I am just getting started with SOAP web services and stumbled across WS-Addressing.
I have read the Wikipedia page, but I'm having a hard time understanding just what the point of WS-Addressing is.
According to Wikipedia and various sources on the web, WS-Addressing allows to put "addressing information" or "routing information" into the header of a SOAP request.
Why is this useful? If I send a request via HTTP (or even via SMTP or UDP), then the address I send to is the address of the server which will process my request, and the server can simply reply by the same channel. So why is addressing/routing information needed?
I'd be particularly interested in some real-world (more or less) example where WS-Addressing is helpful.
I've found WS-Addressing particularly useful in situations where the SOAP response can't be served immediately. Either the resources to form the response are not available right away or the result itself takes a long time to be generated.
That can happen when your business process involves "a human touch" for example (processes like the ones WS-HumanTask is targeting). You can stick web services in front of your business, but sometimes business takes time. It might be a subscription that must be manually verified, something to be approved, whatever, but it takes days to do it. Are you going to keep the connection opened all that time? Are you going to do nothing else than wait for the response? No! That is inefficient.
What you need is a notification process. The client makes a requests but does not wait for the response. It instead instructs the server where to send the response by use of a "reply to" address. Once the response is available, the server connects to that address and sends the response.
And voila... asynchronous interactions between web services, decoupling the lifetime of the communication process from the lifetime of the HTTP connection. Very useful...
But wait... HTTP connection? Why should I care about that? What if I want the response sent back on another type of protocol? (which SOAP kindly provides as it is not tied to any protocol).
With normal request/response flow, the response comes on the same channel as the request 'cose it's a connection you know.... So for example you have a HTTP connection... that means HTTP in and HTTP out.
But with WS-Addressing you are not tied to that. You can demand the response on another type of channel. Request comes on HTTP for example, but you can instruct the server to send the response back over SMTP, for example.
In this way WS-Addressing defines standard ways
to route a message over multiple transports. As the wiki page is saying:
instead of relying on network-level transport to convey routing information,
a message utilizing WS-Addressing may contain its own dispatch metadata in a standardized SOAP header.
and as for your observation:
and the server can simply reply by the same channel
... what works for some, might not work for others, and for others we have WS-Addressing :D.
Related
I will be happy to get advice from more experienced developers about adding Web Sockets into my HTTP-based project.
That’s the thing. I have developed the REST API based service. Everything works well enough, but… In some special cases my server needs a long time to serve client requests. It may be from 1 minute to several hours (and even days)! I implement some not-so-good algorithm to address this issue:
Client sends HTTP request
Server replies about registering request
Client starts sending HTTP requests to get necessary data (if response does not have needed information the client sends another request and so on)
That is all in a nutshell.
And it seems to be a bad scenario and I am trying to integrate web sockets for adding duplex-channels in this architecture. I hope that my API will be able to send info about updated data as soon as possible without the necessity of many requests from the client.
But I am a bit confused in choosing one of two ways to use web socket (WS).
Variant A.
The server only tells the client via WS that data is ready. And the client gets data by standard request-response HTTP method from REST API.
Variant B.
The server sends all data to the client via WS without HTTP at all.
What variant is more suitable? Or maybe some other variants?
I do not want to remove HTTP at all. I just try to implement WS for a particular kind of end-points.
Variant A would be more suitable and easy to implement. You can send message to the client after the data is ready, and he can then send request for the data. It will be like a simple chat websocket, and will serve your purpose.
For educational purposes I am trying to make a web api in c++. the web api needs to be able to listen for http requests(GET, POST etc.), when it receives a http request it needs to be able to send data back to the client. Because it is for educational purposes I would like to do it without unnecessary libraries. Now the first thing I need to do is make the api able to receive requests and respond on that, after some research on google I found out that winsock is probably the most basic way to setup sockets for windows but I could find very little on receiving http requests.
My question is: Is it possible with winsock to receive a http request from the browser, and send data back to the browser?.
My question is: Is it possible with winsock to receive a http request from the browser, and send data back to the browser?
Yes. ^^
It is, Because HTTP is a protocol that (usually) uses TCP as the underlying transportation protocol.
But trying to build a real HTTP layer on top of a simple win32 socket is a bit too much even for an experienced C++ developer.
