Next.js API routes (and pages) should support reading files

[Timer]

Feature request

Is your feature request related to a problem? Please describe.

It's currently not possible to read files from API routes or pages.

Describe the solution you'd like

I want to be able to call fs.readFile with a __dirname path and have it "just work".

This should work in Development and Production mode.

Describe alternatives you've considered

This may need to integrate with @zeit/webpack-asset-relocator-loader in some capacity. This plugin handles these types of requires.

However, it's not a necessity. I'd be OK with something that only works with __dirname and __filename (no relative or cwd-based paths).

Additional context

Example:

// pages/api/test.js
import fs from 'fs'
import path from 'path'

export default (req, res) => {
  const fileContent = fs.readFileSync(
    path.join(__dirname, '..', '..', 'package.json'), 
    'utf8'
  )
  // ...
}

Note: I know you can cheat the above example ☝️ with require, but that's not the point. 😄

[jasonsilberman]

any movement on this? It would be great to be able to include html email templates for use in API Routes. Right now I am including them in JS files but I am not a particular fan of this hack.

[balthild]

Another hack is to use webpack raw-loader to embed them into js.

yarn add --dev raw-loader

const templates = {
    verify: require("raw-loader!../template/email/verify.hbs").default,
};

Then use templates.verify as a string.

[borispoehland]

There's an issue going on with next-i18next that seems to be related to this one (vercel/vercel#4271) . Basically now doesn't put the .json files located inside /public/static/locales/ into the serverless function. Can anyone provide a workaround until the feature discussed here is added to next?

[BrunoBernardino]

@borispoehland have you tried the import/require workarounds from above? That should work.

[borispoehland]

@borispoehland have you tried the import/require workarounds from above? That should work.

@BrunoBernardino I don't know what exact comment you mean.

Can you give me an example of somehow importing all the .json files inside public/static/locales into the serverless function? And where to do this (in what file)?

I'm using next (as you stated earlier, includeFiles isn't compatible with @now/next, idk if this has any impact on my problem).

Besides, because next-i18next is kind of a blackbox to me (thus I don't want to import the files from there), I search for a way to entirely import them so that next-i18next can directly access them (in other comments above, sometimes only the PROJECT_DIRNAME was defined inside the next.config.json and the import had to be done manually. This is not what I try to reach). Like in vercel/vercel#4271, I just want now to take my .json files into the serverless function somehow.

[BrunoBernardino]

@borispoehland in any file inside pages/api (or that gets called by one there), do something like https://github.com/vercel/next.js/issues/8251#issuecomment-544008976

You don't need to do anything with the import. The point is that the webpack vercel runs will then see those files need to be included, and it should work.

I hope that makes sense.

[borispoehland]

@borispoehland in any file inside pages/api (or that gets called by one there), do something like #8251 (comment)

You don't need to do anything with the import. The point is that the webpack vercel runs will then see those files need to be included, and it should work.

I hope that makes sense.

@BrunoBernardino the problem with this approach is that I have lots of json files. Doing the import manually for every file is kind of cumbersome. Is there a easier way to tell now: "Hey, please pick up all json files inside that directory recursively"? Thanks in advance

Edit: Even manually importing json files results in the same error than before. I'm going to open a new issue for this, I guess

[borispoehland]

I opened a new issue for my problem, in case someone is interested in joining the discussion. Thanks for now, @BrunoBernardino !

[aweber1]

Another option / workaround to enable the ability to use __dirname as you would normally expect it to behave is to adjust the webpack config.

By default, webpack will alias various Node globals with polyfills unless you tell it not to: https://webpack.js.org/configuration/node/ And the webpack default settings are to leave __dirname and __filename alone, i.e. not polyfill them and let node handle them as normal.

However, the Next.js webpack config doesn't use / reflect the webpack defaults https://github.com/vercel/next.js/blob/bb6ae2648ddfb65a810edf6ff90a86201d52320c/packages/next/build/webpack-config.ts#L661-L663

All of that said, I have used the below custom Next config plugin to adjust the webpack config.

IMPORTANT: this works for my use case. It has not been tested in a wide range of environments / configurations nor has it been tested against all of the Next.js unit/integration tests. Using it may have unintended side-effects in your environment. Also, Next may have specific reasons for not using the webpack default settings for __dirname and __filename. So again, the code below may have unintended side-effects and should be used with caution.

