feat(backend): implement download queue and resolve legacy parity gaps

- Add SSRF protection and migrate sensitive credentials to tempfiles
- Refactor aria2c process management to use ephemeral JSON-RPC
- Implement sysinfo recursive process termination for graceful stopping
- Add DownloadManager and MPSC queue for strict concurrency limits
- Configure yt-dlp to delegate download chunking to aria2c

apps/desktop/src-tauri/Cargo.lock

@@ -3909,6 +3909,7 @@ dependencies = [
  "tauri-plugin-notification",
  "tauri-plugin-opener",
  "tauri-plugin-single-instance",
+ "tempfile",
  "tokio",
 ]
 

apps/desktop/src-tauri/Cargo.toml

@@ -25,7 +25,7 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 tokio = { version = "1", features = ["process", "io-util", "rt", "macros"] }
 regex = "1.10"
-reqwest = "0.12"
+reqwest = { version = "0.12", features = ["json"] }
 tauri-plugin-notification = "2.3.3"
 sysinfo = "0.39.3"
 keyring = "3"
@@ -33,3 +33,4 @@ hmac = "0.12"
 sha2 = "0.10"
 tauri-plugin-deep-link = "2"
 tauri-plugin-single-instance = { version = "2", features = ["deep-link"] }
+tempfile = "3"

apps/desktop/src-tauri/src/lib.rs

@@ -29,6 +29,26 @@ async fn fetch_metadata(url: String, user_agent: Option<String>, username: Optio
 
     let client = builder.build().map_err(|e| e.to_string())?;
 
+    if let Ok(parsed) = reqwest::Url::parse(&url) {
+        if let Some(host) = parsed.host_str() {
+            let port = parsed.port_or_known_default().unwrap_or(80);
+            if let Ok(addrs) = std::net::ToSocketAddrs::to_socket_addrs(&(host, port)) {
+                for addr in addrs {
+                    let ip = addr.ip();
+                    if ip.is_loopback() || ip.is_multicast() || ip.is_unspecified() {
+                        return Err("SSRF blocked: Private/local IP not allowed".to_string());
+                    }
+                    match ip {
+                        std::net::IpAddr::V4(ipv4) if ipv4.is_private() || ipv4.is_link_local() => {
+                            return Err("SSRF blocked: Private/local IP not allowed".to_string());
+                        }
+                        _ => {}
+                    }
+                }
+            }
+        }
+    }
+
     let mut head_req = client.head(&url);
     if let Some(ref user) = username {
         if !user.is_empty() {
@@ -114,16 +134,25 @@ async fn fetch_media_metadata(app_handle: tauri::AppHandle, url: String, cookie_
             cmd.arg("--cookies-from-browser").arg(&browser);
         }
     }
+    
+    let mut config_file = tempfile::Builder::new().prefix("ytdlp-").suffix(".conf").tempfile().map_err(|e| e.to_string())?;
+    let mut config_content = String::new();
     if let Some(user) = username {
         if !user.is_empty() {
-            cmd.arg("--username").arg(&user);
+            config_content.push_str(&format!("--username\n{}\n", user));
         }
     }
     if let Some(pass) = password {
         if !pass.is_empty() {
-            cmd.arg("--password").arg(&pass);
+            config_content.push_str(&format!("--password\n{}\n", pass));
         }
     }
+    use std::io::Write;
+    config_file.write_all(config_content.as_bytes()).map_err(|e| e.to_string())?;
+    let config_path = config_file.into_temp_path();
+    if !config_content.is_empty() {
+        cmd.arg("--config-locations").arg(&config_path);
+    }
 
     cmd.arg(&url);
 
@@ -347,10 +376,13 @@ use std::collections::HashMap;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex, RwLock};
 
-struct AppState {
-    tasks: Mutex<HashMap<String, u32>>,
-    extension_pairing_token: extension_server::SharedExtensionToken,
-    extension_frontend_ready: extension_server::SharedFrontendReady,
+mod queue;
+
+pub struct AppState {
+    pub tasks: Arc<Mutex<HashMap<String, u32>>>,
+    pub cmd_tx: tokio::sync::mpsc::UnboundedSender<queue::DownloadCommand>,
+    pub extension_pairing_token: extension_server::SharedExtensionToken,
+    pub extension_frontend_ready: extension_server::SharedFrontendReady,
 }
 
