downloader: Better download interface with errors

Author: cyberphantom52

src/downloader/handle.rs

@@ -25,6 +25,18 @@ impl DownloadHandle {
             cancel,
         }
     }
+
+    pub fn status(&self) -> Status {
+        *self.status.borrow()
+    }
+
+    pub async fn wait_for_status_update(&mut self) -> Result<(), watch::error::RecvError> {
+        self.status.changed().await
+    }
+
+    pub fn cancel(&self) {
+        self.cancel.cancel();
+    }
 }
 
 impl std::future::Future for DownloadHandle {
@@ -43,17 +55,3 @@ impl std::future::Future for DownloadHandle {
         }
     }
 }
-
-impl DownloadHandle {
-    pub fn status(&self) -> Status {
-        *self.status.borrow()
-    }
-
-    pub async fn wait_for_status_update(&mut self) -> Result<(), watch::error::RecvError> {
-        self.status.changed().await
-    }
-
-    pub fn cancel(&self) {
-        self.cancel.cancel();
-    }
-}

src/downloader/manager.rs

@@ -1,10 +1,10 @@
+use super::{download_thread, DownloadHandle, DownloadRequest};
+use crate::{error::DownloadError, Error};
 use reqwest::{Client, Url};
-use std::{path::PathBuf, sync::Arc};
-use tokio::sync::{mpsc, oneshot, watch, Semaphore};
+use std::{path::Path, sync::Arc};
+use tokio::sync::{mpsc, Semaphore};
 use tokio_util::sync::CancellationToken;
 
-use super::{download_thread, DownloadHandle, DownloadRequest, Status};
-
 const QUEUE_SIZE: usize = 100;
 
 #[derive(Debug)]
@@ -36,6 +36,33 @@ impl DownloadManager {
         manager
     }
 
+    pub fn download(
+        &self,
+        url: Url,
+        destination: impl AsRef<Path>,
+    ) -> Result<DownloadHandle, Error> {
+        if self.cancel.is_cancelled() {
+            return Err(Error::Download(DownloadError::ManagerShutdown));
+        }
+
+        let destination = destination.as_ref();
+        if destination.exists() {
+            return Err(Error::Download(DownloadError::FileExists {
+                path: destination.to_path_buf(),
+            }));
+        }
+
+        let cancel = self.cancel.child_token();
+        let (req, handle) = DownloadRequest::new_req_handle_pair(url, destination, cancel);
+
+        self.queue.try_send(req).map_err(|e| match e {
+            mpsc::error::TrySendError::Full(_) => Error::Download(DownloadError::QueueFull),
+            mpsc::error::TrySendError::Closed(_) => Error::Download(DownloadError::ManagerShutdown),
+        })?;
+
+        Ok(handle)
+    }
+
     pub fn set_max_parallel_downloads(&self, limit: usize) {
         let current = self.semaphore.available_permits();
         if limit > current {
@@ -48,24 +75,6 @@ impl DownloadManager {
         }
     }
 
-    pub fn add_request(&self, url: Url, destination: PathBuf) -> DownloadHandle {
-        let (result_tx, result_rx) = oneshot::channel();
-        let (status_tx, status_rx) = watch::channel(Status::Queued);
-        let cancel = self.cancel.child_token();
-
-        let req = DownloadRequest {
-            url,
-            destination,
-            result: result_tx,
-            status: status_tx,
-            cancel: cancel.clone(),
-        };
-
-        let _ = self.queue.try_send(req);
-
-        DownloadHandle::new(result_rx, status_rx, cancel)
-    }
-
     pub fn cancel_all(&self) {
         self.cancel.cancel();
     }

src/downloader/types.rs

@@ -1,7 +1,7 @@
-use super::DownloadProgress;
+use super::{DownloadHandle, DownloadProgress};
 use crate::Error;
 use reqwest::Url;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use tokio::{
     fs::File,
     sync::{oneshot, watch},
@@ -17,6 +17,28 @@ pub(crate) struct DownloadRequest {
     pub cancel: CancellationToken,
 }
 
+impl DownloadRequest {
+    pub fn new_req_handle_pair(
+        url: Url,
+        destination: impl AsRef<Path>,
+        cancel: CancellationToken,
+    ) -> (Self, DownloadHandle) {
+        let (result_tx, result_rx) = oneshot::channel();
+        let (status_tx, status_rx) = watch::channel(Status::Queued);
+
+        (
+            Self {
+                url,
+                destination: destination.as_ref().to_path_buf(),
+                result: result_tx,
+                status: status_tx,
+                cancel: cancel.clone(),
+            },
+            DownloadHandle::new(result_rx, status_rx, cancel),
+        )
+    }
+}
+
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum Status {
     Queued,

src/error.rs

@@ -1,3 +1,4 @@
+use std::path::PathBuf;
 use thiserror::Error;
 
 #[derive(Error, Debug)]
@@ -18,6 +19,12 @@ pub enum Error {
 pub enum DownloadError {
     #[error("Download was cancelled")]
     Cancelled,
-    #[error("Retry limit exceeded")]
+    #[error("Retry limit exceeded: {last_error_msg}")]
     RetriesExhausted { last_error_msg: String },
+    #[error("Download queue is full")]
+    QueueFull,
+    #[error("Download manager has been shut down")]
+    ManagerShutdown,
+    #[error("File already exists: {path}")]
+    FileExists { path: PathBuf },
 }