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mcp: improve event loop and response handling

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- Use an allocating writer in `sendResponse` to handle large payloads.
- Update the main loop to tick the HTTP client and cap poll timeouts.
- Update protocol version and minify tool input schemas.
This commit is contained in:
Adrià Arrufat
2026-03-02 11:12:00 +09:00
parent d4747b5386
commit a91afab038
3 changed files with 36 additions and 74 deletions
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14
src/mcp/Server.zig
View File

@@ -12,7 +12,7 @@ app: *App,
http_client: *HttpClient, http_client: *HttpClient,
notification: *lp.Notification, notification: *lp.Notification,
browser: lp.Browser, browser: *lp.Browser,
session: *lp.Session, session: *lp.Session,
page: *lp.Page, page: *lp.Page,
@@ -53,12 +53,12 @@ pub fn deinit(self: *Self) void {
self.allocator.destroy(self); self.allocator.destroy(self);
} }
pub fn sendResponse(_: *Self, response: anytype) !void { pub fn sendResponse(self: *Self, response: anytype) !void {
var buffer: [8192]u8 = undefined; var aw: std.Io.Writer.Allocating = .init(self.allocator);
var stdout = std.fs.File.stdout().writer(&buffer); defer aw.deinit();
try std.json.Stringify.value(response, .{ .emit_null_optional_fields = false }, &stdout.interface); try std.json.Stringify.value(response, .{ .emit_null_optional_fields = false }, &aw.writer);
try stdout.interface.writeByte('\n'); try aw.writer.writeByte('\n');
try stdout.interface.flush(); try std.fs.File.stdout().writeAll(aw.written());
} }
pub fn sendResult(self: *Self, id: std.json.Value, result: anytype) !void { pub fn sendResult(self: *Self, id: std.json.Value, result: anytype) !void {

37
src/mcp/router.zig
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@@ -17,24 +17,36 @@ pub fn processRequests(server: *Server) !void {
const reader = poller.reader(.stdin); const reader = poller.reader(.stdin);
var arena: std.heap.ArenaAllocator = .init(server.allocator); var arena_instance = std.heap.ArenaAllocator.init(server.allocator);
defer arena.deinit(); defer arena_instance.deinit();
const arena = arena_instance.allocator();
while (server.is_running.load(.acquire)) { while (server.is_running.load(.acquire)) {
// Run ready browser tasks and get time to next one
const ms_to_next_task = (try server.browser.runMacrotasks()) orelse 10_000; const ms_to_next_task = (try server.browser.runMacrotasks()) orelse 10_000;
// Poll until the next macrotask is scheduled. This will block if no data is available. // Keep the loop responsive to network events and stdin.
const poll_ok = try poller.pollTimeout(ms_to_next_task * std.time.ns_per_ms); const ms_to_wait: u64 = @min(50, ms_to_next_task);
// Wait for stdin activity for up to ms_to_wait.
const poll_result = try poller.pollTimeout(ms_to_wait * @as(u64, std.time.ns_per_ms));
// Process any pending network I/O
_ = try server.http_client.tick(0);
// Run V8 microtasks and internal message loop
server.browser.runMessageLoop();
// Process all complete lines available in the buffer
while (true) { while (true) {
const buffered = reader.buffered(); const buffered = reader.buffered();
if (std.mem.indexOfScalar(u8, buffered, '\n')) |idx| { if (std.mem.indexOfScalar(u8, buffered, '\n')) |idx| {
const line = buffered[0..idx]; const line = buffered[0..idx];
if (line.len > 0) { if (line.len > 0) {
handleMessage(server, arena.allocator(), line) catch |err| { handleMessage(server, arena, line) catch |err| {
log.warn(.mcp, "Error processing message", .{ .err = err }); log.warn(.mcp, "Error processing message", .{ .err = err });
}; };
_ = arena.reset(.{ .retain_with_limit = 32 * 1024 }); _ = arena_instance.reset(.{ .retain_with_limit = 32 * 1024 });
} }
reader.toss(idx + 1); reader.toss(idx + 1);
} else { } else {
@@ -42,18 +54,14 @@ pub fn processRequests(server: *Server) !void {
} }
} }
if (!poll_ok) { // pollTimeout returns false when all streams are closed (EOF on stdin)
// Check if we have any data left in the buffer that didn't end with a newline if (!poll_result) {
const buffered = reader.buffered(); const buffered = reader.buffered();
if (buffered.len > 0) { if (buffered.len > 0) {
handleMessage(server, arena.allocator(), buffered) catch |err| { handleMessage(server, arena, buffered) catch {};
log.warn(.mcp, "Error processing last message", .{ .err = err });
};
} }
break; break;
} }
server.browser.runMessageLoop();
} }
} }
@@ -90,9 +98,10 @@ fn handleMessage(server: *Server, arena: std.mem.Allocator, msg: []const u8) !vo
fn handleInitialize(server: *Server, req: protocol.Request) !void { fn handleInitialize(server: *Server, req: protocol.Request) !void {
const result = protocol.InitializeResult{ const result = protocol.InitializeResult{
.protocolVersion = "2024-11-05", .protocolVersion = "2025-11-25",
.capabilities = .{ .capabilities = .{
.logging = .{}, .logging = .{},
.prompts = .{ .listChanged = false },
.resources = .{ .subscribe = false, .listChanged = false }, .resources = .{ .subscribe = false, .listChanged = false },
.tools = .{ .listChanged = false }, .tools = .{ .listChanged = false },
}, },

