read_wrapper.rb in s3io-1.1.0

- old
+ new

@@ -2,10 +2,14 @@
 
   def self.reader(s3object, options = {}, &block)
     open(s3object, 'r', options, &block)
   end
 
+  # This error indicates that the object was modified between being opened
+  # and being read.
+  class ReadModifiedError < IOError; end
+
   class ReadWrapper < Wrapper
 
     # Default buffer size for line parser in bytes
     LINE_BUFFER_SIZE = 5 * 1024 * 1024 # MiB
 
@@ -18,10 +22,11 @@
       super(s3object)
 
       @options = {
         :line_buffer_size => (options[:line_buffer_size] || LINE_BUFFER_SIZE)
       }
+      @last_modified = @s3object.last_modified
     end
 
     # Reads data from S3 object.
     #
     # @param [Integer] bytes number of bytes to read
@@ -34,10 +39,16 @@
 
       upper_bound = @pos + bytes - 1
       upper_bound = (content_length - 1) if upper_bound >= content_length
 
       data = @s3object.read :range => @pos..upper_bound
+
+      last_modified = @s3object.last_modified
+      unless last_modified == @last_modified
+        fail ReadModifiedError, "S3 object #{@s3object.key} was updated during read, last_modified=#{last_modified.to_s} (was #{@last_modified.to_s})"
+      end
+
       @pos = upper_bound + 1
 
       return data
     end
 
@@ -79,8 +90,7 @@
 
       return self
     end
     alias lines each
     alias each_line each
-
   end
 end