Use gorilla/mux for middleware and extend

- Use gorilla/mux for middleware.
- Add Dumper, RequestID, and Logger middlewares.
- Add makeURL helper

vendor/github.com/go-chi/chi/middleware/throttle.go

@@ -0,0 +1,101 @@
+package middleware
+
+import (
+	"net/http"
+	"time"
+)
+
+const (
+	errCapacityExceeded = "Server capacity exceeded."
+	errTimedOut         = "Timed out while waiting for a pending request to complete."
+	errContextCanceled  = "Context was canceled."
+)
+
+var (
+	defaultBacklogTimeout = time.Second * 60
+)
+
+// Throttle is a middleware that limits number of currently processed requests
+// at a time.
+func Throttle(limit int) func(http.Handler) http.Handler {
+	return ThrottleBacklog(limit, 0, defaultBacklogTimeout)
+}
+
+// ThrottleBacklog is a middleware that limits number of currently processed
+// requests at a time and provides a backlog for holding a finite number of
+// pending requests.
+func ThrottleBacklog(limit int, backlogLimit int, backlogTimeout time.Duration) func(http.Handler) http.Handler {
+	if limit < 1 {
+		panic("chi/middleware: Throttle expects limit > 0")
+	}
+
+	if backlogLimit < 0 {
+		panic("chi/middleware: Throttle expects backlogLimit to be positive")
+	}
+
+	t := throttler{
+		tokens:         make(chan token, limit),
+		backlogTokens:  make(chan token, limit+backlogLimit),
+		backlogTimeout: backlogTimeout,
+	}
+
+	// Filling tokens.
+	for i := 0; i < limit+backlogLimit; i++ {
+		if i < limit {
+			t.tokens <- token{}
+		}
+		t.backlogTokens <- token{}
+	}
+
+	fn := func(h http.Handler) http.Handler {
+		t.h = h
+		return &t
+	}
+
+	return fn
+}
+
+// token represents a request that is being processed.
+type token struct{}
+
+// throttler limits number of currently processed requests at a time.
+type throttler struct {
+	h              http.Handler
+	tokens         chan token
+	backlogTokens  chan token
+	backlogTimeout time.Duration
+}
+
+// ServeHTTP is the primary throttler request handler
+func (t *throttler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	ctx := r.Context()
+	select {
+	case <-ctx.Done():
+		http.Error(w, errContextCanceled, http.StatusServiceUnavailable)
+		return
+	case btok := <-t.backlogTokens:
+		timer := time.NewTimer(t.backlogTimeout)
+
+		defer func() {
+			t.backlogTokens <- btok
+		}()
+
+		select {
+		case <-timer.C:
+			http.Error(w, errTimedOut, http.StatusServiceUnavailable)
+			return
+		case <-ctx.Done():
+			http.Error(w, errContextCanceled, http.StatusServiceUnavailable)
+			return
+		case tok := <-t.tokens:
+			defer func() {
+				t.tokens <- tok
+			}()
+			t.h.ServeHTTP(w, r)
+		}
+		return
+	default:
+		http.Error(w, errCapacityExceeded, http.StatusServiceUnavailable)
+		return
+	}
+}