Also, the below plugin has been designed for use with the next-compose-plugins package: https://github.com/cyrilwanner/next-compose-plugins

But should work as a normal plugin as well: https://nextjs.org/docs/api-reference/next.config.js/custom-webpack-config

const withCustomWebpack = (nextCfg) => {
  return Object.assign({}, nextCfg, {
    webpack(webpackConfig, options) {
      // We only want to change the `server` webpack config.
      if (options.isServer) {
        // set `__dirname: false` and/or `__filename: false` here to align with webpack defaults:
        // https://webpack.js.org/configuration/node/
        Object.assign(webpackConfig.node, { __dirname: false });
      }

      if (typeof nextCfg.webpack === 'function') {
        return nextCfg.webpack(webpackConfig, options);
      }

      return webpackConfig;
    },
  });
};

[bengrunfeld]

I implemented the solution by @jkjustjoshing, and while it works great locally, it does not work when I deploy the app to Vercel.

I get the following error:

Error: GraphQL error: ENOENT: no such file or directory, open '/vercel/37166432/public/ts-data.csv'

My code:

const content = await fs.readFile(
  path.join(serverRuntimeConfig.PROJECT_ROOT, "./public/ts-data.csv")
);

Here's a link to the file: https://github.com/bengrunfeld/trend-viewer/blob/master/pages/api/graphql-data.js

[borispoehland]

@bengrunfeld yes, your solution only works locally.

I had a similar problem lately (wanted to read a file in a API route) and the solution was easier than expected.

Try path.resolve('./public/ts-data.csv')

[bengrunfeld]

@borispoehland Thank you SO much!! Your solution worked beautifully!

[borispoehland]

@bengrunfeld no problem, I also found it out on coincidence (@BrunoBernardino ;)). It's the solution to everyone's problem here, I guess.

[bengrunfeld]

Please note, you still need to set next.config.js. I deleted the file after I saw that @borispoehland's solution worked, and received a similar error.

Then I reset it to @jkjustjoshing's solution above, deployed again to Vercel, and it worked.

# next.config.js
module.exports = {
    serverRuntimeConfig: {
        PROJECT_ROOT: __dirname
    }
}

[borispoehland]

Please note, you still need to set next.config.js. I removed it after I saw that @borispoehland's solution worked, and received a similar error.

I reset it to @jkjustjoshing's solution above, deployed again to Vercel, and it worked.

# next.config.js
module.exports = {
    serverRuntimeConfig: {
        PROJECT_ROOT: __dirname
    }
}

@bengrunfeld Really? Maybe you're still using the PROJECT_ROOT approach at another point in the code, because in my project it works without it. How does the error look like?

[mathdroid]

When deploying to Vercel, how do I write a readFile in a Page that will work both in SSG and SSR/Preview mode?

Demo repository of where it does not work: https://github.com/mathdroid/blog-fs-demo

https://blog-fs-demo.vercel.app/

[BrunoBernardino]

@mathdroid try moving readFile and readdir inside the getStaticProps and getStaticPaths functions, respectively, otherwise the code might run in the browser.

Importing fs should be fine on top, though.

Let us know how that works.

[subwaymatch]

@borispoehland Thanks for the wonderful solution. Did not expect path.resolve() to /public would work both locally and on Vercel :eyes:! You're my savior for the day. :+1:

[neckaros]

@borispoehland i tried your solution inside a serverless functionbut still get: ENOENT: no such file or directory, open '/var/task/public/posts.json'

const postsFile = resolve('./public/posts.json');

const updateCache = async (posts: IPost[]): Promise<IPost[]> => {
    postCache = posts;
    fs.writeFileSync(postsFile, JSON.stringify(postCache)); // <====
    return postCache;
}

i tried with our without the next.config.js

module.exports = {
    serverRuntimeConfig: {
        PROJECT_ROOT: __dirname
    }
}

Maybe your solution does not work on serverless functions?

[borispoehland]

@borispoehland i tried your solution inside a serverless functionbut still get: ENOENT: no such file or directory, open '/var/task/public/posts.json'

const postsFile = resolve('./public/posts.json');

const updateCache = async (posts: IPost[]): Promise<IPost[]> => {
    postCache = posts;
    fs.writeFileSync(postsFile, JSON.stringify(postCache)); // <====
    return postCache;
}

i tried with our without the next.config.js

module.exports = {
    serverRuntimeConfig: {
        PROJECT_ROOT: __dirname
    }
}

Maybe your solution does not work on serverless functions?

