Allow for tracking state in Limiter

Extend Allow and ReportResult functions to handle a Context.
Allow can override the passed in Context.
The returned Context is then further passed down to ReportResult.
Using this Context it is then possible to store values/track state
between Allow and ReportResult calls.

Without this tracking HalfOpen/Generation state is hard to implement
efficiently for Circuit Breakers.

options.go

@@ -21,10 +21,12 @@ type Limiter interface {
 	// Allow returns nil if operation is allowed or an error otherwise.
 	// If operation is allowed client must ReportResult of the operation
 	// whether it is a success or a failure.
-	Allow() error
+	// The returned context will be passed to ReportResult.
+	Allow(ctx context.Context) (context.Context, error)
 	// ReportResult reports the result of the previously allowed operation.
 	// nil indicates a success, non-nil error usually indicates a failure.
-	ReportResult(result error)
+	// Context can be used to access state tracked by previous Allow call.
+	ReportResult(ctx context.Context, result error)
 }
 
 // Options keeps the settings to set up redis connection.

osscluster.go

@@ -1319,7 +1319,7 @@ func (c *ClusterClient) processPipelineNode(
 	ctx context.Context, node *clusterNode, cmds []Cmder, failedCmds *cmdsMap,
 ) {
 	_ = node.Client.withProcessPipelineHook(ctx, cmds, func(ctx context.Context, cmds []Cmder) error {
-		cn, err := node.Client.getConn(ctx)
+		ctx, cn, err := node.Client.getConn(ctx)
 		if err != nil {
 			node.MarkAsFailing()
 			_ = c.mapCmdsByNode(ctx, failedCmds, cmds)
@@ -1504,7 +1504,7 @@ func (c *ClusterClient) processTxPipelineNode(
 ) {
 	cmds = wrapMultiExec(ctx, cmds)
 	_ = node.Client.withProcessPipelineHook(ctx, cmds, func(ctx context.Context, cmds []Cmder) error {
-		cn, err := node.Client.getConn(ctx)
+		ctx, cn, err := node.Client.getConn(ctx)
 		if err != nil {
 			_ = c.mapCmdsByNode(ctx, failedCmds, cmds)
 			setCmdsErr(cmds, err)

redis.go

@@ -237,23 +237,24 @@ func (c *baseClient) newConn(ctx context.Context) (*pool.Conn, error) {
 	return cn, nil
 }
 
-func (c *baseClient) getConn(ctx context.Context) (*pool.Conn, error) {
+func (c *baseClient) getConn(ctx context.Context) (context.Context, *pool.Conn, error) {
+	var err error
 	if c.opt.Limiter != nil {
-		err := c.opt.Limiter.Allow()
+		ctx, err = c.opt.Limiter.Allow(ctx)
 		if err != nil {
-			return nil, err
+			return ctx, nil, err
 		}
 	}
 
 	cn, err := c._getConn(ctx)
 	if err != nil {
 		if c.opt.Limiter != nil {
-			c.opt.Limiter.ReportResult(err)
+			c.opt.Limiter.ReportResult(ctx, err)
 		}
-		return nil, err
+		return ctx, nil, err
 	}
 
-	return cn, nil
+	return ctx, cn, nil
 }
 
 func (c *baseClient) _getConn(ctx context.Context) (*pool.Conn, error) {
@@ -365,7 +366,7 @@ func (c *baseClient) initConn(ctx context.Context, cn *pool.Conn) error {
 
 func (c *baseClient) releaseConn(ctx context.Context, cn *pool.Conn, err error) {
 	if c.opt.Limiter != nil {
-		c.opt.Limiter.ReportResult(err)
+		c.opt.Limiter.ReportResult(ctx, err)
 	}
 
 	if isBadConn(err, false, c.opt.Addr) {
@@ -378,7 +379,7 @@ func (c *baseClient) releaseConn(ctx context.Context, cn *pool.Conn, err error)
 func (c *baseClient) withConn(
 	ctx context.Context, fn func(context.Context, *pool.Conn) error,
 ) error {
-	cn, err := c.getConn(ctx)
+	ctx, cn, err := c.getConn(ctx)
 	if err != nil {
 		return err
 	}