# Subscan Module
`SubscanModule` components are the core components that can be executed by `Subscan`. Each module capable of performing subdomain discovery is named a `SubscanModule`, and when the [`subscan scan`](../../user-guide/commands/scan.md) command is run, these modules are read from an in-memory cache and executed asynchronously. This architecture makes `Subscan` extensible and modular
A `SubscanModule` may contain various components such as `Requester` and `Extractor`. Most modules implemented in `Subscan` use these components. You can list the implemented modules with their details using the [`subscan module list`](../../user-guide/commands/module.md#list) command. If you'd like to view the in-memory cache, you can check the [CacheManager](https://docs.rs/subscan/latest/subscan/cache/struct.CacheManager.html) struct, which is another component designed for operations like filtering the cache or accessing a specific module
## Create Your Own Module
Each `SubscanModule` component should be implemented following the interface below. For a better understanding, you can explore the [docs.rs](https://docs.rs/subscan/latest/subscan/interfaces/module/index.html) page and review the crates listed below
- [`async_trait`](https://github.com/dtolnay/async-trait)
- [`enum_dispatch`](https://gitlab.com/antonok/enum_dispatch)
```rust,ignore
#[async_trait]
#[enum_dispatch]
pub trait SubscanModuleInterface: Sync + Send {
/// Returns module name, name should clarify what does module
async fn name(&self) -> &str;
/// Loads `.env` file and fetches module environment variables with variable name.
/// If system environment variable set with same name, `.env` file will be overrode
/// See the [`SubscanModuleEnvs`](crate::types::env::SubscanModuleEnvs) for details
async fn envs(&self) -> SubscanModuleEnvs {
self.name().await.into()
}
/// Returns module requester address as a mutable reference if available
async fn requester(&self) -> Option<&Mutex<RequesterDispatcher>>;
/// Returns module extractor reference if available
async fn extractor(&self) -> Option<&SubdomainExtractorDispatcher>;
/// Configure module requester instance
async fn configure(&self, rconfig: RequesterConfig) {
if let Some(requester) = self.requester().await {
requester.lock().await.configure(rconfig).await;
}
}
/// Just like a `main` method, when the module run this `run` method will be called.
/// So this method should do everything
async fn run(&mut self, domain: &str, results: Sender<OptionalSubscanModuleResult>);
/// Builds [`OptionalSubscanModuleResult`](crate::enums::result::OptionalSubscanModuleResult)
/// with any [`Subdomain`](crate::types::core::Subdomain)
async fn item(&self, sub: &Subdomain) -> OptionalSubscanModuleResult {
(self.name().await, sub).into()
}
/// Builds [`OptionalSubscanModuleResult`](crate::enums::result::OptionalSubscanModuleResult)
/// with any [`SubscanModuleStatus`](crate::types::result::status::SubscanModuleStatus)
async fn status(&self, status: SubscanModuleStatus) -> OptionalSubscanModuleResult {
(self.name().await, status).into()
}
/// Builds [`OptionalSubscanModuleResult`](crate::enums::result::OptionalSubscanModuleResult)
/// with custom error message
async fn error(&self, msg: &str) -> OptionalSubscanModuleResult {
(self.name().await, msg).into()
}
}
```
Below is a simple example of a custom module. For more examples, you can check the [examples/](https://github.com/eredotpkfr/subscan/tree/main/examples) folder on the project's GitHub page. You can also refer to the source code of predefined requester implementations for a better understanding
```rust,ignore
pub struct CustomModule {
pub requester: Mutex<RequesterDispatcher>,
pub extractor: SubdomainExtractorDispatcher,
}
#[async_trait]
impl SubscanModuleInterface for CustomModule {
async fn name(&self) -> &str {
&"name"
}
async fn requester(&self) -> Option<&Mutex<RequesterDispatcher>> {
Some(&self.requester)
}
async fn extractor(&self) -> Option<&SubdomainExtractorDispatcher> {
Some(&self.extractor)
}
async fn run(&mut self, _domain: &str, results: Sender<OptionalSubscanModuleResult>) {
let subdomains = BTreeSet::from_iter([Subdomain::from("bar.foo.com")]);
for subdomain in &subdomains {
results.send((self.name().await, subdomain).into()).unwrap();
}
}
}
```