FastOG
Tópico

Geração de Imagens OG para Aplicações React

Gere og:image com React usando a API FastOG — com uma subscrição Dynamic API (crie a sua chave de API no dashboard), baseada em subscrição, protegida por HMAC. Este guia mostra como criar um utilitário de assinatura (signer) para URLs de imagens OG assinadas com HMAC e renderizar imagens Open Graph dinâmicas em tempo real. Experimente o Testador de Imagens OG Gratuito para pré-visualizar o seu design antes de publicar.

Início Rápido

1. Criar o utilitário de assinatura (signer)

javascript
// src/utils/og-image-signer.js
export async function generateSignedOgUrl(params, options = {}) {
    const {
        baseUrl = "https://fastog.com/api/v1/og",
        apiKey = import.meta.env.VITE_FASTOG_API_KEY ||
            process.env.REACT_APP_FASTOG_API_KEY,
        hmacSecret = import.meta.env.VITE_FASTOG_HMAC_SECRET ||
            process.env.REACT_APP_FASTOG_HMAC_SECRET,
    } = options;

    if (!apiKey || !hmacSecret) {
        throw new Error("Missing FASTOG_API_KEY or FASTOG_HMAC_SECRET");
    }

    // RFC-3986 percent-encoding: keep A-Za-z0-9-._~
    const enc = (s) =>
        encodeURIComponent(s).replace(
            /[!'()*]/g,
            (c) => "%" + c.charCodeAt(0).toString(16).toUpperCase(),
        );

    // Every query param except the signature, INCLUDING key
    const all = { ...params, key: apiKey };

    // Canonical query: sorted enc(key)=enc(value) pairs joined with &
    const pairs = [];
    for (const [k, v] of Object.entries(all)) {
        for (const vv of Array.isArray(v) ? v : [v]) {
            pairs.push(`${enc(k)}=${enc(vv)}`);
        }
    }
    pairs.sort();
    const canonical = pairs.join("&");

    // Sign the exact bytes the server will verify (Web Crypto HMAC-SHA256)
    const signingKey = await crypto.subtle.importKey(
        "raw",
        new TextEncoder().encode(hmacSecret),
        { name: "HMAC", hash: "SHA-256" },
        false,
        ["sign"],
    );
    const signature = Array.from(
        new Uint8Array(
            await crypto.subtle.sign(
                "HMAC",
                signingKey,
                new TextEncoder().encode(`GET/api/v1/og\n${canonical}`),
            ),
        ),
    )
        .map((b) => b.toString(16).padStart(2, "0"))
        .join("");

    // Build the URL from the same pairs so bytes match the canonical form
    const url = new URL(baseUrl);
    for (const [k, v] of Object.entries(all)) {
        for (const vv of Array.isArray(v) ? v : [v]) {
            url.searchParams.append(Array.isArray(v) ? `${k}[]` : k, vv);
        }
    }
    url.searchParams.set("s", signature);

    return url.toString();
}

⚠️ Importante: Em SPAs React, a assinatura ocorre no lado do cliente. Para produção, mova a assinatura para uma rota de API no backend para manter o segredo HMAC seguro.

Backend Express

javascript
// server/routes/og.js
import express from "express";
import crypto from "crypto";

const router = express.Router();

router.get("/api/og", (req, res) => {
    const { title, template = "default", ...params } = req.query;

    if (!title) {
        return res.status(400).json({ error: "Missing title" });
    }

    const apiKey = process.env.FASTOG_API_KEY;
    const hmacSecret = process.env.FASTOG_HMAC_SECRET;

    const enc = (s) =>
        encodeURIComponent(s).replace(
            /[!'()*]/g,
            (c) => "%" + c.charCodeAt(0).toString(16).toUpperCase(),
        );

    const all = { template, title, ...params, key: apiKey };

    const pairs = [];
    for (const [k, v] of Object.entries(all)) {
        for (const vv of Array.isArray(v) ? v : [v]) {
            pairs.push(`${enc(k)}=${enc(vv)}`);
        }
    }
    pairs.sort();
    const canonical = pairs.join("&");

    const signature = crypto
        .createHmac("sha256", hmacSecret)
        .update(`GET/api/v1/og\n${canonical}`)
        .digest("hex");

    const url = new URL("https://fastog.com/api/v1/og");
    for (const [k, v] of Object.entries(all)) {
        for (const vv of Array.isArray(v) ? v : [v]) {
            url.searchParams.append(Array.isArray(v) ? `${k}[]` : k, vv);
        }
    }
    url.searchParams.set("s", signature);

    res.json({ ogImageUrl: url.toString() });
});

export default router;

