initial commit

.gitignore

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+ddns
+KEY

ddns.go

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+package main
+
+import (
+	"crypto/subtle"
+	"net/http"
+	"sync"
+)
+
+var (
+	mu  sync.RWMutex
+	ip  string
+	key string
+)
+
+func main() {
+	http.HandleFunc("/get", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == "GET" {
+			mu.RLock()
+			defer mu.RUnlock()
+			w.Write([]byte(ip))
+			return
+		}
+		http.Error(w, "bad request", http.StatusBadRequest)
+	})
+	http.HandleFunc("/set", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method == "GET" {
+			r.ParseForm()
+			if subtle.ConstantTimeCompare([]byte(key), []byte(r.FormValue("token"))) == 1 {
+				mu.Lock()
+				defer mu.Unlock()
+				ip = r.FormValue("ip")
+				w.Write([]byte("ok"))
+				return
+			}
+		}
+		http.Error(w, "bad request", http.StatusBadRequest)
+	})
+	panic(http.ListenAndServe("127.0.0.1:9090", nil))
+}

make.sh

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+#!/bin/sh
+go build -ldflags="-X main.key=$(cat KEY) -s -w"