middleware/debug: add (#735)

* middleware/debug: add

Add a debug "middleware" that disables the recover() and just lets
CoreDNS crash; very useful for testing.

Fixes ##563

* fix test

* Feedback: check the value of Debug

8 files changed, 137 insertions, 28 deletions

diff --git a/core/dnsserver/config.go b/core/dnsserver/config.go
index 942d43d58..c0f879a31 100644
--- a/core/dnsserver/config.go
+++ b/core/dnsserver/config.go
@@ -23,6 +23,9 @@ type Config struct {
 	// First consumer is the file middleware to looks for zone files in this place.
 	Root string
 
+	// Debug controls the panic/recover mechanism that is enabled by default.
+	Debug bool
+
 	// The transport we implement, normally just "dns" over TCP/UDP, but could be
 	// DNS-over-TLS or DNS-over-gRPC.
 	Transport string
diff --git a/core/dnsserver/server.go b/core/dnsserver/server.go
index 5bbbf9f9c..61ef6ac65 100644
--- a/core/dnsserver/server.go
+++ b/core/dnsserver/server.go
@@ -36,6 +36,7 @@ type Server struct {
 	dnsWg       sync.WaitGroup     // used to wait on outstanding connections
 	connTimeout time.Duration      // the maximum duration of a graceful shutdown
 	trace       trace.Trace        // the trace middleware for the server
+	debug       bool               // disable recover()
 }
 
 // NewServer returns a new CoreDNS server and compiles all middleware in to it.
@@ -56,6 +57,9 @@ func NewServer(addr string, group []*Config) (*Server, error) {
 	s.dnsWg.Add(1)
 
 	for _, site := range group {
+		if site.Debug {
+			s.debug = true
+		}
 		// set the config per zone
 		s.zones[site.Zone] = site
 		// compile custom middleware for everything
@@ -166,13 +170,15 @@ func (s *Server) Address() string { return s.Addr }
 // defined in the request so that the correct zone
 // (configuration and middleware stack) will handle the request.
 func (s *Server) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) {
-	defer func() {
-		// In case the user doesn't enable error middleware, we still
-		// need to make sure that we stay alive up here
-		if rec := recover(); rec != nil {
-			DefaultErrorFunc(w, r, dns.RcodeServerFailure)
-		}
-	}()
+	if !s.debug {
+		defer func() {
+			// In case the user doesn't enable error middleware, we still
+			// need to make sure that we stay alive up here
+			if rec := recover(); rec != nil {
+				DefaultErrorFunc(w, r, dns.RcodeServerFailure)
+			}
+		}()
+	}
 
