1 files changed, 96 insertions, 0 deletions
diff --git a/app/models/blob_viewer/base.rb b/app/models/blob_viewer/base.rb
new file mode 100644
index 00000000000..f944b00c9d3
--- /dev/null
+++ b/app/models/blob_viewer/base.rb
@@ -0,0 +1,96 @@
+module BlobViewer
+  class Base
+    class_attribute :partial_name, :type, :extensions, :client_side, :binary, :switcher_icon, :switcher_title, :max_size, :absolute_max_size
+
+    delegate :partial_path, :rich?, :simple?, :client_side?, :server_side?, :text?, :binary?, to: :class
+
+    attr_reader :blob
+    attr_accessor :override_max_size
+
+    def initialize(blob)
+      @blob = blob
+    end
+
+    def self.partial_path
+      "projects/blob/viewers/#{partial_name}"
+    end
+
+    def self.rich?
+      type == :rich
+    end
+
+    def self.simple?
+      type == :simple
+    end
+
+    def self.client_side?
+      client_side
+    end
+
+    def self.server_side?
+      !client_side?
+    end
+
+    def self.binary?
+      binary
+    end
+
+    def self.text?
+      !binary?
+    end
+
+    def self.can_render?(blob)
+      !extensions || extensions.include?(blob.extension)
+    end
+
+    def too_large?
+      blob.raw_size > max_size
+    end
+
+    def absolutely_too_large?
+      blob.raw_size > absolute_max_size
+    end
+
+    def can_override_max_size?
+      too_large? && !absolutely_too_large?
+    end
+
+    # This method is used on the server side to check whether we can attempt to
+    # render the blob at all. Human-readable error messages are found in the
+    # `BlobHelper#blob_render_error_reason` helper.
+    #
+    # This method does not and should not load the entire blob contents into
+    # memory, and should not be overridden to do so in order to validate the
+    # format of the blob.
+    #
+    # Prefer to implement a client-side viewer, where the JS component loads the
+    # binary from `blob_raw_url` and does its own format validation and error
+    # rendering, especially for potentially large binary formats.
+    def render_error
+      return @render_error if defined?(@render_error)
+
+      @render_error =
+        if server_side_but_stored_in_lfs?
+          # Files stored in LFS can only be rendered using a client-side viewer,
+          # since we do not want to read large amounts of data into memory on the
+          # server side. Client-side viewers use JS and can fetch the file from
+          # `blob_raw_url` using AJAX.
+          :server_side_but_stored_in_lfs
+        elsif override_max_size ? absolutely_too_large? : too_large?
+          :too_large
+        end
+    end
+
+    def prepare!
+      if server_side? && blob.project
+        blob.load_all_data!(blob.project.repository)
+      end
+    end
+
+    private
+
+    def server_side_but_stored_in_lfs?
+      server_side? && blob.valid_lfs_pointer?
+    end
+  end
+end