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mcp: improve evaluate error reporting and refactor tool result types

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This commit is contained in:
Adrià Arrufat
2026-03-03 15:17:59 +09:00
parent f982f073df
commit 48df38cbfe
3 changed files with 98 additions and 29 deletions
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13
src/browser/js/TryCatch.zig
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@@ -134,4 +134,17 @@ pub const Caught = struct {
try writer.write(prefix ++ ".line", self.line);
try writer.write(prefix ++ ".caught", self.caught);
}
pub fn jsonStringify(self: Caught, jw: anytype) !void {
try jw.beginObject();
try jw.objectField("exception");
try jw.write(self.exception);
try jw.objectField("stack");
try jw.write(self.stack);
try jw.objectField("line");
try jw.write(self.line);
try jw.objectField("caught");
try jw.write(self.caught);
try jw.endObject();
}
};

14
src/mcp/protocol.zig
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@@ -149,6 +149,20 @@ pub const Resource = struct {
mimeType: ?[]const u8 = null,
};
pub fn TextContent(comptime T: type) type {
return struct {
type: []const u8 = "text",
text: T,
};
}
pub fn CallToolResult(comptime T: type) type {
return struct {
content: []const TextContent(T),
isError: bool = false,
};
}
pub const JsonEscapingWriter = struct {
inner_writer: *std.Io.Writer,
writer: std.Io.Writer,

100
src/mcp/tools.zig
View File

@@ -204,8 +204,8 @@ fn handleGoto(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arg
const args = try parseArguments(GotoParams, arena, arguments, server, id, "goto");
try performGoto(server, args.url, id);
const content = [_]struct { type: []const u8, text: []const u8 }{.{ .type = "text", .text = "Navigated successfully." }};
try server.sendResult(id, .{ .content = &content });
const content = [_]protocol.TextContent([]const u8){.{ .text = "Navigated successfully." }};
try server.sendResult(id, protocol.CallToolResult([]const u8){ .content = &content });
}
fn handleSearch(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
@@ -222,8 +222,8 @@ fn handleSearch(server: *Server, arena: std.mem.Allocator, id: std.json.Value, a
try performGoto(server, url, id);
const content = [_]struct { type: []const u8, text: []const u8 }{.{ .type = "text", .text = "Search performed successfully." }};
try server.sendResult(id, .{ .content = &content });
const content = [_]protocol.TextContent([]const u8){.{ .text = "Search performed successfully." }};
try server.sendResult(id, protocol.CallToolResult([]const u8){ .content = &content });
}
fn handleMarkdown(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
@@ -238,15 +238,10 @@ fn handleMarkdown(server: *Server, arena: std.mem.Allocator, id: std.json.Value,
} else |_| {}
}
const result = struct {
content: []const struct { type: []const u8, text: ToolStreamingText },
}{
.content = &.{.{
.type = "text",
.text = .{ .server = server, .action = .markdown },
}},
};
try server.sendResult(id, result);
const content = [_]protocol.TextContent(ToolStreamingText){.{
.text = .{ .server = server, .action = .markdown },
}};
try server.sendResult(id, protocol.CallToolResult(ToolStreamingText){ .content = &content });
}
fn handleLinks(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
@@ -261,15 +256,10 @@ fn handleLinks(server: *Server, arena: std.mem.Allocator, id: std.json.Value, ar
} else |_| {}
}
const result = struct {
content: []const struct { type: []const u8, text: ToolStreamingText },
}{
.content = &.{.{
.type = "text",
.text = .{ .server = server, .action = .links },
}},
};
try server.sendResult(id, result);
const content = [_]protocol.TextContent(ToolStreamingText){.{
.text = .{ .server = server, .action = .links },
}};
try server.sendResult(id, protocol.CallToolResult(ToolStreamingText){ .content = &content });
}
fn handleEvaluate(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
@@ -283,22 +273,30 @@ fn handleEvaluate(server: *Server, arena: std.mem.Allocator, id: std.json.Value,
server.page.js.localScope(&ls);
defer ls.deinit();
const js_result = ls.local.compileAndRun(args.script, null) catch {
const content = [_]struct { type: []const u8, text: []const u8 }{.{ .type = "text", .text = "Script evaluation failed." }};
return server.sendResult(id, .{ .content = &content, .isError = true });
var try_catch: js.TryCatch = undefined;
try_catch.init(&ls.local);
defer try_catch.deinit();
const js_result = ls.local.compileAndRun(args.script, null) catch |err| {
const caught = try_catch.caughtOrError(arena, err);
var aw: std.Io.Writer.Allocating = .init(arena);
try caught.format(&aw.writer);
const content = [_]protocol.TextContent([]const u8){.{ .text = aw.written() }};
return server.sendResult(id, protocol.CallToolResult([]const u8){ .content = &content, .isError = true });
};
const str_result = js_result.toStringSliceWithAlloc(arena) catch "undefined";
const content = [_]struct { type: []const u8, text: []const u8 }{.{ .type = "text", .text = str_result }};
try server.sendResult(id, .{ .content = &content });
const content = [_]protocol.TextContent([]const u8){.{ .text = str_result }};
try server.sendResult(id, protocol.CallToolResult([]const u8){ .content = &content });
}
fn handleOver(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
const args = try parseArguments(OverParams, arena, arguments, server, id, "over");
const content = [_]struct { type: []const u8, text: []const u8 }{.{ .type = "text", .text = args.result }};
try server.sendResult(id, .{ .content = &content });
const content = [_]protocol.TextContent([]const u8){.{ .text = args.result }};
try server.sendResult(id, protocol.CallToolResult([]const u8){ .content = &content });
}
fn parseArguments(comptime T: type, arena: std.mem.Allocator, arguments: ?std.json.Value, server: *Server, id: std.json.Value, tool_name: []const u8) !T {
@@ -326,3 +324,47 @@ fn performGoto(server: *Server, url: [:0]const u8, id: std.json.Value) !void {
}
const testing = @import("../testing.zig");
const router = @import("router.zig");
test "MCP - evaluate error reporting" {
defer testing.reset();
const allocator = testing.allocator;
const app = testing.test_app;
var out_alloc: std.io.Writer.Allocating = .init(testing.arena_allocator);
defer out_alloc.deinit();
var server = try Server.init(allocator, app, &out_alloc.writer);
defer server.deinit();
const aa = testing.arena_allocator;
// Call evaluate with a script that throws an error
const msg =
\\{
\\ "jsonrpc": "2.0",
\\ "id": 1,
\\ "method": "tools/call",
\\ "params": {
\\ "name": "evaluate",
\\ "arguments": {
\\ "script": "throw new Error('test error')"
\\ }
\\ }
\\}
;
try router.handleMessage(server, aa, msg);
try testing.expectJson(
\\{
\\ "id": 1,
\\ "result": {
\\ "isError": true,
\\ "content": [
\\ { "type": "text" }
\\ ]
\\ }
\\}
, out_alloc.writer.buffered());
}