Is there anyway to view the actual content of a request sent between a client and service? Specifically I know the Server UUID and the Process ID and I would like to be able to view what requests the client makes corresponding to various client side actions.
I thought the two communicated via HTTP, but I've been trying to view this info using Wireshark and haven't found any relation between requests made on the client side and those caught by Wireshark.
Suggestions or reading material would be appreciated, I'm fairly new to this.
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I am a beginner in web and server side development and have just read about Ajax. It is used on client side to access any resource over the internet.
But I am thinking of some utility on the server side as ajax so that server is able to send request to the client and client responds to the request.
Do you people know how to achieve this? Basically what I want to achieve is that I have a server which sends the curent server time to the connected client each second.
Thank you!
This can be achieved with websockets.
In .NET we use SignalR to achieve what you need. Server sends a message and client replies to it. This is pubsub scenario.
https://hackernoon.com/create-your-own-pubsub-client-server-use-websocket-65dd1820e997
I have a Client that tell my server to contact another server and save the data there upon saving if successful I can receive a callback, how can I then tell the Client to refresh the page because this 2nd Server is also sending data to the Client, can I do it using headers?
There is no tranditional ways to push messages (refresh request and so on) to the webpage directly from the server.
Before giving some solutions, I'm sorry to say that your description to your question is quite ambiguous. server, another server, this 2nd Server is also sending data to the Client does not make much sense. You may reorganize your description to show the whole business logic better. Giving necessary code will be better.
So focusing on sending message from server to client within browser environment, there are several ways you could consider:
Ajax
You could use ajax to request the server at client side. You can poll the server at regular intervals, checking the response to determine whether the page should be refreshed.
Pro: widely supported, easy for both client side and server side
Con: polling is not a real-time solution and will make some redundant requests
Websocket
Pro: real-time bidirectional socket-like communication
Con: may be too heavy for the simple task you mentioned
Server push
Part of PWA specification
Pro: allow direct communication from server to client
Con: complexity, insufficient browser support
I have an API running on a server, which handle users connection and a messaging system.
Beside that, I launched a websocket on that same server, waiting for connections and stuff.
And let's say we can get access to this by an Android app.
I'm having troubles to figure out what I should do now, here are my thoughts:
1 - When a user connect to the app, the API connect to the websocket. We allow the Android app only to listen on this socket to get new messages. When the user want to answer, the Android app send a message to the API. The API writes itself the received message to the socket, which will be read back by the Android app used by another user.
This way, the API can store the message in database before writing it in the socket.
2- The API does not connect to the websocket in any way. The Android app listen and write to the websocket when needed, and should, when writing to the websocket, also send a request to the API so it can store the message in DB.
May be none of the above is correct, please let me know
EDIT
I already understood why I should use a websocket, seems like it's the best way to have this "real time" system (when getting a new message for example) instead of forcing the client to make an HTTP request every x seconds to check if there are new messages.
What I still don't understand, is how it is suppose to communicate with my database. Sorry if my example is not clear, but I'll try to keep going with it :
My messaging system need to store all messages in my API database, to have some kind of historic of the conversation.
But it seems like a websocket must be running separately from the API, I mean it's another program right? Because it's not for HTTP requests
So should the API also listen to this websocket to catch new messages and store them?
You really have not described what the requirements are for your application so it's hard for us to directly advise what your app should do. You really shouldn't start out your analysis by saying that you have a webSocket and you're trying to figure out what to do with it. Instead, lay out the requirements of your app and figure out what technology will best meet those requirements.
Since your requirements are not clear, I'll talk about what a webSocket is best used for and what more traditional http requests are best used for.
Here are some characteristics of a webSocket:
It's designed to be continuously connected over some longer duration of time (much longer than the duration of one exchange between client and server).
The connection is typically made from a client to a server.
Once the connection is established, then data can be sent in either direction from client to server or from server to client at any time. This is a huge difference from a typical http request where data can only be requested by the client - with an http request the server can not initiate the sending of data to the client.
