[mcp-server] Expose fuzzy file search in MCP (#2677)

## Summary
Expose a simple fuzzy file search implementation for mcp clients to work
with

## Testing
- [x] Tested locally

codex-rs/Cargo.lock

@@ -916,6 +916,7 @@ dependencies = [
  "codex-arg0",
  "codex-common",
  "codex-core",
+ "codex-file-search",
  "codex-login",
  "codex-protocol",
  "core_test_support",

codex-rs/file-search/src/lib.rs

@@ -287,10 +287,27 @@ pub fn run(
 
 /// Sort matches in-place by descending score, then ascending path.
 fn sort_matches(matches: &mut [(u32, String)]) {
-    matches.sort_by(|a, b| match b.0.cmp(&a.0) {
-        std::cmp::Ordering::Equal => a.1.cmp(&b.1),
+    matches.sort_by(cmp_by_score_desc_then_path_asc::<(u32, String), _, _>(
+        |t| t.0,
+        |t| t.1.as_str(),
+    ));
+}
+
+/// Returns a comparator closure suitable for `slice.sort_by(...)` that orders
+/// items by descending score and then ascending path using the provided accessors.
+pub fn cmp_by_score_desc_then_path_asc<T, FScore, FPath>(
+    score_of: FScore,
+    path_of: FPath,
+) -> impl FnMut(&T, &T) -> std::cmp::Ordering
+where
+    FScore: Fn(&T) -> u32,
+    FPath: Fn(&T) -> &str,
+{
+    use std::cmp::Ordering;
+    move |a, b| match score_of(b).cmp(&score_of(a)) {
+        Ordering::Equal => path_of(a).cmp(path_of(b)),
         other => other,
-    });
+    }
 }
 
 /// Maintains the `max_count` best matches for a given pattern.

codex-rs/mcp-server/Cargo.toml

@@ -19,6 +19,7 @@ anyhow = { workspace = true }
 codex-arg0 = { workspace = true }
 codex-common = { workspace = true, features = ["cli"] }
 codex-core = { workspace = true }
+codex-file-search = { workspace = true }
 codex-login = { workspace = true }
 codex-protocol = { workspace = true }
 mcp-types = { workspace = true }

codex-rs/mcp-server/src/codex_message_processor.rs

@@ -1,5 +1,6 @@
 use crate::error_code::INTERNAL_ERROR_CODE;
 use crate::error_code::INVALID_REQUEST_ERROR_CODE;
+use crate::fuzzy_file_search::run_fuzzy_file_search;
 use crate::json_to_toml::json_to_toml;
 use crate::outgoing_message::OutgoingMessageSender;
 use crate::outgoing_message::OutgoingNotification;
@@ -52,6 +53,8 @@ use codex_protocol::mcp_protocol::ExecArbitraryCommandResponse;
 use codex_protocol::mcp_protocol::ExecCommandApprovalParams;
 use codex_protocol::mcp_protocol::ExecCommandApprovalResponse;
 use codex_protocol::mcp_protocol::ExecOneOffCommandParams;
+use codex_protocol::mcp_protocol::FuzzyFileSearchParams;
+use codex_protocol::mcp_protocol::FuzzyFileSearchResponse;
 use codex_protocol::mcp_protocol::GetUserAgentResponse;
 use codex_protocol::mcp_protocol::GetUserSavedConfigResponse;
 use codex_protocol::mcp_protocol::GitDiffToRemoteResponse;
@@ -88,6 +91,8 @@ use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::path::PathBuf;
 use std::sync::Arc;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
 use std::time::Duration;
 use tokio::select;
 use tokio::sync::Mutex;
@@ -122,6 +127,7 @@ pub(crate) struct CodexMessageProcessor {
     active_login: Arc<Mutex<Option<ActiveLogin>>>,
     // Queue of pending interrupt requests per conversation. We reply when TurnAborted arrives.
     pending_interrupts: Arc<Mutex<HashMap<ConversationId, Vec<RequestId>>>>,
+    pending_fuzzy_searches: Arc<Mutex<HashMap<String, Arc<AtomicBool>>>>,
 }
 
 impl CodexMessageProcessor {
@@ -141,6 +147,7 @@ impl CodexMessageProcessor {
             conversation_listeners: HashMap::new(),
             active_login: Arc::new(Mutex::new(None)),
             pending_interrupts: Arc::new(Mutex::new(HashMap::new())),
+            pending_fuzzy_searches: Arc::new(Mutex::new(HashMap::new())),
         }
     }
 
