Add the name resolver API

grpc/Cargo.toml

@@ -7,6 +7,16 @@ license = "Apache-2.0"
 
 [dependencies]
 url = "2.5.0"
-tokio = { version = "1.37.0", features = ["sync"] }
+tokio = { version = "1.37.0", features = ["sync", "rt", "net", "time", "macros"] }
 tonic = { version = "0.13.0", path = "../tonic", default-features = false, features = ["codegen"] }
 futures-core = "0.3.31"
+once_cell = "1.19.0"
+hickory-resolver = { version = "0.25.1", optional = true }
+rand = "0.8.5"
+
+[dev-dependencies]
+hickory-server =  "0.25.2"
+
+[features]
+default = ["hickory_dns"]
+hickory_dns = ["dep:hickory-resolver"]

grpc/src/client/mod.rs

@@ -19,9 +19,9 @@
 use std::fmt::Display;
 
 pub mod channel;
-pub mod service;
 pub(crate) mod load_balancing;
 pub(crate) mod name_resolution;
+pub mod service;
 pub mod service_config;
 
 /// A representation of the current state of a gRPC channel, also used for the

grpc/src/client/name_resolution/backoff.rs

@@ -0,0 +1,225 @@
+/*
+ *
+ * Copyright 2025 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+use rand::Rng;
+use std::{sync::Mutex, time::Duration};
+
+#[derive(Clone)]
+pub struct BackoffConfig {
+    /// The amount of time to backoff after the first failure.
+    pub base_delay: Duration,
+
+    /// The factor with which to multiply backoffs after a
+    /// failed retry. Should ideally be greater than 1.
+    pub multiplier: f64,
+
+    /// The factor with which backoffs are randomized.
+    pub jitter: f64,
+
+    /// The upper bound of backoff delay.
+    pub max_delay: Duration,
+}
+
+pub struct ExponentialBackoff {
+    config: BackoffConfig,
+
+    /// The delay for the next retry, without the random jitter. Store as f64
+    /// to avoid rounding errors.
+    next_delay_secs: Mutex<f64>,
+}
+
+/// This is a backoff configuration with the default values specified
+/// at https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
+///
+/// This should be useful for callers who want to configure backoff with
+/// non-default values only for a subset of the options.
+pub const DEFAULT_EXPONENTIAL_CONFIG: BackoffConfig = BackoffConfig {
+    base_delay: Duration::from_secs(1),
+    multiplier: 1.6,
+    jitter: 0.2,
+    max_delay: Duration::from_secs(120),
+};
+
+impl ExponentialBackoff {
+    pub fn new(mut config: BackoffConfig) -> Self {
+        // Adjust params to get them in valid ranges.
+        // 0 <= base_dealy <= max_delay
+        config.base_delay = config.base_delay.min(config.max_delay);
+        // 1 <= multiplier
+        config.multiplier = config.multiplier.max(1.0);
+        // 0 <= jitter <= 1
+        config.jitter = config.jitter.max(0.0);
+        config.jitter = config.jitter.min(1.0);
+        let next_delay_secs = config.base_delay.as_secs_f64();
+        ExponentialBackoff {
+            config,
+            next_delay_secs: Mutex::new(next_delay_secs),
+        }
+    }
+
+    pub fn reset(&self) {
+        let mut next_delay = self.next_delay_secs.lock().unwrap();
+        *next_delay = self.config.base_delay.as_secs_f64();
+    }
+
+    pub fn backoff_duration(&self) -> Duration {
+        let mut next_delay = self.next_delay_secs.lock().unwrap();
+        let cur_delay =
+            *next_delay * (1.0 + self.config.jitter * rand::thread_rng().gen_range(-1.0..1.0));
+        *next_delay = self
+            .config
+            .max_delay
+            .as_secs_f64()
+            .min(*next_delay * self.config.multiplier);
+        Duration::from_secs_f64(cur_delay)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use crate::client::name_resolution::backoff::{BackoffConfig, ExponentialBackoff};
+
+    // Epsilon for floating point comparisons if needed, though Duration
+    // comparisons are often better.
+    const EPSILON: f64 = 1e-9;
+
+    #[test]
+    fn base_less_than_max() {
+        let config = BackoffConfig {
+            base_delay: Duration::from_secs(10),
+            multiplier: 123.0,
+            jitter: 0.0,
+            max_delay: Duration::from_secs(100),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(10));
+    }
+
+    #[test]
+    fn base_more_than_max() {
