19.11 Proxy CacheProxy caches save resources in local storage so that requests can be satisfied locally. The cache can be in memory or on disk.Starting with the proxymonitor of Section 19.10, write a program called proxycache that stores all the resources from the remote hosts on disk. Each unique resource must be stored in a unique file. One way to do this is to use sequential file names like cache00001, cache00002, etc., and keep a list containing host name, resource name and filename. Most proxy implementations use some type of hashing or digest mechanism to efficiently represent and search the contents of the cache for a particular resource.Start by just storing the resources without modifying the communication. If the same resource is requested again, update the stored value rather than create a new entry. Keep track of the number of hits on each resource.The child processes must coordinate their access to the list of resources, and they must coordinate the generation of unique file names. Consider using threads, shared memory or message passing to implement the coordination.Once you have the coordination working, implement the code to satisfy requests for cached items locally. Keep track of the total number of bytes transferred from client to proxy, proxy to server, server to proxy and proxy to client. Now the last two of these should be different. Remember that when you are testing with a browser, the browser also does caching, so some requests will not even go to the proxy server. Either turn off the browser's caching or force a remote access in the browser (usually by holding down the SHIFT key and pressing reload or refresh).Real proxy caches need to contend with a number of issues.
How many of the above issues can you resolve in your implementation? What else could be added to this list? |
لطفا منتظر باشید ...
