[4.0] Recreate EOS VM OC code cache if corrupt

[heifner]

On startup recreate the EOS VM OC code cache if it is corrupt. The code cache is strictly a cache and can be recreated at anytime. No reason to stop startup with an error if it is corrupt, simply remove it and start over.

Also when --replay-blockchain is specified remove the code cache as it is likely not going to be useful and better to start from a clean slate.

Resolves #1406

[spoonincode]

Was the code originally doing something else -- not immediately seeing the need for the while(true) & break here..

[heifner]

Before it would throw on dirty. Now it will attempt to re-create, but still throw if after the create it still hits an issue.

[spoonincode]

thoughts on need for a unit test?

[heifner]

thoughts on need for a unit test?

Not sure how to create a dirty code cache file in a test. I manually tested with a code cache file that is dirty. I guess we could check a dirty code cache file into the repo for a test like that. Thoughts?

[greg7mdp]

If you wanted to get rid of the while loop, you could do something like this which essentially the same thing, but maybe a little bit more straightforward to understand:

   code_cache_header cache_header;
   auto check_code_cache = [&]() {
      char header_buff[total_header_size];
      std::ifstream hs(_cache_file_path.generic_string(), std::ifstream::binary);
      hs.read(header_buff, sizeof(header_buff));
      EOS_ASSERT(!hs.fail(), bad_database_version_exception, "failed to read code cache header");
      memcpy((char*)&cache_header, header_buff + header_offset, sizeof(cache_header));
         
      EOS_ASSERT(cache_header.id == header_id, bad_database_version_exception, "existing EOS VM OC code cache not compatible with this version");
      EOS_ASSERT(!cache_header.dirty, database_exception, "code cache is dirty");
   };

      
   try {
      check_code_cache();
   } catch (const fc::exception&) {
      if (created_file)
            throw;

      ilog("EOS VM optimized Compiler code cache corrupt, recreating");
      create_code_cache_file();
      check_code_cache();
   }

[heifner]

Done.