Next.js - Error: only absolute urls are supported - reactjs

Question

I'm using express as my custom server for next.js. Everything is fine, when I click the products to the list of products
Step 1: I click the product Link
Step 2: It will show the products in the database.
However if I refresh the /products page, I will get this Error
Server code (Look at /products endpoint)
app.prepare()
.then(() => {
const server = express()
// This is the endpoints for products
server.get('/api/products', (req, res, next) => {
// Im using Mongoose to return the data from the database
Product.find({}, (err, products) => {
res.send(products)
})
})
server.get('*', (req, res) => {
return handle(req, res)
})
server.listen(3000, (err) => {
if (err) throw err
console.log('> Ready on http://localhost:3000')
})
})
.catch((ex) => {
console.error(ex.stack)
process.exit(1)
})
Pages - products.js (Simple layout that will loop the products json data)
import Layout from '../components/MyLayout.js'
import Link from 'next/link'
import fetch from 'isomorphic-unfetch'
const Products = (props) => (
<Layout>
<h1>List of Products</h1>
<ul>
{ props.products.map((product) => (
<li key={product._id}>{ product.title }</li>
))}
</ul>
</Layout>
)
Products.getInitialProps = async function() {
const res = await fetch('/api/products')
const data = await res.json()
console.log(data)
console.log(`Showed data fetched. Count ${data.length}`)
return {
products: data
}
}
export default Products

Answer 1

As the error states, you will have to use an absolute URL for the fetch you're making. I'm assuming it has something to do with the different environments (client & server) on which your code can be executed. Relative URLs are just not explicit & reliable enough in this case.
One way to solve this would be to just hardcode the server address into your fetch request, another to set up a config module that reacts to your environment:
/config/index.js
const dev = process.env.NODE_ENV !== 'production';
export const server = dev ? 'http://localhost:3000' : 'https://your_deployment.server.com';
products.js
import { server } from '../config';
// ...
Products.getInitialProps = async function() {
const res = await fetch(`${server}/api/products`)
const data = await res.json()
console.log(data)
console.log(`Showed data fetched. Count ${data.length}`)
return {
products: data
}
}

Answer 2

Similar to the #Shanker's answer, but if you prefer not to install the additional package for this, here is how to do it.
async getInitialProps({ req }) {
const protocol = req.headers['x-forwarded-proto'] || 'http'
const baseUrl = req ? `${protocol}://${req.headers.host}` : ''
const res = await fetch(baseUrl + '/api/products')
}

Answer 3

It sounds silly but worth mentioning. If you're using SSR in your webapp the fetch call will work with a relative link on the client but will fail on the server. Only the server needs an absolute link!
If you want to prevent the server from making the request just wrap it in logic
if(global.window){
const req = fetch('/api/test');
...
}

Answer 4

You could utilize environment variables if your project is hosted on a provider that supports it.
env.local
// Local
URL="http://localhost:3000"
// Production
URL="https://prod.com"
Then you can use the following.
const { URL } = process.env;
const data = await fetcher(URL + '/api');

Answer 5

This simple solution worked for me without having to add an additional config file,
Install
npm install --save next-absolute-url
Usage
import absoluteUrl from "next-absolute-url";
async getInitialProps({ req }){
const { origin } = absoluteUrl(req, req.headers.host);
console.log('Requested URL ->',origin);
// (or) other way
const host = absoluteUrl(req, req.headers.host);
console.log('Requested URL ->',host.origin);
}

Answer 6

Case 1. It's not an error. The isomorphic-unfetch is running by SSR mode, so Node.js needs to know the absolute url to fetch from it, because the back-end doesn't know your browser settings.
Case 2. Another scenario is to prevent the http host poisoning headers attack.
append secret keys and tokens to links containing it:
<a href="http://_SERVER['HOST']?token=topsecret"> (Django, Gallery, others)
....and even directly import scripts from it:
<script src="http://_SERVER['HOST']/misc/jquery.js?v=1.4.4">
Case 3. The isomorphic-unfetch it's the library we are going to use to fetch data. It's a simple implementation of the browser fetch API, but works both in client and server environments.
Read more about it:
Isomorphic unfetch - Switches between unfetch & node-fetch for client & server
Prevent http host headers attack
Fetching Data for Pages

