# RocketMQ-Rust Macros
Using macros to automate repetitive tasks.
## Overview
This crate is primarily for the macros used in RocketMQ-Rust. The currently defined macros are as follows:
- **RequestHeaderCodec([Derive Macros](https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros))**
- **RemotingSerializable([Derive Macros](https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros))** - Currently not in use, implemented via alternative methods.
## RequestHeaderCodec Macro
The `RequestHeaderCodec` macro implements serialization and deserialization for RocketMQ's `RequestHeader`. It automatically implements the **`CommandCustomHeader trait`** and the **`FromMap trait`**. This macro includes an attribute: **`required`**, which indicates that a field of the struct must be present during deserialization; otherwise, it will result in an error.
> Note: The `required` attribute corresponds to the `@CFNotNull` annotation in the Java version and is implemented in this way in Rust.
Example usage is shown below:
```rust
#[derive(Debug, Clone, Serialize, Deserialize, Default, RequestHeaderCodec)]
#[serde(rename_all = "camelCase")]
pub struct SendMessageRequestHeader {
#[required] // this field is required
pub producer_group: CheetahString,
pub topic: CheetahString,
pub default_topic: CheetahString,
pub default_topic_queue_nums: i32,
pub queue_id: Option<i32>,
pub sys_flag: i32,
pub born_timestamp: i64,
pub flag: i32,
pub properties: Option<CheetahString>,
pub reconsume_times: Option<i32>,
pub unit_mode: Option<bool>,
pub batch: Option<bool>,
pub max_reconsume_times: Option<i32>,
#[serde(flatten)]
pub topic_request_header: Option<TopicRequestHeader>,
}
```
In this example, the `SendMessageRequestHeader` struct is annotated with the `RequestHeaderCodec` derive macro, along with other standard Rust attributes like `Debug`, `Clone`, `Serialize`, `Deserialize`, and `Default`. The `#[required]` attribute is used on the `producer_group` field to denote that it is mandatory for successful deserialization.