fix(http): set I/O timeout to 1 minute rather than whole request timeout

Before the fix HTTP client
had no connection timeout,
so it only had a chance
to test one IPv6 and one IPv4
address if the first addresses timed out.
Now it can test at least 4 addresses
of each family and more if some addresses
refuse connection rather than time out.

src/net.rs

@@ -27,6 +27,13 @@ use tls::wrap_tls;
 /// This constant should be more than the largest expected RTT.
 pub(crate) const TIMEOUT: Duration = Duration::from_secs(60);
 
+/// Transaction timeout, e.g. for a GET or POST request
+/// together with all connection attempts.
+///
+/// This is the worst case time user has to wait on a very slow network
+/// after clicking a button and before getting an error message.
+pub(crate) const TRANSACTION_TIMEOUT: Duration = Duration::from_secs(300);
+
 /// TTL for caches in seconds.
 pub(crate) const CACHE_TTL: u64 = 30 * 24 * 60 * 60;
 

src/net/http.rs

@@ -136,8 +136,24 @@ pub(crate) async fn get_client(context: &Context, load_cache: bool) -> Result<re
     let socks5_config = Socks5Config::from_database(&context.sql).await?;
     let resolver = Arc::new(CustomResolver::new(context.clone(), load_cache));
 
+    // `reqwest` uses `hyper-util` crate internally which implements
+    // [Happy Eyeballs](https://datatracker.ietf.org/doc/html/rfc6555) algorithm.
+    // On a dual-stack host it starts IPv4 connection attempts in parallel
+    // to IPv6 connection attempts after 300 ms.
+    // In the worst case of all connection attempts
+    // timing out this allows to try four IPv6 and four IPv4
+    // addresses before request expires
+    // if request timeout is set to 5 minutes
+    // and connection timeout is set to 1 minute.
+    //
+    // We do not set write timeout because `reqwest`
+    // does not support it, but request timeout
+    // should prevent deadlocks if the server
+    // does not read the data.
     let builder = reqwest::ClientBuilder::new()
-        .timeout(super::TIMEOUT)
+        .connect_timeout(super::TIMEOUT)
+        .read_timeout(super::TIMEOUT)
+        .timeout(super::TRANSACTION_TIMEOUT)
         .add_root_certificate(LETSENCRYPT_ROOT.clone())
         .dns_resolver(resolver);