feat: sanitize post metadata and implement webhook fallback for 400 errors

apps/backend/src/routes/post.ts

@@ -76,25 +76,63 @@ async function sendDiscordNotification(payload: {
         return;
     }
 
+    const safeTitle = (payload.title || "New post").slice(0, 256);
+    const safeAuthor = (payload.author || "unknown").slice(0, 256);
+    const safeTags = (payload.tags.join(", ") || "None").slice(0, 1024);
+
+    const isValidHttpUrl = (value?: string) => {
+        if (!value) return false;
+        try {
+            const parsed = new URL(value);
+            return parsed.protocol === "http:" || parsed.protocol === "https:";
+        } catch {
+            return false;
+        }
+    };
+
+    const safeUrl = isValidHttpUrl(payload.url) ? payload.url : undefined;
+    const safeImageUrl = isValidHttpUrl(payload.imageUrl) ? payload.imageUrl : undefined;
+
+    const embed: Record<string, unknown> = {
+        title: safeTitle,
+        author: { name: safeAuthor },
+        fields: [{ name: "Tags", value: safeTags }],
+        color: 0x00ff00,
+    };
+
+    if (safeUrl) embed.url = safeUrl;
+    if (safeImageUrl) embed.image = { url: safeImageUrl };
+
+    const body = {
+        content: `${safeTitle}${safeUrl ? `\n${safeUrl}` : ""}`,
+        embeds: [embed],
+    };
+
     try {
         const response = await fetch(webhookUrl, {
             method: "POST",
             headers: { "Content-Type": "application/json" },
-            body: JSON.stringify({
-                embeds: [{
-                    title: payload.title,
-                    url: payload.url,
-                    author: { name: payload.author },
-                    fields: [{ name: "Tags", value: payload.tags.join(", ") || "None" }],
-                    image: payload.imageUrl ? { url: payload.imageUrl } : undefined,
-                    color: 0x00ff00,
-                }],
-            }),
+            body: JSON.stringify(body),
         });
 
         if (!response.ok) {
             const errorText = await response.text().catch(() => "");
             console.error(`[Discord Webhook] failed status=${response.status} body=${errorText}`);
+
+            if (response.status === 400) {
+                const fallbackResponse = await fetch(webhookUrl, {
+                    method: "POST",
+                    headers: { "Content-Type": "application/json" },
+                    body: JSON.stringify({
+                        content: `${safeTitle}${safeUrl ? `\n${safeUrl}` : ""}\nAuthor: ${safeAuthor}\nTags: ${safeTags}`,
+                    }),
+                });
+
+                if (!fallbackResponse.ok) {
+                    const fallbackErrorText = await fallbackResponse.text().catch(() => "");
+                    console.error(`[Discord Webhook] fallback failed status=${fallbackResponse.status} body=${fallbackErrorText}`);
+                }
+            }
         }
     } catch (error) {
         console.error("[Discord Webhook Error]", error);