abenn135 commented on code in PR #1943: URL: https://github.com/apache/cassandra-gocql-driver/pull/1943#discussion_r3209914936
########## example_interceptor_test.go: ########## @@ -0,0 +1,138 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +/* + * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40 + * Copyright (c) 2016, The Gocql authors, + * provided under the BSD-3-Clause License. + * See the NOTICE file distributed with this work for additional information. + */ + +package gocql_test + +import ( + "context" + "log" + "time" + + gocql "github.com/apache/cassandra-gocql-driver/v2" +) + +type MyQueryAttemptInterceptor struct { + injectFault bool +} + +func (q MyQueryAttemptInterceptor) Intercept( + ctx context.Context, + attempt gocql.QueryAttempt, + handler gocql.QueryAttemptHandler, +) (*gocql.Iter, error) { + switch q := attempt.Statement.Statement().(type) { + case *gocql.Query: + // Inspect query + log.Println(q.Statement()) + case *gocql.Batch: + // Inspect batch + + log.Println(q.Entries[0].Stmt) + } + + // Inspect or modify context + ctx = context.WithValue(ctx, "trace-id", "123") + + // Optionally bypass the handler and return an error to prevent query execution. + // For example, to simulate query timeouts. + if q.injectFault && attempt.Attempts == 0 { + <-time.After(1 * time.Second) + return nil, gocql.RequestErrWriteTimeout{} + } + + // The interceptor *must* invoke the handler to execute the query. + return handler(ctx) +} + +// Example_interceptor demonstrates how to implement a QueryAttemptInterceptor. +func Example_interceptor() { + cluster := gocql.NewCluster("localhost:9042") + cluster.QueryAttemptInterceptor = MyQueryAttemptInterceptor{injectFault: true} + + session, err := cluster.CreateSession() + if err != nil { + log.Fatal(err) + } + defer session.Close() + + ctx := context.Background() + + var stringValue string + err = session.Query("select now() from system.local"). + RetryPolicy(&gocql.SimpleRetryPolicy{NumRetries: 2}). + ScanContext(ctx, &stringValue) + if err != nil { + log.Fatalf("query failed %T", err) + } +} + +type QueryAttemptInterceptorChain struct { Review Comment: Done, thanks. ########## example_interceptor_test.go: ########## @@ -0,0 +1,138 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +/* + * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40 + * Copyright (c) 2016, The Gocql authors, + * provided under the BSD-3-Clause License. + * See the NOTICE file distributed with this work for additional information. + */ + +package gocql_test + +import ( + "context" + "log" + "time" + + gocql "github.com/apache/cassandra-gocql-driver/v2" +) + +type MyQueryAttemptInterceptor struct { + injectFault bool +} + +func (q MyQueryAttemptInterceptor) Intercept( + ctx context.Context, + attempt gocql.QueryAttempt, + handler gocql.QueryAttemptHandler, +) (*gocql.Iter, error) { + switch q := attempt.Statement.Statement().(type) { + case *gocql.Query: + // Inspect query + log.Println(q.Statement()) + case *gocql.Batch: + // Inspect batch + + log.Println(q.Entries[0].Stmt) + } Review Comment: Yikes, I'm sorry, I didn't realize until now that Go abstract type members keep a pointer (not a copy) of the underlying type. Looking at how we would use this internally, we're hoping to have the following at intercept time: * the ctx that is being used to invoke `Exec()` * the statement body itself (or an exemplar for a `Batch`) * the host ID it will be sent to (for testing fault injection) * an ability to set the trace per attempt It might also be useful for other customers to learn other values on the `Query`, such as current consistency setting, idempotency setting, and keyspace. Perhaps the play is to do the following: * provide a way to optionally set the trace (we just need the context to do this, though others might want other information) * provide a read-only deep copy of just those fields of the Query or Batch that might be useful for interception What do you think? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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