--- /dev/null
+package dns
+
+import (
+ "bytes"
+ "sync"
+)
+
+// ServeMux is an DNS request multiplexer. It matches the zone name of
+// each incoming request against a list of registered patterns add calls
+// the handler for the pattern that most closely matches the zone name.
+//
+// ServeMux is DNSSEC aware, meaning that queries for the DS record are
+// redirected to the parent zone (if that is also registered), otherwise
+// the child gets the query.
+//
+// ServeMux is also safe for concurrent access from multiple goroutines.
+//
+// The zero ServeMux is empty and ready for use.
+type ServeMux struct {
+ z map[string]Handler
+ m sync.RWMutex
+}
+
+// NewServeMux allocates and returns a new ServeMux.
+func NewServeMux() *ServeMux {
+ return new(ServeMux)
+}
+
+// DefaultServeMux is the default ServeMux used by Serve.
+var DefaultServeMux = NewServeMux()
+
+func (mux *ServeMux) match(q string, t uint16) Handler {
+ mux.m.RLock()
+ defer mux.m.RUnlock()
+ if mux.z == nil {
+ return nil
+ }
+
+ var handler Handler
+
+ // TODO(tmthrgd): Once https://go-review.googlesource.com/c/go/+/137575
+ // lands in a go release, replace the following with strings.ToLower.
+ var sb bytes.Buffer
+ for i := 0; i < len(q); i++ {
+ c := q[i]
+ if !(c >= 'A' && c <= 'Z') {
+ continue
+ }
+
+ sb.Grow(len(q))
+ sb.WriteString(q[:i])
+
+ for ; i < len(q); i++ {
+ c := q[i]
+ if c >= 'A' && c <= 'Z' {
+ c += 'a' - 'A'
+ }
+
+ sb.WriteByte(c)
+ }
+
+ q = sb.String()
+ break
+ }
+
+ for off, end := 0, false; !end; off, end = NextLabel(q, off) {
+ if h, ok := mux.z[q[off:]]; ok {
+ if t != TypeDS {
+ return h
+ }
+ // Continue for DS to see if we have a parent too, if so delegate to the parent
+ handler = h
+ }
+ }
+
+ // Wildcard match, if we have found nothing try the root zone as a last resort.
+ if h, ok := mux.z["."]; ok {
+ return h
+ }
+
+ return handler
+}
+
+// Handle adds a handler to the ServeMux for pattern.
+func (mux *ServeMux) Handle(pattern string, handler Handler) {
+ if pattern == "" {
+ panic("dns: invalid pattern " + pattern)
+ }
+ mux.m.Lock()
+ if mux.z == nil {
+ mux.z = make(map[string]Handler)
+ }
+ mux.z[Fqdn(pattern)] = handler
+ mux.m.Unlock()
+}
+
+// HandleFunc adds a handler function to the ServeMux for pattern.
+func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
+ mux.Handle(pattern, HandlerFunc(handler))
+}
+
+// HandleRemove deregisters the handler specific for pattern from the ServeMux.
+func (mux *ServeMux) HandleRemove(pattern string) {
+ if pattern == "" {
+ panic("dns: invalid pattern " + pattern)
+ }
+ mux.m.Lock()
+ delete(mux.z, Fqdn(pattern))
+ mux.m.Unlock()
+}
+
+// ServeDNS dispatches the request to the handler whose pattern most
+// closely matches the request message.
+//
+// ServeDNS is DNSSEC aware, meaning that queries for the DS record
+// are redirected to the parent zone (if that is also registered),
+// otherwise the child gets the query.
+//
+// If no handler is found, or there is no question, a standard SERVFAIL
+// message is returned
+func (mux *ServeMux) ServeDNS(w ResponseWriter, req *Msg) {
+ var h Handler
+ if len(req.Question) >= 1 { // allow more than one question
+ h = mux.match(req.Question[0].Name, req.Question[0].Qtype)
+ }
+
+ if h != nil {
+ h.ServeDNS(w, req)
+ } else {
+ HandleFailed(w, req)
+ }
+}
+
+// Handle registers the handler with the given pattern
+// in the DefaultServeMux. The documentation for
+// ServeMux explains how patterns are matched.
+func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
+
+// HandleRemove deregisters the handle with the given pattern
+// in the DefaultServeMux.
+func HandleRemove(pattern string) { DefaultServeMux.HandleRemove(pattern) }
+
+// HandleFunc registers the handler function with the given pattern
+// in the DefaultServeMux.
+func HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
+ DefaultServeMux.HandleFunc(pattern, handler)
+}
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