From 8adfa27bd6c4500d2ccbc6366fa8dce53cea2cef Mon Sep 17 00:00:00 2001
From: Milos Stojanovic <alcalbg@gmail.com>
Date: Wed, 17 Nov 2021 12:13:32 +0100
Subject: [PATCH] cont

---
 .env.example |   7 ++++
 .gitignore   |   2 +
 README.md    |  20 ++++++++++
 go.mod       |   8 ++++
 go.sum       |   4 ++
 main.go      | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 147 insertions(+)
 create mode 100644 .env.example
 create mode 100644 .gitignore
 create mode 100644 README.md
 create mode 100644 go.mod
 create mode 100644 go.sum
 create mode 100644 main.go

diff --git a/.env.example b/.env.example
new file mode 100644
index 0000000..d09c2ae
--- /dev/null
+++ b/.env.example
@@ -0,0 +1,7 @@
+ADDR=":8888"
+LINK_PREVIEW_KEY="123456"
+
+# optional ssl certificates
+SSL_CERT="cert.pem"
+SSL_KEY="cert.key"
+
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..163ad08
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.env
+v1
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..dfba813
--- /dev/null
+++ b/README.md
@@ -0,0 +1,20 @@
+# LinkPreview.net Proxy Server in Go
+
+
+How to use:
+
+1. Download executable
+2. Create .env file configuration, see .env.example
+
+
+Sample .env file:
+
+```
+ADDR="localhost:8000"
+LINK_PREVIEW_KEY="123456"
+```
+
+3. Start your server
+
+
+
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..04589f8
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,8 @@
+module linkpreview.net/proxy/v1
+
+go 1.17
+
+require (
+	github.com/joho/godotenv v1.4.0
+	github.com/muesli/cache2go v0.0.0-20211005105910-8e46465cca4a
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..58f0c61
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,4 @@
+github.com/joho/godotenv v1.4.0 h1:3l4+N6zfMWnkbPEXKng2o2/MR5mSwTrBih4ZEkkz1lg=
+github.com/joho/godotenv v1.4.0/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
+github.com/muesli/cache2go v0.0.0-20211005105910-8e46465cca4a h1:IZxQOY9gAiiGGuEdlOBnqaC3yumj8UvyQluBNqGP2Ek=
+github.com/muesli/cache2go v0.0.0-20211005105910-8e46465cca4a/go.mod h1:WERUkUryfUWlrHnFSO/BEUZ+7Ns8aZy7iVOGewxKzcc=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..d2ea88e
--- /dev/null
+++ b/main.go
@@ -0,0 +1,106 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/joho/godotenv"
+	"github.com/muesli/cache2go"
+)
+
+const linkpreviewAPI = "https://api.linkpreview.net"
+
+var linkpreviewKey = ""
+
+var cache *cache2go.CacheTable
+
+type cachedResponse struct {
+	body   []byte
+	status int
+}
+
+type lpreq struct {
+	Key    string `json:"key"`
+	Q      string `json:"q"`
+	Fields string `json:"fields"`
+}
+
+func main() {
+
+	err := godotenv.Load()
+	if err != nil {
+		log.Fatal("Error loading .env file")
+	}
+
+	addr := os.Getenv("ADDR")
+	linkpreviewKey = os.Getenv("LINK_PREVIEW_KEY")
+
+	cache = cache2go.Cache("myCache")
+
+	http.HandleFunc("/", proxyHandler)
+
+	if os.Getenv("SSL_CERT") != "" && os.Getenv("SSL_KEY") != "" {
+		fmt.Printf("Proxy secure server started on https://%s\n", addr)
+		if err := http.ListenAndServeTLS(addr, os.Getenv("SSL_CERT"), os.Getenv("SSL_KEY"), nil); err != nil {
+			panic(err)
+		}
+	}
+
+	fmt.Printf("Proxy server started on http://%s\n", addr)
+	if err := http.ListenAndServe(addr, nil); err != nil {
+		panic(err)
+	}
+
+}
+
+func proxyHandler(w http.ResponseWriter, r *http.Request) {
+
+	query := r.URL.Query().Get("q")
+
+	// keep results in cache for one day (based on the key scheme)
+	cacheKey := fmt.Sprintf("%s%d", query, time.Now().Day())
+
+	cached, err := cache.Value(cacheKey)
+	if err == nil {
+		fmt.Println("Serving from Cache: " + query)
+		w.WriteHeader(cached.Data().(*cachedResponse).status)
+		w.Write(cached.Data().(*cachedResponse).body)
+		return
+	}
+
+	body, _ := json.Marshal(&lpreq{
+		Key:    linkpreviewKey,
+		Q:      query,
+		Fields: "title,description,image,url", // see https://docs.linkpreview.net/#query-parameters
+	})
+
+	fmt.Println("Requesting from the API: " + query)
+	client := &http.Client{}
+	req, _ := http.NewRequest("POST", linkpreviewAPI, bytes.NewBuffer(body))
+	resp, err := client.Do(req)
+	if err != nil {
+		http.Error(w, "Server Error", http.StatusInternalServerError)
+		return
+	}
+	defer resp.Body.Close()
+
+	cr := cachedResponse{}
+	cr.body, err = io.ReadAll(resp.Body)
+	cr.status = resp.StatusCode
+	if err != nil {
+		http.Error(w, "Server Error", http.StatusInternalServerError)
+		return
+	}
+
+	w.WriteHeader(cr.status)
+	w.Write(cr.body)
+
+	// add to cache and automatically expire unused after one day
+	cache.Add(cacheKey, 24*time.Hour, &cr)
+}