OpenAPI 3.0 (and Swagger v2) implementation for Go (parsing, converting, validation, and more)
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# Introduction
A [Go](https://golang.org) project for handling [OpenAPI](https://www.openapis.org/) files. We target:
* [OpenAPI `v2.0`](https://github.com/OAI/OpenAPI-Specification/blob/main/versions/2.0.md) (formerly known as Swagger)
* [OpenAPI `v3.0`](https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md)
* [OpenAPI `v3.1`](https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.1.0.md) Soon! [Tracking issue here.](https://github.com/getkin/kin-openapi/issues/230)

Licensed under the [MIT License](./LICENSE).

## Contributors, users and sponsors
The project has received pull requests [from many people](https://github.com/getkin/kin-openapi/graphs/contributors). Thanks to everyone!

Be sure to [give back to this project](https://github.com/sponsors/fenollp) like our sponsors:

<p align="center">
	<a href="//www.speakeasyapi.dev"><img src=".github/sponsors/speakeasy.png" alt="Speakeasy" height="100px"/></a>
</p>

Here's some projects that depend on _kin-openapi_:
  * [github.com/Tufin/oasdiff](https://github.com/Tufin/oasdiff) - "A diff tool for OpenAPI Specification 3"
  * [github.com/danielgtaylor/apisprout](https://github.com/danielgtaylor/apisprout) - "Lightweight, blazing fast, cross-platform OpenAPI 3 mock server with validation"
  * [github.com/deepmap/oapi-codegen](https://github.com/deepmap/oapi-codegen) - "Generate Go client and server boilerplate from OpenAPI 3 specifications"
  * [github.com/dunglas/vulcain](https://github.com/dunglas/vulcain) - "Use HTTP/2 Server Push to create fast and idiomatic client-driven REST APIs"
  * [github.com/danielgtaylor/restish](https://github.com/danielgtaylor/restish) - "...a CLI for interacting with REST-ish HTTP APIs with some nice features built-in"
  * [github.com/goadesign/goa](https://github.com/goadesign/goa) - "Design-based APIs and microservices in Go"
  * [github.com/hashicorp/nomad-openapi](https://github.com/hashicorp/nomad-openapi) - "Nomad is an easy-to-use, flexible, and performant workload orchestrator that can deploy a mix of microservice, batch, containerized, and non-containerized applications. Nomad is easy to operate and scale and has native Consul and Vault integrations."
  * [gitlab.com/jamietanna/httptest-openapi](https://gitlab.com/jamietanna/httptest-openapi) ([*blog post*](https://www.jvt.me/posts/2022/05/22/go-openapi-contract-test/)) - "Go OpenAPI Contract Verification for use with `net/http`"
  * [github.com/SIMITGROUP/openapigenerator](https://github.com/SIMITGROUP/openapigenerator) - "Openapi v3 microservices generator"
  * (Feel free to add your project by [creating an issue](https://github.com/getkin/kin-openapi/issues/new) or a pull request)

## Alternatives
* [go-swagger](https://github.com/go-swagger/go-swagger) stated [*OpenAPIv3 won't be supported*](https://github.com/go-swagger/go-swagger/issues/1122#issuecomment-575968499)
* [swaggo](https://github.com/swaggo/swag) has an [open issue on OpenAPIv3](https://github.com/swaggo/swag/issues/386)
* [go-openapi](https://github.com/go-openapi)'s [spec3](https://github.com/go-openapi/spec3)
	* an iteration on [spec](https://github.com/go-openapi/spec) (for OpenAPIv2)
	* see [README](https://github.com/go-openapi/spec3/tree/3fab9faa9094e06ebd19ded7ea96d156c2283dca#oai-object-model---) for the missing parts

Be sure to check [OpenAPI Initiative](https://github.com/OAI)'s [great tooling list](https://github.com/OAI/OpenAPI-Specification/blob/master/IMPLEMENTATIONS.md) as well as [OpenAPI.Tools](https://openapi.tools/).