I don't know why it doesn't work on your end... Sorry

[neckaros]

Ok i made it work for read using @bengrunfeld code but unfortunately you cannot write: [Error: EROFS: read-only file system, open '/var/task/public/posts.json'] So no way to update a cache to avoid too much database calls :(

[borispoehland]

@neckaros have you tried using my approach to read a file other than .json, e.g. a .jpg file?

[BrunoBernardino]

Ok i made it work for read using @bengrunfeld code but unfortunately you cannot write:

[Error: EROFS: read-only file system, open '/var/task/public/posts.json']

So no way to update a cache to avoid too much database calls :(

@neckaros you should be able to write and read from S3 (or some other, external filesystem), but I usually use redis for quick, cached things that can be volatile. https://redislabs.com keeps it "serverless", and I've got production-ready code examples in https://nextjs-boilerplates.brn.sh if you want.

[neckaros]

@borispoehland i could read but not write from serveless function. But I ended up having it working by refresh my cache in the incremental builds (revalidate) instead of on add new content . Which I guess is not a bad pattern. Thanks for your help!

@BrunoBernardino thanks i will have a look. Really looking to a fully free hobbyist solution that does not break once you have a few users :)

[BrunoBernardino]

Really looking to a fully free hobbyist solution that does not break once you have a few users :)

Copy that. RedisLabs and Vercel did that for me. 💯

[Edjevw12]

After some digging I got writing files working with the extended os package...

import { tmpdir } from "os";
const doc = new PDFDocument()
const pdfPath = path.join(tmpdir(), `${store.id}${moment().format('YYYYMMDD')}.pdf`)
const writeStream = doc.pipe(fs.createWriteStream(pdfPath)

reading a file works with @subwaymatch solution const logoPath = path.resolve('./public/logo.png')

[marklundin]

After some digging I got writing files working with the extended os package...

import { tmpdir } from "os";
const doc = new PDFDocument()
const pdfPath = path.join(tmpdir(), `${store.id}${moment().format('YYYYMMDD')}.pdf`)
const writeStream = doc.pipe(fs.createWriteStream(pdfPath)

reading a file works with @subwaymatch solution const logoPath = path.resolve('./public/logo.png')

Nice, are you able to read back the contents of this file? Is the directory accessible and permanent?

[Svish]

@marklundin With a function named tmpdir I doubt it's permanent, but if this works, then it would be good to know how temporary actually tmpdir is, yeah... 🤔

[wiesson]

Any updates on this? I'm wondering why it works in getInitialProps, but not in API routes 🤷‍♂️

My current workaround

const data = await import(`../../../../data/de/my-nice-file.json`);
res.json(data.default);

[mattvb91]

currently having this issue in API routes too

[BrunoBernardino]

currently having this issue in API routes too

There are a few working solutions here, what problem are you having, specifically?

[HDv2b]

I'm struggling to get this working even with suggestions from this thread. My use-case is I'm writing a guide and want to show the source-code for the component alongside the component itself. My method for doing this is using fs to load the component's jsx file inside getServerSideProps and passing the string value of the file contents as a prop.

I was feeling over the moon about having it working locally, but then when I went to deploy it, the joy has gone :(

Please see: https://github.com/ElGoorf/i18next-guide/blob/fix-example-components/pages/plurals.jsx

[BrunoBernardino]

@ElGoorf your problem is that the public files are on an edge, and the functions are on a lambda. Now, @vercel/next still doesn't allow for includeFiles, so the easiest way for you to get it working would be to use a lambda function with it.

Here's some sample code that helped others here: https://github.com/vercel/next.js/issues/8251#issuecomment-614220305

[HDv2b]

Thanks @BrunoBernardino I didn't realise I'd missed the "x hidden items load more..." and thought I was going crazy from the thread losing meaning!

Unfortunately, I struggled with your solution, as it's the first time I've heard of Edge/Lambda, however, I found @balthild's solution was closer to what I was originally after before trying the node.fs method: https://github.com/vercel/next.js/issues/8251#issuecomment-634829189

[BrunoBernardino]

Great! Did you get it working? Or are you still having issues?

I'm not sure Vercel even uses that terminology, but by Edge I mean CDN, where static files are served from, and by lambda I mean the "backend" functions that get called from the API routes, which are isolated like AWS Lambda functions.

