mcp_memory/
server.rs

1use serde_json::{Value, json};
2use std::num::NonZeroUsize;
3use std::path::Path;
4use std::sync::Arc;
5use std::time::Duration;
6
7use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
8use tokio::net::TcpListener;
9use tokio::sync::Semaphore;
10use tracing::{error, info};
11
12use crate::actions::memory;
13use crate::config::Config;
14use crate::errors::{MCSError, Result};
15use crate::kg::GraphHandle;
16use crate::protocol::{JsonRpcRequest, JsonRpcResponse};
17use crate::tools;
18
19/// Outcome of processing a request: either a pre-escaped JSON Value (small
20/// payloads) or a pre-serialized JSON *string* of the `result` field (avoids
21/// a second serialization pass for large payloads such as `read_graph`).
22enum HandlerResult {
23    Value(Value),
24    RawResult(String),
25}
26
27const BUFFER_CAPACITY: usize = 65536;
28const NEWLINE: &[u8] = b"\n";
29/// Maximum size of a single inbound JSON-RPC message (shared by all transports).
30pub const MAX_REQUEST_BYTES: usize = 16 * 1024 * 1024;
31/// Maximum number of concurrent TCP connections (C4).
32const MAX_TCP_CONNECTIONS: usize = 128;
33
34enum LineRead {
35    Line,
36    Eof,
37    TooLong,
38}
39
40async fn read_line_capped<R>(
41    reader: &mut R,
42    out: &mut String,
43    max: usize,
44) -> std::io::Result<LineRead>
45where
46    R: AsyncBufReadExt + Unpin,
47{
48    out.clear();
49    let mut buf: Vec<u8> = Vec::new();
50    loop {
51        let available = reader.fill_buf().await?;
52        if available.is_empty() {
53            if buf.is_empty() {
54                return Ok(LineRead::Eof);
55            }
56            // Move `buf` into the String — no copy. `buf` is not used afterward.
57            *out = String::from_utf8(buf).map_err(|_| {
58                std::io::Error::new(std::io::ErrorKind::InvalidData, "Non-UTF-8 input")
59            })?;
60            return Ok(LineRead::Line);
61        }
62        match available.iter().position(|&b| b == b'\n') {
63            Some(i) => {
64                if buf.len() + i + 1 > max {
65                    reader.consume(i + 1);
66                    return Ok(LineRead::TooLong);
67                }
68                buf.extend_from_slice(&available[..=i]);
69                reader.consume(i + 1);
70                *out = String::from_utf8(buf).map_err(|_| {
71                    std::io::Error::new(std::io::ErrorKind::InvalidData, "Non-UTF-8 input")
72                })?;
73                return Ok(LineRead::Line);
74            }
75            None => {
76                let take = available.len();
77                if buf.len() + take > max {
78                    reader.consume(take);
79                    return Ok(LineRead::TooLong);
80                }
81                buf.extend_from_slice(available);
82                reader.consume(take);
83            }
84        }
85    }
86}
87
88fn parse_error(msg: String) -> JsonRpcResponse {
89    let mcp_error = MCSError::ParseError(msg);
90    JsonRpcResponse::error(None, mcp_error.error_code(), mcp_error.to_string())
91}
92
93/// Process one parsed JSON-RPC message. `None` means "no reply" — the message
94/// was a notification (no `id`), per JSON-RPC.
95pub fn process_value(value: Value, kg: &GraphHandle) -> Option<Value> {
96    let req: JsonRpcRequest = match serde_json::from_value(value) {
97        Ok(r) => r,
98        Err(e) => return Some(to_value(parse_error(e.to_string()))),
99    };
100    req.id.as_ref()?;
101    
102    match process_request(&req, kg) {
103        Ok(HandlerResult::Value(result)) => {
104            Some(to_value(JsonRpcResponse::success(req.id, result)))
105        }
106        Ok(HandlerResult::RawResult(_)) => {
107            // RawResult cannot pass through Value — dispatch_line and
108            // dispatch_http_body handle it via separate code paths.