# Structure
  * _openapi2_ ([godoc](https://godoc.org/github.com/getkin/kin-openapi/openapi2))
    * Support for OpenAPI 2 files, including serialization, deserialization, and validation.
  * _openapi2conv_ ([godoc](https://godoc.org/github.com/getkin/kin-openapi/openapi2conv))
    * Converts OpenAPI 2 files into OpenAPI 3 files.
  * _openapi3_ ([godoc](https://godoc.org/github.com/getkin/kin-openapi/openapi3))
    * Support for OpenAPI 3 files, including serialization, deserialization, and validation.
  * _openapi3filter_ ([godoc](https://godoc.org/github.com/getkin/kin-openapi/openapi3filter))
    * Validates HTTP requests and responses
    * Provides a [gorilla/mux](https://github.com/gorilla/mux) router for OpenAPI operations
  * _openapi3gen_ ([godoc](https://godoc.org/github.com/getkin/kin-openapi/openapi3gen))
    * Generates `*openapi3.Schema` values for Go types.

# Some recipes
## Validating an OpenAPI document
```shell
go run github.com/getkin/kin-openapi/cmd/validate@latest [--defaults] [--examples] [--ext] [--patterns] -- <local YAML or JSON file>
```

## Loading OpenAPI document
Use `openapi3.Loader`, which resolves all references:
```go
doc, err := openapi3.NewLoader().LoadFromFile("swagger.json")
```

## Getting OpenAPI operation that matches request
```go
loader := openapi3.NewLoader()
doc, _ := loader.LoadFromData([]byte(`...`))
_ := doc.Validate(loader.Context)
router, _ := gorillamux.NewRouter(doc)
route, pathParams, _ := router.FindRoute(httpRequest)
// Do something with route.Operation
```

## Validating HTTP requests/responses
```go
package main

import (
	"context"
	"fmt"
	"net/http"

	"github.com/getkin/kin-openapi/openapi3"
	"github.com/getkin/kin-openapi/openapi3filter"
	"github.com/getkin/kin-openapi/routers/gorillamux"
)

func main() {
	ctx := context.Background()
	loader := &openapi3.Loader{Context: ctx, IsExternalRefsAllowed: true}
	doc, _ := loader.LoadFromFile(".../My-OpenAPIv3-API.yml")
	// Validate document
	_ := doc.Validate(ctx)
	router, _ := gorillamux.NewRouter(doc)
	httpReq, _ := http.NewRequest(http.MethodGet, "/items", nil)

	// Find route
	route, pathParams, _ := router.FindRoute(httpReq)

	// Validate request
	requestValidationInput := &openapi3filter.RequestValidationInput{
		Request:    httpReq,
		PathParams: pathParams,
		Route:      route,
	}
	_ := openapi3filter.ValidateRequest(ctx, requestValidationInput)

	// Handle that request
	// --> YOUR CODE GOES HERE <--
	responseHeaders := http.Header{"Content-Type": []string{"application/json"}}
	responseCode := 200
	responseBody := []byte(`{}`)

	// Validate response
	responseValidationInput := &openapi3filter.ResponseValidationInput{
		RequestValidationInput: requestValidationInput,
		Status:                 responseCode,
		Header:                 responseHeaders,
	}
	responseValidationInput.SetBodyBytes(responseBody)
	_ := openapi3filter.ValidateResponse(ctx, responseValidationInput)
}
```