A webSocket is not a request/response architecture by default. In fact to make it work like request/response requires building a layer on top of the webSocket protocol so you can tell which response goes with which request. http is natively request/response.
Because a webSocket is designed to be continuously connected (or at least connected for some duration of time), it works very well (and with lower overhead) for situations where there is frequent communication between the two endpoints. The connection is already established and data can just be sent without any connection establishment overhead. In addition, the overhead per message is typically smaller with a webSocket than with http.
So, here are a couple typical reasons why you might choose one over the other.
If you need to be able to send data from server to client without having the client regular poll for new data, then a webSocket is very well designed for that and http cannot do that.
If you are frequently sending lots of small bits of data (for example, a temperature probe sending the current temperature every 10 seconds), then a webSocket will incur less network and server overhead than initiating a new http request for every new piece of data.
If you don't have either of the above situations, then you may not have any real need for a webSocket and an http request/response model may just be simpler.
If you really need request/response where a specific response is tied to a specific request, then that is built into http and is not a built-in feature of webSockets.
You may also find these other posts useful:
What are the pitfalls of using Websockets in place of RESTful HTTP?
What's the difference between WebSocket and plain socket communication?
Push notification | is websocket mandatory?
How does WebSockets server architecture work?
Response to Your Edit
But it seems like a websocket must be running separately from the API,
I mean it's another program right? Because it's not for HTTP requests
The same process that supports your API can also be serving the webSocket connections. Thus, when you get incoming data on the webSocket, you can just write it directly to the database the same way the API would access the database. So, NO the webSocket server does not have to be a separate program or process.
So should the API also listen to this websocket to catch new messages
and store them?
No, I don't think so. Only one process can be listening to a set of incoming webSocket connections.
This questions was asked during one of the interview. How to transfer data from one server to another using AJAX? Is it really possible?
AJAX is generally used on the client side, not usually the server side.
It sends requests to a server.
You probably need to provide more information about what you are trying to achieve to get a decent answer.
If you are wanting to transfer data from a "client" to a server then you could send the data in a variety of ways - especially with AJAX. Just how depends on what data type and size. Requests from a client to server (HTTP) can include POST data, which can carry your data to the server.
If you are using AJAX on a client and wanting to use it to transfer data from one remote server to another then you could get AJAX on your client to call a script on the server that would instigate the transfer from the server to another server in some way. (such as FTP or SCP maybe - or even using a server to server HTTP POST)
If you can be a little more specific about what you need to do then I will try and give you a better answer.
I have an intranet based CRM application developed in CodeIgniter 2.1 where the application is running on a local Apache server and around 20 clients are accessing it over LAN. This is to be connected to a call center setup where the call center application (running on a separate server) will do a HTTP post with caller's number as well as terminal number of the agent where the call is arriving to a URL of my Codeigniter application. I am using this data to populate a database table of call records.
Now from the terminal number (each terminal has static IP, and a session in Codeigniter is linked to IP as well) I can find out which user (login session) of my application is about to receive the call. I want to find a way out how I can send data from server side (it will be regarding the call like the number who is calling, past call records etc.) to that specific user's browser via AJAX or something similar? The agent's browser needs to display this information sent from server.
Periodic polling from browser by jquery etc. is not possible as the data needs to be updated almost instantaneously and rapid polling up to this extent will lead to high CPU usage at client end as well as extra load on network.
P.S.: I only want to know how to modify the browser data from server end.
In AJAX, asynchronous request/response doesn't involve polling; there's just an open TCP connection and non-blocking I/O. The client makes a request but returns immediately; when the server sends the response, the client is notified. So you can achieve what you want with AJAX's XMLHttpRequest without polling[1]. All you need is a url from which to serve your notifications. You could have one request thread and a general dispatch method, or different urls and different threads for each, depending on how you needed to scale.
[1] Well, to be honest, with very little polling. You'd really need to establish what the session/global timeout was and reissue requests within that time limit.