1 files changed, 100 insertions, 0 deletions
diff --git a/middleware/errors/errors.go b/middleware/errors/errors.go
new file mode 100644
index 000000000..bf5bc7aae
--- /dev/null
+++ b/middleware/errors/errors.go
@@ -0,0 +1,100 @@
+// Package errors implements an HTTP error handling middleware.
+package errors
+
+import (
+	"fmt"
+	"log"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/dns"
+)
+
+// ErrorHandler handles DNS errors (and errors from other middleware).
+type ErrorHandler struct {
+	Next      middleware.Handler
+	LogFile   string
+	Log       *log.Logger
+	LogRoller *middleware.LogRoller
+	Debug     bool // if true, errors are written out to client rather than to a log
+}
+
+func (h ErrorHandler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	defer h.recovery(w, r)
+
+	rcode, err := h.Next.ServeDNS(w, r)
+
+	if err != nil {
+		errMsg := fmt.Sprintf("%s [ERROR %d %s %s] %v", time.Now().Format(timeFormat), rcode, r.Question[0].Name, dns.Type(r.Question[0].Qclass), err)
+
+		if h.Debug {
+			// Write error to response as a txt message instead of to log
+			answer := debugMsg(rcode, r)
+			txt, _ := dns.NewRR(". IN 0 TXT " + errMsg)
+			answer.Answer = append(answer.Answer, txt)
+			w.WriteMsg(answer)
+			return 0, err
+		}
+		h.Log.Println(errMsg)
+	}
+
+	return rcode, err
+}
+
+func (h ErrorHandler) recovery(w dns.ResponseWriter, r *dns.Msg) {
+	rec := recover()
+	if rec == nil {
+		return
+	}
+
+	// Obtain source of panic
+	// From: https://gist.github.com/swdunlop/9629168
+	var name, file string // function name, file name
+	var line int
+	var pc [16]uintptr
+	n := runtime.Callers(3, pc[:])
+	for _, pc := range pc[:n] {
+		fn := runtime.FuncForPC(pc)
+		if fn == nil {
+			continue
+		}
+		file, line = fn.FileLine(pc)
+		name = fn.Name()
+		if !strings.HasPrefix(name, "runtime.") {
+			break
+		}
+	}
+
+	// Trim file path
+	delim := "/coredns/"
+	pkgPathPos := strings.Index(file, delim)
+	if pkgPathPos > -1 && len(file) > pkgPathPos+len(delim) {
+		file = file[pkgPathPos+len(delim):]
+	}
+
+	panicMsg := fmt.Sprintf("%s [PANIC %s %s] %s:%d - %v", time.Now().Format(timeFormat), r.Question[0].Name, dns.Type(r.Question[0].Qtype), file, line, rec)
+	if h.Debug {
+		// Write error and stack trace to the response rather than to a log
+		var stackBuf [4096]byte
+		stack := stackBuf[:runtime.Stack(stackBuf[:], false)]
+		answer := debugMsg(dns.RcodeServerFailure, r)
+		// add stack buf in TXT, limited to 255 chars for now.
+		txt, _ := dns.NewRR(". IN 0 TXT " + string(stack[:255]))
+		answer.Answer = append(answer.Answer, txt)
+		w.WriteMsg(answer)
+	} else {
+		// Currently we don't use the function name, since file:line is more conventional
+		h.Log.Printf(panicMsg)
+	}
+}
+
+// debugMsg creates a debug message that gets send back to the client.
+func debugMsg(rcode int, r *dns.Msg) *dns.Msg {
+	answer := new(dns.Msg)
+	answer.SetRcode(r, rcode)
+	return answer
+}
+
+const timeFormat = "02/Jan/2006:15:04:05 -0700"