feat(mcp) add MCP control for Cap. #1942
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,289 @@ | ||
| use std::io::Write; | ||
|
|
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| use serde::Deserialize; | ||
| use serde_json::{Value, json}; | ||
| use tokio::io::AsyncBufReadExt; | ||
|
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| const DESKTOP_BUNDLE_IDS: [&str; 2] = ["so.cap.desktop", "so.cap.desktop.dev"]; | ||
| const PROTOCOL_VERSION: &str = "2025-11-25"; | ||
|
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| #[derive(clap::Args)] | ||
| pub struct McpArgs {} | ||
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| #[derive(Deserialize)] | ||
| #[serde(rename_all = "camelCase", default)] | ||
| struct DesktopMcpSettings { | ||
| enabled: bool, | ||
| token: Option<String>, | ||
| port: Option<u16>, | ||
| } | ||
|
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| impl Default for DesktopMcpSettings { | ||
| fn default() -> Self { | ||
| Self { | ||
| enabled: false, | ||
| token: None, | ||
| port: None, | ||
| } | ||
| } | ||
| } | ||
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| struct McpEndpoint { | ||
| endpoint: String, | ||
| token: String, | ||
| } | ||
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| impl McpArgs { | ||
| pub async fn run(self) -> Result<(), String> { | ||
| run_stdio().await | ||
| } | ||
| } | ||
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| async fn run_stdio() -> Result<(), String> { | ||
| let endpoint = load_endpoint(); | ||
| let client = reqwest::Client::builder() | ||
| .no_proxy() | ||
| .build() | ||
| .map_err(|err| format!("Failed to create MCP HTTP client: {err}"))?; | ||
| let mut session_id: Option<String> = None; | ||
| let mut lines = tokio::io::BufReader::new(tokio::io::stdin()).lines(); | ||
|
|
||
| while let Some(line) = lines | ||
| .next_line() | ||
| .await | ||
| .map_err(|err| format!("Failed to read MCP stdin: {err}"))? | ||
| { | ||
| if line.trim().is_empty() { | ||
| continue; | ||
| } | ||
|
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| let id = request_id(&line); | ||
| let result = match &endpoint { | ||
| Ok(endpoint) => forward_message(&client, endpoint, &line, session_id.as_deref()).await, | ||
| Err(message) => Err(message.clone()), | ||
| }; | ||
|
|
||
| match result { | ||
| Ok(ForwardedResponse::Accepted) => {} | ||
| Ok(ForwardedResponse::Json { | ||
| body, | ||
| next_session_id, | ||
| }) => { | ||
| if let Some(next_session_id) = next_session_id { | ||
| session_id = Some(next_session_id); | ||
| } | ||
| write_json_line(&body)?; | ||
| } | ||
| Err(message) => { | ||
| if let Some(id) = id { | ||
| write_json_line(&json_rpc_error( | ||
| id, | ||
| -32000, | ||
| format!( | ||
| "{message}. Launch Cap Desktop and enable MCP before using cap mcp." | ||
| ), | ||
| ))?; | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
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| if let (Ok(endpoint), Some(session_id)) = (&endpoint, session_id.as_deref()) | ||
| && let Err(err) = delete_session(&client, endpoint, session_id).await | ||
| { | ||
| eprintln!("Failed to close Cap Desktop MCP session: {err}"); | ||
| } | ||
|
|
||
| Ok(()) | ||
| } | ||
|
|
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| enum ForwardedResponse { | ||
| Accepted, | ||
| Json { | ||
| body: Value, | ||
| next_session_id: Option<String>, | ||
| }, | ||
| } | ||
|
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| async fn forward_message( | ||
| client: &reqwest::Client, | ||
| endpoint: &McpEndpoint, | ||
| line: &str, | ||
| session_id: Option<&str>, | ||
| ) -> Result<ForwardedResponse, String> { | ||
| let mut request = client | ||
| .post(&endpoint.endpoint) | ||
| .bearer_auth(&endpoint.token) | ||
| .header("Accept", "application/json, text/event-stream") | ||
| .header("Content-Type", "application/json") | ||
| .header("MCP-Protocol-Version", PROTOCOL_VERSION) | ||
| .body(line.to_string()); | ||
|
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| if let Some(session_id) = session_id { | ||
| request = request.header("Mcp-Session-Id", session_id); | ||
| } | ||
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| let response = request | ||
| .send() | ||
| .await | ||
| .map_err(|err| format!("Cap Desktop MCP endpoint is unavailable: {err}"))?; | ||
|
|
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| if response.status() == reqwest::StatusCode::ACCEPTED { | ||
| return Ok(ForwardedResponse::Accepted); | ||
| } | ||
|
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| let status = response.status(); | ||
| let next_session_id = response | ||
| .headers() | ||
| .get("Mcp-Session-Id") | ||
| .and_then(|value| value.to_str().ok()) | ||
| .map(str::to_string); | ||
| let body = response | ||
| .json::<Value>() | ||
| .await | ||
| .map_err(|err| format!("Cap Desktop returned invalid MCP JSON: {err}"))?; | ||
|
|
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| if !status.is_success() { | ||
| return Err(format!( | ||
| "Cap Desktop MCP request failed with {status}: {body}" | ||
| )); | ||
| } | ||
|
|
