Err is nil when filetype is unknown

[taylorkline]

Expected behavior:

kind, err := filetype.MatchReader(badReader)

We would expect err != nil, but this is not so.

The documentation appears to contradict itself. In one example, we have:

  kind, unknown := filetype.Match(buf)
  if unknown != nil {
    fmt.Printf("Unknown: %s", unknown)
    return
  }

Yet, in another example, we have:

  // Try to match the file
  fooFile := []byte{0x01, 0x02}
  kind, _ := filetype.Match(fooFile)
  if kind == filetype.Unknown {
    fmt.Println("Unknown file type")
  } else {
    fmt.Printf("File type matched: %s\n", kind.Extension)
  }

I would expect the documentation to be consistent and the error to be populated if we have an unknown filetype.

[kmanley]

The error isn't populated if the filetype is unknown. In that case filetype.Unknown is returned and err==nil. An error is only returned if an error occurs. You're correct that this example is wrong though:

kind, unknown := filetype.Match(buf)
  if unknown != nil {
    fmt.Printf("Unknown: %s", unknown)
    return
  }

I submitted #59 to correct that

[h2non]

Should be fixed now. Thanks!