fix: return @@context even when the unless block is not executed.

[choongyong]

When I run the example script, the following output is encountered:

D, [2017-06-29T16:13:24.352294 #2174] DEBUG -- : Library version: libnfc-1.7.1-187-g14f48d0
D, [2017-06-29T16:13:24.354756 #2174] DEBUG -- : Available readers: [#<NFC::Reader:0xcb9d30 @name="acr122_usb:001:007", @ptr=nil>]
/usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb:12: [BUG] Segmentation fault at 0x00140c
ruby 2.4.0p0 (2016-12-24 revision 57164) [armv7l-linux-eabihf]

-- Control frame information -----------------------------------------------
c:0005 p:---- s:0024 e:000023 CFUNC  :nfc_open
c:0004 p:0034 s:0018 e:000017 METHOD /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb:12
c:0003 p:0008 s:0014 e:000013 METHOD /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb:48
c:0002 p:0146 s:0007 E:00093c EVAL   reader.rb:15 [FINISH]
c:0001 p:0000 s:0003 E:001490 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
reader.rb:15:in `<main>'
/usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb:48:in `poll'
/usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb:12:in `connect'
/usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb:12:in `nfc_open'

-- Other runtime information -----------------------------------------------

* Loaded script: reader.rb

* Loaded features:

    0 enumerator.so
    1 thread.rb
    2 rational.so
    3 complex.so
    4 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/encdb.so
    5 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/trans/transdb.so
    6 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/unicode_normalize.rb
    7 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/rbconfig.rb
    8 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/compatibility.rb
    9 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/defaults.rb
   10 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/deprecate.rb
   11 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/errors.rb
   12 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/version.rb
   13 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/requirement.rb
   14 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/platform.rb
   15 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/basic_specification.rb
   16 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/stub_specification.rb
   17 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/util/list.rb
   18 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/stringio.so
   19 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/specification.rb
   20 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/exceptions.rb
   21 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/dependency.rb
   22 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/core_ext/kernel_gem.rb
   23 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/monitor.rb
   24 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/core_ext/kernel_require.rb
   25 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems.rb
   26 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/site_ruby/2.4.0/rubygems/path_support.rb
   27 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/version.rb
   28 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/core_ext/name_error.rb
   29 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/levenshtein.rb
   30 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/jaro_winkler.rb
   31 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/spell_checker.rb
   32 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/delegate.rb
   33 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/spell_checkers/name_error_checkers/class_name_checker.rb
   34 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/spell_checkers/name_error_checkers/variable_name_checker.rb
   35 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/spell_checkers/name_error_checkers.rb
   36 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/spell_checkers/method_name_checker.rb
   37 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/spell_checkers/null_checker.rb
   38 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean/formatter.rb
   39 /usr/local/rvm/gems/ruby-2.4.0@global/gems/did_you_mean-1.1.0/lib/did_you_mean.rb
   40 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/reader.rb
   41 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi_c.so
   42 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/platform.rb
   43 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/types.rb
   44 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/library.rb
   45 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/errno.rb
   46 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/pointer.rb
   47 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/memorypointer.rb
   48 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/struct_layout_builder.rb
   49 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/struct.rb
   50 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/union.rb
   51 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/managedstruct.rb
   52 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/callback.rb
   53 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/io.rb
   54 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/autopointer.rb
   55 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/variadic.rb
   56 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/enum.rb
   57 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi/ffi.rb
   58 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi.rb
   59 /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/logger.rb
   60 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/libnfc.rb
   61 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/nfc.rb
   62 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/tags/tag.rb
   63 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/tags/mifare/tag.rb
   64 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/tags/mifare/classic.rb
   65 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/tags/mifare/ultralight.rb
   66 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/apdu/apdu.rb
   67 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/apdu/request.rb
   68 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/apdu/response.rb
   69 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc/tags/isodep.rb
   70 /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ruby-nfc-1.3/lib/ruby-nfc.rb

* Process memory map:

