Error when trying to load Fedify 2.0 from a Fresh 2.0 app

[jfietkau]

Summary

I am attempting to upgrade my Fedify application from Fedify 1.x and Fresh 1.x to version 2.0 of both frameworks. I am running into fatal errors seemingly related to the multicodec module that prevent the pages from rendering as soon as I invoke Fedify.

Note that this is not about the middleware integration, which I have not yet attempted. This is just about running Fresh 2.0 and Fedify 2.0 within the same codebase.

This bug report comes with a big caveat: I have not yet tested Fedify 2.0 without Fresh 2.0, and as a result I am not sure if Fresh 2.0 is indeed a necessary component to trigger this error. My assumption is that there must be something about my project environment that triggers it for me but not others, and Fresh 2.0 seems like the most obvious candidate.

Expected Behavior

Fedify 2.0 should not prevent Fresh 2.0 apps from functioning.

Actual Behavior

Running Fedify 2.0 in a Fresh 2.0 application causes a fatal error.

Environment

• Deno 2.7.5
• Fedify 2.0.5
• Fresh 2.2.0 (using vite 7.3.1)

Running on Linux

Logs / Screenshots

GET http://localhost:5174/
TypeError: varint.encode is not a function
    at varintEncode (./node_modules/.deno/multicodec@3.2.1/node_modules/multicodec/src/util.js:40:1)
    at ./node_modules/.deno/multicodec@3.2.1/node_modules/multicodec/src/maps.js:20:29
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (./node_modules/.deno/multicodec@3.2.1/node_modules/multicodec/src/index.js:15:1)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/vocab-runtime/2.0.5/src/key.ts:13:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/vocab-runtime/2.0.5/src/mod.ts:27:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/webfinger/2.0.5/src/lookup.ts:4:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/webfinger/2.0.5/src/mod.ts:5:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/vocab/2.0.5/src/actor.ts:8:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/vocab/2.0.5/src/mod.ts:4:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/fedify/2.0.5/src/federation/builder.ts:5:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
    at async SSRCompatModuleRunner.cachedRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1053:73)
    at async eval (deno::0::https://jsr.io/@fedify/fedify/2.0.5/src/federation/mod.ts:9:31)
    at async ESModulesEvaluator.runInlinedModule (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:913:3)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/module-runner.js:1146:59)
    at async SSRCompatModuleRunner.directRequest (./node_modules/.deno/vite@7.3.1/node_modules/vite/dist/node/chunks/config.js:15111:22)
error: Uncaught NotFound: No such file or directory (os error 2) about ["./routes/.goutputstream-RZE2L3"]
    at new FsWatcher (ext:runtime/40_fs_events.js:23:17)
    at Object.watchFs (ext:runtime/40_fs_events.js:73:10)
    at ext:deno_node/_fs/_fs_watch.ts:57:21
    at callback (ext:deno_web/02_timers.js:42:7)

Note: I have replaced my full project path with "." in the above logs.

Steps to Reproduce

1. Create a Fresh 2.0 demo project: deno run -Ar jsr:@fresh/init
2. Navigate into the project directory and add Fedify: deno add jsr:@fedify/fedify
3. Edit routes/index.tsx:
   1. Add import { createFederation } from "@fedify/fedify"; near the top of the file
   2. Somewhere within Home, for example after the console output, add createFederation<null>();
4. Run deno task dev
5. Open the website in the browser and observe the error messages

[dahlia]

Root cause

I was able to reproduce the failure, and this does not appear to be a Fresh-specific logic bug inside Fedify itself. The failure is caused by a dependency boundary that Fresh 2's Vite SSR loader exposes.

@fedify/fedify pulls in @fedify/vocab-runtime, and @fedify/vocab-runtime/src/key.ts imports multicodec. That package (multicodec@3.2.1) is CommonJS-only and internally uses require("varint"). Under Fresh 2's Vite SSR module runner, that CommonJS chain is evaluated in a way that does not preserve the expected shape of the varint export, so multicodec ends up calling varint.encode(...) on something that is not the original CommonJS object.

That is why the crash happens during module evaluation, before any real federation behavior runs. In practice, importing @fedify/fedify in this environment is enough to hit the problem because the module graph reaches @fedify/vocab-runtime/src/key.ts while being loaded.

Why this should be fixed in Fedify

Even if the triggering environment is Fresh 2 + Vite SSR, the problematic part of the stack is our dependency choice: @fedify/vocab-runtime currently depends on multicodec, which is a deprecated CommonJS package. That makes Fedify fragile in SSR and bundler environments that expect clean ESM interop.

So Fresh is the environment that reveals the bug, but the part we control is the multicodec dependency in Fedify.

Proposed action plan

1. Remove the multicodec dependency from @fedify/vocab-runtime.
2. Replace the current usage in src/key.ts with a small internal ESM-safe implementation for the three operations we actually need:
   • read the multicodec varint prefix from a byte array
   • strip that prefix from the payload
   • prepend a varint-encoded prefix when exporting
3. Add a regression test that exercises this code path in a Vite/Fresh-like SSR context, or at minimum a focused test that ensures the replacement logic no longer depends on multicodec.
4. Keep the current public behavior unchanged for supported key types (rsa-pub and ed25519-pub).
5. Optionally document a temporary workaround until a fixed Fedify release is available.

Temporary workaround

Fedify's own Fresh example currently marks @fedify/fedify as external in vite.config.ts, which avoids this exact failure mode there. That may help some users as a temporary workaround, but I do not think it is the right long-term fix. The robust fix is to stop depending on multicodec in this path.

Scope of the change

The code change should be small and localized. As far as I can tell, the only place that actually needs multicodec is @fedify/vocab-runtime/src/key.ts, where we currently use:

• getCodeFromData(...)
• rmPrefix(...)
• addPrefix(...)

Those can be replaced with internal helpers without changing the public API.

Conclusion

I think this issue is valid and should be fixed on the Fedify side. The underlying problem is the CommonJS-only multicodec dependency in @fedify/vocab-runtime, which breaks under Fresh 2's Vite SSR loader. The recommended fix is to remove that dependency and replace the small amount of functionality we need with an internal ESM-safe implementation.

[jfietkau]

I'm taking away two comforting truths from this:

1. The issue wasn't somehow my fault. 😌
2. At least one of my experiments with SSR exclusion during debugging should have worked.

Thank you for working on fixing this going forward!

However, I would like to get the workaround going in the meantime so that I can continue my version migration. I'm finding preciously few guides online for this part of the vite config, could you tell me how you set it up to get Fedify to run? My current vite.config.js looks like this:

import { defineConfig } from "vite";
import { fresh } from "@fresh/plugin-vite";

export default defineConfig({
  plugins: [
    fresh(),
  ],
  ssr: {
    external: true,
  },
});

According to the vite documentation, external: true should externalize everything, but if I do this, I get the same error about varint.encode. If I just put external: ['@fedify/fedify'], I get an error message saying Internal server error: Cannot find module '@fedify/fedify' imported from './encyclia.ts'. What does a working config look like?