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How can I pass a JavaScript variable from the view to Python in controller? I don't want to use request.vars or request.args, because that would allow to user to give arbitrary parameters for the action by typing it into the address bar.

Example view:

<button onclick='myFunction();'>Execute</button>
<script>
    function myFunction();{
        var value = calculateValue();
        //pass value to my_action
        window.location = 'my_action';
    }
</script>

Example controller:

def index():
    return dict()

def my_action():
    #retrieve passed variable
    #handle the variable 
    #...
    redirect(URL('index'))

How can I pass a JavaScript variable from the view to Python in controller? I don't want to use request.vars or request.args, because that would allow to user to give arbitrary parameters for the action by typing it into the address bar.

Example view:

<button onclick='myFunction();'>Execute</button>
<script>
    function myFunction();{
        var value = calculateValue();
        //pass value to my_action
        window.location = 'my_action';
    }
</script>

Example controller:

def index():
    return dict()

def my_action():
    #retrieve passed variable
    #handle the variable 
    #...
    redirect(URL('index'))

• javascript
• python
• web2py

Share Improve this question Follow asked Aug 20, 2015 at 0:11 DiMarzioDiMarzio 15311 silver badge1212 bronze badges 3

• look into args and vars. They are used to pass variable and arguments from URL to controller. – Gaurav Kalyan Commented Aug 20, 2015 at 12:28
• Yes, but as I said, it would allow the user to type something like this into address bar: .../default/my_action/50 to give my_action a parameter of 50. – DiMarzio Commented Aug 20, 2015 at 13:22
• the other way to do it would be creating a session via an ajax call then redirecting to your my_action page which read that session. – Gaurav Kalyan Commented Aug 20, 2015 at 13:26

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 6

You could make an Ajax call:

<script>
    function myFunction();{
        var value = calculateValue();
        ajax('{{=URL('default', 'my_action')}}' + '?value=' + value, [], ':eval');
    }
</script>

Followed by a client-side redirect once the Ajax response is returned:

def my_action():
    value = request.vars.value
    # handle the variable 
    redirect(URL('index'), client_side=True)

Note, however, that even with this method, someone could still make a manual request to /default/my_action?value=some_value to send arbitrary data to your function (of course, they would have to be a little more technically savvy to do so, as the above URL would never appear in the browser address bar for them to observe -- they would have to inspect your code or watch the network traffic to figure out what request to make).

In general, if you are calculating a value in the browser and then submitting it to the server via an HTTP request, there is no way to prevent a knowledgeable attacker from submitting some arbitrary data rather than the value calculated by your Javascript code. Your best bet is to instead focus on doing some server-side validation of the input data, or move the calculation to the server (though presumably the calculation is based on some input that must ultimately e from the browser and therefore be validated in some way).

How can I pass a JavaScript variable from the view to Python in controller? I don't want to use request.vars or request.args, because that would allow to user to give arbitrary parameters for the action by typing it into the address bar.

Example view:

<button onclick='myFunction();'>Execute</button>
<script>
    function myFunction();{
        var value = calculateValue();
        //pass value to my_action
        window.location = 'my_action';
    }
</script>

Example controller:

def index():
    return dict()

def my_action():
    #retrieve passed variable
    #handle the variable 
    #...
    redirect(URL('index'))

How can I pass a JavaScript variable from the view to Python in controller? I don't want to use request.vars or request.args, because that would allow to user to give arbitrary parameters for the action by typing it into the address bar.

Example view:

<button onclick='myFunction();'>Execute</button>
<script>
    function myFunction();{
        var value = calculateValue();
        //pass value to my_action
        window.location = 'my_action';
    }
</script>

Example controller:

def index():
    return dict()

def my_action():
    #retrieve passed variable
    #handle the variable 
    #...
    redirect(URL('index'))

• javascript
• python
• web2py

Share Improve this question Follow asked Aug 20, 2015 at 0:11 DiMarzioDiMarzio 15311 silver badge1212 bronze badges 3

• look into args and vars. They are used to pass variable and arguments from URL to controller. – Gaurav Kalyan Commented Aug 20, 2015 at 12:28
• Yes, but as I said, it would allow the user to type something like this into address bar: .../default/my_action/50 to give my_action a parameter of 50. – DiMarzio Commented Aug 20, 2015 at 13:22
• the other way to do it would be creating a session via an ajax call then redirecting to your my_action page which read that session. – Gaurav Kalyan Commented Aug 20, 2015 at 13:26

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 6

You could make an Ajax call:

<script>
    function myFunction();{
        var value = calculateValue();
        ajax('{{=URL('default', 'my_action')}}' + '?value=' + value, [], ':eval');
    }
</script>

Followed by a client-side redirect once the Ajax response is returned:

def my_action():
    value = request.vars.value
    # handle the variable 
    redirect(URL('index'), client_side=True)

Note, however, that even with this method, someone could still make a manual request to /default/my_action?value=some_value to send arbitrary data to your function (of course, they would have to be a little more technically savvy to do so, as the above URL would never appear in the browser address bar for them to observe -- they would have to inspect your code or watch the network traffic to figure out what request to make).

In general, if you are calculating a value in the browser and then submitting it to the server via an HTTP request, there is no way to prevent a knowledgeable attacker from submitting some arbitrary data rather than the value calculated by your Javascript code. Your best bet is to instead focus on doing some server-side validation of the input data, or move the calculation to the server (though presumably the calculation is based on some input that must ultimately e from the browser and therefore be validated in some way).

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