 #[derive(Clone, Serialize)]
@@ -372,9 +404,32 @@ fn collect_download_uris(url: &str, mirrors: Option<&str>) -> Vec<String> {
     uris
 }
 
+async fn rpc_call(port: u16, secret: &str, method: &str, params: serde_json::Value) -> Result<serde_json::Value, String> {
+    let url = format!("http://127.0.0.1:{}/jsonrpc", port);
+    let mut payload = serde_json::Map::new();
+    payload.insert("jsonrpc".to_string(), serde_json::json!("2.0"));
+    payload.insert("id".to_string(), serde_json::json!("1"));
+    payload.insert("method".to_string(), serde_json::json!(method));
+    
+    let mut p = vec![serde_json::json!(format!("token:{}", secret))];
+    if let serde_json::Value::Array(arr) = params {
+        p.extend(arr);
+    }
+    payload.insert("params".to_string(), serde_json::json!(p));
+
+    let client = reqwest::Client::new();
+    let res = client.post(&url)
+        .json(&payload)
+        .send()
+        .await
+        .map_err(|e| e.to_string())?;
+    
+    let json: serde_json::Value = res.json().await.map_err(|e| e.to_string())?;
+    Ok(json)
+}
+
 #[tauri::command]
 async fn start_download(
-    app_handle: tauri::AppHandle,
     state: tauri::State<'_, AppState>,
     id: String,
     url: String,
@@ -392,7 +447,38 @@ async fn start_download(
     max_tries: Option<i32>,
     proxy: Option<String>,
 ) -> Result<(), String> {
-    println!("start_download called for id: {}", id);
+    let task = queue::DownloadTask {
+        is_media: false,
+        id, url, destination, filename, connections, speed_limit, username, password, headers, checksum, cookies, mirrors, user_agent, max_tries, proxy,
+        format_selector: None, cookie_source: None,
+    };
+    state.cmd_tx.send(queue::DownloadCommand::Enqueue(task)).map_err(|e| e.to_string())?;
+    Ok(())
+}
+
+pub(crate) async fn start_download_internal(
+    app_handle: tauri::AppHandle,
+    tasks_map: Arc<Mutex<HashMap<String, u32>>>,
+    cmd_tx: tokio::sync::mpsc::UnboundedSender<queue::DownloadCommand>,
+    task: queue::DownloadTask,
+) -> Result<(), String> {
+    let id = task.id;
+    let url = task.url;
+    let destination = task.destination;
+    let filename = task.filename;
+    let connections = task.connections;
+    let speed_limit = task.speed_limit;
+    let username = task.username;
+    let password = task.password;
+    let headers = task.headers;
+    let checksum = task.checksum;
+    let cookies = task.cookies;
+    let mirrors = task.mirrors;
+    let user_agent = task.user_agent;
+    let max_tries = task.max_tries;
+    let proxy = task.proxy;
+
+    println!("start_download_internal called for id: {}", id);
     let resource_dir = app_handle.path().resource_dir().map_err(|e| e.to_string())?;
     let aria2c_path = resource_dir.join("binaries").join("aria2c");
 