Componente React

jsx
// src/components/OgImage.jsx
import { useState, useEffect } from "react";

export function useOgImage(params) {
    const [ogImageUrl, setOgImageUrl] = useState(null);

    useEffect(() => {
        const searchParams = new URLSearchParams(params);
        fetch(`/api/og?${searchParams}`)
            .then((res) => res.json())
            .then((data) => setOgImageUrl(data.ogImageUrl))
            .catch((err) => console.error("Failed to generate OG image:", err));
    }, [JSON.stringify(params)]);

    return ogImageUrl;
}

Exemplo de Publicação de Blog

jsx
// src/pages/BlogPost.jsx
import { useEffect, useState } from "react";
import { useOgImage } from "../components/OgImage";

export default function BlogPost({ post }) {
    const ogImageUrl = useOgImage({
        title: post.title,
        template: "blog",
        subtitle: post.excerpt,
    });

    useEffect(() => {
        const ogImage = document.querySelector('meta[property="og:image"]');
        if (ogImage && ogImageUrl) {
            ogImage.setAttribute("content", ogImageUrl);
        }
    }, [ogImageUrl]);

    return (
        <article>
            <h1>{post.title}</h1>
            <p>{post.excerpt}</p>
        </article>
    );
}

React Helmet (SSR)

jsx
// src/pages/BlogPost.jsx
import { Helmet } from "react-helmet-async";
import { useOgImage } from "../components/OgImage";

export default function BlogPost({ post }) {
    const ogImageUrl = useOgImage({
        title: post.title,
        template: "blog",
        subtitle: post.excerpt,
    });

    return (
        <>
            <Helmet>
                <meta
                    property="og:image"
                    content={ogImageUrl || "/fallback-og.png"}
                />
                <meta property="og:title" content={post.title} />
                <meta property="og:description" content={post.excerpt} />
            </Helmet>
            <article>
                <h1>{post.title}</h1>
            </article>
        </>
    );
}

Next.js (React Framework)

Para Next.js, consulte os tutoriais dedicados Next.js App Router e Next.js Pages Router.

Remix

jsx
// app/routes/blog.$slug.jsx
import { json } from "@remix-run/node";
import { useLoaderData } from "@remix-run/react";
import { generateSignedOgUrl } from "~/lib/og-image-signer.server";

export async function loader({ params }) {
    const post = await getPost(params.slug);

    const ogImageUrl = generateSignedOgUrl({
        template: "blog",
        title: post.title,
        subtitle: post.excerpt,
    });

    return json({ post, ogImageUrl });
}

export function meta({ data }) {
    return [
        { title: data.post.title },
        { property: "og:image", content: data.ogImageUrl },
        { property: "og:title", content: data.post.title },
    ];
}

export default function BlogPost() {
    const { post } = useLoaderData();

    return (
        <article>
            <h1>{post.title}</h1>
        </article>
    );
}

Assinante no lado do servidor (Node.js)

javascript
// lib/og-image-signer.server.js
import crypto from "crypto";

export function generateSignedOgUrl(params, options = {}) {
    const {
        baseUrl = "https://fastog.com/api/v1/og",
        apiKey = process.env.FASTOG_API_KEY,
        hmacSecret = process.env.FASTOG_HMAC_SECRET,
    } = options;

    // RFC-3986 percent-encoding: keep A-Za-z0-9-._~
    const enc = (s) =>
        encodeURIComponent(s).replace(
            /[!'()*]/g,
            (c) => "%" + c.charCodeAt(0).toString(16).toUpperCase(),
        );

    // Every query param except the signature, INCLUDING key
    const all = { ...params, key: apiKey };

    // Canonical query: sorted enc(key)=enc(value) pairs joined with &
    const pairs = [];
    for (const [k, v] of Object.entries(all)) {
        for (const vv of Array.isArray(v) ? v : [v]) {
            pairs.push(`${enc(k)}=${enc(vv)}`);
        }
    }
    pairs.sort();
    const canonical = pairs.join("&");

    // Sign the exact bytes the server will verify
    const signature = crypto
        .createHmac("sha256", hmacSecret)
        .update(`GET/api/v1/og\n${canonical}`)
        .digest("hex");

    // Build the URL from the same pairs so bytes match the canonical form
    const url = new URL(baseUrl);
    for (const [k, v] of Object.entries(all)) {
        for (const vv of Array.isArray(v) ? v : [v]) {
            url.searchParams.append(Array.isArray(v) ? `${k}[]` : k, vv);
        }
    }
    url.searchParams.set("s", signature);

    return url.toString();
}

Variáveis de Ambiente

bash
# .env (Vite)
VITE_FASTOG_API_KEY=sk_your_full_api_key_here
VITE_FASTOG_HMAC_SECRET=your_64_char_hex_secret_here

# .env (Create React App)
REACT_APP_FASTOG_API_KEY=sk_your_full_api_key_here
REACT_APP_FASTOG_HMAC_SECRET=your_64_char_hex_secret_here

# Server .env
FASTOG_API_KEY=sk_your_full_api_key_here
FASTOG_HMAC_SECRET=your_64_char_hex_secret_here

Armadilhas Comuns

Expor o Segredo HMAC no Código do Cliente

❌ Errado:

javascript
// In browser code
const ogUrl = generateSignedOgUrl(params, {
    hmacSecret: import.meta.env.VITE_FASTOG_HMAC_SECRET,
});

✅ Correto:

javascript
// Call your backend API
const res = await fetch(`/api/og?title=${post.title}`);
const { ogImageUrl } = await res.json();

Não Atualizar as Meta Tags

Os crawlers sociais precisam das meta tags no HTML inicial. Use SSR (Next.js, Remix) ou um proxy de backend para um suporte adequado da imagem OG.

Referência Completa da API

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