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Merged
avrabe merged 1 commit into from
Dec 13, 2025
Merged

refactor(server): simplify handler with helper functions #83

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182 changes: 55 additions & 127 deletions mcp-server/src/handler.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,10 +71,44 @@ pub struct GenericServerHandler<B: McpBackend> {
middleware: MiddlewareStack,
/// Global subscription registry tracking subscribed resource URIs
/// Note: This is a simplified global implementation. For per-client
/// subscriptions, use a HashMap<ClientId, HashSet<String>> instead.
/// subscriptions, use a `HashMap<ClientId, HashSet<String>>` instead.
subscriptions: Arc<RwLock<HashSet<String>>>,
}

/// Helper to create a JSON-RPC response with a result
#[inline]
fn make_response(id: Option<NumberOrString>, result: serde_json::Value) -> Response {
Response {
jsonrpc: "2.0".to_string(),
id,
result: Some(result),
error: None,
}
}

/// Helper to create an empty JSON-RPC response (for void methods)
#[inline]
fn make_empty_response(id: Option<NumberOrString>) -> Response {
Response {
jsonrpc: "2.0".to_string(),
id,
result: Some(serde_json::Value::Object(Default::default())),
error: None,
}
}

/// Parse optional paginated params, defaulting to no cursor
#[inline]
fn parse_paginated_params(
params: serde_json::Value,
) -> std::result::Result<PaginatedRequestParam, Error> {
if params.is_null() {
Ok(PaginatedRequestParam { cursor: None })
} else {
serde_json::from_value(params).map_err(Error::from)
}
}

impl<B: McpBackend> GenericServerHandler<B> {
/// Create a new handler
pub fn new(
Expand Down Expand Up @@ -230,24 +264,13 @@ impl<B: McpBackend> GenericServerHandler<B> {

#[instrument(skip(self, request), fields(mcp.method = "tools/list"))]
async fn handle_list_tools(&self, request: Request) -> std::result::Result<Response, Error> {
let params: PaginatedRequestParam = if request.params.is_null() {
PaginatedRequestParam { cursor: None }
} else {
serde_json::from_value(request.params)?
};

let params = parse_paginated_params(request.params)?;
let result = self
.backend
.list_tools(params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

#[instrument(skip(self, request), fields(mcp.method = "tools/call"))]
Expand Down Expand Up @@ -302,103 +325,56 @@ impl<B: McpBackend> GenericServerHandler<B> {
&self,
request: Request,
) -> std::result::Result<Response, Error> {
let params: PaginatedRequestParam = if request.params.is_null() {
PaginatedRequestParam { cursor: None }
} else {
serde_json::from_value(request.params)?
};

let params = parse_paginated_params(request.params)?;
let result = self
.backend
.list_resources(params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_read_resource(&self, request: Request) -> std::result::Result<Response, Error> {
let params: ReadResourceRequestParam = serde_json::from_value(request.params)?;

let result = self
.backend
.read_resource(params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_list_resource_templates(
&self,
request: Request,
) -> std::result::Result<Response, Error> {
let params: PaginatedRequestParam = if request.params.is_null() {
PaginatedRequestParam { cursor: None }
} else {
serde_json::from_value(request.params)?
};

let params = parse_paginated_params(request.params)?;
let result = self
.backend
.list_resource_templates(params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_list_prompts(&self, request: Request) -> std::result::Result<Response, Error> {
let params: PaginatedRequestParam = if request.params.is_null() {
PaginatedRequestParam { cursor: None }
} else {
serde_json::from_value(request.params)?
};

let params = parse_paginated_params(request.params)?;
let result = self
.backend
.list_prompts(params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_get_prompt(&self, request: Request) -> std::result::Result<Response, Error> {
let params: GetPromptRequestParam = serde_json::from_value(request.params)?;

let result = self
.backend
.get_prompt(params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_subscribe(&self, request: Request) -> std::result::Result<Response, Error> {
Expand All @@ -410,19 +386,11 @@ impl<B: McpBackend> GenericServerHandler<B> {

// Track subscription globally
let mut subs = self.subscriptions.write().await;
let is_new = subs.insert(uri.clone());
drop(subs);

if is_new {
if subs.insert(uri.clone()) {
debug!("Subscribed to resource: {}", uri);
}

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::Value::Object(Default::default())),
error: None,
})
Ok(make_empty_response(request.id))
}

async fn handle_unsubscribe(&self, request: Request) -> std::result::Result<Response, Error> {
Expand All @@ -437,67 +405,33 @@ impl<B: McpBackend> GenericServerHandler<B> {

// Remove from subscription tracking
let mut subs = self.subscriptions.write().await;
let was_present = subs.remove(&uri);
drop(subs);

if was_present {
if subs.remove(&uri) {
debug!("Unsubscribed from resource: {}", uri);
}

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::Value::Object(Default::default())),
error: None,
})
Ok(make_empty_response(request.id))
}

async fn handle_complete(&self, request: Request) -> std::result::Result<Response, Error> {
let params: CompleteRequestParam = serde_json::from_value(request.params)?;

let result = self.backend.complete(params).await.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_elicit(&self, request: Request) -> std::result::Result<Response, Error> {
let params: ElicitationRequestParam = serde_json::from_value(request.params)?;

let result = self.backend.elicit(params).await.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::to_value(result)?),
error: None,
})
Ok(make_response(request.id, serde_json::to_value(result)?))
}

async fn handle_set_level(&self, request: Request) -> std::result::Result<Response, Error> {
let params: SetLevelRequestParam = serde_json::from_value(request.params)?;

self.backend.set_level(params).await.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(serde_json::Value::Object(Default::default())),
error: None,
})
Ok(make_empty_response(request.id))
}

async fn handle_ping(&self, _request: Request) -> std::result::Result<Response, Error> {
Ok(Response {
jsonrpc: "2.0".to_string(),
id: _request.id,
result: Some(serde_json::Value::Object(Default::default())),
error: None,
})
async fn handle_ping(&self, request: Request) -> std::result::Result<Response, Error> {
Ok(make_empty_response(request.id))
}

async fn handle_custom_method(&self, request: Request) -> std::result::Result<Response, Error> {
Expand All @@ -506,13 +440,7 @@ impl<B: McpBackend> GenericServerHandler<B> {
.handle_custom_method(&request.method, request.params)
.await
.map_err(|e| e.into())?;

Ok(Response {
jsonrpc: "2.0".to_string(),
id: request.id,
result: Some(result),
error: None,
})
Ok(make_response(request.id, result))
}
}

Expand Down