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mcp: improve argument parsing error handling

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Closes #1960
This commit is contained in:
Adrià Arrufat
2026-03-27 10:04:41 +09:00
parent cdd33621e3
commit da0828620f
1 changed files with 18 additions and 16 deletions
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34
src/mcp/tools.zig
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@@ -325,7 +325,7 @@ fn handleGoto(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arg
} }
fn handleMarkdown(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void { fn handleMarkdown(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
const args = parseArgsOrDefault(UrlParams, arena, arguments); const args = try parseArgsOrDefault(UrlParams, arena, arguments, server, id);
const page = try ensurePage(server, id, args.url); const page = try ensurePage(server, id, args.url);
const content = [_]protocol.TextContent(ToolStreamingText){.{ const content = [_]protocol.TextContent(ToolStreamingText){.{
@@ -335,7 +335,7 @@ fn handleMarkdown(server: *Server, arena: std.mem.Allocator, id: std.json.Value,
} }
fn handleLinks(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void { fn handleLinks(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
const args = parseArgsOrDefault(UrlParams, arena, arguments); const args = try parseArgsOrDefault(UrlParams, arena, arguments, server, id);
const page = try ensurePage(server, id, args.url); const page = try ensurePage(server, id, args.url);
const content = [_]protocol.TextContent(ToolStreamingText){.{ const content = [_]protocol.TextContent(ToolStreamingText){.{
@@ -350,7 +350,7 @@ fn handleSemanticTree(server: *Server, arena: std.mem.Allocator, id: std.json.Va
backendNodeId: ?u32 = null, backendNodeId: ?u32 = null,
maxDepth: ?u32 = null, maxDepth: ?u32 = null,
}; };
const args = parseArgsOrDefault(TreeParams, arena, arguments); const args = try parseArgsOrDefault(TreeParams, arena, arguments, server, id);
const page = try ensurePage(server, id, args.url); const page = try ensurePage(server, id, args.url);
const content = [_]protocol.TextContent(ToolStreamingText){.{ const content = [_]protocol.TextContent(ToolStreamingText){.{
@@ -367,7 +367,7 @@ fn handleSemanticTree(server: *Server, arena: std.mem.Allocator, id: std.json.Va
} }
fn handleInteractiveElements(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void { fn handleInteractiveElements(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
const args = parseArgsOrDefault(UrlParams, arena, arguments); const args = try parseArgsOrDefault(UrlParams, arena, arguments, server, id);
const page = try ensurePage(server, id, args.url); const page = try ensurePage(server, id, args.url);
const elements = lp.interactive.collectInteractiveElements(page.document.asNode(), arena, page) catch |err| { const elements = lp.interactive.collectInteractiveElements(page.document.asNode(), arena, page) catch |err| {
@@ -388,7 +388,7 @@ fn handleInteractiveElements(server: *Server, arena: std.mem.Allocator, id: std.
} }
fn handleStructuredData(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void { fn handleStructuredData(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
const args = parseArgsOrDefault(UrlParams, arena, arguments); const args = try parseArgsOrDefault(UrlParams, arena, arguments, server, id);
const page = try ensurePage(server, id, args.url); const page = try ensurePage(server, id, args.url);
const data = lp.structured_data.collectStructuredData(page.document.asNode(), arena, page) catch |err| { const data = lp.structured_data.collectStructuredData(page.document.asNode(), arena, page) catch |err| {
@@ -403,7 +403,7 @@ fn handleStructuredData(server: *Server, arena: std.mem.Allocator, id: std.json.
} }
fn handleDetectForms(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void { fn handleDetectForms(server: *Server, arena: std.mem.Allocator, id: std.json.Value, arguments: ?std.json.Value) !void {
const args = parseArgsOrDefault(UrlParams, arena, arguments); const args = try parseArgsOrDefault(UrlParams, arena, arguments, server, id);
const page = try ensurePage(server, id, args.url); const page = try ensurePage(server, id, args.url);
const forms_data = lp.forms.collectForms(arena, page.document.asNode(), page) catch |err| { const forms_data = lp.forms.collectForms(arena, page.document.asNode(), page) catch |err| {
@@ -592,13 +592,15 @@ fn ensurePage(server: *Server, id: std.json.Value, url: ?[:0]const u8) !*lp.Page
} }
/// Parses JSON arguments into a given struct type `T`. /// Parses JSON arguments into a given struct type `T`.
/// If the arguments are missing or invalid, it returns a default-initialized `T` (e.g., `.{}`). /// If the arguments are missing, it returns a default-initialized `T` (e.g., `.{}`).
/// Use this for tools where all arguments are optional and validation failures should be silently ignored. /// If the arguments are present but invalid, it sends an MCP error response and returns `error.InvalidParams`.
fn parseArgsOrDefault(comptime T: type, arena: std.mem.Allocator, arguments: ?std.json.Value) T { /// Use this for tools where all arguments are optional.
if (arguments) |args_raw| { fn parseArgsOrDefault(comptime T: type, arena: std.mem.Allocator, arguments: ?std.json.Value, server: *Server, id: std.json.Value) !T {
return std.json.parseFromValueLeaky(T, arena, args_raw, .{ .ignore_unknown_fields = true }) catch .{}; const args_raw = arguments orelse return .{};
} return std.json.parseFromValueLeaky(T, arena, args_raw, .{ .ignore_unknown_fields = true }) catch {
return .{}; try server.sendError(id, .InvalidParams, "Invalid arguments");
return error.InvalidParams;
};
} }
/// Parses JSON arguments into a given struct type `T`. /// Parses JSON arguments into a given struct type `T`.
@@ -606,11 +608,11 @@ fn parseArgsOrDefault(comptime T: type, arena: std.mem.Allocator, arguments: ?st
/// and returns an `error.InvalidParams`. /// and returns an `error.InvalidParams`.
/// Use this for tools that require strict validation or mandatory arguments. /// Use this for tools that require strict validation or mandatory arguments.
fn parseArgs(comptime T: type, arena: std.mem.Allocator, arguments: ?std.json.Value, server: *Server, id: std.json.Value, tool_name: []const u8) !T { fn parseArgs(comptime T: type, arena: std.mem.Allocator, arguments: ?std.json.Value, server: *Server, id: std.json.Value, tool_name: []const u8) !T {
if (arguments == null) { const args_raw = arguments orelse {
try server.sendError(id, .InvalidParams, "Missing arguments"); try server.sendError(id, .InvalidParams, "Missing arguments");
return error.InvalidParams; return error.InvalidParams;
} };
return std.json.parseFromValueLeaky(T, arena, arguments.?, .{ .ignore_unknown_fields = true }) catch { return std.json.parseFromValueLeaky(T, arena, args_raw, .{ .ignore_unknown_fields = true }) catch {
const msg = std.fmt.allocPrint(arena, "Invalid arguments for {s}", .{tool_name}) catch "Invalid arguments"; const msg = std.fmt.allocPrint(arena, "Invalid arguments for {s}", .{tool_name}) catch "Invalid arguments";
try server.sendError(id, .InvalidParams, msg); try server.sendError(id, .InvalidParams, msg);
return error.InvalidParams; return error.InvalidParams;