openapi: Add support for external refs

tpl/openapi/openapi3/integration_test.go

@@ -37,18 +37,20 @@ servers:
     description: Optional server description, e.g. Internal staging server for testing
 paths:
   /users:
-    get:
-      summary: Returns a list of users.
-      description: Optional extended description in CommonMark or HTML.
-      responses:
-        '200':    # status code
-          description: A JSON array of user names
-          content:
-            application/json:
-              schema: 
-                type: array
-                items: 
-                  type: string
+    $ref: ./methods/get.yaml
+-- assets/api/methods/get.yaml --
+get:
+  summary: Returns a list of users.
+  description: Optional extended description in CommonMark or HTML.
+  responses:
+    '200':    # status code
+      description: A JSON array of user names
+      content:
+        application/json:
+          schema: 
+            type: array
+            items: 
+              type: string
 -- config.toml --
 baseURL = 'http://example.com/'
 -- layouts/index.html --

tpl/openapi/openapi3/openapi3.go

@@ -17,6 +17,8 @@ package openapi3
 import (
 	"fmt"
 	"io"
+	"net/url"
+	"strings"
 
 	gyaml "github.com/ghodss/yaml"
 
@@ -90,7 +92,25 @@ func (ns *Namespace) Unmarshal(r resource.UnmarshableResource) (*OpenAPIDocument
 			return nil, err
 		}
 
-		err = kopenapi3.NewLoader().ResolveRefsIn(s, nil)
+		loader := kopenapi3.NewLoader()
+		loader.IsExternalRefsAllowed = true
+		loader.ReadFromURIFunc = func(loader *kopenapi3.Loader, url *url.URL) ([]byte, error) {
+			relativePath := url.Path
+
+			if strings.HasPrefix(url.Path, "./") {
+				relativePath = strings.TrimRightFunc(key, func(r rune) bool { return r != '/' }) + strings.TrimPrefix(url.Path, "./")
+			}
+
+			file, err := ns.deps.SourceFilesystems.Assets.Fs.Open(relativePath)
+			if err != nil {
+				return nil, err
+			}
+			defer file.Close()
+
+			return io.ReadAll(file)
+		}
+
+		err = loader.ResolveRefsIn(s, nil)
 
 		return &OpenAPIDocument{T: s}, err
 	})