From d9ebb8a0260d2c5b5cd8b9defffe05c25433a340 Mon Sep 17 00:00:00 2001
From: Igor Chubin <igor@chub.in>
Date: Fri, 24 Apr 2020 00:16:11 +0200
Subject: [PATCH] initial implementation of go web frontend

---
 cmd/srv.go | 145 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 145 insertions(+)
 create mode 100644 cmd/srv.go

diff --git a/cmd/srv.go b/cmd/srv.go
new file mode 100644
index 0000000..371cf21
--- /dev/null
+++ b/cmd/srv.go
@@ -0,0 +1,145 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/hashicorp/golang-lru"
+)
+
+var lruCache *lru.Cache
+
+type ResponseWithHeader struct {
+	Body       []byte
+	Header     http.Header
+	StatusCode int // e.g. 200
+
+}
+
+func init() {
+	var err error
+	lruCache, err = lru.New(12800)
+	if err != nil {
+		panic(err)
+	}
+
+	dialer := &net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+		DualStack: true,
+	}
+
+	http.DefaultTransport.(*http.Transport).DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
+		addr = "127.0.0.1:8002"
+		return dialer.DialContext(ctx, network, addr)
+	}
+
+}
+
+func readUserIP(r *http.Request) string {
+	IPAddress := r.Header.Get("X-Real-Ip")
+	if IPAddress == "" {
+		IPAddress = r.Header.Get("X-Forwarded-For")
+	}
+	if IPAddress == "" {
+		IPAddress = r.RemoteAddr
+		var err error
+		IPAddress, _, err = net.SplitHostPort(IPAddress)
+		if err != nil {
+			fmt.Printf("userip: %q is not IP:port\n", IPAddress)
+		}
+	}
+	return IPAddress
+}
+
+// implementation of the cache.get_signature of original wttr.in
+func findCacheDigest(req *http.Request) string {
+
+	userAgent := req.Header.Get("User-Agent")
+
+	queryHost := req.Host
+	queryString := req.RequestURI
+
+	clientIpAddress := readUserIP(req)
+
+	lang := req.Header.Get("Accept-Language")
+
+	now := time.Now()
+	secs := now.Unix()
+	timestamp := secs / 1000
+
+	return fmt.Sprintf("%s:%s%s:%s:%s:%d", userAgent, queryHost, queryString, clientIpAddress, lang, timestamp)
+}
+
+func get(req *http.Request) ResponseWithHeader {
+
+	client := &http.Client{}
+
+	queryURL := fmt.Sprintf("http://%s%s", req.Host, req.RequestURI)
+
+	proxyReq, err := http.NewRequest(req.Method, queryURL, req.Body)
+	if err != nil {
+		// handle error
+	}
+
+	// proxyReq.Header.Set("Host", req.Host)
+	// proxyReq.Header.Set("X-Forwarded-For", req.RemoteAddr)
+
+	for header, values := range req.Header {
+		for _, value := range values {
+			proxyReq.Header.Add(header, value)
+		}
+	}
+
+	res, err := client.Do(proxyReq)
+
+	if err != nil {
+		panic(err)
+	}
+
+	body, err := ioutil.ReadAll(res.Body)
+
+	return ResponseWithHeader{
+		Body:       body,
+		Header:     res.Header,
+		StatusCode: res.StatusCode,
+	}
+}
+
+func copyHeader(dst, src http.Header) {
+	for k, vv := range src {
+		for _, v := range vv {
+			dst.Add(k, v)
+		}
+	}
+}
+
+func main() {
+
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		var response ResponseWithHeader
+
+		cacheDigest := findCacheDigest(r)
+		cacheBody, ok := lruCache.Get(cacheDigest)
+		if ok {
+			response = cacheBody.(ResponseWithHeader)
+		} else {
+			fmt.Println(cacheDigest)
+			response = get(r)
+			if response.StatusCode == 200 {
+				lruCache.Add(cacheDigest, response)
+			}
+		}
+		copyHeader(w.Header(), response.Header)
+		w.WriteHeader(response.StatusCode)
+		w.Write(response.Body)
+	})
+
+	log.Fatal(http.ListenAndServe(":8081", nil))
+
+}