## Custom content type for body of HTTP request/response

By default, the library parses a body of HTTP request and response
if it has one of the next content types: `"text/plain"` or `"application/json"`.
To support other content types you must register decoders for them:

```go
func main() {
	// ...

	// Register a body's decoder for content type "application/xml".
	openapi3filter.RegisterBodyDecoder("application/xml", xmlBodyDecoder)

	// Now you can validate HTTP request that contains a body with content type "application/xml".
	requestValidationInput := &openapi3filter.RequestValidationInput{
		Request:    httpReq,
		PathParams: pathParams,
		Route:      route,
	}
	if err := openapi3filter.ValidateRequest(ctx, requestValidationInput); err != nil {
		panic(err)
	}

	// ...

	// And you can validate HTTP response that contains a body with content type "application/xml".
	if err := openapi3filter.ValidateResponse(ctx, responseValidationInput); err != nil {
		panic(err)
	}
}

func xmlBodyDecoder(body io.Reader, h http.Header, schema *openapi3.SchemaRef, encFn openapi3filter.EncodingFn) (decoded interface{}, err error) {
	// Decode body to a primitive, []inteface{}, or map[string]interface{}.
}
```

## Custom function to check uniqueness of array items

By defaut, the library check unique items by below predefined function

```go
func isSliceOfUniqueItems(xs []interface{}) bool {
	s := len(xs)
	m := make(map[string]struct{}, s)
	for _, x := range xs {
		key, _ := json.Marshal(&x)
		m[string(key)] = struct{}{}
	}
	return s == len(m)
}
```

In the predefined function using `json.Marshal` to generate a string can
be used as a map key which is to support check the uniqueness of an array
when the array items are objects or arrays. You can register
you own function according to your input data to get better performance:

```go
func main() {
	// ...

	// Register a customized function used to check uniqueness of array.
	openapi3.RegisterArrayUniqueItemsChecker(arrayUniqueItemsChecker)

	// ... other validate codes
}

func arrayUniqueItemsChecker(items []interface{}) bool {
	// Check the uniqueness of the input slice
}
```

## Custom function to change schema error messages

By default, the error message returned when validating a value includes the error reason, the schema, and the input value.

For example, given the following schema:

```json
{
  "type": "string",
  "allOf": [
    { "pattern": "[A-Z]" },
    { "pattern": "[a-z]" },
    { "pattern": "[0-9]" },
    { "pattern": "[!@#$%^&*()_+=-?~]" }
  ]
}
```

Passing the input value `"secret"` to this schema will produce the following error message:

```
string doesn't match the regular expression "[A-Z]"
Schema:
  {
    "pattern": "[A-Z]"
  }

Value:
  "secret"
```

Including the original value in the error message can be helpful for debugging, but it may not be appropriate for sensitive information such as secrets.

To disable the extra details in the schema error message, you can set the `openapi3.SchemaErrorDetailsDisabled` option to `true`:

```go
func main() {
	// ...

	// Disable schema error detailed error messages
	openapi3.SchemaErrorDetailsDisabled = true

	// ... other validate codes
}
```

This will shorten the error message to present only the reason:

```
string doesn't match the regular expression "[A-Z]"
```

For more fine-grained control over the error message, you can pass a custom `openapi3filter.Options` object to `openapi3filter.RequestValidationInput` that includes a `openapi3filter.CustomSchemaErrorFunc`.

```go
func validationOptions() *openapi3filter.Options {
	options := openapi3filter.DefaultOptions
	options.WithCustomSchemaErrorFunc(safeErrorMessage)
	return options
}

func safeErrorMessage(err *openapi3.SchemaError) string {
	return err.Reason
}
```

This will change the schema validation errors to return only the `Reason` field, which is guaranteed to not include the original value.

## Sub-v0 breaking API changes

### v0.113.0
* The string format `email` has been removed by default. To use it please call `openapi3.DefineStringFormat("email", openapi3.FormatOfStringForEmail)`.
* Field `openapi3.T.Components` is now a pointer.
* Fields `openapi3.Schema.AdditionalProperties` and `openapi3.Schema.AdditionalPropertiesAllowed` are replaced by `openapi3.Schema.AdditionalProperties.Schema` and `openapi3.Schema.AdditionalProperties.Has` respectively.
* Type `openapi3.ExtensionProps` is now just `map[string]interface{}` and extensions are accessible through the `Extensions` field.