59
src/mcp/tools.zig
View File

@@ -13,79 +13,32 @@ pub const tool_list = [_]protocol.Tool{
.{ .{
.name = "goto", .name = "goto",
.description = "Navigate to a specified URL and load the page in memory so it can be reused later for info extraction.", .description = "Navigate to a specified URL and load the page in memory so it can be reused later for info extraction.",
.inputSchema = .{ .json = .inputSchema = .{ .json = "{\"type\":\"object\",\"properties\":{\"url\":{\"type\":\"string\",\"description\":\"The URL to navigate to, must be a valid URL.\"}},\"required\":[\"url\"]}" },
\\{
\\ "type": "object",
\\ "properties": {
\\ "url": { "type": "string", "description": "The URL to navigate to, must be a valid URL." }
\\ },
\\ "required": ["url"]
\\}
},
}, },
.{ .{
.name = "search", .name = "search",
.description = "Use a search engine to look for specific words, terms, sentences. The search page will then be loaded in memory.", .description = "Use a search engine to look for specific words, terms, sentences. The search page will then be loaded in memory.",
.inputSchema = .{ .json = .inputSchema = .{ .json = "{\"type\":\"object\",\"properties\":{\"text\":{\"type\":\"string\",\"description\":\"The text to search for, must be a valid search query.\"}},\"required\":[\"text\"]}" },
\\{
\\ "type": "object",
\\ "properties": {
\\ "text": { "type": "string", "description": "The text to search for, must be a valid search query." }
\\ },
\\ "required": ["text"]
\\}
},
}, },
.{ .{
.name = "markdown", .name = "markdown",
.description = "Get the page content in markdown format. If a url is provided, it navigates to that url first.", .description = "Get the page content in markdown format. If a url is provided, it navigates to that url first.",
.inputSchema = .{ .json = .inputSchema = .{ .json = "{\"type\":\"object\",\"properties\":{\"url\":{\"type\":\"string\",\"description\":\"Optional URL to navigate to before fetching markdown.\"}}}" },
\\{
\\ "type": "object",
\\ "properties": {
\\ "url": { "type": "string", "description": "Optional URL to navigate to before fetching markdown." }
\\ }
\\}
},
}, },
.{ .{
.name = "links", .name = "links",
.description = "Extract all links in the opened page. If a url is provided, it navigates to that url first.", .description = "Extract all links in the opened page. If a url is provided, it navigates to that url first.",
.inputSchema = .{ .json = .inputSchema = .{ .json = "{\"type\":\"object\",\"properties\":{\"url\":{\"type\":\"string\",\"description\":\"Optional URL to navigate to before extracting links.\"}}}" },
\\{
\\ "type": "object",
\\ "properties": {
\\ "url": { "type": "string", "description": "Optional URL to navigate to before extracting links." }
\\ }
\\}
},
}, },
.{ .{
.name = "evaluate", .name = "evaluate",
.description = "Evaluate JavaScript in the current page context. If a url is provided, it navigates to that url first.", .description = "Evaluate JavaScript in the current page context. If a url is provided, it navigates to that url first.",
.inputSchema = .{ .json = .inputSchema = .{ .json = "{\"type\":\"object\",\"properties\":{\"script\":{\"type\":\"string\"},\"url\":{\"type\":\"string\",\"description\":\"Optional URL to navigate to before evaluating.\"}},\"required\":[\"script\"]}" },
\\{
\\ "type": "object",
\\ "properties": {
\\ "script": { "type": "string" },
\\ "url": { "type": "string", "description": "Optional URL to navigate to before evaluating." }
\\ },
\\ "required": ["script"]
\\}
},
}, },
.{ .{
.name = "over", .name = "over",
.description = "Used to indicate that the task is over and give the final answer if there is any. This is the last tool to be called in a task.", .description = "Used to indicate that the task is over and give the final answer if there is any. This is the last tool to be called in a task.",
.inputSchema = .{ .json = .inputSchema = .{ .json = "{\"type\":\"object\",\"properties\":{\"result\":{\"type\":\"string\",\"description\":\"The final result of the task.\"}},\"required\":[\"result\"]}" },
\\{
\\ "type": "object",
\\ "properties": {
\\ "result": { "type": "string", "description": "The final result of the task." }
\\ },
\\ "required": ["result"]
\\}
},
}, },
}; };