@@ -414,11 +500,21 @@ async fn start_download(
         }
     }
 
+    let rpc_port = std::net::TcpListener::bind("127.0.0.1:0")
+        .and_then(|listener| listener.local_addr())
+        .map(|addr| addr.port())
+        .unwrap_or(6800);
+    let rpc_secret = format!("{:x}", std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).unwrap().as_nanos());
+
     let mut cmd = AsyncCommand::new(&aria2c_path);
-    cmd.arg("--enable-rpc=false")
+    cmd.arg("--enable-rpc=true")
+       .arg(format!("--rpc-listen-port={}", rpc_port))
+       .arg("--rpc-listen-all=false")
        .arg("--continue=true")
        .arg("--allow-overwrite=false")
        .arg("--summary-interval=1")
+       .arg("--console-log-level=warn")
+       .arg("--download-result=hide")
        .arg("--check-certificate=false")
        .arg(format!("--dir={}", resolved_dest.to_string_lossy()))
        .arg(format!("--out={}", filename));
@@ -432,21 +528,44 @@ async fn start_download(
             cmd.arg(format!("--max-overall-download-limit={}", limit));
         }
     }
+    
+    let mut config_file = tempfile::Builder::new().prefix("aria2-").suffix(".conf").tempfile().map_err(|e| e.to_string())?;
+    let mut config_content = String::new();
     if let Some(user) = username {
         if !user.is_empty() {
-            cmd.arg(format!("--http-user={}", user));
-            cmd.arg(format!("--ftp-user={}", user));
+            config_content.push_str(&format!("http-user={}\nftp-user={}\n", user, user));
         }
     }
     if let Some(pass) = password {
         if !pass.is_empty() {
-            cmd.arg(format!("--http-passwd={}", pass));
-            cmd.arg(format!("--ftp-passwd={}", pass));
+            config_content.push_str(&format!("http-passwd={}\nftp-passwd={}\n", pass, pass));
         }
     }
     if let Some(hdr) = headers {
-        if !hdr.is_empty() {
-            cmd.arg(format!("--header={}", hdr));
+        for header in hdr.lines().map(str::trim).filter(|h| !h.is_empty()) {
+            config_content.push_str(&format!("header={}\n", header));
+        }
+    }
+    if let Some(cks) = cookies {
+        if !cks.is_empty() {
+            config_content.push_str(&format!("header=Cookie: {}\n", cks));
+        }
+    }
+    if let Some(p) = proxy {
+        if !p.is_empty() {
+            config_content.push_str(&format!("all-proxy={}\n", p));
+        }
+    }
+    use std::io::Write;
+    config_file.write_all(config_content.as_bytes()).map_err(|e| e.to_string())?;
+    let config_path = config_file.into_temp_path();
+    if !config_content.is_empty() {
+        cmd.arg(format!("--conf-path={}", config_path.display()));
+    }
+
+    if let Some(ua) = user_agent {
+        if !ua.is_empty() {
+            cmd.arg(format!("--user-agent={}", ua));
         }
     }
     if let Some(chk) = checksum {
@@ -454,24 +573,9 @@ async fn start_download(
             cmd.arg(format!("--checksum={}", chk));
         }
     }
-    if let Some(cks) = cookies {
-        if !cks.is_empty() {
-            cmd.arg(format!("--header=Cookie: {}", cks));
-        }
-    }
-    if let Some(ua) = user_agent {
-        if !ua.is_empty() {
-            cmd.arg(format!("--user-agent={}", ua));
-        }
-    }
     if let Some(tries) = max_tries {
         cmd.arg(format!("--max-tries={}", tries));
     }
-    if let Some(p) = proxy {
-        if !p.is_empty() {
-            cmd.arg(format!("--all-proxy={}", p));
-        }
-    }
 
     for uri in collect_download_uris(&url, mirrors.as_deref()) {
         cmd.arg(uri);
@@ -485,64 +589,94 @@ async fn start_download(
     let mut child = cmd.spawn().map_err(|e| format!("Failed to spawn aria2c: {}", e))?;
 
     let pid = child.id().unwrap_or(0);
-    state.tasks.lock().unwrap().insert(id.clone(), pid);
+    tasks_map.lock().unwrap().insert(id.clone(), pid);
 
-    let stdout = child.stdout.take().unwrap();
     let app_handle_clone = app_handle.clone();
     let id_clone = id.clone();
+    let id_clone_tx = id.clone();
 
     tokio::spawn(async move {
-        let mut reader = BufReader::new(stdout).lines();
-        let percentage_re = Regex::new(r"\((\d+)%\)").unwrap();
-        let speed_re = Regex::new(r"DL:([^\s\]]+)").unwrap();
-        let eta_re = Regex::new(r"ETA:([^\s\]]+)").unwrap();
-
+        let _keep_alive = config_path; // Keep the temp file alive
+        
         loop {
-            tokio::select! {
-                line_result = reader.next_line() => {
-                    match line_result {
-                        Ok(Some(line)) => {
-                            if line.contains("DL:") {
-                                let fraction = percentage_re.captures(&line)
-                                    .and_then(|cap| cap.get(1))
-                                    .and_then(|m| m.as_str().parse::<f64>().ok())
-                                    .unwrap_or(0.0) / 100.0;
+            tokio::time::sleep(std::time::Duration::from_millis(1000)).await;
 