@@ -206,6 +213,9 @@ impl CodexMessageProcessor {
             ClientRequest::UserInfo { request_id } => {
                 self.get_user_info(request_id).await;
             }
+            ClientRequest::FuzzyFileSearch { request_id, params } => {
+                self.fuzzy_file_search(request_id, params).await;
+            }
             ClientRequest::ExecOneOffCommand { request_id, params } => {
                 self.exec_one_off_command(request_id, params).await;
             }
@@ -1167,6 +1177,46 @@ impl CodexMessageProcessor {
             }
         }
     }
+
+    async fn fuzzy_file_search(&mut self, request_id: RequestId, params: FuzzyFileSearchParams) {
+        let FuzzyFileSearchParams {
+            query,
+            roots,
+            cancellation_token,
+        } = params;
+
+        let cancel_flag = match cancellation_token.clone() {
+            Some(token) => {
+                let mut pending_fuzzy_searches = self.pending_fuzzy_searches.lock().await;
+                // if a cancellation_token is provided and a pending_request exists for
+                // that token, cancel it
+                if let Some(existing) = pending_fuzzy_searches.get(&token) {
+                    existing.store(true, Ordering::Relaxed);
+                }
+                let flag = Arc::new(AtomicBool::new(false));
+                pending_fuzzy_searches.insert(token.clone(), flag.clone());
+                flag
+            }
+            None => Arc::new(AtomicBool::new(false)),
+        };
+
+        let results = match query.as_str() {
+            "" => vec![],
+            _ => run_fuzzy_file_search(query, roots, cancel_flag.clone()).await,
+        };
+
+        if let Some(token) = cancellation_token {
+            let mut pending_fuzzy_searches = self.pending_fuzzy_searches.lock().await;
+            if let Some(current_flag) = pending_fuzzy_searches.get(&token)
+                && Arc::ptr_eq(current_flag, &cancel_flag)
+            {
+                pending_fuzzy_searches.remove(&token);
+            }
+        }
+
+        let response = FuzzyFileSearchResponse { files: results };
+        self.outgoing.send_response(request_id, response).await;
+    }
 }
 
 async fn apply_bespoke_event_handling(

codex-rs/mcp-server/src/fuzzy_file_search.rs

@@ -0,0 +1,84 @@
+use std::num::NonZero;
+use std::num::NonZeroUsize;
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::sync::atomic::AtomicBool;
+
+use codex_file_search as file_search;
+use codex_protocol::mcp_protocol::FuzzyFileSearchResult;
+use tokio::task::JoinSet;
+use tracing::warn;
+
+const LIMIT_PER_ROOT: usize = 50;
+const MAX_THREADS: usize = 12;
+const COMPUTE_INDICES: bool = true;
+
+pub(crate) async fn run_fuzzy_file_search(
+    query: String,
+    roots: Vec<String>,
+    cancellation_flag: Arc<AtomicBool>,
+) -> Vec<FuzzyFileSearchResult> {
+    #[expect(clippy::expect_used)]
+    let limit_per_root =
+        NonZero::new(LIMIT_PER_ROOT).expect("LIMIT_PER_ROOT should be a valid non-zero usize");
+
+    let cores = std::thread::available_parallelism()
+        .map(std::num::NonZero::get)
+        .unwrap_or(1);
+    let threads = cores.min(MAX_THREADS);
+    let threads_per_root = (threads / roots.len()).max(1);
+    let threads = NonZero::new(threads_per_root).unwrap_or(NonZeroUsize::MIN);
+
+    let mut files: Vec<FuzzyFileSearchResult> = Vec::new();
+    let mut join_set = JoinSet::new();
+
+    for root in roots {
+        let search_dir = PathBuf::from(&root);
+        let query = query.clone();
+        let cancel_flag = cancellation_flag.clone();
+        join_set.spawn_blocking(move || {
+            match file_search::run(
+                query.as_str(),
+                limit_per_root,
+                &search_dir,
+                Vec::new(),
+                threads,
+                cancel_flag,
+                COMPUTE_INDICES,
+            ) {
+                Ok(res) => Ok((root, res)),
+                Err(err) => Err((root, err)),
+            }
+        });
+    }
+
+    while let Some(res) = join_set.join_next().await {
+        match res {
+            Ok(Ok((root, res))) => {
+                for m in res.matches {
+                    let result = FuzzyFileSearchResult {
+                        root: root.clone(),
+                        path: m.path,
+                        score: m.score,
+                        indices: m.indices,
+                    };
+                    files.push(result);
+                }
+            }
+            Ok(Err((root, err))) => {
+                warn!("fuzzy-file-search in dir '{root}' failed: {err}");
+            }
+            Err(err) => {
+                warn!("fuzzy-file-search join_next failed: {err}");
+            }
+        }
+    }
+
+    files.sort_by(file_search::cmp_by_score_desc_then_path_asc::<
+        FuzzyFileSearchResult,
+        _,
+        _,
+    >(|f| f.score, |f| f.path.as_str()));
+
+    files
+}

