How to send back the current uri except with a different pagination query parameter?

I am using Axum as my rust web server. Users can make get requests and supply a page number for pagination purposes.

I am trying to figure out what the correct and efficient approach is to return back the "current" uri except with next page number.

For example, users can first retrieve:

http://localhost:8080/posts?sort=top&time=24h

In my response json, I need to return same uri but with next page number:

/posts?sort=top&time=24h&page=2

/posts?sort=top&time=24h&page=3

and so on.

I am able to retrieve the uri using request.uri() in my handler. But what's the most efficient way for me to return the same uri but only a single query parameter being different?

Solution

The most straightforward way would be to have a struct that represents the parsed query string and that implements Deserialize and Serialize. Doing it this way has several advantages:

You can just serialize it back into a query string after adjusting the page number.
You can extract the parsed query string using Query instead of manually parsing it.
Unknown garbage in the query string is stripped out.

For example:

#[derive(Deserialize, Serialize)]
#[serde(rename_all = "lowercase")]
enum Sort {
    Top,
    Bottom,
}

#[derive(Deserialize, Serialize)]
struct PostsQuery {
    pub sort: Sort,
    pub time: String, // Or some other type that represents the parsed state?
    pub page: usize,
}

Now you can extract Query<PostsQuery>.

To serialize it back to a query string, you can use the serde_urlencoded crate, which is what Query uses to deserialize the query string.

async fn handler(Query(mut query): Query<PostsQuery>) {
    query.page += 1;
    let query_string = serde_urlencoded::to_string(&query);
    // Now use query_string in construction of the URL.
}