all: implement server side of disco#info

This finally closes the long standing need for service discovery by
implementing the new design doc from https://mellium.im/design/28_disco!

Fixes #28

Signed-off-by: Sam Whited <sam@samwhited.com>

disco/disco.go

@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 //go:generate go run gen.go
+//go:generate go run ../internal/genfeature -filename features.go -receiver "h *discoHandler" -vars Feature:NSInfo
 
 // Package disco implements service discovery.
 package disco // import "mellium.im/xmpp/disco"

disco/handler.go

@@ -15,7 +15,7 @@ import (
 
 // Handle returns an option that configures a multiplexer to handle service
 // discovery requests by iterating over its own handlers and checking if they
-// implement the interfaces from the info package.
+// implement info.FeatureIter.
 func Handle() mux.Option {
 	return func(m *mux.ServeMux) {
 		h := &discoHandler{ServeMux: m}

disco/info/feature.go

@@ -38,3 +38,9 @@ func (f Feature) TokenReader() xml.TokenReader {
 func (f Feature) WriteXML(w xmlstream.TokenWriter) (int, error) {
 	return xmlstream.Copy(w, f.TokenReader())
 }
+
+// FeatureIter is the interface implemented by types that implement disco
+// features.
+type FeatureIter interface {
+	ForFeatures(node string, f func(Feature) error) error
+}

mux/mux.go

@@ -17,6 +17,7 @@ import (
 
 	"mellium.im/xmlstream"
 	"mellium.im/xmpp"
+	"mellium.im/xmpp/disco/info"
 	"mellium.im/xmpp/internal/ns"
 	"mellium.im/xmpp/stanza"
 )
@@ -209,6 +210,44 @@ func (m *ServeMux) HandleXMPP(t xmlstream.TokenReadEncoder, start *xml.StartElem
 	return h.HandleXMPP(t, start)
 }
 
+// ForFeatures implements info.FeatureIter for the mux by iterating over all
+// child features.
+func (m *ServeMux) ForFeatures(node string, f func(info.Feature) error) error {
+	for _, h := range m.patterns {
+		if featureIter, ok := h.(info.FeatureIter); ok {
+			err := featureIter.ForFeatures(node, f)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	for _, h := range m.iqPatterns {
+		if featureIter, ok := h.(info.FeatureIter); ok {
+			err := featureIter.ForFeatures(node, f)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	for _, h := range m.msgPatterns {
+		if featureIter, ok := h.(info.FeatureIter); ok {
+			err := featureIter.ForFeatures(node, f)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	for _, h := range m.presencePatterns {
+		if featureIter, ok := h.(info.FeatureIter); ok {
+			err := featureIter.ForFeatures(node, f)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 type nopHandler struct{}
 
 func (nopHandler) HandleXMPP(t xmlstream.TokenReadEncoder, start *xml.StartElement) error { return nil }

mux/mux_test.go

@@ -15,13 +15,16 @@ import (
 	"testing"
 
 	"mellium.im/xmlstream"
+	"mellium.im/xmpp/disco/info"
 	"mellium.im/xmpp/internal/marshal"
 	"mellium.im/xmpp/internal/ns"
 	"mellium.im/xmpp/internal/xmpptest"
 	"mellium.im/xmpp/mux"
 	"mellium.im/xmpp/stanza"
 )
 
+var _ info.FeatureIter = (*mux.ServeMux)(nil)
+
 var (
 	errPassTest = errors.New("mux_test: PASSED")
 	errFailTest = errors.New("mux_test: FAILED")