From bb1e6b3f9fa33fe018291ccde6fbfd7a48b459cc Mon Sep 17 00:00:00 2001
From: Petter Rodhelind <petter.rodhelind@gmail.com>
Date: Sun, 21 Feb 2021 22:55:58 +0100
Subject: Implement concurrently safe caching of requests.

---
 main.go | 74 ++++++++++++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 55 insertions(+), 19 deletions(-)

diff --git a/main.go b/main.go
index fc243fa..87d40fa 100644
--- a/main.go
+++ b/main.go
@@ -2,17 +2,40 @@ package main
 
 import (
 	"fmt"
+	"log"
 	"net/http"
 	"strings"
+	"sync"
 	"time"
 )
 
-var outputMode string
+var (
+	// outputMode is either HTML or RSS
+	outputMode string
+
+	// cache will hold all previous network calls and re-use within set timeframe
+	cache safeCache
+
+	// cacheTimeout sets the time in in seconds for how long a channel will be cached
+	cacheTimeout float64
+)
+
+func init() {
+	outputMode = "html"
+	cache = safeCache{v: make(map[string]*channel)}
+	cacheTimeout = 60 * 15 // seconds
+}
+
+type safeCache struct {
+	sync.Mutex
+	v map[string]*channel
+}
 
 type channel struct {
 	Title       string
 	Link        string
 	Name        string
+	Time        time.Time
 	Description string
 	Items       []*post
 }
@@ -65,7 +88,7 @@ func (p *post) String() string {
 
 	var s string
 	// time format: Mon Jan 2 15:04:05 -0700 MST 2006
-	s = strings.Replace(template, "{{time}}", p.Time.Format("Mon, 2 Jan 2006 15:04:05 MST"), 2)
+	s = strings.Replace(template, "{{time}}", p.Time.Format("Mon, 2 Jan 2006 15:04:05"), 2)
 	s = strings.Replace(s, "{{content}}", p.Content, 1)
 	var imgs string
 	for i := range p.Images {
@@ -79,34 +102,40 @@ func (p *post) String() string {
 type handler struct{}
 
 func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path == "/favicon.ico" {
+		return
+	}
 	group := r.URL.Path[1:]
 	if strings.HasSuffix(group, ".rss") {
 		group = strings.TrimSuffix(group, ".rss")
 		outputMode = "rss"
 	}
 
-	c, err := fetch(group)
-	if err != nil {
-		http.Error(w, fmt.Sprintf("error: %s", err), 400)
-		return
-	}
-
-	if c == nil || len(c.Items) < 1 {
-		http.Error(w, fmt.Sprintf("%s", "group not found"), 400)
-		return
+	c, ok := cache.v[group]
+	if !ok || time.Now().Sub(c.Time).Seconds() > cacheTimeout {
+		var err error
+		c, err = fetch(group)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("error: %s", err), 400)
+			return
+		}
+
+		if c == nil || len(c.Items) < 1 {
+			http.Error(w, fmt.Sprintf("%s", "group not found"), 400)
+			return
+		}
+
+		c.Name = group
+		c.Time = time.Now()
+
+		cache.Lock()
+		cache.v[c.Name] = c
+		cache.Unlock()
 	}
 
-	c.Name = group
-
 	fmt.Fprintf(w, "%s\n", c.String())
 }
 
-func main() {
-	outputMode = "html"
-	fmt.Println("Serving: http://localhost:1212")
-	http.ListenAndServe(":1212", handler{})
-}
-
 func fetch(group string) (c *channel, err error) {
 	if group == "" {
 		return
@@ -114,6 +143,8 @@ func fetch(group string) (c *channel, err error) {
 
 	url := "https://www.facebook.com/pg/" + group + "/posts/"
 
+	log.Println("Fetching: ", url)
+
 	resp, err := http.Get(url)
 	if err != nil {
 		return
@@ -129,3 +160,8 @@ func fetch(group string) (c *channel, err error) {
 
 	return
 }
+
+func main() {
+	log.Println("Serving: http://localhost:1212")
+	http.ListenAndServe(":1212", handler{})
+}
-- 
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