What is a callback URL in relation to an API

Question

I ve been scouring the net  and can t seem to wrap my head around the idea of a callback URL  In my case I have a few callback URLs that I have to define myself  A popular one is a  default callback URL   What is this exactly  Can you give an example in plain english

User · Answer

A callback URL will be invoked by the API method you're calling after it's done. So if you call

POST /api.example.com/foo?callbackURL=http://my.server.com/bar

Then when /foo is finished, it sends a request to http://my.server.com/bar. The contents and method of that request are going to vary - check the documentation for the API you're accessing.

User · Answer

Think of it as a letter  Sometimes you get a letter  say asking you to fill in a form then return the form in a pre-addressed envelope which is in the original envelope that was housing the form   Once you have finished filling the form in  you put it in the provided return envelop and send it back   The callbackUrl is like that return envelope  You are basically saying I am sending you this data  Once you are done with it  I am on this callbackUrl waiting for your response  So the API will process the data you have sent then look at the callback to send you the response   This is useful because sometimes you may take ages to process some data and it makes no sense to have the caller wait for a response  For example  say your API allows users to send documents to it and virus scan them  Then you send a report after  The scan could take maybe 3minutes  The user cannot be waiting for 3minutes  So you acknowledge that you got the document and let the caller get on with other business while you do the scan then use the callbackUrl when done to tell them the result of the scan

User · Answer

If you use the callback URL  then the API can connect to the callback URL and send or receive some data  That means API can connect to you later  after API call    Example     YOU send data using request to API API sends data using second request to YOU   Exact definition should be in API documentation

User · Answer

Another use case could be something like OAuth  it s may not be called by the API directly  instead the callback URL will be called by the browser after completing the authencation with the identity provider    Normally after end user key in the username password  the identity service provider will trigger a browser redirect to your  callback  url with the temporary authroization code  e g    https   example com callback code AUTHORIZATION CODE   Then your application could use this authorization code to request a access token with the identity provider which has a much longer lifetime

User · Answer

It s a mechanism to invoke an API in an asynchrounous way  The sequence is the following    your app invokes the url  passing as parameter the callback url the api respond with a 20x http code  201 I guess  but refer to the api docs  the api works on your request for a certain amount of time the api invokes your app to give you the results  at the callback url address    So you can invoke the api and tell your user the request is  processing  or  acquired  for example  and then update the status when you receive the response from the api   Hope it makes sense  -G

User · Answer

I ll make this pretty simple for you  When a transaction is initiated  it goes under processing stage until it reaches the terminal stage  Once it reaches the terminal stage  the transaction status is posted by the payment gateway to the callback url which generally the merchants use as a reference to show the success failure page to the user  Hope this helps

[api] What is a callback URL in relation to an API?

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