109            unreachable!("RawResult must be handled at the dispatch level, not via process_value");
110        }
111        Err(e) => Some(to_value(JsonRpcResponse::error(
112            req.id,
113            e.error_code(),
114            e.to_string(),
115        ))),
116    }
117}
118
119/// Dispatch one framed line (stdio / tcp). Returns the serialized response, or
120/// `None` for a notification.
121pub fn dispatch_line(line: &str, kg: &GraphHandle) -> Option<String> {
122    let trimmed = line.trim();
123    if trimmed.is_empty() {
124        return Some(serde_json::to_string(&parse_error("Empty request".into())).unwrap());
125    }
126    let raw: Value = match serde_json::from_str(trimmed) {
127        Ok(v) => v,
128        Err(e) => return Some(serde_json::to_string(&parse_error(e.to_string())).unwrap()),
129    };
130    let req: JsonRpcRequest = match serde_json::from_value(raw) {
131        Ok(r) => r,
132        Err(e) => return Some(serde_json::to_string(&parse_error(e.to_string())).unwrap()),
133    };
134    req.id.as_ref()?;
135    match process_request(&req, kg) {
136        Ok(HandlerResult::Value(result)) => {
137            let resp = JsonRpcResponse::success(req.id, result);
138            Some(serde_json::to_string(&resp).unwrap())
139        }
140        Ok(HandlerResult::RawResult(result_json)) => {
141            let id_json = serde_json::to_string(&req.id).unwrap();
142            let mut out = String::with_capacity(64 + id_json.len() + result_json.len());
143            out.push_str(r#"{"jsonrpc":"2.0","id":"#);
144            out.push_str(&id_json);
145            out.push_str(",\"result\":");
146            out.push_str(&result_json);
147            out.push('}');
148            Some(out)
149        }
150        Err(e) => {
151            let resp = JsonRpcResponse::error(req.id, e.error_code(), e.to_string());
152            Some(serde_json::to_string(&resp).unwrap())
153        }
154    }
155}
156
157/// Dispatch a Streamable-HTTP POST body, which may be a single JSON-RPC message
158/// or a batch array. `Ok(None)` means the body held only notifications (HTTP
159/// 202, empty body); `Err` means the body was not valid JSON.
160pub fn dispatch_http_body(
161    body: &str,
162    kg: &GraphHandle,
163) -> std::result::Result<Option<Value>, String> {
164    let value: Value = serde_json::from_str(body.trim()).map_err(|e| e.to_string())?;
165    match value {
166        Value::Array(items) => {
167            // Batches are rare and never huge — keep Value path for simplicity.
168            let responses: Vec<Value> = items
169                .into_iter()
170                .filter_map(|v| process_value_http(v, kg))
171                .collect();
172            Ok((!responses.is_empty()).then_some(Value::Array(responses)))
173        }
174        other => Ok(process_value_http(other, kg)),
175    }
176}
177
178/// HTTP variant of process_value that handles RawResult by converting to Value
179/// (acceptable since HTTP payloads are typically much smaller in this context).
180fn process_value_http(value: Value, kg: &GraphHandle) -> Option<Value> {
181    let req: JsonRpcRequest = match serde_json::from_value(value) {
182        Ok(r) => r,
183        Err(e) => return Some(to_value(parse_error(e.to_string()))),
184    };
185    req.id.as_ref()?;
186    match process_request(&req, kg) {
187        Ok(HandlerResult::Value(result)) => {
188            Some(to_value(JsonRpcResponse::success(req.id, result)))
189        }
190        Ok(HandlerResult::RawResult(result_json)) => {
191            // Parse the pre-serialized result back into a Value for HTTP delivery.
192            // This is a small extra cost for the HTTP transport; the stdio/TCP
193            // path (dispatch_line) avoids it entirely.
