API pagination, how to implement page token paging method? - php

Question

I am working on implementing an API interface for my project.
As i know, there are different forms to make pagination through the results, like the following:
https://example.com/api/purchaseorders?page=2&pagesize=25
But, i see many APIs like google use a different approach, in which they use a "pageToken" to let the user move between the pages of results, for example:
https://example.com/api/purchaseorders?pagesize=25&pageToken=ClkKHgoRc291cmNlX2NyZWF0ZWRfYXQSCQjA67Si5sr
So instead of page=2 they used pageToken=[token].
It is not clear for me the idea of pageToken and how to implement it.
It will be helpful if you guide me to any resources so i can get more knowledge.
Thank you.

Answer 1

Here's a very simple standalone example using the filesystem as a keyvalue store (since a filesystem will always be available).
$requestParameters = [];
if (($token = filter_input(INPUT_GET,"pageToken")) && is_readable("/tmp/$token")) {
$requestParameters = file_get_contents("/tmp/$token");
} else {
$requestParameters = [
"q" => filter_input(INPUT_GET,"q"),
"pageSize" => filter_input(INPUT_GET,"pageSize",FILTER_VALIDATE_INT),
"page" => filter_input(INPUT_GET,"page",FILTER_VALIDATE_INT)
];
}
$nextPageRequestParameters = $requestParameters;
$nextPageRequestParameters["page"]++;
$nextPageToken = md5(serialize($nextPageRequestParameters)); //This is not ideal but at least people can't guess it easily.
file_put_contents("/tmp/$nextPageToken", serialize($nextPageRequestParameters));
//Do request using $requestParameters
$result = [ "nextPageToken" => $nextPageToken, "data" => $resultData ];
echo json_encode($result);