Features of http clients should support - 1. Caching Network access is incredibly expensive! The most important thing to realize that any type of web service is that network access is incredibly expensive. It takes an extraordinary long time to open a connection, send a request, and retrieve a response from a remote server.
Even on the fastest broadband connection, a latency can still be higher than we anticipated. A router misbehaves, a packet is dropped, an intermediate proxy is under attack, and so on. There is an entire class of devices called caching proxies whose only job is to sit between us and the rest of the world and minimize network access.
Our company or ISP almost certainly maintains caching proxies, even if we're not aware of them. They work because caching is built into the http protocol. Chrome we can get header http header info: We can use Cache-Control: This way we avoid unneeded further requests if browser already has the component in its cache and therefore primed-cache page views will be performed faster.
The following example shows the response to the request of an image. That page includes an image. When our browser downloads that image, the server includes the following http headers: So, let's look at another site: The Cache-Control and Expires headers tell our browser and any caching proxies between us and the server that this image can be cached for up to 2 minutes from Sun, 20 Jan And if, within that period, we visit the page, our browser will load the page from its cache without generating any network activity whatsoever.
But let's suppose, we're trying to download an image and we have about a month before it expires. And our browser purges the image from our local cache for some reason. But the http headers said that this data could be cached by public caching proxies. Technically, the important thing is what the headers don't say; the Cache-Control header doesn't have the private keyword, so this data is cacheable by default.
Caching proxies are designed to have tons of storage space, probably far more than our local browser has allocated. If our ISP maintain a caching proxy, the proxy may still have the image cached.
When we visit the site again, our browser will look in its local cache for the image, but it won't find it, so it will make a network request to try to download it from the remote server.
But if the caching proxy still has a copy of the image, it will intercept that request and serve the image from its cache. That means that our request will never reach the remote server; in fact, it will never leave our ISP's network.
That makes for a faster download fewer network hops. On one side, servers need to send the correct headers in their response. On the other side, clients need to understand and respect those headers before they request the same data twice.
The proxies in the middle are not a panacea; they can only be as smart as the servers and clients allow them to be. Python's http libraries do not support caching, but httplib2 does.
Features of http clients should support - 2. Last modified checking Some data never changes, while other data changes all the time. In between, there is a vast field of data that might have changed, but hasn't.
In the latter case, I don't want to tell clients to cache my feed for weeks at a time, because then when I do actually post something, people may not read it for weeks because they're respecting my cache headers which said don't bother checking this feed for weeks.
On the other hand, I don't want clients downloading my entire feed once an hour if it hasn't changed! When we request data for the first time, the server can send back a Last-Modified header.Find helpful customer reviews and review ratings for Elements of Programming Interviews: The Insiders' Guide at caninariojana.com Read honest and unbiased product reviews from our users.
Designing a RESTful API with Python and Flask. Posted by Miguel Grinberg under Python, Programming, REST, Designing a simple web service. Let's say we want to write a To Do List application and we want to design a web service for it.
The first thing to do is to decide what is the root URL to access this service. MSDN Magazine Issues and Downloads. Read the magazine online, download a formatted digital version of each issue, or grab sample code and apps. Webservices written with soaplib are simple, lightweight, work well with other SOAP implementations, and can be deployed as WSGI applications.
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