Answer 7

In the NextJS 9.5, we can also use process.cwd().
process.cwd() will give you the directory where Next.js is being executed.
import path from 'path'
import fs from "fs";
export const getStaticProps: GetStaticProps = async () => {
const dataFilePath = path.join(process.cwd(), "jsonFiles", "data.json");
console.log(dataFilePath); // will be YourProject/jsonFiles/data.json
const fileContents = fs.readFileSync(dataFilePath, "utf8");
const data: TypeOfData[] = JSON.parse(fileContents);
return { props: { data } };
};
Ref: https://nextjs.org/docs/basic-features/data-fetching#reading-files-use-processcwd

Answer 8

Putting this out there because this showed up in google results for my problem, even though the question itself isn't really related (outside of the fact that the same dependency is throwing the same error message, albeit in a different context for a different reason).
I got this issue from using hardhat while attempting to verify (verify:verify) my contract on etherscan. The problem was that in the hardhat config, I didn't have a full url under rinkeby (since I was verifying on rinkeby, would be mainnet, etc.). Copy/pasting some config stuff quickly into a project I cloned from someone else, they had a full URL in their .env, while I had the url in the config and stored only my api key in my .env.
To figure this out, though, was straightforward--go into node_modules, then find the node-fetch folder, then lib, (this is from memory--just find the line that is vomitting in your stack trace) then the line number, and put a console log there to see what the "bad" url you're seeing is. Usually that's enough of a clue; in my case, it was an API key, obviously not a URL, and that made it straightforward to solve.

Answer 9

If you have an absolute path issues. Try to use swr to access data.
Notice: This is a React hooks so you must call inside the component.
import useSWR from 'swr';
// optionally you can use unfetch package from npm or built yours to handle promise.
const fetcher = (...args) => fetch(...args).then(res => res.json())
export const AllProducts = () => {
const { data, error } = useSWR('/api/products', fetcher)
if (error) return <div>failed to load</div>
if (!data) return <div>loading...</div>
return (
<div>{data}</div>
);
};
Export or deploying in production
Whenever you are trying to deploy on Vercel you might encounter an error. For instance `
warn - Statically exporting a Next.js application via `next export` disables API routes`.
It means you are trying to export data and NextJS does not support fetching data from pages/api/* directory. To avoid errors, its better to separate build and export command.
// package.json
{
"scripts": {
"dev": "next",
"build": "next build", // No next export command
"start": "next start"
},
}
Thanks folks for great contribution and I hope the answer shared will help somebody too.

Answer 10

Make sure what the value of your API url is
In my case, I was using POST but my url was somewhat undefined.
Use console.log to see where is your request going.

Answer 11

this is a way to get the base hostname to fetch data from external endpoint
without getting that error
function return_url(context) {
if (process.env.NODE_ENV === "production") {
return `https://${context.req.rawHeaders[1]}`;
} else if (process.env.NODE_ENV !== "production") {
return "http://localhost:3000";
}
}
and on the getServerSideProps or getStaticProps functions you use
export async function getServerSideProps(context) {
let url = return_url(context);
const data = await fetch(`${url}/yourEndPoint`).then((res) => res.json());
return {
props: {
data: data,
},
};
}

Answer 12

If you are using next environment config prefix your variables with NEXT_PUBLIC_ as mentioned here Exposing Environment Variables to the Browser.

Answer 13

USE: NEXT_PUBLIC_STRAPI_URL="http://localhost:1337" instead of
NEXT_PUBLIC_STRAPI_URL=http://localhost:1337

Answer 14

use .log(console.log) after nock , so you will get exact unmatched and expected url .
Example:
nock("http://localhost")
.log(console.log)
.persist()
.get("/api/config")
.reply(200, { data: 1234 })