check for ifc file conformity

modules/ifc_models/app/contracts/ifc_models/base_contract.rb

@@ -44,6 +44,7 @@ module IFCModels
       user_allowed_to_manage
       user_is_uploader
       ifc_attachment_existent
+      ifc_attachment_is_ifc
       uploader_is_ifc_attachment_author
 
       super
@@ -65,6 +66,20 @@ module IFCModels
       errors.add :base, :ifc_attachment_missing unless model.ifc_attachment
     end
 
+    def ifc_attachment_is_ifc
+      return unless model.ifc_attachment&.new_record?
+
+      firstline = File.open(model.ifc_attachment.file.file.path, &:readline)
+
+      begin
+        unless firstline.match?(/^ISO-10303-21;/)
+          errors.add :base, :invalid_ifc_file
+        end
+      rescue ArgumentError
+        errors.add :base, :invalid_ifc_file
+      end
+    end
+
     def uploader_is_ifc_attachment_author
       errors.add :uploader_id, :invalid if model.ifc_attachment && model.uploader != model.ifc_attachment.author
     end

modules/ifc_models/config/locales/en.yml

@@ -41,4 +41,5 @@ en:
         ifc_models/ifc_model:
           attributes:
             base:
-              ifc_attachment_missing: "No ifc file attached"
+              ifc_attachment_missing: "No ifc file attached."
+              invalid_ifc_file: "The provided file is not a valid IFC file."

modules/ifc_models/spec/contracts/ifc_models/shared_contract_examples.rb

@@ -106,6 +106,34 @@ shared_examples_for 'ifc model contract' do
     end
   end
 
+  context 'if the new ifc file is no valid ifc file' do
+    let(:ifc_file) { FileHelpers.mock_uploaded_file name: "model.ifc", content_type: 'application/binary', binary: true }
+    let(:ifc_attachment) do
+      User.execute_as current_user do
+        ifc_model.attach_files('first' => { 'file' => ifc_file, 'description' => 'ifc' })
+        ifc_model.attachments.last
+      end
+    end
+
+    it 'is invalid' do
+      expect_valid(false, base: %i(invalid_ifc_file))
+    end
+  end
+
+  context 'if the new ifc file is a valid ifc file' do
+    let(:ifc_file) do
+      FileHelpers.mock_uploaded_file name: "model.ifc", content_type: 'application/binary', binary: true, content: "ISO-10303-21;"
+    end
+    let(:ifc_attachment) do
+      User.execute_as current_user do
+        ifc_model.attach_files('first' => { 'file' => ifc_file, 'description' => 'ifc' })
+        ifc_model.attachments.last
+      end
+    end
+
+    it_behaves_like 'is valid'
+  end
+
   context 'if user is not allowed to manage ifc models' do
     let(:permissions) { [] }