How might I avoid a global mutable variable in this code?

Question

The following code is meant to print There is page two. if it finds a certain div on this website:

use reqwest;
use select::document::Document;
use select::predicate::Name;
use std::io;

static mut DECIDE: bool = false;

fn page_two_filter(x: &str, url: &str) {
    if x == "pSiguiente('?pagina=2')" {
        unsafe {
            DECIDE = true;
        }
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("Give me the URL with the search results?");
    let mut url = String::new();
    io::stdin()
        .read_line(&mut url)
        .expect("Failed to read line");

    let url = url.trim();
    let html = reqwest::get(url).await?.text().await?;

    Document::from(html.as_str())
        .find(Name("div"))
        .filter_map(|n| n.attr("onclick"))
        .for_each(|x| page_two_filter(x, url));
    unsafe {
        if DECIDE == true {
            println!("There is page two.")
        }
    }
    Ok(())
}

Dependencies from Cargo.toml

[dependencies]
futures = "0.3.15"
reqwest = "0.11.9"
scraper = "0.12.0"
select = "0.5.0"
tokio = { version = "1", features = ["full"] }

Is there a safer way, i.e. without the unsafe blocks of code, of doing what that code does? Wanting to avoid global mutable variables, I've tried with redefining page_two_filter and an if statement with the result of the call to page_two_filter, like so:

fn page_two_filter(x: &str, url: &str) -> bool {
    if x == "pSiguiente('?pagina=2')" {
        return true;
    }
    false
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("Give me the URL with the search results?");
    let mut url = String::new();
    io::stdin()
        .read_line(&mut url)
        .expect("Failed to read line");

    let url = url.trim();
    let html = reqwest::get(url).await?.text().await?;
    if Document::from(html.as_str())
        .find(Name("div"))
        .filter_map(|n| n.attr("onclick"))
        .for_each(|x| page_two_filter(x, url))
    {
        println!("There is page two.")
    }
    Ok(())
}

but compiler does not allow me doing this saying:

mismatched types expected `()`, found `bool`

Answer 1

Instead of for_each(), I guess you need find().

This returns Some( found_element ) if found or None if not found.

You can then use the Option returned by find() with if let, match, is_some()...

    if let Some(_) = Document::from(html.as_str())
        .find(Name("div"))
        .filter_map(|n| n.attr("onclick"))
        .find(|x| page_two_filter(x, url))
    {
        println!("There is page two.")
    }

Answer 2

First of all, the

mismatched types expected (), found bool

error is because there is no semicolon after the println statement in the for_each closure.

Secondly, the filter is actually a one-liner, which could be integrated in that very closure

fn page_two_filter(x: &str, url: &str) -> bool {
  x == "pSiguiente('?pagina=2')"
}

Lastly, you already use various iterator methods, so why not continue?

async fn main() -> Result<(), Box<dyn std::error::Error>> {
 println!("Give me the URL with the search results?");  
 let mut url = String::new();
 io::stdin().read_line(&mut url).expect("Failed to read line");
 
 let url = url.trim();
 let html = reqwest::get(url).await?.text().await?;
 if let Some(_) = Document::from(html.as_str())
    .find(Name("div"))
    .filter_map(|n| n.attr("onclick"))
    .find_map(|attr| if attr == "pSiguiente('?pagina=2')" {
        Some(true)
    } else {
        None
    }) {
    
        println!("There is page two.");
    }

    Ok(())

}

Answer 3

You can use Iterator::any which returns true on first find of condition, false otherwise:

fn page_two_filter(x: &str, url: &str) -> bool {
    x == "pSiguiente('?pagina=2')"
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    println!("Give me the URL with the search results?");
    let mut url = String::new();
    io::stdin()
        .read_line(&mut url)
        .expect("Failed to read line");

    let url = url.trim();
    let html = reqwest::get(url).await?.text().await?;

    let found = Document::from(html.as_str())
        .find(Name("div"))
        .filter_map(|n| n.attr("onclick"))
        .any(|x| page_two_filter(x, url));

    if found {
        println!("There is page two.");
    }
}