const std = @import("std"); pub const description_max_bytes: usize = 1024;pub const truncation_marker = "... [truncated]"; pub const JsonType = enum {    string,    integer,    boolean,    object,    array,}; pub const Property = struct {    name: []const u8,    json_type: JsonType,    description: []const u8 = "",    nullable: bool = false,    nullable_description: []const u8 = "",    enum_values: []const []const u8 = &.{},    min_length: ?usize = null,    max_length: ?usize = null,    minimum: ?u64 = null,    maximum: ?u64 = null,    min_items: ?usize = null,    max_items: ?usize = null,    item_json_type: ?JsonType = null,    item_enum_values: []const []const u8 = &.{},    items: ?*const ObjectSchema = null,    object_schema: ?*const ObjectSchema = null,}; pub const ObjectSchema = struct {    properties: []const Property = &.{},    required: []const []const u8 = &.{},    additional_properties: ?bool = null,    min_properties: ?usize = null,    max_properties: ?usize = null,    one_of: []const ObjectSchema = &.{},}; pub const FunctionSchema = struct {    name: []const u8,    description: []const u8,    input_schema: ObjectSchema = .{},}; fn cappedDescriptionAlloc(alloc: std.mem.Allocator, text: []const u8) ![]u8 {    if (text.len <= description_max_bytes) return alloc.dupe(u8, text);     const prefix_len = description_max_bytes - truncation_marker.len;    var out = try alloc.alloc(u8, description_max_bytes);    @memcpy(out[0..prefix_len], text[0..prefix_len]);    @memcpy(out[prefix_len..], truncation_marker);    return out;} fn writeCappedDescriptionJsonString(    alloc: std.mem.Allocator,    writer: *std.Io.Writer,    text: []const u8,) !void {    const capped_description = try cappedDescriptionAlloc(alloc, text);    defer alloc.free(capped_description);    try std.json.Stringify.value(capped_description, .{}, writer);} /// Opens the gateway's flattened function-tool envelope, up to the/// "inputSchema" value. The caller writes the schema and the closing brace.fn writeFunctionSchemaOpen(    writer: *std.Io.Writer,    name: []const u8,    description: []const u8,) !void {    try writer.writeAll("{\"type\":\"function\",\"name\":");    try std.json.Stringify.value(name, .{}, writer);    try writer.writeAll(",\"description\":");    try std.json.Stringify.value(description, .{}, writer);    try writer.writeAll(",\"inputSchema\":");} pub fn writeBuiltinFunctionSchema(    alloc: std.mem.Allocator,    writer: *std.Io.Writer,    schema: FunctionSchema,) !void {    const description = try cappedDescriptionAlloc(alloc, schema.description);    defer alloc.free(description);    try writeFunctionSchemaOpen(writer, schema.name, description);    try writeObjectSchema(alloc, writer, schema.input_schema);    try writer.writeByte('}');} pub fn builtinFunctionSchemaJsonAlloc(alloc: std.mem.Allocator, schema: FunctionSchema) ![]u8 {    var out: std.Io.Writer.Allocating = .init(alloc);    defer out.deinit();    try writeBuiltinFunctionSchema(alloc, &out.writer, schema);    return try out.toOwnedSlice();} /// Envelope for a dynamic (MCP) tool whose input schema is already rendered/// JSON. Caller owns the returned slice.pub fn dynamicFunctionSchemaJsonAlloc(    alloc: std.mem.Allocator,    name: []const u8,    description: []const u8,    input_schema_json: []const u8,) ![]u8 {    var out: std.Io.Writer.Allocating = .init(alloc);    defer out.deinit();    try writeFunctionSchemaOpen(&out.writer, name, description);    try out.writer.writeAll(input_schema_json);    try out.writer.writeByte('}');    return try out.toOwnedSlice();} fn writeObjectSchema(    alloc: std.mem.Allocator,    writer: *std.Io.Writer,    schema: ObjectSchema,) anyerror!void {    if (schema.one_of.len > 0) {        if (schema.properties.len > 0 or            schema.required.len > 0 or            schema.additional_properties != null or            schema.min_properties != null or            schema.max_properties != null)        {            return error.InvalidObjectSchema;        }        try writer.writeAll("{\"oneOf\":[");        for (schema.one_of, 0..) |alternative, index| {            if (index > 0) try writer.writeByte(',');            try writeObjectSchema(alloc, writer, alternative);        }        try writer.writeAll("]}");        return;    }     try writer.writeAll("{\"type\":\"object\",\"properties\":{");    for (schema.properties, 0..) |property, index| {        if (index > 0) try writer.writeByte(',');        try std.json.Stringify.value(property.name, .{}, writer);        try writer.writeByte(':');        try writePropertySchema(alloc, writer, property);    }    try writer.writeByte('}');    if (schema.additional_properties) |value| {        try writer.writeAll(",\"additionalProperties\":");        try writer.writeAll(if (value) "true" else "false");    }    if (schema.min_properties) |value| try writer.print(",\"minProperties\":{d}", .{value});    if (schema.max_properties) |value| try writer.print(",\"maxProperties\":{d}", .