Handle early responses

HTTP servers typically wait until the whole request body has been
received before sending the response. However, some servers might send
out a response early, before they've read the whole request body. For
example, they might detect the request headers were invalid, and they
want to tell that to the client immediately.

For example, sending a large request to http://google.com will return an
early `400 Bad Request` response. In this case HTTP.rb will raise an
Errno::EPIPE exception, because it tried to write to the socket but it
couldn't because the server closed its end. However, the server still
returned a valid response, so it's not really erroneous behaviour (e.g.
curl doesn't print any errors in the same situations).

  # Before
  HTTP.get("http://google.com", body: "a" * 1*1024*1024)
  #~> Errno::EPIPE

  # After
  HTTP.get("http://google.com", body: "a" * 1*1024*1024)
  #=> #<HTTP::Response 400 Bad Request ...>

This commit ignores Errno::EPIPE exceptions when writing request data to
the socket.

lib/http/request/writer.rb

@@ -100,6 +100,8 @@ def write(data)
           break unless data.bytesize > length
           data = data.byteslice(length..-1)
         end
+      rescue Errno::EPIPE
+        # server doesn't need any more data
       rescue IOError, SocketError, SystemCallError => ex
         raise ConnectionError, "error writing to socket: #{ex}", ex.backtrace
       end

spec/lib/http/request/writer_spec.rb

@@ -75,11 +75,21 @@
       end
     end
 
-    context "when writing to socket raises an exception" do
+    context "when server won't accept any more data" do
       before do
         expect(io).to receive(:write).and_raise(Errno::EPIPE)
       end
 
+      it "aborts silently" do
+        writer.stream
+      end
+    end
+
+    context "when writing to socket raises an exception" do
+      before do
+        expect(io).to receive(:write).and_raise(Errno::ECONNRESET)
+      end
+
       it "raises a ConnectionError" do
         expect { writer.stream }.to raise_error(HTTP::ConnectionError)
       end