Create fresh response object in default Fastify handler

[moreal]

Summary

This pull request just let @fedify/fastify create a fresh Response object by default not acceptable handler.

When running the examples/fastify project and executing the following curl command twice:

fastify % curl http://localhost:3000/users/someone
Not Acceptable
fastify % curl http://localhost:3000/users/someone
{"statusCode":500,"code":"FST_ERR_REP_RESPONSE_BODY_CONSUMED","error":"Internal Server Error","message":"Response.body is already consumed."}

It returns 500 error because the response stream is already consumed. You can re-check it by running the regression test (in index.test.ts file)

This pull request just make it return a new Response object for each request.

Related issue

There is no related issue.

Changes

List the specific modifications made in this PR.
Focus on what was changed without going into detail about impact.

• Let default onNotAcceptable handler to create a new Response object.
• Added a regression test about the above situation.

Benefits

It will make server applications using @fedify/fastify without their onNotAcceptable handler return a valid 406 response (Not Acceptable).

Checklist

• Did you add a changelog entry to the CHANGES.md?
• Did you write some relevant docs about this change (if it's a new feature)?
• Did you write a regression test to reproduce the bug (if it's a bug fix)?
• Did you write some tests for this change (if it's a new feature)?
• Did you run mise test on your machine?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Files with missing lines	Coverage Δ
packages/fastify/src/index.ts	82.25% <100.00%> (+0.29%)	⬆️

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug in the @fedify/fastify package where the default onNotAcceptable handler would return a 500 Internal Server Error on subsequent requests after the initial 406 "Not Acceptable" response. This occurred because the Response object's body was being consumed and the same object was reused. The change ensures that a new Response object is generated for every "Not Acceptable" scenario, guaranteeing consistent and correct 406 responses for applications using this plugin.

Highlights

• Fix for onNotAcceptable handler: The default onNotAcceptable handler in @fedify/fastify now creates a fresh Response object for each request, resolving an issue where reusing a shared instance led to Response.body is already consumed errors.
• Regression Test Added: A new test case was introduced to specifically reproduce and verify the fix, ensuring the correct behavior of the 406 "Not Acceptable" response on repeated requests.

Changelog

• CHANGES.md
  • Added an entry documenting the fix for the onNotAcceptable handler in @fedify/fastify.
• packages/fastify/src/index.test.ts
  • Added a test case to verify that the onNotAcceptable handler correctly creates a fresh 406 response for each request.
• packages/fastify/src/index.ts
  • Modified the onNotAcceptable handler to call a function that dynamically creates a new Response object instead of referencing a static, pre-instantiated one.

Activity

• The author moreal initiated this pull request to resolve a bug in the @fedify/fastify package.
• The pull request includes a detailed summary, a description of changes, and the benefits of the fix.
• A changelog entry has been added, and a regression test was written to validate the fix.
• The author has confirmed running mise test.

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[gemini-code-assist]

Code Review

This pull request fixes a bug in the @fedify/fastify package where a shared Response object for 406 Not Acceptable errors was causing a 'body already consumed' error on subsequent requests. The fix refactors the default onNotAcceptable handler to create a new Response object for each request. A regression test is included to cover this scenario, and the changelog has been updated to reflect the change. The implementation correctly resolves the issue.

[dahlia]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

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[Copilot]

Pull request overview

Fixes a Fastify integration bug where the default onNotAcceptable handler reused a single Response instance, causing subsequent requests to fail due to a consumed response body stream.

Changes:

• Replaced the shared default 406 Response with a factory function to create a fresh Response per request.
• Added a regression test that reproduces the “Response.body is already consumed” failure across multiple requests.
• Added a changelog entry under the upcoming release.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/fastify/src/index.ts	Switches default onNotAcceptable from a singleton Response to a per-request factory.
packages/fastify/src/index.test.ts	Adds regression coverage ensuring repeated Not Acceptable requests return 406 consistently.
CHANGES.md	Documents the fix for @fedify/fastify in v2.0.4 notes.

[dahlia]

Thanks!