Monkey patch to Sequel (http://github.com/jeremyevans/sequel) that allows it to optionally open a SQLite database in readonly mode

sequel_sqlite_readonly.rb

# coding: utf-8

require 'sequel/adapters/sqlite'

# monkey patch to optionally open database in read-only mode
class ::Sequel::SQLite::Database

  # [Copied] from sequel-4.5.0/lib/sequel/adapters/sqlite.rb
  def connect(server)
    opts = server_opts(server)
    opts[:database] = ':memory:' if blank_object?(opts[:database])
    db = ::SQLite3::Database.new(opts[:database], readonly: opts[:readonly]) # [Changed]
    db.busy_timeout(opts.fetch(:timeout, 5000))

    connection_pragmas.each{|s| log_yield(s){db.execute_batch(s)}}

    class << db
      attr_reader :prepared_statements
    end
    db.instance_variable_set(:@prepared_statements, {})

    db
  end

end

Obsolete for Sequel 4.12.0 and onwards.
jeremyevans/sequel#832