ftl-core 0.0.2

Core library for FTL tools - lightweight MCP server for WebAssembly
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205

use spin_sdk::http::{Method, Request, Response};

use crate::{server::McpServer, tool::Tool, types::JsonRpcRequest};

/// Create a handler function for serving a single FTL Core tool as an MCP
/// server over HTTP
///
/// This function handles all HTTP/CORS details and delegates MCP protocol
/// handling to the McpServer.
pub fn create_handler<T: Tool + 'static>(
    tool: T,
) -> impl Fn(Request) -> Result<Response, String> + Clone {
    move |req: Request| -> Result<Response, String> {
        let server = McpServer::new(tool.clone());
        handle_mcp_request(server, req)
    }
}

fn handle_mcp_request<T: Tool>(server: McpServer<T>, req: Request) -> Result<Response, String> {
    // Handle CORS preflight requests
    if *req.method() == Method::Options {
        return Ok(Response::builder()
            .status(200)
            .header("Access-Control-Allow-Origin", "*")
            .header("Access-Control-Allow-Methods", "POST, OPTIONS")
            .header("Access-Control-Allow-Headers", "Content-Type")
            .header("Content-Type", "application/json")
            .body("")
            .build());
    }

    // Only handle POST requests for JSON-RPC
    if *req.method() != Method::Post {
        return Ok(Response::builder()
            .status(405)
            .header("Access-Control-Allow-Origin", "*")
            .header("Access-Control-Allow-Methods", "POST, OPTIONS")
            .header("Access-Control-Allow-Headers", "Content-Type")
            .header("Content-Type", "application/json")
            .body("Method not allowed")
            .build());
    }

    // Parse the JSON-RPC request
    match read_request_body(&req) {
        Ok(body_str) => match serde_json::from_str::<JsonRpcRequest>(&body_str) {
            Ok(json_req) => {
                let response_data = server.handle_request(json_req);
                let response_json = serde_json::to_string(&response_data)
                    .map_err(|e| format!("Failed to serialize response: {e}"))?;

                Ok(Response::builder()
                    .status(200)
                    .header("Access-Control-Allow-Origin", "*")
                    .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                    .header("Access-Control-Allow-Headers", "Content-Type")
                    .header("Content-Type", "application/json")
                    .body(response_json)
                    .build())
            }
            Err(e) => {
                eprintln!("Failed to parse JSON-RPC request: {e}");
                let error_response =
                    crate::types::JsonRpcResponse::error(None, -32700, "Parse error");

                let response_json = serde_json::to_string(&error_response)
                    .map_err(|e| format!("Failed to serialize error response: {e}"))?;
                Ok(Response::builder()
                    .status(400)
                    .header("Access-Control-Allow-Origin", "*")
                    .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                    .header("Access-Control-Allow-Headers", "Content-Type")
                    .header("Content-Type", "application/json")
                    .body(response_json)
                    .build())
            }
        },
        Err(e) => {
            eprintln!("Failed to read request body: {e}");
            let error_response =
                crate::types::JsonRpcResponse::error(None, -32700, "Failed to read request body");

            let response_json = serde_json::to_string(&error_response)
                .map_err(|e| format!("Failed to serialize error response: {e}"))?;
            Ok(Response::builder()
                .status(400)
                .header("Access-Control-Allow-Origin", "*")
                .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                .header("Access-Control-Allow-Headers", "Content-Type")
                .header("Content-Type", "application/json")
                .body(response_json)
                .build())
        }
    }
}

fn read_request_body(req: &Request) -> Result<String, String> {
    String::from_utf8(req.body().to_vec())
        .map_err(|e| format!("Failed to parse request body as UTF-8: {e}"))
}

/// Macro to create the main entry point for a tool server
///
/// Example:
/// ```rust
/// use ftl_core::prelude::*;
///
/// #[derive(Clone)]
/// struct MyTool;
///
/// impl Tool for MyTool {
///     fn name(&self) -> &'static str {
///         "my-tool"
///     }
///     fn description(&self) -> &'static str {
///         "Example tool"
///     }
///     fn input_schema(&self) -> serde_json::Value {
///         serde_json::json!({})
///     }
///     fn call(&self, _args: &serde_json::Value) -> Result<ToolResult, ToolError> {
///         Ok(ToolResult::text("Hello".to_string()))
///     }
/// }
///
/// // Then use the macro:
/// // ftl_mcp_server!(MyTool);
/// ```
#[macro_export]
macro_rules! ftl_mcp_server {
    ($tool:expr) => {
        #[spin_sdk::http_component]
        fn handle_mcp_request(req: spin_sdk::http::Request) -> spin_sdk::http::Response {
            let server = $crate::McpServer::new($tool);

            // Helper function to create error responses
            let create_error_response = |status: u16, message: &str| {
                spin_sdk::http::Response::builder()
                    .status(status)
                    .header("Access-Control-Allow-Origin", "*")
                    .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                    .header("Access-Control-Allow-Headers", "Content-Type")
                    .header("Content-Type", "application/json")
                    .body(message)
                    .build()
            };

            match req.method() {
                &spin_sdk::http::Method::Options => spin_sdk::http::Response::builder()
                    .status(200)
                    .header("Access-Control-Allow-Origin", "*")
                    .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                    .header("Access-Control-Allow-Headers", "Content-Type")
                    .header("Content-Type", "application/json")
                    .body("")
                    .build(),
                &spin_sdk::http::Method::Post => {
                    let body_str = match String::from_utf8(req.body().to_vec()) {
                        Ok(s) => s,
                        Err(_) => {
                            return create_error_response(400, "Invalid UTF-8 in request body");
                        }
                    };

                    match serde_json::from_str::<$crate::JsonRpcRequest>(&body_str) {
                        Ok(json_req) => {
                            let response_data = server.handle_request(json_req);
                            match serde_json::to_string(&response_data) {
                                Ok(response_json) => spin_sdk::http::Response::builder()
                                    .status(200)
                                    .header("Access-Control-Allow-Origin", "*")
                                    .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                                    .header("Access-Control-Allow-Headers", "Content-Type")
                                    .header("Content-Type", "application/json")
                                    .body(response_json)
                                    .build(),
                                Err(_) => {
                                    create_error_response(500, "Failed to serialize response")
                                }
                            }
                        }
                        Err(_) => {
                            let error_response =
                                $crate::JsonRpcResponse::error(None, -32700, "Parse error");
                            match serde_json::to_string(&error_response) {
                                Ok(response_json) => spin_sdk::http::Response::builder()
                                    .status(400)
                                    .header("Access-Control-Allow-Origin", "*")
                                    .header("Access-Control-Allow-Methods", "POST, OPTIONS")
                                    .header("Access-Control-Allow-Headers", "Content-Type")
                                    .header("Content-Type", "application/json")
                                    .body(response_json)
                                    .build(),
                                Err(_) => {
                                    create_error_response(500, "Failed to serialize error response")
                                }
                            }
                        }
                    }
                }
                _ => create_error_response(405, "Method not allowed"),
            }
        }
    };
}