Handle string reuse by body.each when buffering bodies in Rack::Response (#2044)

An alternative approach would be using a single string inside an array
and appending to that.  This approach is more backwards compatible,
but results in more memory usage.

Fixes #1957

2 files changed, 21 insertions, 0 deletions

diff --git a/lib/rack/response.rb b/lib/rack/response.rb
index 4a6af373..20a87159 100644
--- a/lib/rack/response.rb
+++ b/lib/rack/response.rb
@@ -342,6 +342,7 @@ module Rack
       end
 
       def append(chunk)
+        chunk = chunk.dup unless chunk.frozen?
         @body << chunk
 
         unless chunked?
diff --git a/test/spec_response.rb b/test/spec_response.rb
index 68227fa6..6a6957e5 100644
--- a/test/spec_response.rb
+++ b/test/spec_response.rb
@@ -604,6 +604,26 @@ describe Rack::Response do
     res.finish.last.must_equal ["Foo", "Bar"]
   end
 
+  it "handles string reuse in existing body when calling #write" do
+    body_class = Class.new do
+      def initialize(file)
+        @file = file
+      end
+
+      def each
+        buffer = String.new
+
+        while @file.read(5, buffer)
+          yield(buffer)
+        end
+      end
+    end
+    body = body_class.new(StringIO.new('Large large file content'))
+    res = Rack::Response.new(body)
+    res.write(" written")
+    res.finish.last.must_equal ["Large", " larg", "e fil", "e con", "tent", " written"]
+  end
+
   it "calls close on #body" do
     res = Rack::Response.new
     res.body = StringIO.new