Golang struct to Json schema - go

Question

Hi I need to infer a json schema (github.com/go-openapi/spec.Schema) from a struct :
type Testcase struct {
Id string `json:"id,omitempty"` // id of this test case
Name string `json:"name,omitempty"` // name of this test case
CreationDate time.Time `json:"creation_date,omitempty"` // timestamp when the scenario was first created
UpdateDate time.Time `json:"update_date,omitempty"` // last update timestamp
Steps []Step `json:"steps,omitempty"` // list of steps type:"[]StepCcs"
}
I can't find a simple way to do so.
I guess that this is a prerequisite for many REST frameworks out there that generate open api spec from the code.
Can someone point me out to a package that contains such helper : ie
func toSchema(obj interface{}) (spec.Schema, error)

Answer 1

https://github.com/invopop/jsonschema
is what you are looking for.
type TestUser struct {
ID int `json:"id"`
Name string `json:"name" jsonschema:"title=the name,description=The name of a friend,example=joe,example=lucy,default=alex"`
Friends []int `json:"friends,omitempty" jsonschema_description:"The list of IDs, omitted when empty"`
Tags map[string]interface{} `json:"tags,omitempty" jsonschema_extras:"a=b,foo=bar,foo=bar1"`
BirthDate time.Time `json:"birth_date,omitempty" jsonschema:"oneof_required=date"`
YearOfBirth string `json:"year_of_birth,omitempty" jsonschema:"oneof_required=year"`
Metadata interface{} `json:"metadata,omitempty" jsonschema:"oneof_type=string;array"`
FavColor string `json:"fav_color,omitempty" jsonschema:"enum=red,enum=green,enum=blue"`
}
Results in following JSON Schema:
jsonschema.Reflect(&TestUser{})

Answer 2

Huma's schema package can do this. Be sure to check out all the validation tags that are available. Example:
import "github.com/danielgtaylor/huma/schema"
// First define some structs:
type Child struct {
Name string `json:"name" doc:"Child name"`
}
type Hello struct {
Greeting string `json:"greeting" maxLength:"80" doc:"A greeting message"`
Optional uint `json:"optional,omitempty" doc:"Optional integer example"`
Child *Child `json:"child,omitempty" doc:"Child struct example"`
Labels []string `json:"labels" maxItems:"10" doc:"Array example"`
Created time.Time `json:"created" doc:"Created time for this greeting"`
}
// Then later you can do:
s, err := schema.Generate(reflect.TypeOf(Hello{}))
https://go.dev/play/p/4F8NpcgZ4Yh
This will output:
{
"type": "object",
"properties": {
"child": {
"type": "object",
"description": "Child struct example",
"properties": {
"name": {
"type": "string",
"description": "Child name"
}
},
"additionalProperties": false,
"required": [
"name"
]
},
"created": {
"type": "string",
"description": "Created time for this greeting",
"format": "date-time"
},
"greeting": {
"type": "string",
"description": "A greeting message",
"maxLength": 80
},
"labels": {
"type": "array",
"description": "Array example",
"items": {
"type": "string"
},
"maxItems": 10
},
"optional": {
"type": "integer",
"description": "Optional integer example",
"format": "int32",
"minimum": 0
}
},
"additionalProperties": false,
"required": [
"greeting",
"labels",
"created"
]
}