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| Ok(ForwardedResponse::Json { | ||
| body, | ||
| next_session_id, | ||
| }) | ||
| } | ||
|
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| async fn delete_session( | ||
| client: &reqwest::Client, | ||
| endpoint: &McpEndpoint, | ||
| session_id: &str, | ||
| ) -> Result<(), String> { | ||
| let response = delete_session_request(client, endpoint, session_id) | ||
| .send() | ||
| .await | ||
| .map_err(|err| format!("Failed to delete MCP session: {err}"))?; | ||
|
|
||
| if matches!( | ||
| response.status(), | ||
| reqwest::StatusCode::ACCEPTED | reqwest::StatusCode::NOT_FOUND | ||
| ) { | ||
| Ok(()) | ||
| } else { | ||
| Err(format!( | ||
| "Cap Desktop returned {} while deleting the MCP session", | ||
| response.status() | ||
| )) | ||
| } | ||
| } | ||
|
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| fn delete_session_request( | ||
| client: &reqwest::Client, | ||
| endpoint: &McpEndpoint, | ||
| session_id: &str, | ||
| ) -> reqwest::RequestBuilder { | ||
| client | ||
| .delete(&endpoint.endpoint) | ||
| .bearer_auth(&endpoint.token) | ||
| .header("MCP-Protocol-Version", PROTOCOL_VERSION) | ||
| .header("Mcp-Session-Id", session_id) | ||
| } | ||
|
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| fn load_endpoint() -> Result<McpEndpoint, String> { | ||
| let data_dir = dirs::data_dir().ok_or("Cap Desktop data directory was not found")?; | ||
|
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| for bundle_id in DESKTOP_BUNDLE_IDS { | ||
| let path = data_dir.join(bundle_id).join("store"); | ||
| let Ok(bytes) = std::fs::read(&path) else { | ||
| continue; | ||
| }; | ||
| let store: Value = serde_json::from_slice(&bytes) | ||
| .map_err(|err| format!("Failed to parse Cap Desktop store: {err}"))?; | ||
| let settings = store | ||
| .get("mcp") | ||
| .cloned() | ||
| .map(serde_json::from_value::<DesktopMcpSettings>) | ||
| .transpose() | ||
| .map_err(|err| format!("Failed to parse Cap Desktop MCP settings: {err}"))? | ||
| .unwrap_or_default(); | ||
|
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| if !settings.enabled { | ||
| continue; | ||
| } | ||
|
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| let token = settings | ||
| .token | ||
| .filter(|token| !token.is_empty()) | ||
| .ok_or("Cap Desktop MCP token is missing")?; | ||
| let port = settings.port.ok_or("Cap Desktop MCP port is missing")?; | ||
|
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| return Ok(McpEndpoint { | ||
| endpoint: format!("http://127.0.0.1:{port}/mcp"), | ||
| token, | ||
| }); | ||
| } | ||
|
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| Err("Cap Desktop MCP is not enabled or no running endpoint was found".to_string()) | ||
| } | ||
|
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| fn request_id(line: &str) -> Option<Value> { | ||
| serde_json::from_str::<Value>(line) | ||
| .ok() | ||
| .and_then(|value| value.get("id").cloned()) | ||
| } | ||
|
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| fn json_rpc_error(id: Value, code: i64, message: String) -> Value { | ||
| json!({ | ||
| "jsonrpc": "2.0", | ||
| "id": id, | ||
| "error": { | ||
| "code": code, | ||
| "message": message | ||
| } | ||
| }) | ||
| } | ||
|
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| fn write_json_line(value: &Value) -> Result<(), String> { | ||
| let mut stdout = std::io::stdout().lock(); | ||
| serde_json::to_writer(&mut stdout, value) | ||
| .map_err(|err| format!("Failed to write MCP stdout: {err}"))?; | ||
| stdout | ||
| .write_all(b"\n") | ||
| .map_err(|err| format!("Failed to write MCP stdout: {err}"))?; | ||
| stdout | ||
| .flush() | ||
| .map_err(|err| format!("Failed to flush MCP stdout: {err}")) | ||
| } | ||
|
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| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
|
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| #[test] | ||
| fn builds_authenticated_session_delete_request() { | ||
| let client = reqwest::Client::builder().no_proxy().build().unwrap(); | ||
| let endpoint = McpEndpoint { | ||
| endpoint: "http://127.0.0.1:1234/mcp".to_string(), | ||
| token: "test-token".to_string(), | ||
| }; | ||
| let request = delete_session_request(&client, &endpoint, "test-session") | ||
| .build() | ||
| .unwrap(); | ||
|
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| assert_eq!(request.method(), reqwest::Method::DELETE); | ||
| assert_eq!(request.url().as_str(), endpoint.endpoint); | ||
| assert_eq!( | ||
| request.headers().get("authorization").unwrap(), | ||
| "Bearer test-token" | ||
| ); | ||
| assert_eq!( | ||
| request.headers().get("mcp-protocol-version").unwrap(), | ||
| PROTOCOL_VERSION | ||
| ); | ||
| assert_eq!( | ||
| request.headers().get("mcp-session-id").unwrap(), | ||
| "test-session" | ||
| ); | ||
| } | ||
| } | ||
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You’re advertising
text/event-streamhere but the client always tries to parse the response body as JSON. If the desktop endpoint ever switches to SSE for streaming responses, this will fail; consider restricting theAcceptheader to JSON unless you’re going to implement SSE parsing.