Many un-experienced C++ developers would probably dismiss this task as a "well, you just need to read some data, parse the headers, assemble your own HTTP response and send it back".
but..
You will have to support
TLS, with all the nasty private keys/public keys implementation
Redirection
Chunked Transfer
G-Zip transfer
and the list goes on and on..
So practically speaking, if you just want to to accept a socket, read some data and send some basic HTTP response than yes. If you want a reliable, professional HTTP library - probably no.
You can check this page https://github.com/ReneNyffenegger/cpp-webserver to see simple winsock server implementation for HTTP. Web server implementation is not so difficult. Of course you should have time for it.
I have a tornado HTTP server.
How can I implement broad-cast message with the tornado server?
Is there any function for that or I just have to send normal HTTP message all clients looping.
I think if I send normal HTTP message, the server should wait for the response.
It seems not the concept of broad-cast.
Otherwise, I need another third-part option for broad-cast?
Please give me any suggestion to implement broad-cast message.
Short answer: you might be interested in WebSockets. Tornado seems to have support for this.
Longer answer: I assume you're referring to broadcast from the server to all the clients.
Unfortunately that's not doable conceptually in HTTP/1.1 because of the way it's thought out. The client asks something of the server, and the server responds, independently of all the others.
Furthermore, while there is no request going on between a client and a server, that relationship can be said to not exist at all. So if you were to broadcast, you'd be missing out on clients not currently communicating with the server.
Granted, things are not as simple. Many clients keep a long-lived TCP connection when talking to the server, and pipeline HTTP requests for it on that. Also, a single request is not atomic, and the response is sent in packets. People implemented server-push/long-polling before WebSockets or HTTP/2 with this approach, but there are better ways to go about this now.
There is no built-in idea of a broadcast message in Tornado. The websocket chat demo included with Tornado demonstrates how to loop over the list of clients sending a message to each:
def send_updates(cls, chat):
logging.info("sending message to %d waiters", len(cls.waiters))
for waiter in cls.waiters:
try:
waiter.write_message(chat)
except:
logging.error("Error sending message", exc_info=True)
See https://github.com/tornadoweb/tornado/blob/master/demos/websocket/chatdemo.py
The concept of Asynchronous Web Service is a web service where the client does not have to wait to receive a response from the server. in AJAX this is implemented by having a callback function to process the response. So the server indeed still sends the response to the client.
Is it possible to have an Asynchronous Web Service without response? Is there any platform that provide this?
Thank you.
I have done asynch web services in the past. They are very useful. YOu do not need a detailed response but you at least need an HTTP response, like 200 OK. If the client that makes the request provides some sort of ID or key for that request, then the client can use the same ID/key to later on query for the result/response of the request.
As far as frameworks that provide this, I do not know of any. In the past I would just have a shared memory store, like Memcache, to store the state and result of the request. As long as the state is shared across all nodes, any node can then process the call back request.
EDIT: Providing a key in the request can be done in either REST or SOAP environment. HTTP provides multiple places where a key can be communicated.
GET query param (REST)
HTTP header (SOAP/REST)
Added to the message body of a POST request. This can be done through two ways.
param in the message body (REST)
variable or attribute in serialized object (SOAP/REST))
Suppose that I have Apache/lighttpd or whatever to receive http requests. Now I want the web servers to act as a proxy for my web services running on internal servers written in Java/Clojure/Erlang?
What I want is to separate the layer that handles client connections and the server that handle application logic. These two should be separated and language independent. Is JSON or XML the format for communicating? If so, how do I perform it from the web servers?
Note: May be I missed the point of your question in this response. Pls do let me know if that is the case.
I dont think you should consider this as "forwarding" of the original request.
If your web-tier that receives the original request makes a call to one/more underlying services (thru HTTP or otherwise) it is part of the "processing" of the original request.
So, there is nothing different here than what you are already familiar with.
i.e You make a HTTP request in place where you would make a SOAP/XML request or a DB call or post a message.
When you say or think in terms of "forwarding", it is misleading.
Also, the data exchanged between your controller and services is solely based on your convenience.
It could be XML or JSON or regular POST parameters that gets sent over HTTP transport