194            let result_val: Value = serde_json::from_str(&result_json).unwrap_or(Value::Null);
195            Some(to_value(JsonRpcResponse::success(req.id, result_val)))
196        }
197        Err(e) => Some(to_value(JsonRpcResponse::error(
198            req.id,
199            e.error_code(),
200            e.to_string(),
201        ))),
202    }
203}
204
205#[inline]
206fn to_value(resp: JsonRpcResponse) -> Value {
207    serde_json::to_value(resp).expect("JsonRpcResponse always serializes")
208}
209
210pub struct MCPServer {
211    config: Arc<Config>,
212    kg: Arc<GraphHandle>,
213}
214
215impl MCPServer {
216    pub fn new(config: Config) -> Result<Self> {
217        let path = Path::new(&config.memory_file_path);
218        let lru_cache = NonZeroUsize::new(config.lru_cache_size).unwrap_or_else(|| {
219            NonZeroUsize::new(10000).expect("10000 > 0")
220        });
221        let kg = GraphHandle::new(
222            path,
223            config.durability,
224            config.mmap_size,
225            lru_cache,
226            config.read_pool_size,
227        )?;
228
229        Ok(Self {
230            config: Arc::new(config),
231            kg: Arc::new(kg),
232        })
233    }
234
235    /// Expose the shared graph handle (used to drive the HTTP transport).
236    pub fn graph(&self) -> Arc<GraphHandle> {
237        Arc::clone(&self.kg)
238    }
239
240    /// stdio transport: newline-delimited JSON-RPC over stdin/stdout.
241    pub async fn run_stdio(&self) -> Result<()> {
242        spawn_maintenance(self.kg.clone());
243        let stdin = tokio::io::stdin();
244        let mut reader = BufReader::with_capacity(BUFFER_CAPACITY, stdin);
245        let mut stdout = tokio::io::stdout();
246        serve_line_conn(&mut reader, &mut stdout, Arc::clone(&self.kg)).await
247    }
248
249    /// TCP transport: each accepted connection speaks newline-delimited
250    /// JSON-RPC, exactly like stdio. Connections are served concurrently (up to
251    /// [`MAX_TCP_CONNECTIONS`]) and share the one graph behind its mutex.
252    pub async fn run_tcp(&self, addr: &str) -> Result<()> {
253        spawn_maintenance(self.kg.clone());
254        let listener = TcpListener::bind(addr).await.map_err(MCSError::IoError)?;
255        let semaphore = Arc::new(Semaphore::new(MAX_TCP_CONNECTIONS));
256        let auth_token = self.config.auth_token.clone();
257        info!(
258            "Listening for TCP MCP connections on {addr} (max {MAX_TCP_CONNECTIONS}, auth {})",
259            if auth_token.is_some() { "on" } else { "off" }
260        );
261        loop {
262            let permit = Arc::clone(&semaphore).acquire_owned().await;
263            let (socket, peer) = listener.accept().await.map_err(MCSError::IoError)?;
264            let kg = Arc::clone(&self.kg);
265            let auth_token = auth_token.clone();
266            tokio::spawn(async move {
267                let _permit = permit; // held for the connection lifetime
268                let (read_half, mut write_half) = socket.into_split();
269                let mut reader = BufReader::with_capacity(BUFFER_CAPACITY, read_half);
270                // When a token is configured, the client must send it as the
271                // first line before any JSON-RPC traffic.
272                if let Some(ref expected) = auth_token {
273                    match authenticate_line_conn(&mut reader, expected).await {
274                        Ok(true) => {}
275                        Ok(false) => {
276                            let _ = write_half.write_all(AUTH_REQUIRED_LINE.as_bytes()).await;
277                            let _ = write_half.flush().await;
278                            return;
279                        }
280                        Err(e) => {
281                            error!("TCP auth error for {peer}: {e}");
282                            return;
283                        }
284                    }
285                }
286                if let Err(e) = serve_line_conn(&mut reader, &mut write_half, kg).await {
287                    error!("TCP connection {peer} error: {e}");
288                }
289            });
290        }
291    }
292
293    /// MCP Streamable HTTP transport (POST/GET `/mcp`, JSON or SSE responses).
294    pub async fn run_http(&self, addr: &str) -> Result<()> {
295        spawn_maintenance(self.kg.clone());
296        crate::http::run(addr, self.graph(), self.config.auth_token.clone()).await
297    }
298}
299
300/// Spawn a background task that runs periodic database maintenance every
301/// 5 minutes until the runtime shuts down.