-                                let speed = speed_re.captures(&line)
-                                    .and_then(|cap| cap.get(1))
-                                    .map(|m| m.as_str().to_string())
-                                    .unwrap_or_else(|| "-".to_string());
+            if let Ok(Some(status)) = child.try_wait() {
+                if status.success() {
+                    let _ = app_handle_clone.emit("download-complete", id_clone.clone());
+                } else {
+                    let _ = app_handle_clone.emit("download-failed", id_clone.clone());
+                }
+                break;
+            }
 
-                                let eta = eta_re.captures(&line)
-                                    .and_then(|cap| cap.get(1))
-                                    .map(|m| m.as_str().to_string())
-                                    .unwrap_or_else(|| "-".to_string());
+            if let Ok(json) = rpc_call(rpc_port, &rpc_secret, "aria2.tellActive", serde_json::json!([["status", "completedLength", "totalLength", "downloadSpeed"]])).await {
+                if let Some(arr) = json.get("result").and_then(|r| r.as_array()) {
+                    if let Some(item) = arr.first() {
+                        let completed = item.get("completedLength").and_then(|v| v.as_str()).and_then(|s| s.parse::<f64>().ok()).unwrap_or(0.0);
+                        let total = item.get("totalLength").and_then(|v| v.as_str()).and_then(|s| s.parse::<f64>().ok()).unwrap_or(1.0);
+                        let speed_bytes = item.get("downloadSpeed").and_then(|v| v.as_str()).and_then(|s| s.parse::<f64>().ok()).unwrap_or(0.0);
+                        
+                        let fraction = if total > 0.0 { completed / total } else { 0.0 };
+                        let speed = if speed_bytes > 1024.0 * 1024.0 {
+                            format!("{:.1} MB/s", speed_bytes / (1024.0 * 1024.0))
+                        } else if speed_bytes > 1024.0 {
+                            format!("{:.1} KB/s", speed_bytes / 1024.0)
+                        } else {
+                            format!("{:.0} B/s", speed_bytes)
+                        };
 
-                                let _ = app_handle_clone.emit("download-progress", DownloadProgressEvent {
-                                    id: id_clone.clone(),
-                                    fraction,
-                                    speed,
-                                    eta,
-                                });
+                        let eta = if speed_bytes > 0.0 && total > completed {
+                            let seconds = (total - completed) / speed_bytes;
+                            if seconds > 3600.0 {
+                                format!("{:.0}h {:.0}m", seconds / 3600.0, (seconds % 3600.0) / 60.0)
+                            } else if seconds > 60.0 {
+                                format!("{:.0}m {:.0}s", seconds / 60.0, seconds % 60.0)
+                            } else {
+                                format!("{:.0}s", seconds)
                             }
-                        }
-                        _ => break, // EOF or error
+                        } else {
+                            "-".to_string()
+                        };
+
+                        let _ = app_handle_clone.emit("download-progress", DownloadProgressEvent {
+                            id: id_clone.clone(),
+                            fraction,
+                            speed,
+                            eta,
+                        });
+                        continue;
                     }
                 }
-                status = child.wait() => {
-                    println!("child exit status: {:?}", status);
-                    if let Ok(exit_status) = status {
-                        if exit_status.success() {
-                            let _ = app_handle_clone.emit("download-complete", id_clone.clone());
-                        } else {
-                            // If it exited with error, emit failed (7 means paused/aborted usually, but we emit failed anyway, UI can filter)
-                            let _ = app_handle_clone.emit("download-failed", id_clone.clone());
-                        }
+            }
+            
+            if let Ok(json) = rpc_call(rpc_port, &rpc_secret, "aria2.tellStopped", serde_json::json!([0, 10, ["status", "completedLength", "totalLength"]])).await {
+                if let Some(arr) = json.get("result").and_then(|r| r.as_array()) {
+                    if arr.iter().any(|item| item.get("status").and_then(|v| v.as_str()) == Some("complete")) {
+                        let _ = app_handle_clone.emit("download-complete", id_clone.clone());
+                        let _ = rpc_call(rpc_port, &rpc_secret, "aria2.shutdown", serde_json::json!([])).await;
+                        break;
+                    }
+                    if arr.iter().any(|item| item.get("status").and_then(|v| v.as_str()) == Some("error")) {
+                        // check if it actually completed length == total length
+                        if let Some(item) = arr.iter().find(|i| i.get("status").and_then(|v| v.as_str()) == Some("error")) {
+                            let comp = item.get("completedLength").and_then(|v| v.as_str()).and_then(|s| s.parse::<f64>().ok()).unwrap_or(0.0);
+                            let tot = item.get("totalLength").and_then(|v| v.as_str()).and_then(|s| s.parse::<f64>().ok()).unwrap_or(1.0);
+                            if comp > 0.0 && comp >= tot {
+                                let _ = app_handle_clone.emit("download-complete", id_clone.clone());
+                                let _ = rpc_call(rpc_port, &rpc_secret, "aria2.shutdown", serde_json::json!([])).await;
+                                break;
+                            }
+                        }
+                        
+                        let _ = app_handle_clone.emit("download-failed", id_clone.clone());
+                        let _ = rpc_call(rpc_port, &rpc_secret, "aria2.shutdown", serde_json::json!([])).await;
+                        break;
                     }
-                    break;
                 }
             }
         }
+        let _ = cmd_tx.send(queue::DownloadCommand::TaskFinished(id_clone_tx));
     });
 
