plugin/view: Advanced routing interface and new 'view' plugin (#5538)

* introduce new interface "dnsserver.Viewer", that allows a plugin implementing it to decide if a query should be routed into its server block.
* add new plugin "view", that uses the new interface to enable a user to define expression based conditions that must be met for a query to be routed to its server block.

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/plugin/metrics/context.go b/plugin/metrics/context.go
index da6bdb12d..ae2856dd5 100644
--- a/plugin/metrics/context.go
+++ b/plugin/metrics/context.go
@@ -22,3 +22,16 @@ func WithServer(ctx context.Context) string {
 	}
 	return srv.(*dnsserver.Server).Addr
 }
+
+// WithView returns the name of the view currently handling the request, if a view is defined.
+//
+// Basic usage with a metric:
+//
+// <metric>.WithLabelValues(metrics.WithView(ctx), labels..).Add(1)
+func WithView(ctx context.Context) string {
+	v := ctx.Value(dnsserver.ViewKey{})
+	if v == nil {
+		return ""
+	}
+	return v.(string)
+}