### v0.112.0
* `(openapi3.ValidationOptions).ExamplesValidationDisabled` has been unexported.
* `(openapi3.ValidationOptions).SchemaFormatValidationEnabled` has been unexported.
* `(openapi3.ValidationOptions).SchemaPatternValidationDisabled` has been unexported.

### v0.111.0
* Changed `func (*_) Validate(ctx context.Context) error` to `func (*_) Validate(ctx context.Context, opts ...ValidationOption) error`.
* `openapi3.WithValidationOptions(ctx context.Context, opts *ValidationOptions) context.Context` prototype changed to `openapi3.WithValidationOptions(ctx context.Context, opts ...ValidationOption) context.Context`.

### v0.101.0
* `openapi3.SchemaFormatValidationDisabled` has been removed in favour of an option `openapi3.EnableSchemaFormatValidation()` passed to `openapi3.T.Validate`. The default behaviour is also now to not validate formats, as the OpenAPI spec mentions the `format` is an open value.

### v0.84.0
* The prototype of `openapi3gen.NewSchemaRefForValue` changed:
	* It no longer returns a map but that is still accessible under the field `(*Generator).SchemaRefs`.
	* It now takes in an additional argument (basically `doc.Components.Schemas`) which gets written to so `$ref` cycles can be properly handled.

### v0.61.0
* Renamed `openapi2.Swagger` to `openapi2.T`.
* Renamed `openapi2conv.FromV3Swagger` to `openapi2conv.FromV3`.
* Renamed `openapi2conv.ToV3Swagger` to `openapi2conv.ToV3`.
* Renamed `openapi3.LoadSwaggerFromData` to `openapi3.LoadFromData`.
* Renamed `openapi3.LoadSwaggerFromDataWithPath` to `openapi3.LoadFromDataWithPath`.
* Renamed `openapi3.LoadSwaggerFromFile` to `openapi3.LoadFromFile`.
* Renamed `openapi3.LoadSwaggerFromURI` to `openapi3.LoadFromURI`.
* Renamed `openapi3.NewSwaggerLoader` to `openapi3.NewLoader`.
* Renamed `openapi3.Swagger` to `openapi3.T`.
* Renamed `openapi3.SwaggerLoader` to `openapi3.Loader`.
* Renamed `openapi3filter.ValidationHandler.SwaggerFile` to `openapi3filter.ValidationHandler.File`.
* Renamed `routers.Route.Swagger` to `routers.Route.Spec`.

### v0.51.0
* Type `openapi3filter.Route` moved to `routers` (and `Route.Handler` was dropped. See https://github.com/getkin/kin-openapi/issues/329)
* Type `openapi3filter.RouteError` moved to `routers` (so did `ErrPathNotFound` and `ErrMethodNotAllowed` which are now `RouteError`s)
* Routers' `FindRoute(...)` method now takes only one argument: `*http.Request`
* `getkin/kin-openapi/openapi3filter.Router` moved to `getkin/kin-openapi/routers/legacy`
* `openapi3filter.NewRouter()` and its related `WithSwaggerFromFile(string)`, `WithSwagger(*openapi3.Swagger)`, `AddSwaggerFromFile(string)` and `AddSwagger(*openapi3.Swagger)` are all replaced with a single `<router package>.NewRouter(*openapi3.Swagger)`
	* NOTE: the `NewRouter(doc)` call now requires that the user ensures `doc` is valid (`doc.Validate() != nil`). This used to be asserted.

### v0.47.0
Field `(*openapi3.SwaggerLoader).LoadSwaggerFromURIFunc` of type `func(*openapi3.SwaggerLoader, *url.URL) (*openapi3.Swagger, error)` was removed after the addition of the field `(*openapi3.SwaggerLoader).ReadFromURIFunc` of type `func(*openapi3.SwaggerLoader, *url.URL) ([]byte, error)`.