     Ok(())
@@ -550,7 +684,6 @@ async fn start_download(
 
 #[tauri::command]
 async fn start_media_download(
-    app_handle: tauri::AppHandle,
     state: tauri::State<'_, AppState>,
     id: String,
     url: String,
@@ -562,7 +695,36 @@ async fn start_media_download(
     username: Option<String>,
     password: Option<String>,
     headers: Option<String>,
+    proxy: Option<String>,
 ) -> Result<(), String> {
+    let task = queue::DownloadTask {
+        is_media: true,
+        id, url, destination, filename, speed_limit, username, password, headers, proxy,
+        connections: None, checksum: None, cookies: None, mirrors: None, user_agent: None, max_tries: None,
+        format_selector, cookie_source,
+    };
+    state.cmd_tx.send(queue::DownloadCommand::Enqueue(task)).map_err(|e| e.to_string())?;
+    Ok(())
+}
+
+pub(crate) async fn start_media_download_internal(
+    app_handle: tauri::AppHandle,
+    tasks_map: Arc<Mutex<HashMap<String, u32>>>,
+    cmd_tx: tokio::sync::mpsc::UnboundedSender<queue::DownloadCommand>,
+    task: queue::DownloadTask,
+) -> Result<(), String> {
+    let id = task.id;
+    let url = task.url;
+    let destination = task.destination;
+    let filename = task.filename;
+    let format_selector = task.format_selector;
+    let cookie_source = task.cookie_source;
+    let speed_limit = task.speed_limit;
+    let username = task.username;
+    let password = task.password;
+    let headers = task.headers;
+    let proxy = task.proxy;
+
     println!("start_media_download called for id: {}", id);
     let resource_dir = app_handle.path().resource_dir().map_err(|e| e.to_string())?;
     let ytdlp_path = resource_dir.join("binaries").join("yt-dlp");
@@ -599,6 +761,9 @@ async fn start_media_download(
        .arg("--socket-timeout").arg("20")
        .arg("--retries").arg("3")
        .arg("--extractor-retries").arg("3")
+       .arg("--downloader").arg("aria2c")
+       .arg("--downloader-args").arg("aria2c:-x 16 -s 16 -k 1M")
+       .arg("--concurrent-fragments").arg("4")
        .arg("-o").arg(out_path.to_string_lossy().to_string());
 
     if let Some(limit) = speed_limit {
@@ -607,12 +772,42 @@ async fn start_media_download(
         }
     }
 
+    if let Some(p) = proxy {
+        if !p.is_empty() {
+            cmd.arg("--proxy").arg(p);
+        }
+    }
+
     if let Some(cs) = cookie_source {
         if !cs.is_empty() && cs != "none" {
             cmd.arg("--cookies-from-browser").arg(cs);
         }
     }
 
