toptobes commented on code in PR #1943:
URL:
https://github.com/apache/cassandra-gocql-driver/pull/1943#discussion_r3607108512
##########
query_executor.go:
##########
@@ -69,16 +71,151 @@ type internalRequest interface {
}
type queryExecutor struct {
- pool *policyConnPool
- policy HostSelectionPolicy
+ pool *policyConnPool
+ policy HostSelectionPolicy
+ interceptor ExecAttemptInterceptor
}
-func (q *queryExecutor) attemptQuery(ctx context.Context, qry internalRequest,
conn *Conn) *Iter {
+type OpType int
+
+const (
+ OpQuery OpType = iota
+ OpBatch
+)
+
+type ImmutableQuery interface {
+ Statement() string
+ Values() []interface{}
+}
+
+type immutableQuery struct {
+ query *Query
+}
+
+func (q *immutableQuery) Statement() string {
+ return q.query.stmt
+}
+
+func (q *immutableQuery) Values() []interface{} {
+ return q.query.values
+}
+
+type ImmutableBatch interface {
+ Type() BatchType
+ Entries() []BatchEntry
+ Cons() Consistency
+}
+
+type immutableBatch struct {
+ batch *Batch
+}
+
+func (b *immutableBatch) Type() BatchType {
+ return b.batch.Type
+}
+
+func (b *immutableBatch) Entries() []BatchEntry {
+ return b.batch.Entries
+}
+
+func (b *immutableBatch) Cons() Consistency {
+ return b.batch.Cons
+}
+
+type QueryAttempt struct {
+ // The op type, whether query or batch.
+ Type OpType
+ // Only one of Query or Batch will be set, depending on the op type.
+ Query ImmutableQuery
+ Batch ImmutableBatch
+ // The host that will receive the query.
+ Host *HostInfo
+ // The local address of the connection used to execute the query.
+ LocalAddr net.Addr
+ // The remote address of the connection used to execute the query.
+ RemoteAddr net.Addr
+ // The number of this query attempt. 0 for the initial attempt, 1 for
the first retry, etc. Note that there may be multiple serial Attempts to
different hosts within a single execution, whether main execution or
speculative.
+ Attempts int
+ // The index of the speculative execution attempt this attempt is
associated with, starting with index 1. -1 indicates this is the "main"
execution.
+ SpeculativeExecutionCount int
+}
+
+// QueryAttemptHandler is a function that attempts query execution. The
interceptor must call this once if it does not return an error.
+type QueryAttemptHandler = func(context.Context) (*Iter, error)
+
+// ExecAttemptInterceptor is the interface implemented by interceptors /
middleware.
+//
+// Interceptors are well-suited to logic that is not specific to a single
query or batch, such as flow control.
+type ExecAttemptInterceptor interface {
+ // Intercept is invoked once immediately before a query or batch
execution attempt, including retry attempts and
+ // speculative execution attempts.
+ //
+ // The interceptor is responsible for calling the `handler` function
and returning the handler result. If the
+ // interceptor wants to bypass the handler and skip query execution, it
should return an error. Failure to
+ // return either the handler result or an error will panic.
+ //
+ // Note that there is no affordance to mutate the query or batch at
this stage -- the handler already encapsulates the original query/batch and
cannot be modified.
+ Intercept(ctx context.Context, attempt QueryAttempt, handler
QueryAttemptHandler) (*Iter, error)
+}
+
+// Use an ExecAttemptInterceptorChain to apply multiple Interceptors at
Intercept time.
+type ExecAttemptInterceptorChain struct {
+ Interceptors []ExecAttemptInterceptor
+}
+
+func (c ExecAttemptInterceptorChain) Intercept(
+ ctx context.Context,
+ attempt QueryAttempt,
+ handler QueryAttemptHandler,
+) (*Iter, error) {
+ return c.Interceptors[0].Intercept(ctx, attempt, c.getNextHandler(0,
attempt, handler))
Review Comment:
I believe this will panic without mercy if you create an empty chain (didn't
see any checks which would stop `Intercept` being called here in case of an
empty chain)
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