Gateways
The history behind HTTP extensions and interfaces was driven by people’s needs. When the desire to put more complicated resources on the Web emerged, it rapidly became clear that no single application could handle all imaginable resources.
To get around this problem, developers came up with the notion of a gateway that could serve as a sort of interpreter, abstracting a way to get at the resource. A gateway is the glue between resources and applications. An application can ask (through HTTP or some other defined interface) a gateway to handle the request, and the gateway can provide a response. The gateway can speak the query language to the database or generate the dynamic content, acting like a portal: a request goes in, and a response comes out.
Figure 8-1 depicts a kind of resource gateway. Here, the Joe’s Hardware server is acting as a gateway to database content—note that the client is simply asking for a resource through HTTP, and the Joe’s Hardware server is interfacing with a gateway to get at the resource.
Figure 8-1. Gateway magic
Some gateways automatically translate HTTP traffic to other protocols, so HTTP clients can interface with other applications without the clients needing to know other protocols (Figure 8-2).
Figure 8-2. Three web gateway examples
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