+    let mut config_file = tempfile::Builder::new().prefix("ytdlp-").suffix(".conf").tempfile().map_err(|e| e.to_string())?;
+    let mut config_content = String::new();
+    if let Some(user) = username {
+        if !user.is_empty() {
+            config_content.push_str(&format!("--username\n{}\n", user));
+        }
+    }
+    if let Some(pass) = password {
+        if !pass.is_empty() {
+            config_content.push_str(&format!("--password\n{}\n", pass));
+        }
+    }
+    if let Some(headers) = headers {
+        for header in headers.lines().map(str::trim).filter(|header| !header.is_empty()) {
+            config_content.push_str(&format!("--add-header\n{}\n", header));
+        }
+    }
+    use std::io::Write;
+    config_file.write_all(config_content.as_bytes()).map_err(|e| e.to_string())?;
+    let config_path = config_file.into_temp_path();
+    if !config_content.is_empty() {
+        cmd.arg("--config-locations").arg(&config_path);
+    }
+
     if let Some(format) = format_selector {
         cmd.arg("-f").arg(format);
         // If the filename implies an audio format, use it as audio output
@@ -634,33 +829,18 @@ async fn start_media_download(
         }
     }
 
-    if let Some(user) = username {
-        if !user.is_empty() {
-            cmd.arg("--username").arg(&user);
-        }
-    }
-    if let Some(pass) = password {
-        if !pass.is_empty() {
-            cmd.arg("--password").arg(&pass);
-        }
-    }
-    if let Some(headers) = headers {
-        for header in headers.lines().map(str::trim).filter(|header| !header.is_empty()) {
-            cmd.arg("--add-headers").arg(header);
-        }
-    }
-
     cmd.arg(&url);
     cmd.stdout(Stdio::piped());
     cmd.stderr(Stdio::piped()); // Also pipe stderr for better error reporting
 
     let mut child = cmd.spawn().map_err(|e| format!("Failed to spawn yt-dlp: {}", e))?;
     let pid = child.id().unwrap_or(0);
-    state.tasks.lock().unwrap().insert(id.clone(), pid);
+    tasks_map.lock().unwrap().insert(id.clone(), pid);
 
     let stdout = child.stdout.take().unwrap();
     let app_handle_clone = app_handle.clone();
     let id_clone = id.clone();
+    let id_clone_tx = id.clone();
 
     // yt-dlp parsing regex
     let pct_re = Regex::new(r"\[download\]\s+(\d+(?:\.\d+)?)%").unwrap();
@@ -668,6 +848,7 @@ async fn start_media_download(
     let eta_re = Regex::new(r"ETA\s+([^\s]+)").unwrap();
 
     tokio::spawn(async move {
+        let _keep_alive = config_path; // Keep the temp file alive
         let mut reader = BufReader::new(stdout).lines();
         let mut current_track: f64 = 0.0;
         let mut last_fraction: f64 = 0.0;
@@ -712,10 +893,12 @@ async fn start_media_download(
                     }
                 }
                 status = child.wait() => {
+                    println!("child exit status: {:?}", status);
                     if let Ok(exit_status) = status {
                         if exit_status.success() {
                             let _ = app_handle_clone.emit("download-complete", id_clone.clone());
                         } else {
+                            // If it exited with error, emit failed (7 means paused/aborted usually, but we emit failed anyway, UI can filter)
                             let _ = app_handle_clone.emit("download-failed", id_clone.clone());
                         }
                     }
@@ -723,6 +906,7 @@ async fn start_media_download(
                 }
             }
         }
+        let _ = cmd_tx.send(queue::DownloadCommand::TaskFinished(id_clone_tx));
     });
 