{value});    if (schema.required.len > 0) {        try writer.writeAll(",\"required\":[");        for (schema.required, 0..) |name, index| {            if (index > 0) try writer.writeByte(',');            try std.json.Stringify.value(name, .{}, writer);        }        try writer.writeByte(']');    }    try writer.writeByte('}');} fn writePropertySchema(    alloc: std.mem.Allocator,    writer: *std.Io.Writer,    property: Property,) anyerror!void {    if (property.nullable) {        var concrete = property;        concrete.nullable = false;        concrete.nullable_description = "";        try writer.writeAll("{\"anyOf\":[");        try writePropertySchema(alloc, writer, concrete);        try writer.writeAll(",{\"type\":\"null\"}]");        if (property.nullable_description.len > 0) {            try writer.writeAll(",\"description\":");            try writeCappedDescriptionJsonString(                alloc,                writer,                property.nullable_description,            );        }        try writer.writeByte('}');        return;    }    if (property.object_schema) |object_schema| {        try writeObjectSchema(alloc, writer, object_schema.*);        return;    }    try writer.writeAll("{\"type\":");    try std.json.Stringify.value(@tagName(property.json_type), .{}, writer);    if (property.enum_values.len > 0) {        try writer.writeAll(",\"enum\":[");        for (property.enum_values, 0..) |value, index| {            if (index > 0) try writer.writeByte(',');            try std.json.Stringify.value(value, .{}, writer);        }        try writer.writeByte(']');    }    if (property.min_length) |value| try writer.print(",\"minLength\":{d}", .{value});    if (property.max_length) |value| try writer.print(",\"maxLength\":{d}", .{value});    if (property.minimum) |value| try writer.print(",\"minimum\":{d}", .{value});    if (property.maximum) |value| try writer.print(",\"maximum\":{d}", .{value});    if (property.description.len > 0) {        try writer.writeAll(",\"description\":");        try writeCappedDescriptionJsonString(alloc, writer, property.description);    }    if (property.min_items) |value| try writer.print(",\"minItems\":{d}", .{value});    if (property.max_items) |value| try writer.print(",\"maxItems\":{d}", .{value});    if (property.item_json_type) |item_json_type| {        try writer.writeAll(",\"items\":{\"type\":");        try std.json.Stringify.value(@tagName(item_json_type), .{}, writer);        if (property.item_enum_values.len > 0) {            try writer.writeAll(",\"enum\":[");            for (property.item_enum_values, 0..) |value, index| {                if (index > 0) try writer.writeByte(',');                try std.json.Stringify.value(value, .{}, writer);            }            try writer.writeByte(']');        }        try writer.writeByte('}');    } else if (property.items) |items| {        try writer.writeAll(",\"items\":");        try writeObjectSchema(alloc, writer, items.*);    }    try writer.writeByte('}');} test "nullable properties preserve concrete constraints and add one null branch" {    const alloc = std.testing.allocator;    const object_value_schema = ObjectSchema{        .properties = &.{.{ .name = "kind", .json_type = .string }},        .required = &.{"kind"},        .additional_properties = false,    };    const schema = FunctionSchema{        .name = "nullable",        .description = "nullable",        .input_schema = .{            .properties = &.{                .{                    .name = "choice",                    .json_type = .string,                    .description = "Concrete choice.",                    .nullable = true,                    .nullable_description = "Concrete choice. Set null when unused.",                    .enum_values = &.{ "one", "two" },                },                .{                    .name = "config",                    .json_type = .object,                    .nullable = true,                    .nullable_description = "Set null when unused.",                    .object_schema = &object_value_schema,                },            },            .required = &.{ "choice", "config" },        },    };     const json = try builtinFunctionSchemaJsonAlloc(alloc, schema);    defer alloc.free(json);    var parsed = try std.json.parseFromSlice(std.json.Value, alloc, json, .{});    defer parsed.deinit();     const properties = parsed.value.object.get("inputSchema").?.object.get("properties").?.object;    const choice = properties.get("choice").?.object;    try std.testing.expectEqualStrings(        "Concrete choice. Set null when unused.",        choice.get("description").?.string,    );    const choice_alternatives = choice.get("anyOf").?.array.items;    try std.testing.expectEqual(@as(usize, 2), choice_alternatives.len);    try std.testing.expectEqualStrings("string", choice_alternatives[0].object.get("type").?.string);    try std.testing.expectEqual(@as(usize, 2), choice_alternatives[0].object.get("enum").?.array.items.len);    try std.testing.expectEqualStrings("null", choice_alternatives[1].object.get("type").?.string);     const config_alternatives = properties.get("config").?.object.get("anyOf").?.array.items;    try std.testing.expectEqualStrings("object", config_alternatives[0].object.get("type").?.string);    try std.testing.expectEqual(false, config_alternatives[0].object.get("additionalProperties").?.bool);    try std.testing.expectEqualStrings("null", config_alternatives[1].object.get("type").?.string);} test "nested object schema serializes exact property bounds" {    const alloc = std.testing.allocator;    const nested = ObjectSchema{        .properties = &.