lib/http: add evaluator, a middleware between request and handler

4 files changed, 107 insertions, 3 deletions

diff --git a/lib/http/evaluator.go b/lib/http/evaluator.go
new file mode 100644
index 00000000..16fcd477
--- /dev/null
+++ b/lib/http/evaluator.go
@@ -0,0 +1,21 @@
+// Copyright 2018, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http
+
+import (
+	"net/http"
+)
+
+//
+// Evaluator is an interface for middleware between actual request and handler.
+//
+type Evaluator interface {
+	//
+	// Evaluate the request.  If request is invalid, the error will tell
+	// the response code and the error message to be written back to
+	// client.
+	//
+	Evaluate(req *http.Request, reqBody []byte) error
+}
diff --git a/lib/http/handler.go b/lib/http/handler.go
index 0328f6fc..f35a968c 100644
--- a/lib/http/handler.go
+++ b/lib/http/handler.go
@@ -21,7 +21,9 @@ type handler struct {
 	cb      Callback
 }
 
-func (h *handler) call(res http.ResponseWriter, req *http.Request) {
+func (h *handler) call(res http.ResponseWriter, req *http.Request,
+	evaluators []Evaluator,
+) {
 	var (
 		e       error
 		reqBody []byte
@@ -56,6 +58,14 @@ func (h *handler) call(res http.ResponseWriter, req *http.Request) {
 		log.Printf("> request body: %s\n", reqBody)
 	}
 
+	for _, eval := range evaluators {
+		e := eval.Evaluate(req, reqBody)
+		if e != nil {
+			h.error(res, e)
+			return
+		}
+	}
+
 	rspb, e := h.cb(req, reqBody)
 	if e != nil {
 		log.Printf("handler.call: %d %s %s %s\n",
diff --git a/lib/http/server.go b/lib/http/server.go
index 5ae5808d..6f72b630 100644
--- a/lib/http/server.go
+++ b/lib/http/server.go
@@ -23,6 +23,7 @@ import (
 //
 type Server struct {
 	mfs       *memfs.MemFS
+	evals     []Evaluator
 	conn      *http.Server
 	regDelete map[string]*handler
 	regGet    map[string]*handler
@@ -80,6 +81,14 @@ func (srv *Server) RegisterDelete(
 }
 
 //
+// RegisterEvaluator register HTTP middleware that will be called before
+// handler callback is called.
+//
+func (srv *Server) RegisterEvaluator(eval Evaluator) {
+	srv.evals = append(srv.evals, eval)
+}
+
+//
 // RegisterGet register HTTP method GET with callback to handle it.
 //
 func (srv *Server) RegisterGet(
@@ -167,7 +176,7 @@ func (srv *Server) ServeHTTP(res http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	h.call(res, req)
+	h.call(res, req, srv.evals)
 }
 
 //
@@ -238,7 +247,7 @@ func (srv *Server) handleFS(
 func (srv *Server) handleGet(res http.ResponseWriter, req *http.Request) {
 	h, ok := srv.regGet[req.URL.Path]
 	if ok {
-		h.call(res, req)
+		h.call(res, req, srv.evals)
 		return
 	}
 
diff --git a/lib/http/server_test.go b/lib/http/server_test.go
index beefad40..e40276e4 100644
--- a/lib/http/server_test.go
+++ b/lib/http/server_test.go
@@ -180,6 +180,70 @@ func TestRegisterDelete(t *testing.T) {
 	}
 }
 
+type testEvaluator struct{}
+
+func (te *testEvaluator) Evaluate(req *http.Request, reqBody []byte) error {
+	k := req.Form.Get("k")
+
+	if len(k) == 0 {
+		return &errors.E{
+			Code:    http.StatusBadRequest,
+			Message: "Missing input value for k",
+		}
+	}
+
+	return nil
+}
+
+func TestRegisterEvaluator(t *testing.T) {
+	te := new(testEvaluator)
+
+	testServer.RegisterDelete("/evaluate", ResponseTypeJSON, cbPlain)
+
+	testServer.RegisterEvaluator(te)
+
+	cases := []struct {
+		desc          string
+		reqURL        string
+		expStatusCode int
+	}{{
+		desc:          "With invalid evaluate",
+		reqURL:        "http://127.0.0.1:8080/evaluate",
+		expStatusCode: http.StatusBadRequest,
+	}, {
+		desc:          "With valid evaluate",
+		reqURL:        "http://127.0.0.1:8080/evaluate?k=v",
+		expStatusCode: http.StatusOK,
+	}}
+
+	for _, c := range cases {
+		t.Log(c.desc)
+
+		req, e := http.NewRequest(http.MethodDelete, c.reqURL, nil)
+		if e != nil {
+			t.Fatal(e)
+		}
+
+		res, e := client.Do(req)
+		if e != nil {
+			t.Fatal(e)
+		}
+
+		_, e = ioutil.ReadAll(res.Body)
+		if e != nil {
+			t.Fatal(e)
+		}
+
+		e = res.Body.Close()
+		if e != nil {
+			t.Fatal(e)
+		}
+
+		test.Assert(t, "StatusCode", c.expStatusCode, res.StatusCode,
+			true)
+	}
+}
+
 func TestRegisterGet(t *testing.T) {
 	testServer.RegisterGet("/get", ResponseTypePlain, cbPlain)