问题
I know there are ways to fake it, polling (or long polling) but is there any way to have the server contact the browser to push out information?
Either polling option wastes resources on the server and depending on the server can lock it up (apache and iis for example).
Seems like a lot of sites are using long polling to fake a server-side push mechanism over http. Wouldn't it just be better to have a true push protocol built into a browser?
What options are there that are server friendly to push (fake or otherwise) information to web browsers?
回答1:
I know there are ways to fake it, polling (or long polling) but is there any way to have the server contact the browser to push out information?
The connection must be first established by the client to the server. There's no way of a server contacting a web client.
Either polling option wastes resources on the server and depending on the server can lock it up (apache and iis for example).
That's correct. Frequent polling is inefficient which is one of the reasons we are moving to a push world with persistent connections. WebSockets will be the best solution for this. I work for Pusher, a hosted realtime WebSocket solution, and we've seen a massive uptake in this technology driven by a community that believe it's the best solution to the resource and realtime communication problem.
Seems like a lot of sites are using long polling to fake a server-side push mechanism over http. Wouldn't it just be better to have a true push protocol built into a browser?
Yes, that's why we now have WebSockets. HTTP solutions to web browsers are ultimately a hack and don't work consistently (in the same way) between browsers.
What options are there that are server friendly to push (fake or otherwise) information to web browsers?
- HTTP Long-Polling: The connection is held open until the server has new information. Note: this is different to standard polling where requests for new information can be a complete wast of time.
- HTTP Streaming: This is probably the solution you are looking for (answering the HTTP question). Using this technique the connection is held open and new pieces of information can be pushed over that existing connection, from server to client, without the connection being closed and re-opened as it is with HTTP Long-Polling.
- HTTP/2 Server Push: Another standardised mechanism for pushing from server to client. These are known as "pushed responses" and the browser may cache these.
- WebSockets: Full bi-directional and full duplex communication over a single TCP connection within a web browser (or any web client).
Related information and resources:
- You can think Server-Sent Events (the EventSource API) as a standardisation of of HTTP Long-Polling and HTTP-Streaming.
- HTTP/2 Server Push
回答2:
Um, no.
Your browser doesn't listen for incoming connections.
Nor would you want it to be able to. We have enough exploits as it is.
回答3:
If you're using RIA technology like Adobe Flex, I believe the Flex version of a "server push" (AMF messaging) would meet your definition of a server push.
Of course you can also do the primitive ajax-y (hacky) polling method too, but there's no reason unless you're forced to.
回答4:
You don't need to "fake" anything. Flash has a really nice and well fleshed out Socket object that works brilliantly, and you can write a tiny little Flash app that talks out to the web page, so you don't have to do anything in Flash other than the communication with the server (if you would prefer to build the page in HTML). You'll need a server side socket listener, of course, but those are pretty easy to throw together as well. Lots of documentation on-line for how to implement the whole thing.... Here's the first example I found (didn't look it over too closely, but looks like it would work nicely). http://www.giantflyingsaucer.com/blog/?p=205
回答5:
I would think WebSockets (see http://en.m.wikipedia.org/wiki/WebSocket) is real push, so the answer would be: it depends upon the browser. If you need wide compatibility, the best you can do today is JavaScript libraries that will choose the best available protocol for the browser it's running in (e.g. https://github.com/ffdead/jquery-graceful-websocket). But you wanted server-friendly, and supporting multiple protocols is not server friendly. The current state-of-the-art is that doing cool stuff that works across browsers is engineering-intensive.
回答6:
As others stated it is impossible for server to contact client without client request (on regular HTTP).
But if you looking for clean solution for push notificatinons, then look at Server-Sent Events. It is regular HTTP and works seamless with most of the browsers which support HTTP 1.1.
SSE works only in a single direction (server -> client), which is the main mechanic for push notifications. For client-> server communication you can always use Ajax. I made a summarize of this in Which technology for realtime communication for a web app?
回答7:
May be technology has advanced from the time the question was asked ... I came across this one searching for something else.
WebPush is available in most of the browsers and there are several Push Notification providers that send information from the server to the browser. Other than few browsers like Safari, one can develop handlers which can be invoked when the notification arrives and perform some action on the client side browser.
来源：https://stackoverflow.com/questions/8110550/is-there-a-real-server-push-over-http