{.{ .name = "create", .json_type = .object, .object_schema = &.{            .properties = &.{.{ .name = "name", .json_type = .string }},            .required = &.{"name"},            .additional_properties = false,        } }},        .additional_properties = false,        .min_properties = 1,        .max_properties = 1,    };    const schema = FunctionSchema{        .name = "nested",        .description = "nested",        .input_schema = nested,    };     const json = try builtinFunctionSchemaJsonAlloc(alloc, schema);    defer alloc.free(json);     try std.testing.expect(std.mem.find(u8, json, "\"minProperties\":1") != null);    try std.testing.expect(std.mem.find(u8, json, "\"maxProperties\":1") != null);    try std.testing.expect(std.mem.find(u8, json, "\"create\":{\"type\":\"object\",\"properties\":{") != null);    try std.testing.expect(std.mem.find(u8, json, "\"additionalProperties\":false") != null);} test "object alternatives serialize as exclusive object branches" {    const alloc = std.testing.allocator;    const alternatives = [_]ObjectSchema{        .{            .properties = &.{                .{ .name = "action", .json_type = .string, .enum_values = &.{"read"} },                .{ .name = "path", .json_type = .string },            },            .required = &.{ "action", "path" },            .additional_properties = false,        },        .{            .properties = &.{                .{ .name = "action", .json_type = .string, .enum_values = &.{"list"} },            },            .required = &.{"action"},            .additional_properties = false,        },    };    const schema = FunctionSchema{        .name = "alternative",        .description = "alternative",        .input_schema = .{ .one_of = &alternatives },    };     const json = try builtinFunctionSchemaJsonAlloc(alloc, schema);    defer alloc.free(json);    var parsed = try std.json.parseFromSlice(std.json.Value, alloc, json, .{});    defer parsed.deinit();     const input_schema = parsed.value.object.get("inputSchema").?.object;    try std.testing.expect(input_schema.get("type") == null);    try std.testing.expect(input_schema.get("properties") == null);    const one_of = input_schema.get("oneOf").?.array.items;    try std.testing.expectEqual(@as(usize, 2), one_of.len);    try std.testing.expectEqualStrings(        "read",        one_of[0].object.get("properties").?.object.get("action").?.object.get("enum").?.array.items[0].string,    );    try std.testing.expectEqualStrings(        "list",        one_of[1].object.get("properties").?.object.get("action").?.object.get("enum").?.array.items[0].string,    );    try std.testing.expectEqual(false, one_of[0].object.get("additionalProperties").?.bool);    try std.testing.expectEqual(false, one_of[1].object.get("additionalProperties").?.bool);} test "object alternatives reject contradictory ordinary object metadata" {    const schema = FunctionSchema{        .name = "invalid_alternative",        .description = "invalid alternative",        .input_schema = .{            .properties = &.{.{ .name = "value", .json_type = .string }},            .one_of = &.{.{                .properties = &.{.{ .name = "action", .json_type = .string }},            }},        },    };     try std.testing.expectError(        error.InvalidObjectSchema,        builtinFunctionSchemaJsonAlloc(std.testing.allocator, schema),    );} test "cappedDescriptionAlloc appends explicit truncation marker" {    const alloc = std.testing.allocator;    const oversized = "x" ** (description_max_bytes + 20);     const capped = try cappedDescriptionAlloc(alloc, oversized);    defer alloc.free(capped);     try std.testing.expectEqual(description_max_bytes, capped.len);    try std.testing.expect(std.mem.endsWith(u8, capped, truncation_marker));} test "builtinFunctionSchemaJsonAlloc serializes strings and object schema" {    const alloc = std.testing.allocator;    const schema = FunctionSchema{        .name = "read_file",        .description = "Read \"quoted\" paths. When to use: test escaping. When NOT to use: unescaped JSON.",        .input_schema = .{            .properties = &.{                .{ .name = "path", .json_type = .string, .description = "File path \"with quotes\"." },            },            .required = &.{"path"},        },    };     const json = try builtinFunctionSchemaJsonAlloc(alloc, schema);    defer alloc.free(json);     var parsed = try std.json.parseFromSlice(std.json.Value, alloc, json, .