Allow empty string to OpenSSL::Cipher#update

[unasuke]

For some reasons, plaintext may be empty string.

ref https://www.rfc-editor.org/rfc/rfc9001.html#section-5.8

[rhenium]

This effectively reverts ruby trunk r9485 (2c1d99d) committed back in 2005. I couldn't find the referenced message [ruby-talk:161220] with a Google search, which may have described the reason for this.

[unasuke]

I found [ruby-talk:161220] from web archive.

• https://web.archive.org/web/20160517163055/http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/161220
  • https://web.archive.org/web/20160911191951/http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/161227
    • https://web.archive.org/web/20160912025957/http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/161237
      • https://web.archive.org/web/20160516234435/http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/161250

[rhenium]

That explains! From https://web.archive.org/web/20160517163055/http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/161220

encrypt('') # -> gives error "evp_enc.c(332): OpenSSL internal error,
assertion failed: inl > 0 \n Abort trap"

This appears to be the assertion removed in this OpenSSL commit: openssl/openssl@2e41577

[rhenium]

Merged, thanks!