1 files changed, 52 insertions, 0 deletions
diff --git a/core/dnsserver/middleware.go b/core/dnsserver/middleware.go
new file mode 100644
index 000000000..5bce304b1
--- /dev/null
+++ b/core/dnsserver/middleware.go
@@ -0,0 +1,52 @@
+package dnsserver
+
+import (
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+type (
+	// Middleware is the middle layer which represents the traditional
+	// idea of middleware: it chains one Handler to the next by being
+	// passed the next Handler in the chain.
+	Middleware func(Handler) Handler
+
+	// Handler is like dns.Handler except ServeDNS may return an rcode
+	// and/or error.
+	//
+	// If ServeDNS writes to the response body, it should return a status
+	// code. If the status code is not one of the following:
+	// * SERVFAIL (dns.RcodeServerFailure)
+	// * REFUSED (dns.RecodeRefused)
+	// * FORMERR (dns.RcodeFormatError)
+	// * NOTIMP (dns.RcodeNotImplemented)
+	//
+	// CoreDNS assumes *no* reply has yet been written. All other response
+	// codes signal other handlers above it that the response message is
+	// already written, and that they should not write to it also.
+	//
+	// If ServeDNS encounters an error, it should return the error value
+	// so it can be logged by designated error-handling middleware.
+	//
+	// If writing a response after calling another ServeDNS method, the
+	// returned rcode SHOULD be used when writing the response.
+	//
+	// If handling errors after calling another ServeDNS method, the
+	// returned error value SHOULD be logged or handled accordingly.
+	//
+	// Otherwise, return values should be propagated down the middleware
+	// chain by returning them unchanged.
+	Handler interface {
+		ServeDNS(context.Context, dns.ResponseWriter, *dns.Msg) (int, error)
+	}
+
+	// HandlerFunc is a convenience type like dns.HandlerFunc, except
+	// ServeDNS returns an rcode and an error. See Handler
+	// documentation for more information.
+	HandlerFunc func(context.Context, dns.ResponseWriter, *dns.Msg) (int, error)
+)
+
+// ServeDNS implements the Handler interface.
+func (f HandlerFunc) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	return f(ctx, w, r)
+}