{});    defer parsed.deinit();     try std.testing.expectEqualStrings("read_file", parsed.value.object.get("name").?.string);    try std.testing.expect(std.mem.find(u8, json, "\\\"quoted\\\"") != null);    try std.testing.expect(std.mem.find(u8, json, "\\\"with quotes\\\"") != null);} test "builtinFunctionSchemaJsonAlloc serializes every supported property shape" {    const alloc = std.testing.allocator;    const object_value_schema = ObjectSchema{        .properties = &.{.{ .name = "name", .json_type = .string }},        .required = &.{"name"},        .additional_properties = false,    };    const array_item_schema = ObjectSchema{        .properties = &.{.{ .name = "id", .json_type = .integer }},        .required = &.{"id"},        .additional_properties = false,    };    const schema = FunctionSchema{        .name = "schema_matrix",        .description = "schema matrix",        .input_schema = .{            .properties = &.{                .{                    .name = "text",                    .json_type = .string,                    .description = "bounded choice",                    .enum_values = &.{ "alpha", "beta" },                    .min_length = 1,                    .max_length = 8,                },                .{ .name = "count", .json_type = .integer, .minimum = 2, .maximum = 9 },                .{ .name = "enabled", .json_type = .boolean },                .{ .name = "config", .json_type = .object, .object_schema = &object_value_schema },                .{                    .name = "tags",                    .json_type = .array,                    .min_items = 1,                    .max_items = 3,                    .item_json_type = .string,                    .item_enum_values = &.{ "red", "blue" },                },                .{ .name = "records", .json_type = .array, .items = &array_item_schema },            },            .required = &.{ "text", "count", "enabled", "config", "tags", "records" },            .additional_properties = false,            .min_properties = 6,            .max_properties = 6,        },    };     const json = try builtinFunctionSchemaJsonAlloc(alloc, schema);    defer alloc.free(json);    var parsed = try std.json.parseFromSlice(std.json.Value, alloc, json, .{});    defer parsed.deinit();     const input_schema = parsed.value.object.get("inputSchema").?.object;    try std.testing.expectEqualStrings("object", input_schema.get("type").?.string);    try std.testing.expectEqual(false, input_schema.get("additionalProperties").?.bool);    try std.testing.expectEqual(@as(i64, 6), input_schema.get("minProperties").?.integer);    try std.testing.expectEqual(@as(i64, 6), input_schema.get("maxProperties").?.integer);    try std.testing.expectEqual(@as(usize, 6), input_schema.get("required").?.array.items.len);     const properties = input_schema.get("properties").?.object;    const text_property = properties.get("text").?.object;    try std.testing.expectEqualStrings("string", text_property.get("type").?.string);    try std.testing.expectEqualStrings("bounded choice", text_property.get("description").?.string);    try std.testing.expectEqual(@as(usize, 2), text_property.get("enum").?.array.items.len);    try std.testing.expectEqual(@as(i64, 1), text_property.get("minLength").?.integer);    try std.testing.expectEqual(@as(i64, 8), text_property.get("maxLength").?.integer);     const count_property = properties.get("count").?.object;    try std.testing.expectEqualStrings("integer", count_property.get("type").?.string);    try std.testing.expectEqual(@as(i64, 2), count_property.get("minimum").?.integer);    try std.testing.expectEqual(@as(i64, 9), count_property.get("maximum").?.integer);    try std.testing.expectEqualStrings("boolean", properties.get("enabled").?.object.get("type").?.string);     const config_property = properties.get("config").?.object;    try std.testing.expectEqualStrings("object", config_property.get("type").?.string);    try std.testing.expectEqual(false, config_property.get("additionalProperties").?.bool);    try std.testing.expectEqualStrings(        "string",        config_property.get("properties").?.object.get("name").?.object.get("type").?.string,    );     const tags_property = properties.get("tags").?.object;    try std.testing.expectEqualStrings("array", tags_property.get("type").?.string);    try std.testing.expectEqual(@as(i64, 1), tags_property.get("minItems").?.integer);    try std.testing.expectEqual(@as(i64, 3), tags_property.get("maxItems").?.integer);    try std.testing.expectEqualStrings("string", tags_property.get("items").?.object.get("type").?.string);    try std.testing.expectEqual(@as(usize, 2), tags_property.get("items").?.object.get("enum").?.array.items.len);     const record_items = properties.get("records").?.object.get("items").?.object;    try std.testing.expectEqualStrings("object", record_items.get("type").?.string);

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