feat: introduce read preference (#5783)

* feat: introduce read preference

* feat: introduce `RegionQueryHandlerFactory`

* feat: extract ReadPreference from http header

* test: add more tests

* chore: apply suggestions from CR

* chore: apply suggestions from CR

src/common/session/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "common-session"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[lints]
+workspace = true
+
+[dependencies]
+strum.workspace = true

src/common/session/src/lib.rs

@@ -0,0 +1,45 @@
+// Copyright 2023 Greptime Team
+//
+// 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 strum::{AsRefStr, Display, EnumString};
+
+/// Defines the read preference for frontend route operations,
+/// determining whether to read from the region leader or follower.
+#[derive(Debug, Clone, Copy, Default, EnumString, Display, AsRefStr, PartialEq, Eq)]
+pub enum ReadPreference {
+    #[default]
+    // Reads all operations from the region leader. This is the default mode.
+    #[strum(serialize = "leader", to_string = "LEADER")]
+    Leader,
+}
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+
+    use crate::ReadPreference;
+
+    #[test]
+    fn test_read_preference() {
+        assert_eq!(ReadPreference::Leader.to_string(), "LEADER");
+
+        let read_preference = ReadPreference::from_str("LEADER").unwrap();
+        assert_eq!(read_preference, ReadPreference::Leader);
+
+        let read_preference = ReadPreference::from_str("leader").unwrap();
+        assert_eq!(read_preference, ReadPreference::Leader);
+
+        ReadPreference::from_str("follower").unwrap_err();
+    }
+}