feat: some helper function for mailbox message (#37)

* feat: some helper function for mailbox message

* feat: some helper function for mailbox message

* feat: some helper function for mailbox message

src/v1/meta.rs

@@ -14,6 +14,8 @@
 
 tonic::include_proto!("greptime.v1.meta");
 
+mod mailbox;
+
 use std::collections::HashMap;
 use std::hash::{Hash, Hasher};
 

src/v1/meta/mailbox.rs

@@ -0,0 +1,52 @@
+// 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 crate::v1::meta::mailbox_message::Payload;
+use crate::v1::meta::MailboxMessage;
+use serde::Serialize;
+use serde_json::Result;
+use std::fmt::{Display, Formatter};
+
+impl MailboxMessage {
+    pub fn json_message<T>(
+        subject: &str,
+        from: &str,
+        to: &str,
+        timestamp_millis: i64,
+        payload: &T,
+    ) -> Result<MailboxMessage>
+    where
+        T: ?Sized + Serialize + Display,
+    {
+        let payload = serde_json::to_string(payload)?;
+        Ok(MailboxMessage {
+            id: 0, // "id" will be set by the mailbox.
+            subject: subject.to_string(),
+            from: from.to_string(),
+            to: to.to_string(),
+            timestamp_millis,
+            payload: Some(Payload::Json(payload)),
+        })
+    }
+}
+
+impl Display for MailboxMessage {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "MailboxMessage(id={}, subject={}, from={}, to={}, timestamp_millis={}, payload={:?})",
+            self.id, self.subject, self.from, self.to, self.timestamp_millis, self.payload
+        )
+    }
+}