feat: support OAS 2.0

Some users have aep-compliant schemas, but OAS 2.0
descriptions.

This is especially common for translation gateways
like grpc-gateway (which currently only supports 2.0).

Fixes #10.

Author: toumorokoshi

internal/openapi/openapi.go

@@ -63,6 +63,8 @@ type Parameter struct {
 type Response struct {
 	Description string               `json:"description"`
 	Content     map[string]MediaType `json:"content"`
+	// oas 2.0 has the schema in the response.
+	Schema *Schema `json:"schema,omitempty"`
 }
 
 type RequestBody struct {

internal/service/service_definition.go

@@ -19,6 +19,7 @@ type ServiceDefinition struct {
 
 func GetServiceDefinition(api *openapi.OpenAPI, pathPrefix string) (*ServiceDefinition, error) {
 	slog.Debug("parsing openapi", "pathPrefix", pathPrefix)
+	oasVersion := api.Info.Version
 	resourceBySingular := make(map[string]*Resource)
 	// we try to parse the paths to find possible resources, since
 	// they may not always be annotated as such.
@@ -40,15 +41,13 @@ func GetServiceDefinition(api *openapi.OpenAPI, pathPrefix string) (*ServiceDefi
 			}
 			if pathItem.Get != nil {
 				if resp, ok := pathItem.Get.Responses["200"]; ok {
-					ct := resp.Content[contentType]
-					sRef = ct.Schema
+					sRef = getSchemaFromResponse(resp, oasVersion)
 					r.GetMethod = &GetMethod{}
 				}
 			}
 			if pathItem.Patch != nil {
 				if resp, ok := pathItem.Patch.Responses["200"]; ok {
-					ct := resp.Content[contentType]
-					sRef = ct.Schema
+					sRef = getSchemaFromResponse(resp, oasVersion)
 					r.UpdateMethod = &UpdateMethod{}
 				}
 			}
@@ -57,8 +56,7 @@ func GetServiceDefinition(api *openapi.OpenAPI, pathPrefix string) (*ServiceDefi
 			if pathItem.Post != nil {
 				// check if there is a query parameter "id"
 				if resp, ok := pathItem.Post.Responses["200"]; ok {
-					ct := resp.Content[contentType]
-					sRef = ct.Schema
+					sRef = getSchemaFromResponse(resp, oasVersion)
 					supportsUserSettableCreate := false
 					for _, param := range pathItem.Post.Parameters {
 						if param.Name == "id" {
@@ -73,7 +71,8 @@ func GetServiceDefinition(api *openapi.OpenAPI, pathPrefix string) (*ServiceDefi
 			if pathItem.Get != nil {
 				if resp, ok := pathItem.Get.Responses["200"]; ok {
 					ct := resp.Content[contentType]
-					resolvedSchema, err := dereferencedSchema(*ct.Schema, api)
+					respSchema := getSchemaFromResponse(resp, oasVersion)
+					resolvedSchema, err := dereferencedSchema(*respSchema, api)
 					if err != nil {
 						return nil, fmt.Errorf("error dereferencing schema %q: %v", ct.Schema.Ref, err)
 					}
@@ -237,3 +236,13 @@ func dereferencedSchema(schema openapi.Schema, api *openapi.OpenAPI) (*openapi.S
 	}
 	return &schema, nil
 }
+
+func getSchemaFromResponse(r openapi.Response, oasVersion string) *openapi.Schema {
+	switch oasVersion {
+	case "2.0":
+		return r.Schema
+	default:
+		ct := r.Content[contentType]
+		return ct.Schema
+	}
+}

internal/service/service_definition_test.go

@@ -202,6 +202,42 @@ func TestGetServiceDefinition(t *testing.T) {
 					"should support user-settable create")
 			},
 		},
+		{
+			name: "OAS 2.0 style schema in response",
+			api: &openapi.OpenAPI{
+				Info:    openapi.Info{Version: "2.0"},
+				Servers: []openapi.Server{{URL: "https://api.example.com"}},
+				Paths: map[string]openapi.PathItem{
+					"/widgets/{widget}": {
+						Get: &openapi.Operation{
+							Responses: map[string]openapi.Response{
+								"200": {
+									Schema: &openapi.Schema{
+										Ref: "#/components/schemas/Widget",
+									},
+								},
+							},
+						},
+					},
+				},
+				Components: openapi.Components{
+					Schemas: map[string]openapi.Schema{
+						"Widget": {
+							Type: "object",
+							Properties: map[string]openapi.Schema{
+								"name": {Type: "string"},
+							},
+						},
+					},
+				},
+			},
+			validateResult: func(t *testing.T, sd *ServiceDefinition) {
+				widget, ok := sd.Resources["widget"]
+				assert.True(t, ok, "widget resource should exist")
+				assert.NotNil(t, widget.GetMethod, "should have GET method")
+				assert.Equal(t, []string{"widgets", "{widget}"}, widget.Pattern)
+			},
+		},
 	}
 
 	for _, tt := range tests {