Fix issue #8 - 'Bug when getting a value over 8K in length'

spec/redis_spec.cr

@@ -1104,4 +1104,15 @@ describe Redis do
       callbacks_received.should eq(["psubscribe", "pmessage", "punsubscribe"])
     end
   end
+
+  describe "large values" do
+    redis = Redis.new
+
+    it "sends and receives a large value correctly" do
+      redis.del("foo")
+      large_value = "0123456789" * 100_000 # 1 MB
+      redis.set("foo", large_value)
+      redis.get("foo").should eq(large_value)
+    end
+  end
 end

src/redis/connection.cr

@@ -87,9 +87,10 @@ class Redis::Connection
       # The "Null bulk string" aka nil
       return nil if length == -1
 
-      slice = Slice(UInt8).new(length)
-      @socket.read(slice)
-      bulk_string = String.new(slice)
+      bulk_string = String.new(length) do |buffer|
+        @socket.read_fully(Slice.new(buffer, length))
+        {length, 0}
+      end
       # Ignore CR/LF
       @socket.skip(2)
       bulk_string