00010000-00011000 r-xp 00000000 b3:02 269468     /usr/local/rvm/rubies/ruby-2.4.0/bin/ruby
00020000-00021000 rw-p 00000000 b3:02 269468     /usr/local/rvm/rubies/ruby-2.4.0/bin/ruby
00b69000-00e5d000 rw-p 00000000 00:00 0          [heap]
7659b000-766e0000 r-xp 00000000 b3:02 25944      /usr/lib/arm-linux-gnueabihf/libcrypto.so.1.0.0
766e0000-766f0000 ---p 00145000 b3:02 25944      /usr/lib/arm-linux-gnueabihf/libcrypto.so.1.0.0
766f0000-766fd000 r--p 00145000 b3:02 25944      /usr/lib/arm-linux-gnueabihf/libcrypto.so.1.0.0
766fd000-76705000 rw-p 00152000 b3:02 25944      /usr/lib/arm-linux-gnueabihf/libcrypto.so.1.0.0
76705000-76709000 rw-p 00000000 00:00 0 
76709000-7671a000 r-xp 00000000 b3:02 341        /usr/lib/libfreefare.so.0.0.0
7671a000-7672a000 ---p 00011000 b3:02 341        /usr/lib/libfreefare.so.0.0.0
7672a000-7672b000 rw-p 00011000 b3:02 341        /usr/lib/libfreefare.so.0.0.0
7672b000-7672c000 rw-p 00000000 00:00 0 
7672c000-76732000 r-xp 00000000 b3:02 132473     /lib/arm-linux-gnueabihf/libusb-0.1.so.4.4.4
76732000-76741000 ---p 00006000 b3:02 132473     /lib/arm-linux-gnueabihf/libusb-0.1.so.4.4.4
76741000-76742000 r--p 00005000 b3:02 132473     /lib/arm-linux-gnueabihf/libusb-0.1.so.4.4.4
76742000-76743000 rw-p 00006000 b3:02 132473     /lib/arm-linux-gnueabihf/libusb-0.1.so.4.4.4
76743000-76744000 rw-p 00000000 00:00 0 
76744000-76758000 r-xp 00000000 b3:02 31201      /usr/local/lib/libnfc.so.5.0.1
76758000-76768000 ---p 00014000 b3:02 31201      /usr/local/lib/libnfc.so.5.0.1
76768000-7676a000 rw-p 00014000 b3:02 31201      /usr/local/lib/libnfc.so.5.0.1
7676a000-76787000 r-xp 00000000 b3:02 132408     /lib/arm-linux-gnueabihf/libgcc_s.so.1
76787000-76796000 ---p 0001d000 b3:02 132408     /lib/arm-linux-gnueabihf/libgcc_s.so.1
76796000-76797000 rw-p 0001c000 b3:02 132408     /lib/arm-linux-gnueabihf/libgcc_s.so.1
76797000-7679e000 r-xp 00000000 b3:02 70040      /usr/lib/arm-linux-gnueabihf/libffi.so.6.0.2
7679e000-767ad000 ---p 00007000 b3:02 70040      /usr/lib/arm-linux-gnueabihf/libffi.so.6.0.2
767ad000-767ae000 r--p 00006000 b3:02 70040      /usr/lib/arm-linux-gnueabihf/libffi.so.6.0.2
767ae000-767af000 rw-p 00007000 b3:02 70040      /usr/lib/arm-linux-gnueabihf/libffi.so.6.0.2
767c3000-767e0000 r-xp 00000000 b3:02 779767     /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi_c.so
767e0000-767f0000 ---p 0001d000 b3:02 779767     /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi_c.so
767f0000-767f1000 rw-p 0001d000 b3:02 779767     /usr/local/rvm/gems/ruby-2.4.0@nfctest/gems/ffi-1.9.18/lib/ffi_c.so
767f1000-767f7000 r-xp 00000000 b3:02 269903     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/stringio.so
767f7000-76807000 ---p 00006000 b3:02 269903     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/stringio.so
76807000-76808000 rw-p 00006000 b3:02 269903     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/stringio.so
76808000-7680a000 r-xp 00000000 b3:02 778268     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/trans/transdb.so
7680a000-76819000 ---p 00002000 b3:02 778268     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/trans/transdb.so
76819000-7681a000 rw-p 00001000 b3:02 778268     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/trans/transdb.so
7681a000-7689b000 rw-p 00000000 00:00 0 
7689b000-76a26000 r--p 00000000 b3:02 129808     /usr/lib/locale/locale-archive
76a26000-76b51000 r-xp 00000000 b3:02 138591     /lib/arm-linux-gnueabihf/libc-2.19.so
76b51000-76b61000 ---p 0012b000 b3:02 138591     /lib/arm-linux-gnueabihf/libc-2.19.so
76b61000-76b63000 r--p 0012b000 b3:02 138591     /lib/arm-linux-gnueabihf/libc-2.19.so
76b63000-76b64000 rw-p 0012d000 b3:02 138591     /lib/arm-linux-gnueabihf/libc-2.19.so
76b64000-76b67000 rw-p 00000000 00:00 0 
76b67000-76bd0000 r-xp 00000000 b3:02 138595     /lib/arm-linux-gnueabihf/libm-2.19.so
76bd0000-76be0000 ---p 00069000 b3:02 138595     /lib/arm-linux-gnueabihf/libm-2.19.so
76be0000-76be1000 r--p 00069000 b3:02 138595     /lib/arm-linux-gnueabihf/libm-2.19.so
76be1000-76be2000 rw-p 0006a000 b3:02 138595     /lib/arm-linux-gnueabihf/libm-2.19.so