codex-rs/mcp-server/src/lib.rs

@@ -25,6 +25,7 @@ mod codex_tool_config;
 mod codex_tool_runner;
 mod error_code;
 mod exec_approval;
+mod fuzzy_file_search;
 mod json_to_toml;
 pub(crate) mod message_processor;
 mod outgoing_message;

codex-rs/mcp-server/tests/common/mcp_process.rs

@@ -357,6 +357,23 @@ impl McpProcess {
         self.send_request("logoutChatGpt", None).await
     }
 
+    /// Send a `fuzzyFileSearch` JSON-RPC request.
+    pub async fn send_fuzzy_file_search_request(
+        &mut self,
+        query: &str,
+        roots: Vec<String>,
+        cancellation_token: Option<String>,
+    ) -> anyhow::Result<i64> {
+        let mut params = serde_json::json!({
+            "query": query,
+            "roots": roots,
+        });
+        if let Some(token) = cancellation_token {
+            params["cancellationToken"] = serde_json::json!(token);
+        }
+        self.send_request("fuzzyFileSearch", Some(params)).await
+    }
+
     async fn send_request(
         &mut self,
         method: &str,

codex-rs/mcp-server/tests/suite/fuzzy_file_search.rs

@@ -0,0 +1,104 @@
+use mcp_test_support::McpProcess;
+use mcp_types::JSONRPCResponse;
+use mcp_types::RequestId;
+use pretty_assertions::assert_eq;
+use serde_json::json;
+use tempfile::TempDir;
+use tokio::time::timeout;
+
+const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_fuzzy_file_search_sorts_and_includes_indices() {
+    // Prepare a temporary Codex home and a separate root with test files.
+    let codex_home = TempDir::new().expect("create temp codex home");
+    let root = TempDir::new().expect("create temp search root");
+
+    // Create files designed to have deterministic ordering for query "abc".
+    std::fs::write(root.path().join("abc"), "x").expect("write file abc");
+    std::fs::write(root.path().join("abcde"), "x").expect("write file abcx");
+    std::fs::write(root.path().join("abexy"), "x").expect("write file abcx");
+    std::fs::write(root.path().join("zzz.txt"), "x").expect("write file zzz");
+
+    // Start MCP server and initialize.
+    let mut mcp = McpProcess::new(codex_home.path()).await.expect("spawn mcp");
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize())
+        .await
+        .expect("init timeout")
+        .expect("init failed");
+
+    let root_path = root.path().to_string_lossy().to_string();
+    // Send fuzzyFileSearch request.
+    let request_id = mcp
+        .send_fuzzy_file_search_request("abe", vec![root_path.clone()], None)
+        .await
+        .expect("send fuzzyFileSearch");
+
+    // Read response and verify shape and ordering.
+    let resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(request_id)),
+    )
+    .await
+    .expect("fuzzyFileSearch timeout")
+    .expect("fuzzyFileSearch resp");
+
+    let value = resp.result;
+    assert_eq!(
+        value,
+        json!({
+            "files": [
+                { "root": root_path.clone(), "path": "abexy", "score": 88, "indices": [0, 1, 2] },
+                { "root": root_path.clone(), "path": "abcde", "score": 74, "indices": [0, 1, 4] },
+            ]
+        })
+    );
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_fuzzy_file_search_accepts_cancellation_token() {
+    let codex_home = TempDir::new().expect("create temp codex home");
+    let root = TempDir::new().expect("create temp search root");
+
+    std::fs::write(root.path().join("alpha.txt"), "contents").expect("write alpha");
+
+    let mut mcp = McpProcess::new(codex_home.path()).await.expect("spawn mcp");
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize())
+        .await
+        .expect("init timeout")
+        .expect("init failed");
+
+    let root_path = root.path().to_string_lossy().to_string();
+    let request_id = mcp
+        .send_fuzzy_file_search_request("alp", vec![root_path.clone()], None)
+        .await
+        .expect("send fuzzyFileSearch");
+
+    let request_id_2 = mcp
+        .send_fuzzy_file_search_request(
+            "alp",
+            vec![root_path.clone()],
+            Some(request_id.to_string()),
+        )
+        .await
+        .expect("send fuzzyFileSearch");
+
+    let resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(request_id_2)),
+    )
+    .await
+    .expect("fuzzyFileSearch timeout")
+    .expect("fuzzyFileSearch resp");
+
+    let files = resp
+        .result
+        .get("files")
+        .and_then(|value| value.as_array())
+        .cloned()
+        .expect("files array");
+
+    assert_eq!(files.len(), 1);
+    assert_eq!(files[0]["root"], root_path);
+    assert_eq!(files[0]["path"], "alpha.txt");
+}

