carrierwave: when migrating, create an empty blob if file is missing

app/services/carrierwave_active_storage_migration_service.rb

@@ -79,7 +79,7 @@ class CarrierwaveActiveStorageMigrationService
 
     ActiveStorage::Blob.create(
       filename: filename || uploader.filename,
-      content_type: uploader.content_type,
+      content_type: content_type,
       byte_size: uploader.size,
       checksum: checksum(uploader),
       created_at: created_at,
@@ -87,6 +87,20 @@ class CarrierwaveActiveStorageMigrationService
     )
   end
 
+  def make_empty_blob(uploader, created_at, filename: nil)
+    content_type = uploader.content_type || 'text/plain'
+
+    blob = ActiveStorage::Blob.build_after_upload(
+      io: StringIO.new('File not found when migrating from CarrierWave.'),
+      filename: filename || uploader.filename,
+      content_type: content_type || 'text/plain',
+      metadata: { virus_scan_result: ActiveStorage::VirusScanner::SAFE }
+    )
+    blob.created_at = created_at
+    blob.save!
+    blob
+  end
+
   def checksum(uploader)
     hex_to_base64(uploader.file.send(:file).etag)
   end

app/services/piece_justificative_to_champ_piece_jointe_migration_service.rb

@@ -75,6 +75,8 @@ class PieceJustificativeToChampPieceJointeMigrationService
   end
 
   def convert_pj_to_champ!(pj, champ)
+    actual_file_exists = pj.content.file.send(:file)
+    if actual_file_exists
       blob = make_blob(pj)
 
       # Upload the file before creating the attachment to make sure MIME type
@@ -82,6 +84,10 @@ class PieceJustificativeToChampPieceJointeMigrationService
       storage_service.copy_from_carrierwave_to_active_storage!(pj.content.path, blob)
       attachment = storage_service.make_attachment(champ, 'piece_justificative_file', blob)
 
+    else
+      make_empty_blob(pj)
+    end
+
     # By reloading, we force ActiveStorage to look at the attachment again, and see
     # that one exists now. We do this so that, if we need to roll back and destroy the champ,
     # the blob, the attachment and the actual file on OpenStack also get deleted.
@@ -112,4 +118,8 @@ class PieceJustificativeToChampPieceJointeMigrationService
   def make_blob(pj)
     storage_service.make_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename)
   end
+
+  def make_empty_blob(pj)
+    storage_service.make_empty_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename)
+  end
 end

spec/services/carrierwave_active_storage_migration_service_spec.rb

@@ -8,7 +8,7 @@ describe CarrierwaveActiveStorageMigrationService do
   end
 
   describe '.make_blob' do
-    let(:pj) { create(:piece_justificative, :rib) }
+    let(:pj) { create(:piece_justificative, :rib, updated_at: Time.zone.local(2019, 01, 01, 12, 00)) }
     let(:identify) { false }
 
     before do
@@ -17,6 +17,8 @@ describe CarrierwaveActiveStorageMigrationService do
 
     subject(:blob) { service.make_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename, identify: identify) }
 
+    it { expect(blob.created_at).to eq pj.updated_at }
+
     it 'marks the blob as already scanned by the antivirus' do
       expect(blob.metadata[:virus_scan_result]).to eq(ActiveStorage::VirusScanner::SAFE)
     end
@@ -34,4 +36,37 @@ describe CarrierwaveActiveStorageMigrationService do
       end
     end
   end
+
+  describe '.make_empty_blob' do
+    let(:pj) { create(:piece_justificative, :rib, updated_at: Time.zone.local(2019, 01, 01, 12, 00)) }
+
+    before 'set the underlying stored file as missing' do
+      allow(pj.content.file).to receive(:file).and_return(nil)
+    end
+
+    subject(:blob) { service.make_empty_blob(pj.content, pj.updated_at.iso8601, filename: pj.original_filename) }
+
+    it { expect(blob.created_at).to eq pj.updated_at }
+
+    it 'marks the blob as already scanned by the antivirus' do
+      expect(blob.metadata[:virus_scan_result]).to eq(ActiveStorage::VirusScanner::SAFE)
+    end
+
+    it 'sets the blob MIME type from the file' do
+      expect(blob.identified).to be true
+      expect(blob.content_type).to eq 'application/pdf'
+    end
+
+    context 'when the file metadata are also missing' do
+      before do
+        allow(pj).to receive(:original_filename).and_return(nil)
+        allow(pj.content).to receive(:content_type).and_return(nil)
+      end
+
+      it 'fallbacks on default values' do
+        expect(blob.filename).to eq pj.content.filename
+        expect(blob.content_type).to eq 'text/plain'
+      end
+    end
+  end
 end