One of the main challenges in integrating wireless sensor networks with the Internet is the need of an intermediary mechanism for interconnecting two different protocols, i.e. Hypertext Transfer Protocol (HTTP) and Constrained Application Protocol (CoAP), allowing users to access the sensors over standard the Unified Resource Locator (URL). Such mechanism can be implemented using a cross-protocol reverse proxy. This paper focuses on the design, implementation, and evaluation of the HTTP-CoAP proxy prototype for wireless sensor and actuator networks with HTTP-CoAP mapping and a caching mechanism. The designed proxy was able to handle 25 requests per second in real-time. The proxy had a linear increment of latency with respect to the number of clients by the scale of 23.667. The caching mechanism in the proxy was proven to effectively reduce the latency with the effective value of 5 to 20 seconds of the maximum age of the data in the cache. The obtained data may be used for building Internet of Things systems for the given system requirements.