initial version; nixos module untested

birdtown-visit-counter.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+	"sync"
+)
+
+type visitsStore struct {
+	m map[string]int
+	*sync.RWMutex
+}
+
+func (s *visitsStore) visit(ending string) int {
+	s.Lock()
+	defer s.Unlock()
+	oldVisits, has := s.m[ending]
+	var newVisits int
+	if has {
+		newVisits = oldVisits + 1
+	} else {
+		newVisits = 1
+	}
+	s.m[ending] = newVisits
+	return newVisits
+}
+
+type visitsHandler struct {
+	store *visitsStore
+}
+
+func (h *visitsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// CORS: this is expected to be called from a different domain,
+	// hoops require jumping
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	w.Header().Set("Access-Control-Max-Age", "86400")
+	w.Header().Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS")
+	w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization")
+
+	w.Header().Set("content-type", "application/json")
+
+	if r.Method == http.MethodPost {
+		var s string
+		if err := json.NewDecoder(r.Body).Decode(&s); err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte("cannot parse data"))
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		w.Write(([]byte)(strconv.Itoa(h.store.visit(s))))
+		return
+	}
+	if r.Method == http.MethodGet {
+		jsonBytes, err := json.Marshal(h.store.m)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte("cannot serialize"))
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		w.Write(jsonBytes)
+		return
+	}
+	if r.Method == http.MethodOptions {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+	w.Header().Set("Allow", "POST, GET, OPTIONS")
+	w.WriteHeader(http.StatusMethodNotAllowed)
+}
+
+func main() {
+	addr := flag.String("addr", ":11568", "Listen address")
+	initialFile := flag.String("file", "visits.json", "File with initial data in JSON format")
+	flag.Parse()
+
+	initialVisits := make(map[string]int)
+	initialVisitsJson, err := os.ReadFile(*initialFile)
+	if err == nil {
+		json.Unmarshal(initialVisitsJson, &initialVisits)
+	} else {
+		log.Println("initial file", *initialFile, "could not be read, defaulting to empty data")
+	}
+
+	store := visitsStore{m: initialVisits, RWMutex: &sync.RWMutex{}}
+	visitsH := &visitsHandler{store: &store}
+	http.Handle("/visits", visitsH)
+
+	log.Println("Starting web server...")
+	http.ListenAndServe(*addr, nil)
+}