[emomooney]

Hey,

Any update on writing to files using next.js on vercel? I can read no problem. Using the const logoPath = path.resolve('./public/logo.png')

I'm attempting to overwrite the public/sitemap.xml file (due to the size limits on vercel) I can only return it without error as a static file in the public folder. I have previously implemented the sitemap with zlib and streaming the response but it seems to wait until the stream is finished and then return it. This doesn't hit the size limitation error, but unfortunately it's very slow. I'm open to any suggestions people might have. The sitemap is built from an API call to a separate backend and needs to be updated regularly.

Things I have attempted :

• Zipping and streaming the xml - works but very slow.
• Building and returning sitemap from an api function, unfortunately this hits the size limit.
• Reading static xml file from public folder (works) regardless of size, but not updatable.
• Test writing to this file, doesn't work. Test writing to any file/folder doesnt work
• Test returning static xml file from "api" function, size error. This works locally.
• Test returning static xml file from "page" getServerSideProp size error. This works locally.
• Would appreciate any ideas at all?

[BrunoBernardino]

Hey @emomooney, I don't imagine Vercel ever allowing to write files in a function (even for caching), since the main "advantage" of serverless is its statelessness, and that would add state to it, so I think you'll need to use the edge/cdn for it.

I have previously implemented the sitemap with zlib and streaming the response but it seems to wait until the stream is finished and then return it.

I'm curious if you were just experiencing this slowness for subsequent calls, or just the first, for the cold start? I imagine this was an API call to Vercel via a next.js api function, or a dedicated lambda, similar to what I do here.

If it was and it was still too slow, is your "separate backend" outside of Vercel? If so, you can potentially use it to build a sitemap.xml file and vercel --prod it into a domain, basically "caching" the file to be readable and accessible, and you'd just need to update the robots.txt to link the sitemap to another domain/subdomain.

[PepijnSenders]

Also just ran into this issue, and this one becomes extra annoying when your next app is part of a monorepo setup, since ./ can mean very different things depending on the environment you're running the API handler in.

[remjx]

I'm trying to read a directory (pages directory) in an API route.

When I try @jkjustjoshing's workaround and do readdirSync(join(serverRuntimeConfig.PROJECT_ROOT, './pages')), I get this error in Vercel Functions realtime logs:

2020-12-23T16:05:16.924Z    9292cb9e-55fa-4f62-af7e-416dbd7b81cc    ERROR   Error: ENOENT: no such file or directory, scandir '/vercel/workpath0/pages'
    at readdirSync (fs.js:955:3)
    at Module.IPik (/var/task/.next/serverless/pages/api/testFunc.js:227:58)
    at __webpack_require__ (/var/task/.next/serverless/pages/api/testFunc.js:23:31)
    at module.exports.OjAL.__webpack_exports__.default (/var/task/.next/serverless/pages/api/testFunc.js:485:34) {
  errno: -2,
  syscall: 'scandir',
  code: 'ENOENT',
  path: '/vercel/workpath0/pages'
}
2020-12-23T16:05:16.925Z    9292cb9e-55fa-4f62-af7e-416dbd7b81cc    ERROR   Unhandled Promise Rejection     {"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"Error: ENOENT: no such file or directory, scandir '/vercel/workpath0/pages'","reason":{"errorType":"Error","errorMessage":"ENOENT: no such file or directory, scandir '/vercel/workpath0/pages'","code":"ENOENT","errno":-2,"syscall":"scandir","path":"/vercel/workpath0/pages","stack":["Error: ENOENT: no such file or directory, scandir '/vercel/workpath0/pages'","    at readdirSync (fs.js:955:3)","    at Module.IPik (/var/task/.next/serverless/pages/api/testFunc.js:227:58)","    at __webpack_require__ (/var/task/.next/serverless/pages/api/testFunc.js:23:31)","    at module.exports.OjAL.__webpack_exports__.default (/var/task/.next/serverless/pages/api/testFunc.js:485:34)"]},"promise":{},"stack":["Runtime.UnhandledPromiseRejection: Error: ENOENT: no such file or directory, scandir '/vercel/workpath0/pages'","    at process.<anonymous> (/var/runtime/index.js:35:15)","    at process.emit (events.js:326:22)","    at processPromiseRejections (internal/process/promises.js:209:33)","    at processTicksAndRejections (internal/process/task_queues.js:98:32)"]}
Unknown application error occurred

Which presumably doesn't work because those files aren't being copied into the serverless environment?

Is there a way to do this?