76be2000-76be9000 r-xp 00000000 b3:02 138593     /lib/arm-linux-gnueabihf/libcrypt-2.19.so
76be9000-76bf8000 ---p 00007000 b3:02 138593     /lib/arm-linux-gnueabihf/libcrypt-2.19.so
76bf8000-76bf9000 r--p 00006000 b3:02 138593     /lib/arm-linux-gnueabihf/libcrypt-2.19.so
76bf9000-76bfa000 rw-p 00007000 b3:02 138593     /lib/arm-linux-gnueabihf/libcrypt-2.19.so
76bfa000-76c21000 rw-p 00000000 00:00 0 
76c21000-76c23000 r-xp 00000000 b3:02 138594     /lib/arm-linux-gnueabihf/libdl-2.19.so
76c23000-76c32000 ---p 00002000 b3:02 138594     /lib/arm-linux-gnueabihf/libdl-2.19.so
76c32000-76c33000 r--p 00001000 b3:02 138594     /lib/arm-linux-gnueabihf/libdl-2.19.so
76c33000-76c34000 rw-p 00002000 b3:02 138594     /lib/arm-linux-gnueabihf/libdl-2.19.so
76c34000-76c95000 r-xp 00000000 b3:02 26046      /usr/lib/arm-linux-gnueabihf/libgmp.so.10.2.0
76c95000-76ca4000 ---p 00061000 b3:02 26046      /usr/lib/arm-linux-gnueabihf/libgmp.so.10.2.0
76ca4000-76ca5000 r--p 00060000 b3:02 26046      /usr/lib/arm-linux-gnueabihf/libgmp.so.10.2.0
76ca5000-76ca6000 rw-p 00061000 b3:02 26046      /usr/lib/arm-linux-gnueabihf/libgmp.so.10.2.0
76ca6000-76cba000 r-xp 00000000 b3:02 138610     /lib/arm-linux-gnueabihf/libpthread-2.19.so
76cba000-76cca000 ---p 00014000 b3:02 138610     /lib/arm-linux-gnueabihf/libpthread-2.19.so
76cca000-76ccb000 r--p 00014000 b3:02 138610     /lib/arm-linux-gnueabihf/libpthread-2.19.so
76ccb000-76ccc000 rw-p 00015000 b3:02 138610     /lib/arm-linux-gnueabihf/libpthread-2.19.so
76ccc000-76cce000 rw-p 00000000 00:00 0 
76cd0000-76cd2000 r-xp 00000000 b3:02 778291     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/encdb.so
76cd2000-76ce1000 ---p 00002000 b3:02 778291     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/encdb.so
76ce1000-76ce2000 rw-p 00001000 b3:02 778291     /usr/local/rvm/rubies/ruby-2.4.0/lib/ruby/2.4.0/armv7l-linux-eabihf/enc/encdb.so
76ce2000-76f6a000 r-xp 00000000 b3:02 269470     /usr/local/rvm/rubies/ruby-2.4.0/lib/libruby.so.2.4.0
76f6a000-76f79000 ---p 00288000 b3:02 269470     /usr/local/rvm/rubies/ruby-2.4.0/lib/libruby.so.2.4.0
76f79000-76f7e000 rw-p 00287000 b3:02 269470     /usr/local/rvm/rubies/ruby-2.4.0/lib/libruby.so.2.4.0
76f7e000-76f84000 rw-p 00000000 00:00 0 
76f84000-76f89000 r-xp 00000000 b3:02 25886      /usr/lib/arm-linux-gnueabihf/libarmmem.so
76f89000-76f98000 ---p 00005000 b3:02 25886      /usr/lib/arm-linux-gnueabihf/libarmmem.so
76f98000-76f99000 rw-p 00004000 b3:02 25886      /usr/lib/arm-linux-gnueabihf/libarmmem.so
76f99000-76fb9000 r-xp 00000000 b3:02 138588     /lib/arm-linux-gnueabihf/ld-2.19.so
76fbd000-76fbe000 rw-p 00000000 00:00 0 
76fbe000-76fbf000 r-xp 00000000 00:00 0 
76fbf000-76fc0000 ---p 00000000 00:00 0 
76fc0000-76fc3000 rwxp 00000000 00:00 0 
76fc3000-76fc8000 rw-p 00000000 00:00 0 
76fc8000-76fc9000 r--p 0001f000 b3:02 138588     /lib/arm-linux-gnueabihf/ld-2.19.so
76fc9000-76fca000 rw-p 00020000 b3:02 138588     /lib/arm-linux-gnueabihf/ld-2.19.so
7e1f4000-7e9f3000 rwxp 00000000 00:00 0          [stack]
7ef6d000-7ef6e000 r-xp 00000000 00:00 0          [sigpage]
7ef6e000-7ef6f000 r--p 00000000 00:00 0          [vvar]
7ef6f000-7ef70000 r-xp 00000000 00:00 0          [vdso]
ffff0000-ffff1000 r-xp 00000000 00:00 0          [vectors]

I investigated and found that the @@context pointer is populated and returned in the unless block within the self.context method the first time it is invoked, but the second time self.context is invoked, nothing is returned, and the resulting NFC.context would be a null pointer, causing the error above.

This PR is to add one line in self.context to return @@context regardless of whether it has just been assigned or it has been assigned previously.

Versions:
Ruby: ruby 2.4.0p0 (2016-12-24 revision 57164) [armv7l-linux-eabihf] (I am running this in a Raspberry Pi 3 Model B)
LibFreeFare: libfreefare-0.4.0 (compiled from source)
Libnfc: libnfc-1.7.1 (compiled from source)

[choongyong]

Thanks!

…

On 1 Jul 2017, 02:17 +0800, Maxim Chechel ***@***.***>, wrote: Merged #4. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.