Return response body chunks in specified encoding

MRI will return content read from the socket in the ASCII-8BIT (binary)
encoding, whereas JRuby will return it in the UTF-8 encoding. In
whichever encoding the body is retrieved, we want to force its encoding
to the one specified (charset response header if present, otherwise
binary). This is already the behaviour in Response#to_s, we just extend
it to Response#readpartial as well.

Fixes httprb#413

lib/http/response/body.rb

@@ -20,14 +20,15 @@ def initialize(stream, length: nil, encoding: Encoding::BINARY)
         @connection = stream.is_a?(Inflater) ? stream.connection : stream
         @streaming  = nil
         @contents   = nil
-        @encoding   = encoding
+        @encoding   = find_encoding(encoding)
         @length     = length || Float::INFINITY
       end
 
       # (see HTTP::Client#readpartial)
       def readpartial(*args)
         stream!
-        @stream.readpartial(*args)
+        chunk = @stream.readpartial(*args)
+        chunk.force_encoding(@encoding) if chunk
       end
 
       # Iterate over the body, allowing it to be enumerable
@@ -43,22 +44,15 @@ def to_s
 
         raise StateError, "body is being streamed" unless @streaming.nil?
 
-        # see issue 312
-        begin
-          encoding = Encoding.find @encoding
-        rescue ArgumentError
-          encoding = Encoding::BINARY
-        end
-
         begin
           @streaming  = false
-          @contents   = String.new("").force_encoding(encoding)
+          @contents   = String.new("").force_encoding(@encoding)
 
           length = @length
 
           while length > 0 && (chunk = @stream.readpartial)
             length -= chunk.bytesize
-            @contents << chunk.force_encoding(encoding)
+            @contents << chunk.force_encoding(@encoding)
           end
         rescue
           @contents = nil
@@ -79,6 +73,15 @@ def stream!
       def inspect
         "#<#{self.class}:#{object_id.to_s(16)} @streaming=#{!!@streaming}>"
       end
+
+      private
+
+      # Retrieve encoding by name. If encoding cannot be found, default to binary.
+      def find_encoding(encoding)
+        Encoding.find encoding
+      rescue ArgumentError
+        Encoding::BINARY
+      end
     end
   end
 end

spec/lib/http/response/body_spec.rb

@@ -37,6 +37,18 @@
         body.readpartial
       end
     end
+
+    it "returns content in specified encoding" do
+      body = described_class.new(connection)
+      expect(connection).to receive(:readpartial).
+        and_return(String.new("content").force_encoding(Encoding::UTF_8))
+      expect(body.readpartial.encoding).to eq Encoding::BINARY
+
+      body = described_class.new(connection, :encoding => Encoding::UTF_8)
+      expect(connection).to receive(:readpartial).
+        and_return(String.new("content").force_encoding(Encoding::BINARY))
+      expect(body.readpartial.encoding).to eq Encoding::UTF_8
+    end
   end
 
   context "when body is gzipped" do
@@ -58,7 +70,7 @@
       it "streams decoded body" do
         [
           "Hi, HTTP ",
-          String.new("here ☺").force_encoding("ASCII-8BIT"),
+          "here ☺",
           nil
         ].each do |part|
           expect(subject.readpartial).to eq(part)