fix(go): prevent infinite recursion during json unmarshal of enums (#163)

relates to STACKITSDK-162

Author: rubenhoenle

openapi-generator-config-go.yml

@@ -0,0 +1,7 @@
+templateDir: templates/go
+files:
+  custom/model_test.mustache:
+    # TODO: this should be 'ModelTests' instead of 'Model'
+    # 'Model' was used because 'ModelTests' didn't stick to golangs file naming conventions
+    templateType: Model
+    destinationFilename: _test.go

scripts/generate-sdk/languages/go.sh

@@ -153,15 +153,16 @@ generate_go_sdk() {
             --input-spec ${service_json} \
             --output ${SERVICES_FOLDER}/${service} \
             --package-name ${service} \
-            --template-dir ${ROOT_DIR}/templates/go/ \
             --enable-post-process-file \
             --git-host ${GIT_HOST} \
             --git-user-id ${GIT_USER_ID} \
             --git-repo-id ${GIT_REPO_ID} \
             --global-property apis,models,modelTests=true,modelDocs=false,apiDocs=false,supportingFiles \
             --additional-properties=isGoSubmodule=true,enumClassPrefix=true,generateInterfaces=true,$regional_api \
-	          --http-user-agent stackit-sdk-go/${service} \
-            --reserved-words-mappings type=types
+	        --http-user-agent stackit-sdk-go/${service} \
+            --reserved-words-mappings type=types \
+            --config openapi-generator-config-go.yml
+            
         # Remove unnecessary files
         rm ${SERVICES_FOLDER}/${service}/.openapi-generator-ignore
         rm ${SERVICES_FOLDER}/${service}/.openapi-generator/FILES

templates/go/custom/model_simple_test.mustache

@@ -0,0 +1,49 @@
+{{! NOTE: This is a custom STACKIT template which is not present in upsteam to support testing of enum models}}
+
+{{#vars}}
+{{! special handling for enums}}
+{{#isEnumRef}}
+{{#isEnum}}
+// isEnum
+
+func Test{{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titlecase}}_UnmarshalJSON(t *testing.T) {
+	type args struct {
+		src []byte
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+	}{
+	{{#allowableValues}}
+	{{#enumVars}}
+		{
+			name: `success - possible enum value no. {{-index}}`,
+			args: args{
+				src: []byte(`{{{value}}}`),
+			},
+			wantErr: false,
+		},
+	{{/enumVars}}
+	{{/allowableValues}}
+		{
+			name: "fail",
+			args: args{
+				src: []byte("\"FOOBAR\""),
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			v := {{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titlecase}}({{#isNumeric}}-1{{/isNumeric}}{{^isNumeric}}""{{/isNumeric}})
+			if err := v.UnmarshalJSON(tt.args.src); (err != nil) != tt.wantErr {
+				t.Errorf("UnmarshalJSON() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+{{/isEnum}}
+{{/isEnumRef}}
+{{/vars}}

templates/go/custom/model_test.mustache

@@ -0,0 +1,20 @@
+{{#models}}
+
+{{>partial_header}}
+package {{packageName}}
+
+import (
+	"testing"
+{{#imports}}
+	"{{import}}"
+{{/imports}}
+)
+
+{{#model}}
+{{^isEnum}}
+{{^oneOf}}{{^anyOf}}
+{{>custom/model_simple_test}}
+{{/anyOf}}{{/oneOf}}
+{{/isEnum}}
+{{/model}}
+{{/models}}

templates/go/model_simple.mustache

@@ -305,13 +305,16 @@ var Allowed{{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titl
 }
 
 func (v *{{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titlecase}}) UnmarshalJSON(src []byte) error {
-	var value {{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titlecase}}
+	// use a type alias to prevent infinite recursion during unmarshal, 
+	// see https://biscuit.ninja/posts/go-avoid-an-infitine-loop-with-custom-json-unmarshallers
+	type TmpJson {{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titlecase}}
+	var value TmpJson
 	err := json.Unmarshal(src, &value)
 	if err != nil {
 		return err
 	}
 	// Allow unmarshalling zero value for testing purposes
-	var zeroValue {{{classname}}}{{#lambda.titlecase}}{{nameInCamelCase}}{{/lambda.titlecase}}
+	var zeroValue TmpJson
 	if value == zeroValue {
 		return nil
 	}