codex-rs/mcp-server/tests/suite/mod.rs

@@ -5,6 +5,7 @@ mod codex_message_processor_flow;
 mod codex_tool;
 mod config;
 mod create_conversation;
+mod fuzzy_file_search;
 mod interrupt;
 mod list_resume;
 mod login;

codex-rs/protocol-ts/src/lib.rs

@@ -39,6 +39,9 @@ pub fn generate_ts(out_dir: &Path, prettier: Option<&Path>) -> Result<()> {
     codex_protocol::mcp_protocol::GetAuthStatusResponse::export_all_to(out_dir)?;
     codex_protocol::mcp_protocol::ApplyPatchApprovalResponse::export_all_to(out_dir)?;
     codex_protocol::mcp_protocol::ExecCommandApprovalResponse::export_all_to(out_dir)?;
+    codex_protocol::mcp_protocol::FuzzyFileSearchParams::export_all_to(out_dir)?;
+    codex_protocol::mcp_protocol::FuzzyFileSearchResult::export_all_to(out_dir)?;
+    codex_protocol::mcp_protocol::FuzzyFileSearchResponse::export_all_to(out_dir)?;
     codex_protocol::mcp_protocol::GetUserSavedConfigResponse::export_all_to(out_dir)?;
     codex_protocol::mcp_protocol::SetDefaultModelResponse::export_all_to(out_dir)?;
     codex_protocol::mcp_protocol::GetUserAgentResponse::export_all_to(out_dir)?;

codex-rs/protocol/src/mcp_protocol.rs

@@ -184,6 +184,11 @@ pub enum ClientRequest {
         #[serde(rename = "id")]
         request_id: RequestId,
     },
+    FuzzyFileSearch {
+        #[serde(rename = "id")]
+        request_id: RequestId,
+        params: FuzzyFileSearchParams,
+    },
     /// Execute a command (argv vector) under the server's sandbox.
     ExecOneOffCommand {
         #[serde(rename = "id")]
@@ -662,6 +667,32 @@ pub struct ApplyPatchApprovalResponse {
     pub decision: ReviewDecision,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(rename_all = "camelCase")]
+pub struct FuzzyFileSearchParams {
+    pub query: String,
+    pub roots: Vec<String>,
+    // if provided, will cancel any previous request that used the same value
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cancellation_token: Option<String>,
+}
+
+/// Superset of [`codex_file_search::FileMatch`]
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, TS)]
+pub struct FuzzyFileSearchResult {
+    pub root: String,
+    pub path: String,
+    pub score: u32,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub indices: Option<Vec<u32>>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, TS)]
+pub struct FuzzyFileSearchResponse {
+    pub files: Vec<FuzzyFileSearchResult>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct LoginChatGptCompleteNotification {