diff -r 9d7e8333948b -r ebb86cbdd218 filter.go
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/filter.go	Mon Sep 02 20:38:02 2013 -0700
@@ -0,0 +1,64 @@
+package xmpp
+
+// Manages the stack of filters that can read and modify stanzas on
+// their way from the remote to the application.
+
+// Receive new filters on filterAdd; those new filters get added to
+// the top of the stack. Receive stanzas at the bottom of the stack on
+// input. Send stanzas out the top of the stack on output.
+func filterMgr(filterAdd <-chan Filter, input <-chan Stanza, output chan<- Stanza) {
+	botFiltIn := output
+	topFiltOut := input
+
+loop:
+	for {
+		select {
+		case stan, ok := <-input:
+			if !ok {
+				break loop
+			}
+			botFiltIn <- stan
+
+		case stan, ok := <-topFiltOut:
+			if !ok {
+				break loop
+			}
+			output <- stan
+
+		case filt := <-filterAdd:
+			newTop := make(chan Stanza)
+			go filt(topFiltOut, newTop)
+			topFiltOut = newTop
+		}
+	}
+	close(botFiltIn)
+}
+
+// Starts the filter chain. Filters will all interpose themselves
+// between srvIn and cliOut.
+func (cl *Client) startFilters(srvIn, cliIn <-chan Stanza) (<-chan Stanza, <-chan Stanza) {
+	cliOut := make(chan Stanza)
+	srvOut := make(chan Stanza)
+	go filterMgr(cl.sendFilterAdd, srvIn, cliOut)
+	go filterMgr(cl.recvFilterAdd, cliIn, srvOut)
+	return cliOut, srvOut
+}
+
+// AddRecvFilter adds a new filter to the top of the stack through which
+// incoming stanzas travel on their way up to the client.
+func (cl *Client) AddRecvFilter(filt Filter) {
+	if filt == nil {
+		return
+	}
+	cl.recvFilterAdd <- filt
+}
+
+// AddSendFilter adds a new filter to the top of the stack through
+// which outgoing stanzas travel on their way down from the client to
+// the network.
+func (cl *Client) AddSendFilter(filt Filter) {
+	if filt == nil {
+		return
+	}
+	cl.sendFilterAdd <- filt
+}