[Go] Adding response middleware (#16641)

* Add optional response middleware to go template

Also adds a request middleware which can return an error

* Re-adding newline to fix tests

* Fixing docs

modules/openapi-generator/src/main/resources/go/api.mustache

@@ -352,6 +352,15 @@ func (a *{{{classname}}}Service) {{nickname}}Execute(r {{#structPrefix}}{{&class
 		return {{#returnType}}localVarReturnValue, {{/returnType}}localVarHTTPResponse, err
 	}
 
+{{#withCustomMiddlewareFunction}}
+	if a.client.cfg.ResponseMiddleware != nil {
+		err = a.client.cfg.ResponseMiddleware(localVarHTTPResponse, localVarBody)
+		if err != nil {
+			return {{#returnType}}localVarReturnValue, {{/returnType}}localVarHTTPResponse, err
+		}
+	}
+
+{{/withCustomMiddlewareFunction}}
 	if localVarHTTPResponse.StatusCode >= 300 {
 		newErr := &GenericOpenAPIError{
 			body:  localVarBody,

modules/openapi-generator/src/main/resources/go/client.mustache

@@ -487,6 +487,13 @@ func (c *APIClient) prepareRequest(
 		c.cfg.Middleware(localVarRequest)
 	}
 
+	if c.cfg.MiddlewareWithError != nil {
+		err = c.cfg.MiddlewareWithError(localVarRequest)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 {{/withCustomMiddlewareFunction}}
 {{#hasHttpSignatureMethods}}
 	if ctx != nil {

modules/openapi-generator/src/main/resources/go/configuration.mustache

@@ -104,9 +104,15 @@ type ServerConfiguration struct {
 type ServerConfigurations []ServerConfiguration
 
 {{#withCustomMiddlewareFunction}}
-// MiddlewareFunction provides way to implement custom middleware
+// MiddlewareFunction provides way to implement custom middleware in the prepareRequest
 type MiddlewareFunction func(*http.Request)
 
+// MiddlewareFunctionWithError provides way to implement custom middleware with errors in the prepareRequest
+type MiddlewareFunctionWithError func(*http.Request) error
+
+// ResponseMiddlewareFunction provides way to implement custom middleware with errors after the response is received
+type ResponseMiddlewareFunction func(*http.Response, []byte) error
+
 {{/withCustomMiddlewareFunction}}
 // Configuration stores the configuration of the API client
 type Configuration struct {
@@ -119,7 +125,9 @@ type Configuration struct {
 	OperationServers map[string]ServerConfigurations
 	HTTPClient       *http.Client
 	{{#withCustomMiddlewareFunction}}
-	Middleware       MiddlewareFunction
+	Middleware          MiddlewareFunction
+	MiddlewareWithError MiddlewareFunctionWithError
+	ResponseMiddleware  ResponseMiddlewareFunction
 	{{/withCustomMiddlewareFunction}}
 }