Ruby-on-rails – Begin and Rescue block exception handling

exception handlingrubyruby-on-rails

I have little experience in rails exception handling. I have this snippet

def update
  @game = Game.find(params[:id])
  begin
    params[:game][:tier] = eval(params[:game][:tier]) 
  rescue 
    @game.errors.add(:tier, "Please make sure the correct format for tier, example [100, 1000, 10000]")
  end
#.... more code
end

In case params[:game][:tier] = "[100,200]" everything is perfect.
In case of error case of ruby syntax like params[:game][:tier] = "[100,200] abc" it catch the error however the application just crush.

How can I handle exception with 'eval()' such that it won't crush the app? Why begin and rescue does not work in this case? Appreciate any help for ruby enlightenment thanks 🙂

Best Answer

What if params[:game][:tier] was "[100,200]; system('rm -rf /')"?

Since the incoming data is expected to be an array, I would not use eval but JSON.parse instead:

> JSON.parse("[100,200]")
 => [100, 200]
> JSON.parse("[100,200] abc")
JSON::ParserError: 746: unexpected token at 'abc'...

Then rescue from only a JSON::ParserError exception

rescue JSON::ParserError => e

This will also solve the rescue not catching the exception problem you're having.

Related Solutions

Python – How to test that a Python function throws an exception

Use TestCase.assertRaises (or TestCase.failUnlessRaises) from the unittest module, for example:

import mymod

class MyTestCase(unittest.TestCase):
    def test1(self):
        self.assertRaises(SomeCoolException, mymod.myfunc)

C# – Why catch and rethrow an exception in C#

First; the way that the code in the article does it is evil. throw ex will reset the call stack in the exception to the point where this throw statement is; losing the information about where the exception actually was created.

Second, if you just catch and re-throw like that, I see no added value, the code example above would be just as good (or, given the throw ex bit, even better) without the try-catch.

However, there are cases where you might want to catch and rethrow an exception. Logging could be one of them:

try 
{
    // code that may throw exceptions    
}
catch(Exception ex) 
{
    // add error logging here
    throw;
}

Best Answer

Related Solutions

Python – How to test that a Python function throws an exception

C# – Why catch and rethrow an exception in C#

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