Merge pull request #125 from razvandimescu/worktree-fix-blocklist-bootstrap

fix(blocklist): retry on transient download failures (#122)

src/blocklist.rs

@@ -1,5 +1,5 @@
 use std::collections::HashSet;
-use std::time::Instant;
+use std::time::{Duration, Instant};
 
 use log::{info, warn};
 
@@ -355,27 +355,139 @@ mod tests {
     }
 }
 
+const RETRY_DELAYS_SECS: &[u64] = &[2, 10, 30];
+
 pub async fn download_blocklists(lists: &[String]) -> Vec<(String, String)> {
     let client = reqwest::Client::builder()
-        .timeout(std::time::Duration::from_secs(30))
+        .timeout(Duration::from_secs(30))
         .gzip(true)
         .build()
         .unwrap_or_default();
 
-    let mut results = Vec::new();
+    let fetches = lists.iter().map(|url| {
+        let client = &client;
+        async move {
+            let text = fetch_with_retry(client, url).await?;
+            info!("downloaded blocklist: {} ({} bytes)", url, text.len());
+            Some((url.clone(), text))
+        }
+    });
+    futures::future::join_all(fetches)
+        .await
+        .into_iter()
+        .flatten()
+        .collect()
+}
 
-    for url in lists {
-        match client.get(url).send().await {
-            Ok(resp) => match resp.text().await {
-                Ok(text) => {
-                    info!("downloaded blocklist: {} ({} bytes)", url, text.len());
-                    results.push((url.clone(), text));
-                }
-                Err(e) => warn!("failed to read blocklist body {}: {}", url, e),
-            },
-            Err(e) => warn!("failed to download blocklist {}: {}", url, e),
+async fn fetch_with_retry(client: &reqwest::Client, url: &str) -> Option<String> {
+    fetch_with_retry_delays(client, url, RETRY_DELAYS_SECS).await
+}
+
+async fn fetch_with_retry_delays(
+    client: &reqwest::Client,
+    url: &str,
+    delays: &[u64],
+) -> Option<String> {
+    let total = delays.len() + 1;
+    for attempt in 1..=total {
+        match fetch_once(client, url).await {
+            Ok(text) => return Some(text),
+            Err(msg) if attempt < total => {
+                let delay = delays[attempt - 1];
+                warn!(
+                    "blocklist {} attempt {}/{} failed: {} — retrying in {}s",
+                    url, attempt, total, msg, delay
+                );
+                tokio::time::sleep(Duration::from_secs(delay)).await;
+            }
+            Err(msg) => {
+                warn!(
+                    "blocklist {} attempt {}/{} failed: {} — giving up",
+                    url, attempt, total, msg
+                );
+            }
         }
     }
-
-    results
+    None
+}
+
+async fn fetch_once(client: &reqwest::Client, url: &str) -> Result<String, String> {
+    let resp = client
+        .get(url)
+        .send()
+        .await
+        .map_err(|e| format_error_chain(&e))?;
+    resp.text().await.map_err(|e| format_error_chain(&e))
+}
+
+fn format_error_chain(e: &(dyn std::error::Error + 'static)) -> String {
+    let mut parts = vec![e.to_string()];
+    let mut src = e.source();
+    while let Some(s) = src {
+        parts.push(s.to_string());
+        src = s.source();
+    }
+    parts.join(": ")
+}
+
+#[cfg(test)]
+mod retry_tests {
+    use super::*;
+    use std::net::SocketAddr;
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    use tokio::net::TcpListener;
+
+    async fn flaky_http_server(drop_first_n: usize, body: &'static str) -> SocketAddr {
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let addr = listener.local_addr().unwrap();
+        tokio::spawn(async move {
+            for _ in 0..drop_first_n {
+                if let Ok((sock, _)) = listener.accept().await {
+                    drop(sock);
+                }
+            }
+            loop {
+                let Ok((mut sock, _)) = listener.accept().await else {
+                    return;
+                };
+                tokio::spawn(async move {
+                    let mut buf = [0u8; 2048];
+                    let _ = sock.read(&mut buf).await;
+                    let response = format!(
+                        "HTTP/1.1 200 OK\r\nContent-Length: {}\r\nContent-Type: text/plain\r\nConnection: close\r\n\r\n{}",
+                        body.len(),
+                        body,
+                    );
+                    let _ = sock.write_all(response.as_bytes()).await;
+                    let _ = sock.shutdown().await;
+                });
+            }
+        });
+        addr
+    }
+
+    fn zero_delays() -> Vec<u64> {
+        vec![0; RETRY_DELAYS_SECS.len()]
+    }
+
+    #[tokio::test]
+    async fn retry_succeeds_on_final_attempt() {
+        let body = "ads.example.com\ntracker.example.net\n";
+        let delays = zero_delays();
+        let addr = flaky_http_server(delays.len(), body).await;
+        let client = reqwest::Client::new();
+        let url = format!("http://{addr}/");
+        let result = fetch_with_retry_delays(&client, &url, &delays).await;
+        assert_eq!(result.as_deref(), Some(body));
+    }
+
+    #[tokio::test]
+    async fn retry_gives_up_when_all_attempts_fail() {
+        let delays = zero_delays();
+        let addr = flaky_http_server(delays.len() + 2, "unreachable").await;
+        let client = reqwest::Client::new();
+        let url = format!("http://{addr}/");
+        let result = fetch_with_retry_delays(&client, &url, &delays).await;
+        assert_eq!(result, None);
+    }
 }