feat: implement relay endpoint (see #237)

routes/relay/relay.go

@@ -0,0 +1,75 @@
+package relay
+
+import (
+	"github.com/gorilla/mux"
+	conf "github.com/muety/wakapi/config"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"regexp"
+)
+
+const targetUrlHeader = "X-Target-URL"
+const pathMatcherPattern = `^/api/(heartbeat|heartbeats|summary|users|v1/users|compat/wakatime)`
+
+type RelayHandler struct {
+	config *conf.Config
+}
+
+func NewRelayHandler() *RelayHandler {
+	return &RelayHandler{
+		config: conf.Get(),
+	}
+}
+
+type filteringMiddleware struct {
+	handler     http.Handler
+	pathMatcher *regexp.Regexp
+}
+
+func newFilteringMiddleware() func(http.Handler) http.Handler {
+	return func(h http.Handler) http.Handler {
+		return &filteringMiddleware{
+			handler:     h,
+			pathMatcher: regexp.MustCompile(pathMatcherPattern),
+		}
+	}
+}
+
+func (m *filteringMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	targetUrl, err := url.Parse(r.Header.Get(targetUrlHeader))
+	if err != nil || !m.pathMatcher.MatchString(targetUrl.Path) {
+		w.WriteHeader(http.StatusForbidden)
+		w.Write([]byte{})
+		return
+	}
+	m.handler.ServeHTTP(w, r)
+}
+
+func (h *RelayHandler) RegisterRoutes(router *mux.Router) {
+	if !h.config.Security.EnableProxy {
+		return
+	}
+
+	r := router.PathPrefix("/relay").Subrouter()
+	r.Use(newFilteringMiddleware())
+	r.Path("").HandlerFunc(h.Any)
+}
+
+func (h *RelayHandler) Any(w http.ResponseWriter, r *http.Request) {
+	targetUrl, err := url.Parse(r.Header.Get(targetUrlHeader))
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte{})
+		return
+	}
+
+	p := httputil.ReverseProxy{
+		Director: func(r *http.Request) {
+			r.URL = targetUrl
+			r.Host = targetUrl.Host
+		},
+	}
+
+	p.ServeHTTP(w, r)
+}