Fix seg faults in SAJ parser

[stanhu]

Previously if add_big_*() were called, Ruby code would seg fault:

-- C level backtrace information -------------------------------------------
/opt/gitlab/embedded/lib/libruby.so.2.7(rb_vm_bugreport+0x561) [0x7ff955dd2da1] vm_dump.c:755
[0x7ff955bf5e61]
/opt/gitlab/embedded/lib/libruby.so.2.7(sigsegv+0x59) [0x7ff955d2eca9] signal.c:946
/lib/x86_64-linux-gnu/libc.so.6(0x7ff9559700c0) [0x7ff9559700c0]
/opt/gitlab/embedded/lib/libruby.so.2.7(rb_id_table_lookup+0x7) [0x7ff955d6e727] symbol.h:72
/opt/gitlab/embedded/lib/libruby.so.2.7(lookup_method_table+0x14) [0x7ff955da6a5c] vm_method.c:188
/opt/gitlab/embedded/lib/libruby.so.2.7(method_entry_get) vm_method.c:747
/opt/gitlab/embedded/lib/libruby.so.2.7(rb_callable_method_entry+0x20) [0x7ff955daea70] vm_method.c:891
/opt/gitlab/embedded/lib/libruby.so.2.7(rb_call0+0x145) [0x7ff955dc5115] vm_eval.c:654
/opt/gitlab/embedded/lib/libruby.so.2.7(rb_funcallv+0x38) [0x7ff955dc5c68] vm_eval.c:718
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/oj-3.13.18/lib/oj/oj.so(add_big_loc+0xac) [0x7ff9491815cc] saj2.c:300
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/oj-3.13.18/lib/oj/oj.so(calc_num+0xf0) [0x7ff949172e40] parser.c:531
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/oj-3.13.18/lib/oj/oj.so(parse+0x336) [0x7ff949174136] parser.c:713
/opt/gitlab/embedded/lib/ruby/gems/2.7.0/gems/oj-3.13.18/lib/oj/oj.so(parser_parse+0x9b) [0x7ff94917691b] parser.c:1344
[0x7ff955daaebd]

This appears to be happening due to improper pointer casting.

[stanhu]

I will look at writing a test later, though I don't fully understand yet when add_big_loc is called.

[ohler55]

Thanks for the fix. That code would be exercised with the new parser when a large number is encountered. Something like 20 digits or so. I'll wait to merge if you want to write a test.

[stanhu]

Yeah, that's what I thought. But in my test I'm not seeing the number yet. I'll keep digging.

Feel free to merge; I'll submit a follow-up pull request later.

[ohler55]

Okay but I'll wait to release.

[stanhu]

Ok, I confirmed that these entries in the JSON payload were causing this crash:

{
     "y": [
          -11.899999999999999,
          -10.2,
          -8.5,
          -6.800000000000001
     ]
}

Though I'm not sure why this isn't crashing at the moment:

diff --git a/test/test_saj.rb b/test/test_saj.rb
index 806b22e..ad250fe 100755
--- a/test/test_saj.rb
+++ b/test/test_saj.rb
@@ -12,7 +12,7 @@ $json = %{{
       "string": "message",
       "hash"  : {
         "h2"  : {
-          "a" : [ 1, 2, 3 ]
+          "a" : [ 1, 2, 3, -11.899999999999999 ]
         }
       }
     }
@@ -164,6 +164,7 @@ class SajTest < Minitest::Test
                   [:add_value, 1, nil],
                   [:add_value, 2, nil],
                   [:add_value, 3, nil],
+                  [:add_value, -11.899999999999999, nil],
                   [:array_end, 'a'],
                   [:hash_end, 'h2'],
                   [:hash_end, 'hash'],

[stanhu]

Ok, #800 should do the trick.