Add expvar middleware

Right now it has a very simple configuration:

	expvar /debug/vars

It will return a JSON object with memory statistics and the command line
used to start caddy, which are the two expvars that expvar registers by
default.

caddy/directives.go

@@ -62,6 +62,7 @@ var directiveOrder = []directive{
 	{"basicauth", setup.BasicAuth},
 	{"internal", setup.Internal},
 	{"pprof", setup.PProf},
+	{"expvar", setup.ExpVar},
 	{"proxy", setup.Proxy},
 	{"fastcgi", setup.FastCGI},
 	{"websocket", setup.WebSocket},

caddy/setup/expvar.go

+package setup
+
+import (
+	_ "expvar"
+
+	"github.com/mholt/caddy/middleware"
+	"github.com/mholt/caddy/middleware/expvar"
+)
+
+// ExpVar configures a new ExpVar middleware instance.
+func ExpVar(c *Controller) (middleware.Middleware, error) {
+	resource, err := expVarParse(c)
+	if err != nil {
+		return nil, err
+	}
+
+	expvar := expvar.ExpVar{Resource: resource}
+
+	return func(next middleware.Handler) middleware.Handler {
+		expvar.Next = next
+		return expvar
+	}, nil
+}
+
+func expVarParse(c *Controller) (expvar.Resource, error) {
+	var resource expvar.Resource
+
+	var err error
+	for c.Next() {
+		args := c.RemainingArgs()
+
+		switch len(args) {
+		case 1:
+			resource = expvar.Resource(args[0])
+		default:
+			return resource, c.ArgErr()
+		}
+	}
+
+	return resource, err
+}

caddy/setup/expvar_test.go

+package setup
+
+import (
+	"testing"
+
+	"github.com/mholt/caddy/middleware/expvar"
+)
+
+func TestExpvar(t *testing.T) {
+	c := NewTestController(`expvar /d/v`)
+
+	mid, err := ExpVar(c)
+
+	if err != nil {
+		t.Errorf("Expected no errors, got: %v", err)
+	}
+
+	if mid == nil {
+		t.Fatal("Expected middleware, was nil instead")
+	}
+
+	handler := mid(EmptyNext)
+	myHandler, ok := handler.(expvar.ExpVar)
+
+	if !ok {
+		t.Fatalf("Expected handler to be type ExpVar, got: %#v", handler)
+	}
+
+	if myHandler.Resource != "/d/v" {
+		t.Errorf("Expected /d/v as expvar resource")
+	}
+
+	if !SameNext(myHandler.Next, EmptyNext) {
+		t.Error("'Next' field of handler was not set properly")
+	}
+}

middleware/expvar/expvar.go

+package expvar
+
+import (
+	"expvar"
+	"fmt"
+	"net/http"
+
+	"github.com/mholt/caddy/middleware"
+)
+
+// ExpVar is a simple struct to hold expvar's configuration
+type ExpVar struct {
+	Next     middleware.Handler
+	Resource Resource
+}
+
+// ServeHTTP handles requests to expvar's configured entry point with
+// expvar, or passes all other requests up the chain.
+func (e ExpVar) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
+	if middleware.Path(r.URL.Path).Matches(string(e.Resource)) {
+		expvarHandler(w, r)
+		return 0, nil
+	}
+
+	return e.Next.ServeHTTP(w, r)
+}
+
+// expvarHandler returns a JSON object will all the published variables.
+//
+// This is lifted straight from the expvar package.
+func expvarHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	fmt.Fprintf(w, "{\n")
+	first := true
+	expvar.Do(func(kv expvar.KeyValue) {
+		if !first {
+			fmt.Fprintf(w, ",\n")
+		}
+		first = false
+		fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
+	})
+	fmt.Fprintf(w, "\n}\n")
+}
+
+// Resource contains the path to the expvar entry point
+type Resource string

middleware/expvar/expvar_test.go

+package expvar
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/mholt/caddy/middleware"
+)
+
+func TestExpVar(t *testing.T) {
+	rw := ExpVar{
+		Next:     middleware.HandlerFunc(contentHandler),
+		Resource: "/d/v",
+	}
+
+	tests := []struct {
+		from   string
+		result int
+	}{
+		{"/d/v", 0},
+		{"/x/y", http.StatusOK},
+	}
+
+	for i, test := range tests {
+		req, err := http.NewRequest("GET", test.from, nil)
+		if err != nil {
+			t.Fatalf("Test %d: Could not create HTTP request %v", i, err)
+		}
+		rec := httptest.NewRecorder()
+		result, err := rw.ServeHTTP(rec, req)
+		if err != nil {
+			t.Fatalf("Test %d: Could not ServeHTTP %v", i, err)
+		}
+		if result != test.result {
+			t.Errorf("Test %d: Expected Header '%d' but was '%d'",
+				i, test.result, result)
+		}
+	}
+}
+
+func contentHandler(w http.ResponseWriter, r *http.Request) (int, error) {
+	fmt.Fprintf(w, r.URL.String())
+	return http.StatusOK, nil
+}