302fn spawn_maintenance(kg: Arc<GraphHandle>) {
303    tokio::spawn(async move {
304        let mut interval = tokio::time::interval(Duration::from_secs(300));
305        interval.tick().await; // skip immediate first tick
306        loop {
307            interval.tick().await;
308            let kg = kg.clone();
309            tokio::task::spawn_blocking(move || {
310                if let Err(e) = kg.run_maintenance() {
311                    tracing::warn!("Maintenance error: {e}");
312                }
313            })
314            .await
315            .ok();
316        }
317    });
318}
319
320/// JSON-RPC error line returned to a TCP client that fails authentication.
321const AUTH_REQUIRED_LINE: &str = "{\"jsonrpc\":\"2.0\",\"error\":{\"code\":-32001,\
322\"message\":\"Authentication required: send the bearer token as the first line\"},\"id\":null}\n";
323
324/// Read the first line of a connection and compare it (constant-time) to the
325/// expected bearer token. Returns `Ok(false)` on EOF / oversized first line.
326async fn authenticate_line_conn<R>(reader: &mut R, expected: &str) -> Result<bool>
327where
328    R: AsyncBufReadExt + Unpin,
329{
330    let mut line = String::new();
331    match read_line_capped(reader, &mut line, MAX_REQUEST_BYTES)
332        .await
333        .map_err(MCSError::IoError)?
334    {
335        LineRead::Line => Ok(token_matches(&line, expected)),
336        _ => Ok(false),
337    }
338}
339
340/// Drive one line-framed connection (stdio or a single TCP socket): read
341/// newline-delimited JSON-RPC requests, write newline-delimited responses.
342/// Notifications produce no output. Returns when the peer closes the stream.
343/// The dispatch path (graph lock + optional fsync) is offloaded to
344/// [`tokio::task::spawn_blocking`] to keep the async reactor responsive (C3).
345async fn serve_line_conn<R, W>(reader: &mut R, writer: &mut W, kg: Arc<GraphHandle>) -> Result<()>
346where
347    R: AsyncBufReadExt + Unpin,
348    W: AsyncWriteExt + Unpin,
349{
350    let mut line = String::with_capacity(1024);
351    let mut out = Vec::with_capacity(BUFFER_CAPACITY);
352
353    loop {
354        match read_line_capped(reader, &mut line, MAX_REQUEST_BYTES).await {
355            Ok(LineRead::Eof) => break,
356            Ok(LineRead::Line) => {
357                let line_copy = line.clone();
358                let kg_clone = Arc::clone(&kg);
359                let resp =
360                    tokio::task::spawn_blocking(move || dispatch_line(&line_copy, &kg_clone))
361                        .await
362                        .map_err(|join_err| {
363                            error!("dispatch task panicked: {join_err}");
364                            MCSError::IoError(std::io::Error::other("dispatch task panicked"))
365                        })?;
366                if let Some(resp) = resp {
367                    out.clear();
368                    out.extend_from_slice(resp.as_bytes());
369                    out.extend_from_slice(NEWLINE);
370                    writer.write_all(&out).await.map_err(MCSError::IoError)?;
371                    writer.flush().await.map_err(MCSError::IoError)?;
372                }
373            }
374            Ok(LineRead::TooLong) => {
375                let err = MCSError::InvalidParams("Request exceeds maximum size of 16MB".into());
376                let response = JsonRpcResponse::error(None, err.error_code(), err.to_string());
377                out.clear();
378                serde_json::to_writer(&mut out, &response).map_err(MCSError::JsonError)?;
379                out.extend_from_slice(NEWLINE);
380                writer.write_all(&out).await.map_err(MCSError::IoError)?;
381                writer.flush().await.map_err(MCSError::IoError)?;
382                break;
383            }
384            Err(e) => {
385                error!("IO error: {}", e);
386                break;
387            }
388        }
389    }
390    Ok(())
391}
392
393fn process_request(req: &JsonRpcRequest, kg: &GraphHandle) -> Result<HandlerResult> {
394    match req.method.as_str() {
395        "initialize" => Ok(HandlerResult::Value(handle_initialize(req))),
396        "tools/list" => Ok(HandlerResult::Value(handle_tools_list())),
397        "tools/call" => handle_tools_call(req, kg),
398        "ping" => Ok(HandlerResult::Value(Value::Null)),
399        method if method.starts_with("notifications/") => {
400            tracing::trace!("Received notification: {method}");
401            Ok(HandlerResult::Value(Value::Null))
402        }
403        _ => Err(MCSError::MethodNotFound(req.method.clone())),
404    }
405}
406
407/// MCP protocol revisions this server can speak, newest first (for `initialize`
408/// version negotiation).