+        let config = BackoffConfig {
+            multiplier: 123.0,
+            jitter: 0.0,
+            base_delay: Duration::from_secs(100),
+            max_delay: Duration::from_secs(10),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(10));
+    }
+
+    #[test]
+    fn negative_multiplier() {
+        let config = BackoffConfig {
+            multiplier: -123.0,
+            jitter: 0.0,
+            base_delay: Duration::from_secs(10),
+            max_delay: Duration::from_secs(100),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        // multiplier gets clipped to 1.
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(10));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(10));
+    }
+
+    #[test]
+    fn negative_jitter() {
+        let config = BackoffConfig {
+            multiplier: 1.0,
+            jitter: -10.0,
+            base_delay: Duration::from_secs(10),
+            max_delay: Duration::from_secs(100),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        // jitter gets clipped to 0.
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(10));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(10));
+    }
+
+    #[test]
+    fn jitter_greater_than_one() {
+        let config = BackoffConfig {
+            multiplier: 1.0,
+            jitter: 2.0,
+            base_delay: Duration::from_secs(10),
+            max_delay: Duration::from_secs(100),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        // jitter gets clipped to 1.
+        // 0 <= duration <= 20.
+        let duration = backoff.backoff_duration();
+        assert_eq!(duration.lt(&Duration::from_secs(20)), true);
+        assert_eq!(duration.gt(&Duration::from_secs(0)), true);
+
+        let duration = backoff.backoff_duration();
+        assert_eq!(duration.lt(&Duration::from_secs(20)), true);
+        assert_eq!(duration.gt(&Duration::from_secs(0)), true);
+    }
+
+    #[test]
+    fn backoff_reset_no_jitter() {
+        let config = BackoffConfig {
+            multiplier: 2.0,
+            jitter: 0.0,
+            base_delay: Duration::from_secs(1),
+            max_delay: Duration::from_secs(15),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(1));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(2));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(4));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(8));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(15));
+        // Duration is capped to max_delay.
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(15));
+
+        // reset and repeat.
+        backoff.reset();
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(1));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(2));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(4));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(8));
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(15));
+        // Duration is capped to max_delay.
+        assert_eq!(backoff.backoff_duration(), Duration::from_secs(15));
+    }
+
+    #[test]
+    fn backoff_with_jitter() {
+        let config = BackoffConfig {
+            multiplier: 2.0,
+            jitter: 0.2,
+            base_delay: Duration::from_secs(1),
+            max_delay: Duration::from_secs(15),
+        };
+        let backoff = ExponentialBackoff::new(config.clone());
+        // 0.8 <= duration <= 1.2.
+        let duration = backoff.backoff_duration();
+        assert_eq!(duration.gt(&Duration::from_secs_f64(0.8 - EPSILON)), true);
+        assert_eq!(duration.lt(&Duration::from_secs_f64(1.2 + EPSILON)), true);
+        // 1.6 <= duration <= 2.4.
+        let duration = backoff.backoff_duration();
+        assert_eq!(duration.gt(&Duration::from_secs_f64(1.6 - EPSILON)), true);
+        assert_eq!(duration.lt(&Duration::from_secs_f64(2.4 + EPSILON)), true);
+        // 3.2 <= duration <= 4.8.
+        let duration = backoff.backoff_duration();
+        assert_eq!(duration.gt(&Duration::from_secs_f64(3.2 - EPSILON)), true);
+        assert_eq!(duration.lt(&Duration::from_secs_f64(4.8 + EPSILON)), true);
+    }
+}