ctx := usb.NewContext()
  defer ctx.Close()


  ctx.Debug(3)

  var thePrinter *usb.Device

  devs, _ := ctx.ListDevices(func(desc *usb.Descriptor) bool {
    if strings.Contains(usbid.Describe(desc), "Seiko Epson Corp") {
      fmt.Printf("Printer found: %03d.%03d %s
", desc.Bus, desc.Address, usbid.Describe(desc))
      return true
    } else {
      return false
    }

  })

  fmt.Printf("Length of device array: %d
", len(devs))

  for x, dev := range devs {
    fmt.Printf("[%d] %03d.%03d %s - %s
", x, dev.Bus, dev.Address, dev.Vendor, dev.Product)

    for i, cfg := range dev.Configs {
      // This loop just uses more of the built-in and usbid pretty printing to list
      // the USB devices.
      fmt.Printf("  [%d] %s [%d]
", i, cfg, cfg.Config)
      for j, alt := range cfg.Interfaces {
        fmt.Printf("    [%d]--------------[%d]
", j, alt.Number)
        for k, iface := range alt.Setups {
          fmt.Printf("    [%d] %s [%d]
", k, iface, iface.Number)
          fmt.Printf("      %s
", usbid.Classify(iface))
          for l, end := range iface.Endpoints {
            fmt.Printf("      [%d] [%d] %s [%s]
", l, end.Address, end, end.Direction() )
          }
        }
      }
      fmt.Printf("    --------------
")
    }



    thePrinter=dev
  }

  outEP, err := thePrinter.OpenEndpoint(1,0,0,1)

  fmt.Printf("OpenEndpoint Err: [%s]
", err)

  fmt.Printf("direction: [%s] %d
", outEP.Info().Direction(), outEP.Info().Address)

  message := []byte("hi there!
")

  _, outerr := outEP.Write(message)

  fmt.Printf("write Err: [%s]", outerr)

}

EDIT: I was asked to examine the error returned by OpenEndpoint prior to looking at the value of the endpoint. Here is what was returned (it was nil)

OpenEndpoint Err: [%!s(<nil>)]
direction: [IN] 130
OpenEndpoint Err: [%!s(<nil>)]
libusb: warning [libusb_exit] application left some devices open
write Err: [usb: write: not an OUT endpoint]
[Finished in 1.512s]

This is what I receive when I send an endpoint number of zero:

OpenEndpoint Err: [usb: unknown endpoint 00]
libusb: warning [libusb_exit] application left some devices open
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x41e94c4]

goroutine 1 [running]:
main.main()
    /Users/.../go/src/github.com/deltasonic/epson/main.go:63 +0xcb4
exit status 2
[Finished in 0.817s]

EDIT:

I'm attempting this on a mac, Mac OS 10.12.

Answer 1

The package github.com/kylelemons/gousb has been deprecated in favor of github.com/google/gousb. Please note that the new package has a slightly different API - we think it should be less confusing.

That being said, your call with OpenEndpoint(1,0,0,1) looks correct - it should set configuration #1 on the device, claim interface #0 with alt setting #0 and then return a representation of an endpoint with address 0x01, which is an OUT endpoint. Looking at the gousb code, I can't find any obvious issues. You can try again with the current head of the package from github, and if it still returns EP address 130 (0x82) after OpenEndpoint(1,0,0,1), please file an issue on github, this definitely should not be happening.