test(tvix/castore): use tokio-retry for exp backoff

Rather than using this loop, use exponential backoff while waiting for
the socket path to be created.

Change-Id: I18706a64ce06f8916a07892dfbcd409ac5b3bff1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9568
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/castore/Cargo.toml

@@ -34,7 +34,8 @@ tonic-build = "0.10.2"
 [dev-dependencies]
 test-case = "2.2.2"
 tempfile = "3.3.0"
+tokio-retry = "0.3.0"
 
 [features]
 default = []
-tonic-reflection = ["dep:tonic-reflection"]
+tonic-reflection = ["dep:tonic-reflection"]

tvix/castore/src/blobservice/grpc.rs

@@ -281,10 +281,12 @@ impl<W: tokio::io::AsyncWrite + Unpin> tokio::io::AsyncWrite for GRPCBlobWriter<
 #[cfg(test)]
 mod tests {
     use std::sync::Arc;
+    use std::time::Duration;
 
     use tempfile::TempDir;
     use tokio::net::UnixListener;
-    use tokio::time;
+    use tokio_retry::strategy::ExponentialBackoff;
+    use tokio_retry::Retry;
     use tokio_stream::wrappers::UnixListenerStream;
 
     use crate::blobservice::MemoryBlobService;
@@ -374,22 +376,18 @@ mod tests {
         });
 
         // wait for the socket to be created
-        {
-            let mut socket_created = false;
-            // TODO: exponential backoff urgently
-            for _try in 1..20 {
+        Retry::spawn(
+            ExponentialBackoff::from_millis(20).max_delay(Duration::from_secs(10)),
+            || async {
                 if socket_path.exists() {
-                    socket_created = true;
-                    break;
+                    Ok(())
+                } else {
+                    Err(())
                 }
-                tokio::time::sleep(time::Duration::from_millis(20)).await;
-            }
-
-            assert!(
-                socket_created,
-                "expected socket path to eventually get created, but never happened"
-            );
-        }
+            },
+        )
+        .await
+        .expect("failed to wait for socket");
 
         // prepare a client
         let grpc_client = {