feat: add link-preview handler

go.mod

@@ -21,6 +21,7 @@ require (
 	github.com/tinode/snowflake v1.0.0
 	go.mongodb.org/mongo-driver v1.12.1
 	golang.org/x/crypto v0.21.0
+	golang.org/x/net v0.23.0
 	golang.org/x/oauth2 v0.16.0
 	golang.org/x/text v0.14.0
 	google.golang.org/api v0.148.0
@@ -68,7 +69,6 @@ require (
 	github.com/xdg-go/stringprep v1.0.4 // indirect
 	github.com/youmark/pkcs8 v0.0.0-20201027041543-1326539a0a0a // indirect
 	go.opencensus.io v0.24.0 // indirect
-	golang.org/x/net v0.23.0 // indirect
 	golang.org/x/sync v0.4.0 // indirect
 	golang.org/x/sys v0.18.0 // indirect
 	golang.org/x/time v0.3.0 // indirect

server/linkpreview.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"encoding/json"
+	"golang.org/x/net/html"
+	"net/http"
+	"strings"
+	"time"
+)
+
+type LinkPreview struct {
+	Title       string `json:"title"`
+	Description string `json:"description"`
+	Image       string `json:"image"`
+	URL         string `json:"url"`
+}
+
+// PreviewLink handles the HTTP request, fetches the URL, and returns the link preview
+func PreviewLink(w http.ResponseWriter, r *http.Request) {
+	url := r.URL.Query().Get("url")
+	if url == "" {
+		http.Error(w, "Missing 'url' query parameter", http.StatusBadRequest)
+		return
+	}
+
+	req, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+
+	client := &http.Client{
+		Timeout: time.Second * 5,
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		http.Error(w, "Non-OK HTTP status", http.StatusInternalServerError)
+		return
+	}
+
+	doc, err := html.Parse(resp.Body)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	metadata := extractMetadata(doc)
+
+	linkPreview := LinkPreview{
+		Title:       metadata["og:title"],
+		Description: metadata["og:description"],
+		Image:       metadata["og:image"],
+		URL:         url,
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if err := json.NewEncoder(w).Encode(linkPreview); err != nil {
+		http.Error(w, "Failed to encode response", http.StatusInternalServerError)
+	}
+}
+
+func extractMetadata(n *html.Node) map[string]string {
+	metaTags := map[string]string{}
+	var traverse func(*html.Node)
+	traverse = func(n *html.Node) {
+		if n.Type == html.ElementNode && n.Data == "meta" {
+			attrs := make(map[string]string)
+			for _, attr := range n.Attr {
+				attrs[attr.Key] = attr.Val
+			}
+			name := attrs["name"]
+			property := attrs["property"]
+			content := attrs["content"]
+
+			if strings.HasPrefix(property, "og:") && content != "" {
+				metaTags[property] = content
+			} else if name != "" && content != "" {
+				metaTags[name] = content
+			}
+		}
+
+		for child := n.FirstChild; child != nil; child = child.NextSibling {
+			traverse(child)
+		}
+	}
+
+	traverse(n)
+
+	if _, exists := metaTags["og:title"]; !exists {
+		metaTags["og:title"] = extractTitle(n)
+	}
+	return metaTags
+}
+
+func extractTitle(n *html.Node) string {
+	if n.Type == html.ElementNode && n.Data == "title" {
+		if n.FirstChild != nil {
+			return n.FirstChild.Data
+		}
+	}
+	for child := n.FirstChild; child != nil; child = child.NextSibling {
+		title := extractTitle(child)
+		if title != "" {
+			return title
+		}
+	}
+	return ""
+}

server/main.go

@@ -734,6 +734,8 @@ func main() {
 		mux.HandleFunc("/", serve404)
 	}
 
+	mux.HandleFunc(config.ApiPath+"v0/preview-link", PreviewLink)
+
 	if err = listenAndServe(config.Listen, mux, tlsConfig, signalHandler()); err != nil {
 		logs.Err.Fatal(err)
 	}