[BE] Replace once_cell with RwLock. Fix classroom empty users error

backend/Cargo.lock

@@ -131,7 +131,7 @@ dependencies = [
  "chrono",
  "dotenvy",
  "isahc",
- "once_cell",
+ "lazy_static",
  "reqwest",
  "rocket",
  "scraper",

backend/Cargo.toml

@@ -9,12 +9,12 @@ edition = "2021"
 reqwest = { version = "0.11", features = ["json", "cookies"] }
 rocket = { version = "=0.5.0-rc.3" , features = ["json", "msgpack", "uuid"] }
 sqlx = { version = "0.7.1", features = [ "runtime-tokio", "tls-rustls", "mysql", "macros", "chrono" ] }
-once_cell = "1.18.0"
 dotenvy = "0.15.7"
 serde = "1.0.188"
 chrono = "0.4.27"
 scraper = "0.17.1"
 isahc = { version = "1.7.2", features = ["cookies"] }
 urlencoding = "2.1.3"
+lazy_static = "1.4.0"
 
 

backend/src/online_classroom/session.rs

@@ -1,12 +1,21 @@
+use lazy_static::lazy_static;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 use isahc::{cookies::CookieJar, prelude::*, Request};
-use once_cell::sync::OnceCell;
+use std::sync::RwLock;
+
+struct CookieHold {
+    pub jar: CookieJar,
+}
+
+
+lazy_static! {
+    /// Stores a client with a persistent cookie store
+    static ref SESSION_COOKIE: RwLock<CookieHold> = RwLock::new(CookieHold { jar: CookieJar::new()});
+    /// Stores the last time a request was made, in seconds since UNIX epoch
+    static ref SESSION_TIME: RwLock<u64> = RwLock::new(0);
+}
 
-/// Stores a client with a persistent cookie store
-static SESSION_COOKIE: OnceCell<CookieJar> = OnceCell::new();
-/// Stores the last time a request was made, in seconds since UNIX epoch
-static SESSION_TIME: OnceCell<u64> = OnceCell::new();
 
 /// Makes a request to the online classroom, and returns the html string
 pub async fn request(url: String) -> Result<String, String> {
@@ -15,9 +24,7 @@ pub async fn request(url: String) -> Result<String, String> {
     ensure_session().await?;
 
     // Get the stored client
-    let jar = SESSION_COOKIE
-        .get()
-        .expect("SESSION_COOKIE was not set, even after calling ensure_session");
+    let jar = SESSION_COOKIE.read().unwrap().jar.clone();
 
     let uri = format!("{}{}", classroom_url, url);
 
@@ -41,10 +48,7 @@ pub async fn request(url: String) -> Result<String, String> {
 
 /// Makes sure that the session cookie is set, and that it is valid
 pub async fn ensure_session() -> Result<(), String> {
-    let last_usage_time = match SESSION_TIME.get() {
-        Some(time) => *time,
-        None => 0,
-    };
+    let last_usage_time = SESSION_TIME.read().unwrap().clone();
 
     // Get current time in seconds
     let current_time = SystemTime::now()
@@ -57,9 +61,9 @@ pub async fn ensure_session() -> Result<(), String> {
     // Default PHP session timeout is 1440 seconds. Use a 1400 seconds timeout to be safe
     if time_passed > 1400 {
         login().await?;
-        if let Err(err) = SESSION_TIME.set(current_time) {
-            return Err(format!("Error setting session time: {:?}", err));
-        }
+
+        let mut time_ptr = SESSION_TIME.write().unwrap();
+        *time_ptr = current_time;
     }
 
     Ok(())
@@ -86,10 +90,10 @@ async fn login() -> Result<(), String> {
         .send();
 
     match response {
-        Ok(_) => match SESSION_COOKIE.set(jar.clone()) {
-            Ok(_) => Ok(()),
-            Err(error) => Err(format!("Error saving client: {:?}", error)),
-        },
+        Ok(_) => {
+            SESSION_COOKIE.write().unwrap().jar = jar.clone();
+            Ok(())
+        }
         Err(error) => Err(format!("Error connecting to online classroom: {:?}", error)),
     }
 }

backend/src/online_classroom/users.rs

@@ -53,11 +53,19 @@ fn parse_users(file: &str) -> Result<Vec<ClassroomPerson>, String> {
 
     let fragment = Html::parse_document(file);
 
-    // TODO: If no users are found, the form is not rendered, and the html is different
-    //      Handle this case
     let form_element = match fragment.select(&form_selector).next() {
         Some(el) => el,
-        None => return Err("Error selecting form#form_users_id: not found".into()),
+        // If the form is not found, it may mean that no users were found
+        None => {
+            let Ok(secondary_button) = Selector::parse("#img_plus_and_minus") else {
+                return Err("Error parsing secondary button selector".into());
+            };
+
+            match fragment.select(&secondary_button).next() {
+                Some(_) => return Ok(Vec::new()),
+                None => return Err("Error parsing html: no form or empty form found.".into()),
+            }
+        }
     };
 
     let mut result_vec = Vec::new();