Add basic retry policies to zebra-network.

This should be removed when tower-rs/tower#414 lands
but is good enough for our purposes for now.

zebra-network/src/lib.rs

@@ -52,6 +52,7 @@ mod config;
 mod constants;
 mod meta_addr;
 mod network;
+mod policies;
 mod peer;
 mod peer_set;
 mod protocol;
@@ -62,6 +63,7 @@ pub use crate::{
     config::Config,
     peer_set::init,
     protocol::internal::{Request, Response},
+    policies::{RetryErrors, RetryLimit},
 };
 
 /// Types used in the definition of [`Request`] and [`Response`] messages.

zebra-network/src/policies.rs

@@ -0,0 +1,61 @@
+use tower::retry::Policy;
+use futures::future;
+
+/// A very basic retry policy with a limited number of retry attempts.
+///
+/// XXX Remove this when https://github.com/tower-rs/tower/pull/414 lands.
+#[derive(Clone, Debug)]
+pub struct RetryLimit {
+    remaining_tries: usize,
+}
+
+impl RetryLimit {
+    /// Create a policy with the given number of retry attempts.
+    pub fn new(retry_attempts: usize) -> Self {
+        RetryLimit {
+            remaining_tries: retry_attempts,
+        }
+    }
+}
+
+impl<Req: Clone, Res, E> Policy<Req, Res, E> for RetryLimit {
+    type Future = future::Ready<Self>;
+    fn retry(&self, _: &Req, result: Result<&Res, &E>) -> Option<Self::Future> {
+        if result.is_err() {
+            if self.remaining_tries > 0 {
+                Some(future::ready(RetryLimit {
+                    remaining_tries: self.remaining_tries - 1,
+                }))
+            } else {
+                None
+            }
+        } else {
+            None
+        }
+    }
+
+    fn clone_request(&self, req: &Req) -> Option<Req> {
+        Some(req.clone())
+    }
+}
+
+/// A very basic retry policy that always retries failed requests.
+///
+/// XXX remove this when https://github.com/tower-rs/tower/pull/414 lands.
+#[derive(Clone, Debug)]
+pub struct RetryErrors;
+
+impl<Req: Clone, Res, E> Policy<Req, Res, E> for RetryErrors {
+    type Future = future::Ready<Self>;
+    fn retry(&self, _: &Req, result: Result<&Res, &E>) -> Option<Self::Future> {
+        if result.is_err() {
+            Some(future::ready(RetryErrors))
+        } else {
+            None
+        }
+    }
+
+    fn clone_request(&self, req: &Req) -> Option<Req> {
+        Some(req.clone())
+    }
+}