make sure we only do the work once

app/models/upload.rb

@@ -13,17 +13,18 @@ class Upload < ActiveRecord::Base
   validates_presence_of :original_filename
 
   def self.create_for(user_id, file)
-    # retrieve image info
-    image_info = FastImage.new(file.tempfile, raise_on_failure: true)
-    # compute image aspect ratio
-    width, height = ImageSizer.resize(*image_info.size)
     # compute the sha
     sha = Digest::SHA1.file(file.tempfile).hexdigest
     # check if the file has already been uploaded
     upload = Upload.where(sha: sha).first
+
     # otherwise, create it
     if upload.blank?
-
+      # retrieve image info
+      image_info = FastImage.new(file.tempfile, raise_on_failure: true)
+      # compute image aspect ratio
+      width, height = ImageSizer.resize(*image_info.size)
+      # create a db record (so we can use the id)
       upload = Upload.create!({
         user_id: user_id,
         original_filename: file.original_filename,
@@ -33,23 +34,20 @@ class Upload < ActiveRecord::Base
         height: height,
         url: ""
       })
-
       # make sure we're at the beginning of the file (FastImage is moving the pointer)
       file.rewind
-
       # store the file and update its url
-      upload.url = Upload.store_file(file, image_info, upload.id)
+      upload.url = Upload.store_file(file, sha, image_info, upload.id)
-
+      # save the url
       upload.save
-
     end
-
+    # return the uploaded file
     upload
   end
 
-  def self.store_file(file, image_info, upload_id)
+  def self.store_file(file, sha, image_info, upload_id)
-    return S3.store_file(file, image_info, upload_id)    if SiteSetting.enable_s3_uploads?
+    return S3.store_file(file, sha, image_info, upload_id)    if SiteSetting.enable_s3_uploads?
-    return LocalStore.store_file(file, image_info, upload_id)
+    return LocalStore.store_file(file, sha, image_info, upload_id)
   end
 
 end

lib/local_store.rb

@@ -1,6 +1,6 @@
 module LocalStore
 
-  def self.store_file(file, image_info, upload_id)
+  def self.store_file(file, sha, image_info, upload_id)
     clean_name = Digest::SHA1.hexdigest("#{Time.now.to_s}#{file.original_filename}")[0,16] + ".#{image_info.type}"
     url_root = "/uploads/#{RailsMultisite::ConnectionManagement.current_db}/#{upload_id}"
     path = "#{Rails.root}/public#{url_root}"
@@ -15,4 +15,4 @@ module LocalStore
     return Discourse::base_uri + "#{url_root}/#{clean_name}"
   end
 
-end
+end

lib/s3.rb

@@ -1,15 +1,13 @@
 module S3
 
-  def self.store_file(file, image_info, upload_id)
+  def self.store_file(file, sha, image_info, upload_id)
     raise Discourse::SiteSettingMissing.new("s3_upload_bucket")     if SiteSetting.s3_upload_bucket.blank?
     raise Discourse::SiteSettingMissing.new("s3_access_key_id")     if SiteSetting.s3_access_key_id.blank?
     raise Discourse::SiteSettingMissing.new("s3_secret_access_key") if SiteSetting.s3_secret_access_key.blank?
 
     @fog_loaded = require 'fog' unless @fog_loaded
 
-    blob = file.read
+    remote_filename = "#{upload_id}#{sha}.#{image_info.type}"
-    sha1 = Digest::SHA1.hexdigest(blob)
-    remote_filename = "#{upload_id}#{sha1}.#{image_info.type}"
 
     options = S3.generate_options
     directory = S3.get_or_create_directory(SiteSetting.s3_upload_bucket, options)

spec/components/local_store_spec.rb

@@ -21,8 +21,8 @@ describe LocalStore do
       File.stubs(:open)
       # The Time needs to be frozen as it is used to generate a clean & unique name
       Time.stubs(:now).returns(Time.utc(2013, 2, 17, 12, 0, 0, 0))
-      # 
+      #
-      LocalStore.store_file(file, image_info, 1).should == '/uploads/default/1/253dc8edf9d4ada1.png'
+      LocalStore.store_file(file, "", image_info, 1).should == '/uploads/default/1/253dc8edf9d4ada1.png'
     end
 
   end

spec/components/s3_spec.rb

@@ -16,7 +16,7 @@ describe S3 do
 
     let(:image_info) { FastImage.new(file) }
 
-    before(:each) do 
+    before(:each) do
       SiteSetting.stubs(:s3_upload_bucket).returns("s3_upload_bucket")
       SiteSetting.stubs(:s3_access_key_id).returns("s3_access_key_id")
       SiteSetting.stubs(:s3_secret_access_key).returns("s3_secret_access_key")
@@ -24,7 +24,7 @@ describe S3 do
     end
 
     it 'returns the url of the S3 upload if successful' do
-      S3.store_file(file, image_info, 1).should == '//s3_upload_bucket.s3.amazonaws.com/1e8b1353813a7d091231f9a27f03566f123463fc1.png'
+      S3.store_file(file, "SHA", image_info, 1).should == '//s3_upload_bucket.s3.amazonaws.com/1SHA.png'
     end
 
     after(:each) do

spec/models/upload_spec.rb

@@ -1,4 +1,5 @@
 require 'spec_helper'
+require 'digest/sha1'
 
 describe Upload do
 
@@ -31,6 +32,7 @@ describe Upload do
         upload.user_id.should == user_id
         upload.original_filename.should == logo.original_filename
         upload.filesize.should == File.size(logo.tempfile)
+        upload.sha.should == Digest::SHA1.file(logo.tempfile).hexdigest
         upload.width.should == 244
         upload.height.should == 66
         upload.url.should == url