danielgtaylor · danielgtaylor · Mar 21, 2022 · Mar 19, 2022
diff --git a/README.md b/README.md
@@ -45,6 +45,7 @@ Features include:
   - SDKs with [OpenAPI Generator](https://github.com/OpenAPITools/openapi-generator)
   - CLI with [Restish](https://rest.sh/)
   - And [plenty](https://openapi.tools/) [more](https://apis.guru/awesome-openapi3/category.html)
+- Generates JSON Schema for each resource using `describedby` link relation headers as well as optional `$schema` properties in returned objects that integrate into editors for validation & completion.
 
 This project was inspired by [FastAPI](https://fastapi.tiangolo.com/). Look at the [benchmarks](https://github.com/danielgtaylor/huma/tree/master/benchmark) to see how Huma compares.
 
@@ -788,7 +789,16 @@ app.DocsHandler(huma.ReDocHandler("My API"))
 
 > :whale: Pass a custom handler function to have even more control for branding or browser authentication.
 
-## Custom OpenAPI Fields
+## OpenAPI
+
+By default, the generated OpenAPI and autogenerated documentation are served in the root at `/openapi.json` and `/docs` respectively. This default path can be modified:
+
+```go
+// Serve `/public/openapi.json and `/public/docs`:
+app.DocsPrefix("/public")
+```
+
+### Custom OpenAPI Fields
 
 Use the OpenAPI hook for OpenAPI customization. It gives you a `*gabs.Container` instance that represents the root of the OpenAPI document.
 
@@ -803,23 +813,28 @@ app.OpenAPIHook(modify)
 
 > :whale: See the [OpenAPI 3 spec](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.3.md) for everything that can be set.
 
-## CLI
+### JSON Schema
 
-The `cli` package provides a convenience layer to create a simple CLI for your server, which lets a user set the host, port, TLS settings, etc when running your service.
+Each resource operation also returns a `describedby` HTTP link relation which references a JSON-Schema file. These schemas re-use the `DocsPrefix` described above and default to the server root. For example:
 
-```go
-app := cli.NewRouter("My API", "1.0.0")
+```http
+Link: </schemas/Note.json>; rel="describedby"
+```
 
-// Do resource/operation setup here...
+Object resources (i.e. not arrays) can also optionally return a `$schema` property with such a link, which enables the described-by relationship to outlive the HTTP request (i.e. saving the body to a file for later editing) and enables some editors like [VSCode](https://code.visualstudio.com/docs/languages/json#_mapping-in-the-json) to provide code completion and validation as you type.
 
-app.Run()
+```json
+{
+  "$schema": "http://localhost:8888/schemas/Note.json",
+  "title": "I am a note title",
+  "contents": "Example note contents",
+  "labels": ["todo"]
+}
 ```
 
-Then run the service:
+Operations which accept objects as input will ignore the `$schema` property, so it is safe to submit back to the API.
 
-```sh
-$ go run yourservice.go --help
-```
+This feature can be disabled if desired by using `app.DisableSchemaProperty`.
 
 ## GraphQL
 
@@ -981,6 +996,24 @@ Result:
 220 complexity
 ```
 
+## CLI
+
+The `cli` package provides a convenience layer to create a simple CLI for your server, which lets a user set the host, port, TLS settings, etc when running your service.
+
+```go
+app := cli.NewRouter("My API", "1.0.0")
+
+// Do resource/operation setup here...
+
+app.Run()
+```
+
+Then run the service:
+
+```sh
+$ go run yourservice.go --help
+```
+
 ## CLI Runtime Arguments & Configuration
 
 The CLI can be configured in multiple ways. In order of decreasing precedence:

diff --git a/context.go b/context.go
@@ -11,6 +11,7 @@ import (
 	"github.com/danielgtaylor/huma/negotiation"
 	"github.com/fxamacker/cbor/v2"
 	"github.com/goccy/go-yaml"
+	"github.com/mitchellh/mapstructure"
 )
 
 // allowedHeaders is a list of built-in headers that are always allowed without
@@ -70,10 +71,13 @@ type Context interface {
 type hcontext struct {
 	context.Context
 	http.ResponseWriter
-	r      *http.Request
-	errors []error
-	op     *Operation
-	closed bool
+	r                     *http.Request
+	errors                []error
+	op                    *Operation
+	closed                bool
+	docsPrefix            string
+	urlPrefix             string
+	disableSchemaProperty bool
 }
 
 func (c *hcontext) WithValue(key, value interface{}) Context {
@@ -193,8 +197,24 @@ func (c *hcontext) WriteModel(status int, model interface{}) {
 	c.writeModel(ct, status, model)
 }
 