409const SUPPORTED_PROTOCOL_VERSIONS: &[&str] =
410    &["2025-11-25", "2025-06-18", "2025-03-26", "2024-11-05"];
411/// Newest revision we implement; offered when the client requests an unknown one.
412const LATEST_PROTOCOL_VERSION: &str = "2025-11-25";
413
414/// `instructions` surfaced to the client and appended to the model's system prompt.
415const SERVER_INSTRUCTIONS: &str = "Knowledge-graph memory MCP server. Entity names are unique and \
416case-sensitive. Use `create_entities`/`create_relations` to build the graph, `add_observations` to \
417attach facts, and `search_nodes`/`open_nodes`/`read_graph` to retrieve. Prefer `upsert_entities` for \
418idempotent writes and `merge_entities` to collapse duplicates. Tool failures are returned with \
419`isError: true` rather than as protocol errors — read the message and retry.";
420
421fn handle_initialize(req: &JsonRpcRequest) -> Value {
422    // Version negotiation: echo a supported requested revision, else offer latest.
423    let protocol_version = req
424        .params
425        .as_ref()
426        .and_then(|p| p.get("protocolVersion"))
427        .and_then(Value::as_str)
428        .filter(|v| SUPPORTED_PROTOCOL_VERSIONS.contains(v))
429        .unwrap_or(LATEST_PROTOCOL_VERSION);
430
431    json!({
432        "protocolVersion": protocol_version,
433        "capabilities": {
434            "tools": { "listChanged": false }
435        },
436        "serverInfo": {
437            "name": "mcp-memory",
438            "version": env!("CARGO_PKG_VERSION")
439        },
440        "instructions": SERVER_INSTRUCTIONS
441    })
442}
443
444/// Wrap a tool execution failure as an MCP `CallToolResult` with `isError: true`
445/// so the model sees the message and can self-correct, instead of receiving an
446/// opaque JSON-RPC protocol error. (Successful results are already content-
447/// wrapped by the action handlers.)
448#[inline]
449fn tool_error(message: &str) -> Value {
450    json!({
451        "content": [{ "type": "text", "text": message }],
452        "isError": true
453    })
454}
455
456/// Constant-time bearer-token check. Accepts the raw token or a `Bearer <token>`
457/// form; surrounding whitespace is trimmed.
458pub fn token_matches(presented: &str, expected: &str) -> bool {
459    use subtle::ConstantTimeEq;
460    let presented = presented.trim();
461    let presented = presented
462        .strip_prefix("Bearer ")
463        .unwrap_or(presented)
464        .trim();
465    presented.as_bytes().ct_eq(expected.as_bytes()).into()
466}
467
468fn handle_tools_list() -> Value {
469    static CACHED: std::sync::OnceLock<Value> = std::sync::OnceLock::new();
470    if let Some(cached) = CACHED.get() {
471        return cached.clone();
472    }
473    let tools_json = include_str!("../tools.json");
474    let tools: Vec<Value> = serde_json::from_str(tools_json)
475        .expect("tools.json is valid JSON compiled at build time");
476    let result = json!({ "tools": tools });
477    let _ = CACHED.set(result.clone());
478    result
479}
480
481fn handle_tools_call(req: &JsonRpcRequest, kg: &GraphHandle) -> Result<HandlerResult> {
482    let tool_name = req
483        .params
484        .as_ref()
485        .and_then(|p| p.get("name").and_then(|v| v.as_str()))
486        .ok_or_else(|| MCSError::InvalidParams("Missing 'name' parameter".into()))?;
487
488    let tool_args = req.params.as_ref().and_then(|p| p.get("arguments"));
489
490    if !tools::tool_exists(tool_name) {
491        return Err(MCSError::MethodNotFound(tool_name.to_string()));
492    }
493
494    let result = match tool_name {
495        // Raw-result handlers (large payloads, avoid second serialization pass).
