fix the filename identification when submitting an assignment

When we’re submitting a file using the LTI tool, in some situations,
we can face a tool that doesn't send the text field in the content item
payload. This field is used to infer the filename and extension of the
submission file.

As a fallback, we'll try to recover the filename from the URL.

closes INTEROP-6483
flag=none

test-plan
* Have an LTI tool installed (you can use lti-1.3-test-tool); You could
  use this  commit https://gerrit.instructure.com/c/lti-1.3-test-tool/+/257525
  to  facilitate the tests in case it was not submitted yet.
* Have a Course recorded;
* Have a Student enrolled in this Course;
* Have an Assignment with online submission recorded to this Course;
* As a Student, you should be able to access the Assignment to submit
  your homework. On the submission homework page, you should be able to
  find LTI tool (usually rendered in a tab);
* After launching the tool, you should be able to select File as the
  Content Item Type and fill the File URL field and submit;
* After submitting the Assignment, you should be able to access the
  Submission Details page, and validate if the specified file was properly
  created/recorded  (name and image);
* I used https://dummyimage.com to generate some images like:
  * https://dummyimage.com/300/09f/sample
  * https://dummyimage.com/300/09f/sample.png
  * https://dummyimage.com/300/09f
  * https://dummyimage.com/300
* You should check if when the LTI tool sends the File Name (text) field
  and everything works as expected;

Change-Id: Iae5f128492834f8efc8934de347cfa5d9944ac1b
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/257523
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Xander Moffatt <xmoffatt@instructure.com>
QA-Review: Xander Moffatt <xmoffatt@instructure.com>
Product-Review: Karl Lloyd <karl@instructure.com>

app/controllers/submissions_api_controller.rb

@@ -621,7 +621,8 @@ class SubmissionsApiController < ApplicationController
     @assignment = api_find(@context.assignments.active, params[:assignment_id])
     @user = get_user_considering_section(params[:user_id])
     if @assignment.allowed_extensions.any?
-      extension = infer_upload_filename(params).split('.').last&.downcase || File.mime_types[infer_upload_content_type(params)]
+      filename = infer_upload_filename(params)
+      extension = filename&.split('.')&.last&.downcase || File.mime_types[infer_upload_content_type(params)]
       reject!(t('unable to find extension')) unless extension
       reject!(t('filetype not allowed')) unless @assignment.allowed_extensions.include?(extension)
     end

lib/api/v1/attachment.rb

@@ -18,6 +18,8 @@
 # with this program. If not, see <http://www.gnu.org/licenses/>.
 #
 
+require 'uri'
+
 module Api::V1::Attachment
   include Api::V1::Json
   include Api::V1::Locked
@@ -172,8 +174,20 @@ module Api::V1::Attachment
     hash
   end
 
+  def infer_filename_from_url(url)
+    return url if url.blank?
+
+    uri = URI.parse(url)
+
+    File.basename(uri.path)
+  rescue URI::InvalidURIError
+    nil
+  end
+
   def infer_upload_filename(params)
-    params[:name] || params[:filename]
+    return nil unless params
+
+    params[:name] || params[:filename] || infer_filename_from_url(params[:url])
   end
 
   def infer_upload_content_type(params, default_mimetype = nil)

spec/apis/v1/submissions_api_spec.rb

@@ -4454,9 +4454,9 @@ describe 'Submissions API', type: :request do
           end
         end
 
-        it "returns upload_params" do
+        it "returns upload_params infering the filename from the URL" do
           upload_json = {
-            "filename" => nil,
+            "filename" => "test",
             "content_type" => nil,
             "target_url" => "http://example.com/test"
           }

spec/lib/api/v1/attachment_spec.rb

@@ -58,4 +58,64 @@ describe Api::V1::Attachment do
       expect(json.fetch('thumbnail_url')).to eq json.fetch('url')
     end
   end
+
+  describe '#infer_upload_filename' do
+    it { expect(infer_upload_filename(nil)).to be_nil }
+
+    it { expect(infer_upload_filename({})).to be_nil }
+
+    it 'return the name when it is given' do
+      params = { name: 'filename', filename: 'filename.jpg' }
+
+      expect(infer_upload_filename(params)).to eq 'filename'
+    end
+
+    it 'return the filename when it is given' do
+      params = { filename: 'filename.png' }
+
+      expect(infer_upload_filename(params)).to eq 'filename.png'
+    end
+
+    it 'return the filename inferred from the url when it is given' do
+      params = { url: 'http://www.example.com/foo/bar/filename.jpg' }
+
+      expect(infer_upload_filename(params)).to eq 'filename.jpg'
+    end
+  end
+
+  describe '#infer_filename_from_url' do
+    it { expect(infer_filename_from_url(nil)).to be_nil }
+
+    it { expect(infer_filename_from_url('')).to be_empty }
+
+    it 'return the filename with extension when it is given' do
+      url = 'http://www.example.com/foo/bar/filename.jpeg?foo=bar&timestamp=123'
+
+      expect(infer_filename_from_url(url)).to eq 'filename.jpeg'
+    end
+
+    it 'return the last path when the URL does not have the filename in the path' do
+      url = 'http://www.example.com/foo'
+
+      expect(infer_filename_from_url(url)).to eq 'foo'
+
+      url = 'https://docs.google.com/spreadsheets/d/xpto/edit#gid=0'
+
+      expect(infer_filename_from_url(url)).to eq 'edit'
+
+      url = 'http://example.com/sites/download.xpto'
+
+      expect(infer_filename_from_url(url)).to eq 'download.xpto'
+
+      url = 'https://via.placeholder.com/150?text=thumbnail'
+
+      expect(infer_filename_from_url(url)).to eq '150'
+    end
+
+    it 'return empty when URL only have the domain' do
+      url = 'http://www.example.com'
+
+      expect(infer_filename_from_url(url)).to be_empty
+    end
+  end
 end