     Ok(())
@@ -733,21 +917,39 @@ async fn pause_download(state: tauri::State<'_, AppState>, id: String) -> Result
     println!("pause_download called for id: {}", id);
     if let Some(pid) = state.tasks.lock().unwrap().remove(&id) {
         if pid > 0 {
-            #[cfg(unix)]
-            {
-                let _ = std::process::Command::new("kill")
-                    .arg("-15") // SIGTERM
-                    .arg(pid.to_string())
-                    .status();
-                println!("Sent SIGTERM to pid: {}", pid);
+            use sysinfo::{System, Pid};
+            let mut sys = System::new_all();
+            sys.refresh_processes(sysinfo::ProcessesToUpdate::All, true);
+            
+            let parent_pid = Pid::from_u32(pid);
+            let mut to_kill = vec![parent_pid];
+            let mut idx = 0;
+            
+            while idx < to_kill.len() {
+                let current = to_kill[idx];
+                for (proc_pid, proc) in sys.processes() {
+                    if let Some(p) = proc.parent() {
+                        if p == current {
+                            to_kill.push(*proc_pid);
+                        }
+                    }
+                }
+                idx += 1;
             }
-            #[cfg(windows)]
-            {
-                let _ = std::process::Command::new("taskkill")
-                    .arg("/PID")
-                    .arg(pid.to_string())
-                    .status();
-                println!("Sent taskkill to pid: {}", pid);
+            
+            for p in to_kill.into_iter().rev() {
+                if let Some(proc) = sys.process(p) {
+                    #[cfg(unix)]
+                    {
+                        if proc.kill_with(sysinfo::Signal::Term).is_none() {
+                            proc.kill(); // Fallback to SIGKILL
+                        }
+                    }
+                    #[cfg(windows)]
+                    proc.kill();
+                    
+                    println!("Sent termination signal to pid: {}", p.as_u32());
+                }
             }
         }
     }
@@ -1099,6 +1301,7 @@ pub fn run() {
     let extension_frontend_ready = Arc::new(AtomicBool::new(false));
     let server_frontend_ready = extension_frontend_ready.clone();
 
+    let (cmd_tx, cmd_rx) = tokio::sync::mpsc::unbounded_channel();
     tauri::Builder::default()
         .plugin(tauri_plugin_single_instance::init(|app, _args, _cwd| {
             if let Some(window) = app.get_webview_window("main") {
@@ -1108,11 +1311,13 @@ pub fn run() {
         }))
         .plugin(tauri_plugin_deep_link::init())
         .manage(AppState {
-            tasks: Mutex::new(HashMap::new()),
+            tasks: Arc::new(Mutex::new(HashMap::new())),
+            cmd_tx,
             extension_pairing_token,
             extension_frontend_ready,
         })
         .setup(move |app| {
+            queue::setup_queue(app.handle().clone(), cmd_rx);
             match extension_server::start_server(
                 app.handle().clone(),
                 server_pairing_token.clone(),

apps/desktop/src-tauri/src/queue.rs

@@ -0,0 +1,70 @@
+use tokio::sync::mpsc;
+use tauri::Manager;
+
+#[derive(Clone)]
+pub struct DownloadTask {
+    pub is_media: bool,
+    pub id: String,
+    pub url: String,
+    pub destination: String,
+    pub filename: String,
+    pub connections: Option<i32>,
+    pub speed_limit: Option<String>,
+    pub username: Option<String>,
+    pub password: Option<String>,
+    pub headers: Option<String>,
+    pub checksum: Option<String>,
+    pub cookies: Option<String>,
+    pub mirrors: Option<String>,
+    pub user_agent: Option<String>,
+    pub max_tries: Option<i32>,
+    pub proxy: Option<String>,
+    pub format_selector: Option<String>,
+    pub cookie_source: Option<String>,
+}
+
+pub enum DownloadCommand {
+    Enqueue(DownloadTask),
+    SetLimit(usize),
+    TaskFinished(String), // id
+}
+
+pub fn setup_queue(app_handle: tauri::AppHandle, mut cmd_rx: mpsc::UnboundedReceiver<DownloadCommand>) {
+    tokio::spawn(async move {
+        let mut queue = std::collections::VecDeque::new();
+        let mut active_count = 0;
+        let mut limit = 3;
+
+        while let Some(cmd) = cmd_rx.recv().await {
+            match cmd {
+                DownloadCommand::Enqueue(task) => {
+                    queue.push_back(task);
+                }
+                DownloadCommand::SetLimit(l) => {
+                    limit = l;
+                }
+                DownloadCommand::TaskFinished(_) => {
+                    if active_count > 0 {
+                        active_count -= 1;
+                    }
+                }
+            }
+
+            while active_count < limit && !queue.is_empty() {
+                if let Some(task) = queue.pop_front() {
+                    active_count += 1;
+                    let ah = app_handle.clone();
+                    let state = ah.state::<crate::AppState>();
+                    let tx = state.cmd_tx.clone();
+                    let tasks_map = state.tasks.clone();
+                    
+                    if task.is_media {
+                        let _ = crate::start_media_download_internal(ah, tasks_map, tx, task).await;
+                    } else {
+                        let _ = crate::start_download_internal(ah, tasks_map, tx, task).await;
+                    }
+                }
+            }
+        }
+    });
+}