[BrunoBernardino]

@remjx it's not currently possible. What are you trying to do? Is it something you can do before deploying? Or can it be deployed as a separate @vercel/node function/build?

[remjx]

@BrunoBernardino I have something like this:

/pages/api/createUser.js
/pages/[userName].jsx
/pages/blog/...

I don't want a User to be able to be created with the name "blog" because it conflicts with an existing route. So I'd like to be able to read the pages directory so I can automatically add "blog" to the list of off-limits usernames.

Is it something you can do before deploying?

Good idea. I'm now generating a .json file in the /public folder during build but am still getting an ENOENT error when I try to read the file.

I don't understand what's going on in your workaround to read files. Is there documentation for these configuration options?

[borispoehland]

@BrunoBernardino I have something like this:

/pages/api/createUser.js
/pages/[userName].jsx
/pages/blog/...

I don't want a User to be able to be created with the name "blog" because it conflicts with an existing route. So I'd like to be able to read the pages directory so I can automatically add "blog" to the list of off-limits usernames.

Is it something you can do before deploying?

Good idea. I'm now generating a .json file in the /public folder during build but am still getting an ENOENT error when I try to read the file.

I don't understand what's going on in your workaround to read files. Is there documentation for these configuration options?

I know this isn't exactly what you'd like to achieve, but have you thought about prepending a "user" in front of the route? /pages/user/[userName].jsx That way, you don't have to worry about conflicting usernames, especially not when new pages are added in the future

Edit: I thought about it for a short time and I'm sure now that you have to prepend at least something to the route. Otherwise, let's assume that your project is successful and you have many users. In the future, you then want to add a new page: /pages/about.jsx. To prevent conflicts, that would mean that you possibly have to delete an existing user account of the user named "about". I don't think that you want this race condition to be possible to occur, so I think the smartest way is to prevent a conflict by prepending something in front of the slug.

[BrunoBernardino]

@remjx

Good idea. I'm now generating a .json file in the /public folder during build but am still getting an ENOENT error when I try to read the file.

Yes, public/* files are deployed to an edge/CDN, not available to the serverless function. You should be able to generate that .json file inside the pages directory and simply import it or require it (make sure your tsconfig.json supports it, maybe also jest if you're using it), and the file will be available.

I don't understand what's going on in your workaround to read files. Is there documentation for these configuration options?

Yes, but it's always changing and it's "deprecated" now: https://vercel.com/docs/configuration#project/builds

[remjx]

@BrunoBernardino moving the .json file to /pages and importing it works. Thank you!

[robertcoopercode]

Did anyone manage to be able to read from their filesystem in getServerSideProps? I tried @jkjustjoshing's suggestion, but it only works locally and not when deployed to Vercel.

Reproducible example: https://github.com/robertcoopercode/with-mdx-remote-app

Related GitHub discussion: https://github.com/vercel/next.js/discussions/22853

[BrunoBernardino]

@robertcoopercode Maybe this code example helps (it used to be d deployed to Vercel, though now it's not). I think you need __dirname or process.cwd()

[mmazzarolo]

Just noticed this thread and wanted to share a short note.

I've been able to read successfully files located in the public dir from serverless functions using fs.readFile/fs.readDir:

fs.readdirSync(path.resolve("./public", "company-logos"));

Today I noticed that enabling Webpack 5 breaks this behaviour (no clue why), causing the function to throw:

ERROR   Error: ENOENT: no such file or directory, scandir '/var/task/packages/website/public/company-logos'

[fernandoabolafio]

@robertcoopercode how did you manage to solve this issue? I am accessing the filesystem using getServerSideProps and process.cwd() which works fine locally but it is still failing on Vercel for me with the following error:

2021-04-28T07:38:22.294Z    060b539a-3bb0-4c61-b009-4870d16fbce4    ERROR   Unhandled error during request: Error: ENOENT: no such file or directory, open '/var/task/content/page.md'
    at Object.openSync (fs.js:476:3)
    at Object.readFileSync (fs.js:377:35)

[BrunoBernardino]

@fernandoabolafio my code example from above worked in Vercel up until very recently (I'm no longer deploying to it, but you should be able to clone and deploy to test). If that no longer works, maybe they changed something.

[fernandoabolafio]

@BrunoBernardino thanks for your answer. I just found this: https://vercel.com/support/articles/how-can-i-use-files-in-serverless-functions. It is an official note from Vercel saying that accessing the filesystem from pages SSR isn't working. It is actually pointing to this thread as a reference.