496        "read_graph" => memory::handle_read_graph(kg, tool_args).map(HandlerResult::RawResult),
497        "search_nodes" => memory::handle_search_nodes(kg, tool_args).map(HandlerResult::RawResult),
498        // Standard Value handlers.
499        "create_entities" => {
500            memory::handle_create_entities(kg, tool_args).map(HandlerResult::Value)
501        }
502        "create_relations" => {
503            memory::handle_create_relations(kg, tool_args).map(HandlerResult::Value)
504        }
505        "add_observations" => {
506            memory::handle_add_observations(kg, tool_args).map(HandlerResult::Value)
507        }
508        "delete_entities" => {
509            memory::handle_delete_entities(kg, tool_args).map(HandlerResult::Value)
510        }
511        "delete_observations" => {
512            memory::handle_delete_observations(kg, tool_args).map(HandlerResult::Value)
513        }
514        "delete_relations" => {
515            memory::handle_delete_relations(kg, tool_args).map(HandlerResult::Value)
516        }
517        "open_nodes" => memory::handle_open_nodes(kg, tool_args).map(HandlerResult::Value),
518        "get_entity" => memory::handle_get_entity(kg, tool_args).map(HandlerResult::Value),
519        "graph_stats" => memory::handle_graph_stats(kg).map(HandlerResult::Value),
520        "search_relations" => {
521            memory::handle_search_relations(kg, tool_args).map(HandlerResult::Value)
522        }
523        "find_path" => memory::handle_find_path(kg, tool_args).map(HandlerResult::Value),
524        "compact" => memory::handle_compact(kg).map(HandlerResult::Value),
525        "get_neighbors" => memory::handle_get_neighbors(kg, tool_args).map(HandlerResult::Value),
526        "describe_entity" => {
527            memory::handle_describe_entity(kg, tool_args).map(HandlerResult::Value)
528        }
529        "list_entity_types" => memory::handle_list_entity_types(kg).map(HandlerResult::Value),
530        "list_relation_types" => memory::handle_list_relation_types(kg).map(HandlerResult::Value),
531        "upsert_entities" => {
532            memory::handle_upsert_entities(kg, tool_args).map(HandlerResult::Value)
533        }
534        "export_graph" => memory::handle_export_graph(kg, tool_args).map(HandlerResult::Value),
535        "merge_entities" => memory::handle_merge_entities(kg, tool_args).map(HandlerResult::Value),
536        "extract_subgraph" => {
537            memory::handle_extract_subgraph(kg, tool_args).map(HandlerResult::Value)
538        }
539        "batch_get_entities" => {
540            memory::handle_batch_get_entities(kg, tool_args).map(HandlerResult::Value)
541        }
542        "find_all_paths" => memory::handle_find_all_paths(kg, tool_args).map(HandlerResult::Value),
543        "entity_exists" => memory::handle_entity_exists(kg, tool_args).map(HandlerResult::Value),
544        "degree" => memory::handle_degree(kg, tool_args).map(HandlerResult::Value),
545        tool => Err(MCSError::MethodNotFound(tool.to_string())),
546    };
547
548    // Tool execution failures become isError CallToolResults so the model can
549    // read the message and self-correct, instead of an opaque protocol error.
550    Ok(result.unwrap_or_else(|e| {
551        error!("Tool '{tool_name}' error: {e}");
552        HandlerResult::Value(tool_error(&e.to_string()))
553    }))
554}
555
556
mcp_memory/server.rs

mcp_memory/
server.rs