 	if m, err := edns.Version(r); err != nil { // Wrong EDNS version, return at once.
 		w.WriteMsg(m)
diff --git a/core/dnsserver/zdirectives.go b/core/dnsserver/zdirectives.go
index a794ce762..1af5d3c7e 100644
--- a/core/dnsserver/zdirectives.go
+++ b/core/dnsserver/zdirectives.go
@@ -14,6 +14,7 @@ var directives = []string{
 	"tls",
 	"root",
 	"bind",
+	"debug",
 	"trace",
 	"health",
 	"pprof",
diff --git a/core/zmiddleware.go b/core/zmiddleware.go
index cd611333e..0496dcd0e 100644
--- a/core/zmiddleware.go
+++ b/core/zmiddleware.go
@@ -8,6 +8,7 @@ import (
 	_ "github.com/coredns/coredns/middleware/bind"
 	_ "github.com/coredns/coredns/middleware/cache"
 	_ "github.com/coredns/coredns/middleware/chaos"
+	_ "github.com/coredns/coredns/middleware/debug"
 	_ "github.com/coredns/coredns/middleware/dnssec"
 	_ "github.com/coredns/coredns/middleware/erratic"
 	_ "github.com/coredns/coredns/middleware/errors"
diff --git a/middleware.cfg b/middleware.cfg
index 562557b73..00e6eba6c 100644
--- a/middleware.cfg
+++ b/middleware.cfg
@@ -22,26 +22,27 @@
 1:tls:tls
 10:root:root
 20:bind:bind
-30:trace:trace
-40:health:health
-50:pprof:pprof
-60:prometheus:metrics
-70:errors:errors
-80:log:log
-90:chaos:chaos
-100:cache:cache
-110:rewrite:rewrite
-120:loadbalance:loadbalance
-130:dnssec:dnssec
-140:reverse:reverse
-150:hosts:hosts
-160:kubernetes:kubernetes
-170:file:file
-180:auto:auto
-190:secondary:secondary
-200:etcd:etcd
-210:proxy:proxy
-220:whoami:whoami
-230:erratic:erratic
+30:debug:debug
+40:trace:trace
+50:health:health
+60:pprof:pprof
+70:prometheus:metrics
+80:errors:errors
+90:log:log
+100:chaos:chaos
+110:cache:cache
+120:rewrite:rewrite
+130:loadbalance:loadbalance
+140:dnssec:dnssec
+150:reverse:reverse
+160:hosts:hosts
+170:kubernetes:kubernetes
+180:file:file
+190:auto:auto
+200:secondary:secondary
+210:etcd:etcd
+220:proxy:proxy
+230:whoami:whoami
+240:erratic:erratic
 500:startup:github.com/mholt/caddy/startupshutdown
 510:shutdown:github.com/mholt/caddy/startupshutdown
diff --git a/middleware/debug/README.md b/middleware/debug/README.md
new file mode 100644
index 000000000..b74d95612
--- /dev/null
+++ b/middleware/debug/README.md
@@ -0,0 +1,20 @@
+# debug
+
+*debug* disables the automatic recovery upon a CoreDNS crash so that you'll get a
+nice stack trace.
+Note that the *errors* middleware (if loaded) will also set a `recover` negating this setting.
+The main use of *debug* is to help testing.
+
+## Syntax
+
+~~~ txt
+debug
+~~~
+
+## Examples
+
+Disable CoreDNS' ability to recover from crashes:
+
+~~~ txt
+debug
+~~~
diff --git a/middleware/debug/debug.go b/middleware/debug/debug.go
new file mode 100644
index 000000000..f92a27554
--- /dev/null
+++ b/middleware/debug/debug.go
@@ -0,0 +1,28 @@
+package debug
+
+import (
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/middleware"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("debug", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	config := dnsserver.GetConfig(c)
+
+	for c.Next() {
+		if c.NextArg() {
+			return middleware.Error("debug", c.ArgErr())
+		}
+		config.Debug = true
+	}
+
+	return nil
+}
diff --git a/middleware/debug/debug_test.go b/middleware/debug/debug_test.go
new file mode 100644
index 000000000..349b362f1
--- /dev/null
+++ b/middleware/debug/debug_test.go
@@ -0,0 +1,49 @@
+package debug
+
+import (
+	"io/ioutil"
+	"log"
+	"testing"
+
+	"github.com/coredns/coredns/core/dnsserver"
+
+	"github.com/mholt/caddy"
+)
+
+func TestDebug(t *testing.T) {
+	log.SetOutput(ioutil.Discard)
+
+	tests := []struct {
+		input         string
+		shouldErr     bool
+		expectedDebug bool
+	}{
+		// positive
+		{
+			`debug`, false, true,
+		},
+		// negative
+		{
+			`debug off`, true, false,
+		},
+	}
+
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.input)
+		err := setup(c)
+		cfg := dnsserver.GetConfig(c)
+
+		if test.shouldErr && err == nil {
+			t.Fatalf("Test %d: Expected error but found %s for input %s", i, err, test.input)
+		}
+
+		if err != nil {
+			if !test.shouldErr {
+				t.Fatalf("Test %d: Expected no error but found one for input %s. Error was: %v", i, test.input, err)
+			}
+		}
+		if cfg.Debug != test.expectedDebug {
+			t.Fatalf("Test %d: Expected debug to be: %t, but got: %t, input: %s", i, test.expectedDebug, test.input)
+		}
+	}
+}