[BUG] Unable to resolve packages with workerd specific entrypoint like xxhash

[timReynolds]

Describe the bug

I was attempting to run mastra within next.js on cloudflare using OpenNext and hit an issue with module resolution for xxhash which provides a conditional import for workerd to support workers. From the error I'm getting it seems to stuggle to create the server bundle due to the wasm/workerd setup within xxhash.

I'm not sure if this is specific to that package or all packages that have added a workerd conditional import, in this case the workerd specific entrypoint is there to allow for wasm to be imported.

I've recreated the setup using the default templates from both, it can be found here.

Would be good if someone outlined if this was expected to work or fell outside the supported path for opennext/cloudflare.

partial error, full error found in repo readme;

Applying code patches: 1.921s
# copyPackageTemplateFiles
⚙️ Bundling the OpenNext server...

✘ [ERROR] Could not resolve "xxhash-wasm"

    .open-next/server-functions/default/node_modules/@mastra/memory/dist/index.js:6:19:
      6 │ import xxhash from 'xxhash-wasm';
        ╵                    ~~~~~~~~~~~~~

  The module "./workerd/xxhash-wasm.js" was not found on the file system:

    .open-next/server-functions/default/node_modules/xxhash-wasm/package.json:10:15:
      10 │     "workerd": "./workerd/xxhash-wasm.js",
         ╵                ~~~~~~~~~~~~~~~~~~~~~~~~~~

  You can mark the path "xxhash-wasm" as external to exclude it from the bundle, which will remove
  this error and leave the unresolved path in the bundle.

✘ [ERROR] Could not resolve "cloudflare/_shims/auto/runtime"

    .open-next/server-functions/default/node_modules/cloudflare/_shims/index.mjs:5:22:
      5 │ import * as auto from 'cloudflare/_shims/auto/runtime';
        ╵                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Steps to reproduce

You can easily create this by setting up mastra on the default template like so https://github.com/timReynolds/my-cf-mastra-next-app

Expected behavior

This runs and deploys as expected

@opennextjs/cloudflare version

latest

Wrangler version

latest

next info output

see example

Additional context

No response

[sommeeeer]

Did you try adding xxhash-wasm to serverExternalPackages?

[timReynolds]

Just tried it in the example repo, it will remove the error about xxhash-wasm but then you hit the same issue but with the cloudflare shim.

You can see the change in timReynolds/my-cf-mastra-next-app#1

Maybe I miss understood how this should be excluded, I did originally follow the docs that says just set @mastra/* as excluded but clearly that isn't enough here.

# copyPackageTemplateFiles
⚙️ Bundling the OpenNext server...

✘ [ERROR] Could not resolve "cloudflare/_shims/auto/runtime"

    .open-next/server-functions/default/node_modules/cloudflare/_shims/index.mjs:5:22:
      5 │ import * as auto from 'cloudflare/_shims/auto/runtime';
        ╵                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  The module "./_shims/auto/runtime.mjs" was not found on the file system:

    .open-next/server-functions/default/node_modules/cloudflare/package.json:70:19:
      70 │         "default": "./_shims/auto/*.mjs"
         ╵                    ~~~~~~~~~~~~~~~~~~~~~

  You can mark the path "cloudflare/_shims/auto/runtime" as external to exclude it from the bundle,
  which will remove this error and leave the unresolved path in the bundle.

/Users/tim/Code/github.com/timreynolds/my-cf-mastra-next-app/node_modules/esbuild/lib/main.js:1463
  let error = new Error(text);
              ^

Error: Build failed with 1 error:

[sommeeeer]

pnpm add cloudflare zod@3 @mastra/cloudflare-d1@latest @mastra/core@latest @mastra/loggers@latest @mastra/memory@latest 

const nextConfig: NextConfig = {
  serverExternalPackages: ["@mastra/*", "xxhash-wasm", "cloudflare"],
};

Then we need to figure out to how to solve that error you just pasted. I found this #603 (comment), but it doesn't seem related since that error was happening in next build. Your error happens during the bundling of OpenNext.

[timReynolds]

I tried a few variations with the example repository, once all the dependencies are updated to the latest version and you add mastra/core to the serverExternalPackages list then this will deploy and work as expected.

I've only tried it with the example app per their documentation which runs on the route /test in that repository which has been updated.

I'll try something more complex shortly to see if this resolves running mastra on cloudflare hosted in next.js

[sommeeeer]

What if you don't have anything in serverExternalPackages btw?

[timReynolds]

From trying this very quickly seems to work, I took the original setup from the docs ( https://mastra.ai/en/docs/frameworks/web-frameworks/next-js#configure-nextjs) which on first pass seem to make sense

…

On Wed, 6 Aug 2025 at 11:29, Magnus ***@***.***> wrote: *sommeeeer* left a comment (opennextjs/opennextjs-cloudflare#845) <#845 (comment)> What if you don't have anything in serverExternalPackages btw? — Reply to this email directly, view it on GitHub <#845 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABJHJVZQDNZ453FY4ZWTFD3MHKJPAVCNFSM6AAAAACDEBXQMWVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTCNJZGMYDSMJVHE> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[conico974]

I'm going to close this one, as the issue is solved.
Feel free to create a PR in the docs to add some info there for mastra https://github.com/opennextjs/docs

[timReynolds]

Sounds good, I've tired a few more examples and this works as you'd expect.