3434e57007
The first of several CLs providing JSON Schema validation. Replace the existing Schema type with one that has all the keywords of the most current version of the JSON Schema spec, called 2020-12. The 2020-12 spec can be represented type-safely in Go with one exception: the "type" keyword can be either a string or a []string. To handle this safely, both Type and Types fields are defined. Custom JSONMarshal/Unmarshal methods handle the conversion. We need the unmarshal anyway because "true" and "false" are valid schemas. Unfortunately, the MCP spec uses the older "draft7" version of JSON Schema, but the two are close enough for code generation to work. I confirmed that the protocol generator produces the identical output. Change-Id: I44f6ea2f3a3f8498979946f69dfb7f50afa1acad Reviewed-on: https://go-review.googlesource.com/c/tools/+/667855 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Alan Donovan <adonovan@google.com>
118 lines
2.8 KiB
Go
118 lines
2.8 KiB
Go
// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
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// Use of this source code is governed by an MIT-style
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// license that can be found in the LICENSE file.
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// This file contains functions that infer a schema from a Go type.
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package jsonschema
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import (
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"fmt"
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"reflect"
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"strings"
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)
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// For constructs a JSON schema object for the given type argument.
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//
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// It is a convenience for ForType.
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func For[T any]() (*Schema, error) {
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return ForType(reflect.TypeFor[T]())
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}
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// It returns an error if t contains (possibly recursively) any of the following Go
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// types, as they are incompatible with the JSON schema spec.
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// - maps with key other than 'string'
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// - function types
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// - complex numbers
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// - unsafe pointers
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//
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// TODO(rfindley): we could perhaps just skip these incompatible fields.
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func ForType(t reflect.Type) (*Schema, error) {
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return typeSchema(t, make(map[reflect.Type]*Schema))
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}
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func typeSchema(t reflect.Type, seen map[reflect.Type]*Schema) (*Schema, error) {
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if t.Kind() == reflect.Pointer {
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t = t.Elem()
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}
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if s := seen[t]; s != nil {
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return s, nil
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}
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var (
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s = new(Schema)
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err error
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)
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seen[t] = s
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switch t.Kind() {
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case reflect.Bool:
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s.Type = "boolean"
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case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
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reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
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reflect.Uintptr:
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s.Type = "integer"
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case reflect.Float32, reflect.Float64:
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s.Type = "number"
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case reflect.Interface:
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// Unrestricted
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case reflect.Map:
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if t.Key().Kind() != reflect.String {
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return nil, fmt.Errorf("unsupported map key type %v", t.Key().Kind())
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}
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s.Type = "object"
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s.AdditionalProperties, err = typeSchema(t.Elem(), seen)
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if err != nil {
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return nil, fmt.Errorf("computing map value schema: %v", err)
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}
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case reflect.Slice, reflect.Array:
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s.Type = "array"
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s.Items, err = typeSchema(t.Elem(), seen)
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if err != nil {
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return nil, fmt.Errorf("computing element schema: %v", err)
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}
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case reflect.String:
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s.Type = "string"
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case reflect.Struct:
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s.Type = "object"
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// no additional properties are allowed
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s.AdditionalProperties = &Schema{Not: &Schema{}}
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for i := range t.NumField() {
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field := t.Field(i)
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name, ok := jsonName(field)
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if !ok {
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continue
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}
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if s.Properties == nil {
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s.Properties = make(map[string]*Schema)
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}
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s.Properties[name], err = typeSchema(field.Type, seen)
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if err != nil {
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return nil, err
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}
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}
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default:
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return nil, fmt.Errorf("type %v is unsupported by jsonschema", t)
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}
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return s, nil
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}
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func jsonName(f reflect.StructField) (string, bool) {
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if !f.IsExported() {
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return "", false
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}
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if tag, ok := f.Tag.Lookup("json"); ok {
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if name, _, _ := strings.Cut(tag, ","); name != "" {
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return name, name != "-"
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}
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}
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return f.Name, true
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}
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