Fix: use nullable to allow empty path param (#271)

* fix: check for nullable parameter and allow empty string

* tests: add tests for nullable parameters

* style: remove line breaks

* fix: account for parameter overriding at operation level

* fix: depend on minLength instead

Author: harshadixit12

openapi2kong/oas3_testfiles/21-nullable-path-param.expected.json

@@ -0,0 +1,55 @@
+{
+    "_format_version": "3.0",
+    "services": [
+      {
+        "host": "backend.com",
+        "id": "aac33fce-7ade-5b69-9249-97bea965698e",
+        "name": "odata-style-api-with-nullable-path-params",
+        "path": "/path",
+        "plugins": [],
+        "port": 80,
+        "protocol": "http",
+        "routes": [
+          {
+            "id": "649b2718-47a3-57ec-aec0-b8a4f1bf010d",
+            "methods": [
+              "GET"
+            ],
+            "name": "odata-style-api-with-nullable-path-params_customproductdata",
+            "paths": [
+              "~/CustomWarehouseData\\(Warehouse='(?\u003cwarehouse\u003e[^#?/]*)',Product='(?\u003cproduct\u003e[^#?/]+)',Location='(?\u003clocation\u003e[^#?/]*)'\\)$"
+            ],
+            "plugins": [],
+            "regex_priority": 100,
+            "strip_path": false,
+            "tags": [
+              "OAS3_import",
+              "OAS3file_21-nullable-path-param.yaml"
+            ]
+          },
+          {
+            "id": "dd39d9e0-196d-509d-b141-13e77ce94f81",
+            "methods": [
+              "GET"
+            ],
+            "name": "odata-style-api-with-nullable-path-params_customdata",
+            "paths": [
+              "~/custom/(?\u003ccustomid\u003e[^#?/]+)$"
+            ],
+            "plugins": [],
+            "regex_priority": 100,
+            "strip_path": false,
+            "tags": [
+              "OAS3_import",
+              "OAS3file_21-nullable-path-param.yaml"
+            ]
+          }
+        ],
+        "tags": [
+          "OAS3_import",
+          "OAS3file_21-nullable-path-param.yaml"
+        ]
+      }
+    ],
+    "upstreams": []
+}

openapi2kong/oas3_testfiles/21-nullable-path-param.yaml

@@ -0,0 +1,70 @@
+openapi: 3.0.0
+info:
+  title: OData style API with nullable path params
+  version: 0.0.1
+servers:
+  - url: http://backend.com/path
+paths:
+  /custom/{customId}:
+    parameters:
+      - name: customId
+        in: path
+        required: true
+        description: Custom ID
+        schema:
+          type: string
+          maxLength: 4
+    get:
+      summary: Read the custom information
+      description: Read the custom information of the API
+      tags:
+        - Metadata
+      responses:
+        "200":
+          description: Retrieved metadata
+        4XX:
+          description: all 4XX errors
+      operationId: customdata
+  ? "/CustomWarehouseData(Warehouse='{Warehouse}',Product='{Product}',Location='{Location}')"
+  : parameters:
+      - name: Warehouse
+        in: path
+        required: true
+        description: ID of warehouse
+        schema:
+          type: string
+          maxLength: 4
+          minLength: 0
+      - name: Product
+        in: path
+        required: true
+        description: Product Number
+        schema:
+          type: string
+          maxLength: 40
+      - name: Location
+        in: path
+        required: true
+        description: Product Number
+        schema:
+          type: string
+          maxLength: 40
+    get:
+      summary: List entities from Warehouse based on product ID, location and warehouse ID
+      parameters:
+        - name: Location #overrides the param defined in path level
+          in: path
+          required: true
+          description: Product Number
+          schema:
+            type: string
+            maxLength: 40
+            minLength: 0
+      tags:
+        - WarehouseProductData
+      responses:
+        "200":
+          description: Retrieved product entities
+        4XX:
+          description: all 4XX errors
+      operationId: customproductdata

openapi2kong/openapi2kong.go

@@ -521,6 +521,27 @@ func getForeignKeyPlugins(
 	return &genericPlugins, &newPluginList
 }
 
+// findParameterSchema returns the Schema for given parameter name.
+// Path level parameters can be overridden at operation level, so we check operation parameters first
+// and then fall back to path.
+func findParameterSchema(
+	operationParameters []*v3.Parameter,
+	pathParameters []*v3.Parameter,
+	paramName string,
+) *openapibase.Schema {
+	for _, param := range operationParameters {
+		if param.Name == paramName {
+			return param.Schema.Schema()
+		}
+	}
+	for _, param := range pathParameters {
+		if param.Name == paramName {
+			return param.Schema.Schema()
+		}
+	}
+	return nil
+}
+
 // MustConvert is the same as Convert, but will panic if an error is returned.
 func MustConvert(content []byte, opts O2kOptions) map[string]interface{} {
 	result, err := Convert(content, opts)
@@ -1085,6 +1106,11 @@ func Convert(content []byte, opts O2kOptions) (map[string]interface{}, error) {
 							varName, captureName)
 					}
 					regexMatch := "(?<" + captureName + ">[^#?/]+)"
+					paramSchema := findParameterSchema(operation.Parameters, pathitem.Parameters, varName)
+					// Check if the parameter has a minLength defined, if 0, allow empty string
+					if paramSchema != nil && paramSchema.MinLength != nil && *paramSchema.MinLength == 0 {
+						regexMatch = "(?<" + captureName + ">[^#?/]*)"
+					}
 					placeHolder := "{" + varName + "}"
 					logbasics.Debug("replacing path parameter", "parameter", placeHolder, "regex", regexMatch)
 					convertedPath = strings.Replace(convertedPath, placeHolder, regexMatch, 1)