Can an LTI call pass the page it is called from?

[maguire]

I am interested in adding a call to an external LTI to announce a student's degree project registration. The idea is to add a button so that when the examiner approves the student's draft to move forward to an oral presentation that they could simply click on a button and then be prompted for the data and time of the presentation (and perhaps the language of the presentation - as we can have presentation in Swedish or English).

While I can add a course_navigation button (labeled "TestButtonLeft") to the left menu (as shown below) I cannot find any variables (including substitutions) that will tell me that the button was pushed for user_id 4 on the course page for People - although I can find in the parameters that are passed to the LTI tool the course_id.

If I cannot know which student it is, then it means that I have to make a list of all the students in this course for the examiner and then have the examiner select the student from the list. In contrast, it seems much simpler for the examiner to click on the student in the grade book (as shown below) and then get the page above and push the button to trigger the LTI tool.

There are lots of other settings where I would like to use this functionality. Note that only a teacher for the course should be able to see and push this button.

Is there something I am missing?

Is an alternative to modify the JavaScript for the page to include xAPI Bookmarklet and then use this to trigger the actions (or alternatively automatically append the user_id into a parameter of the URL for the button on the page)?

As an aside, the above shows one of the great advantages of having Canvas running in containers in a VM - as I can make completely fake users & classes and not upset any administrator.

[maguire]

If I manually modify the button (TestButtonLeft) to the following:

<li class="section"><a href="http://localhost:3597/announce" onclick="location.href=this.href+'?custom_loc='+window.location.href;return false;"
title="TestButtonLeft" class="context_external_tool_3" target="_blank" tabindex="0">TestButtonLeft</a></li>

Now if one clicks the button "TestButtonLeft" - it dispatches to my Sinatra server (running on the local host at the indicate port) via the GET route /announce

Where it outputs:

in route for /announce
custom_loc is http://canvas.docker/courses/5/users/5
request['custom_loc'] is http://canvas.docker/courses/5/users/5
request.path_info is /announce
request.path is /announce
params are {"custom_loc"=>"http://canvas.docker/courses/5/users/5"}

The route itself begins:

get '/announce' do
     puts("in route for /announce")
     custom_loc=params['custom_loc']
     puts("custom_loc is #{custom_loc}")
     @str1=request['custom_loc']
      puts("request['custom_loc'] is #{@str1}")
      path_info=request.path_info
      puts("request.path_info is #{path_info}")
      path=request.path
      puts("request.path is #{path}")

      puts "params are #{params}"

This appears to be an ugly hack and I do not know how to automate this, but that will be the next step - now that I have shown that it is possible to pass the current page's URL to the external server. It certainly would have been easier if the current page's URL was something that one could get as an LTI custom parameter. Perhaps this could be: com.instructure.page.url or something similar.

I would like to thanks the contributors to the discussion Deep linking LTI External Tool . Blixt's response in Passing Javascript variable to - Stack Overflow  as all of these helped me to understand the limitations of the LTI external tool interaction and how to use an onlick action and add the value of "window.location.href" to the key custom_loc.

[maguire · Accepted solution]

The solution to the above is to use a custom Javascript (add-url-to-button-push-for-lti.js) to append the current page's URL as a parameter to the URL used to invoke the LTI tool. This code and document (Adding_URL_to_call_to_external_tool.docx) can be found at https://github.com/gqmaguirejr/E-learning 

[maguire]

One could potentially add the onclick attribute in the code at ./app/helpers/section_tab_helper.rb

in the method:

def a_attributes
{ href: @tab.path,
   title: @tab.label,
   class: a_classes }.tap do |h|
       h[:target] = @tab.target if @tab.target?
    end
end

Alternatively, one needs to add a custom LTI parameter that would reveal the URL of the page where the button is when it was pressed.

[maguire]

Although it is possible to add custom_fields[field_name] to an external tool, the values are static - as can be seen in ./app/coffeescripts/models/ExternalTool.coffee where 

launchUrl: (launchType, options = {})->
    params = for key, value of options
    "#{key}=#{value}"
    url = "/#{@_contextPath()}/external_tools/#{@id}/resource_selection?launch_type=#{launchType}"
    url = "#{url}&#{params.join('&')}" if params.length > 0
    url

[maguire]

Having looked at the code a bit more, it would be interesting to pass the crumbs array to the LTI tool as a custom variable, then you know both which page you were on when you invoked the LTI tool and you also know how you got there.

At the moment the only things that the LTI variable expansion really has available to it (see lib/lti/variable_expander.rb) are @context, @root_account, @controller, and  @current_user (and sometimes @tool).