+// URLPrefix returns the prefix to use for non-relative URL links.
+func (c *hcontext) URLPrefix() string {
+	if c.urlPrefix != "" {
+		return c.urlPrefix
+	}
+
+	scheme := "https"
+	if strings.HasPrefix(c.r.Host, "localhost") {
+		scheme = "http"
+	}
+
+	return scheme + "://" + c.r.Host
+}
+
 func (c *hcontext) writeModel(ct string, status int, model interface{}) {
 	// Is this allowed? Find the right response.
+	modelRef := ""
+	modelType := reflect.TypeOf(model)
 	if c.op != nil {
 		responses := []Response{}
 		names := []string{}
@@ -215,14 +235,49 @@ func (c *hcontext) writeModel(ct string, status int, model interface{}) {
 
 		found := false
 		for _, r := range responses {
-			if r.model == reflect.TypeOf(model) {
+			if r.model == modelType {
 				found = true
+				modelRef = r.modelRef
 				break
 			}
 		}
 
 		if !found {
-			panic(fmt.Errorf("Invalid model %s, expecting %s for %s %s", reflect.TypeOf(model), strings.Join(names, ", "), c.r.Method, c.r.URL.Path))
+			panic(fmt.Errorf("Invalid model %s, expecting %s for %s %s", modelType, strings.Join(names, ", "), c.r.Method, c.r.URL.Path))
+		}
+	}
+
+	// If possible, insert a link relation header to the JSON Schema describing
+	// this response. If it's an object (not an array), then we can also try
+	// inserting the `$schema` key to make editing & validation easier.
+	parts := strings.Split(modelRef, "/")
+	if len(parts) > 0 {
+		id := parts[len(parts)-1]
+
+		link := c.Header().Get("Link")
+		if link != "" {
+			link += ", "
+		}
+		link += "<" + c.docsPrefix + "/schemas/" + id + ".json>; rel=\"describedby\""
+		c.Header().Set("Link", link)
+
+		if !c.disableSchemaProperty && modelType != nil && modelType.Kind() == reflect.Struct {
+			tmp := map[string]interface{}{}
+			decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
+				TagName: "json",
+				Result:  &tmp,
+			})
+			if err != nil {
+				panic(fmt.Errorf("Unable to initialize struct decoder: %w", err))
+			}
+			err = decoder.Decode(model)
+			if err != nil {
+				panic(fmt.Errorf("Unable to convert struct to map: %w", err))
+			}
+			if tmp["$schema"] == nil {
+				tmp["$schema"] = c.URLPrefix() + c.docsPrefix + "/schemas/" + id + ".json"
+			}
+			model = tmp
 		}
 	}
 

diff --git a/context_test.go b/context_test.go
@@ -8,7 +8,7 @@ import (
 	"net/http/httptest"
 	"testing"
 
-	"github.com/fxamacker/cbor"
+	"github.com/fxamacker/cbor/v2"
 	"github.com/goccy/go-yaml"
 	"github.com/stretchr/testify/assert"
 )

diff --git a/go.mod b/go.mod
@@ -3,36 +3,32 @@ module github.com/danielgtaylor/huma
 go 1.13
 
 require (
-	github.com/Jeffail/gabs/v2 v2.6.0
-	github.com/andybalholm/brotli v1.0.0
+	github.com/Jeffail/gabs/v2 v2.6.1
+	github.com/andybalholm/brotli v1.0.4
+	github.com/benbjohnson/clock v1.3.0 // indirect
 	github.com/danielgtaylor/casing v0.0.0-20210126043903-4e55e6373ac3
 	github.com/fatih/structs v1.1.0
-	github.com/fsnotify/fsnotify v1.4.9 // indirect
-	github.com/fxamacker/cbor v1.5.1
-	github.com/fxamacker/cbor/v2 v2.2.0
+	github.com/fxamacker/cbor/v2 v2.4.0
 	github.com/go-chi/chi v4.1.2+incompatible
-	github.com/goccy/go-yaml v1.8.1
+	github.com/goccy/go-yaml v1.9.5
 	github.com/graphql-go/graphql v0.8.0
 	github.com/graphql-go/handler v0.2.3
 	github.com/koron-go/gqlcost v0.2.2
-	github.com/magiconair/properties v1.8.2 // indirect
-	github.com/mattn/go-isatty v0.0.12
-	github.com/mitchellh/mapstructure v1.3.3 // indirect
+	github.com/magiconair/properties v1.8.6 // indirect
+	github.com/mattn/go-isatty v0.0.14
+	github.com/mitchellh/mapstructure v1.4.3
 	github.com/opentracing/opentracing-go v1.2.0
-	github.com/pelletier/go-toml v1.8.0 // indirect
-	github.com/spf13/afero v1.3.4 // indirect
-	github.com/spf13/cast v1.3.1 // indirect
-	github.com/spf13/cobra v1.0.0
-	github.com/spf13/jwalterweatherman v1.1.0 // indirect
-	github.com/spf13/pflag v1.0.5 // indirect
-	github.com/spf13/viper v1.7.1
+	github.com/spf13/afero v1.8.2 // indirect
+	github.com/spf13/cobra v1.4.0
+	github.com/spf13/viper v1.10.1
 	github.com/stretchr/testify v1.7.0
 	github.com/tent/http-link-go v0.0.0-20130702225549-ac974c61c2f9
 	github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb // indirect
 	github.com/xeipuuv/gojsonschema v1.2.0
-	go.uber.org/zap v1.15.0
-	golang.org/x/sys v0.0.0-20200826173525-f9321e4c35a6 // indirect
-	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
-	gopkg.in/ini.v1 v1.60.1 // indirect
+	go.uber.org/atomic v1.9.0 // indirect
+	go.uber.org/multierr v1.8.0 // indirect
+	go.uber.org/zap v1.21.0
+	golang.org/x/sys v0.0.0-20220318055525-2edf467146b5 // indirect
+	gopkg.in/ini.v1 v1.66.4 // indirect
 	launchpad.net/gocheck v0.0.0-20140225173054-000000000087 // indirect
 )