fix(runtime): avoid infinite recursion in fetch for external URLs

[vamsi2246]

Description

The exported fetch function in src/runtime/internal/app.ts shadows the global fetch, causing it to recursively call itself when handling non-root-relative URLs (e.g., full URL strings, URL objects, or Request objects for external endpoints). This results in a RangeError: Maximum call stack size exceeded.

Root Cause

In the fetch() function, the fallback branch for external URLs calls fetch(resource, init) — which resolves to the local function itself rather than the native globalThis.fetch:

// Before (broken)
return fetch(resource, init);

Fix

Explicitly use globalThis.fetch to delegate external requests to the runtime's native fetch implementation:

// After (fixed)
return globalThis.fetch(resource, init);

Changes

• src/runtime/internal/app.ts: Changed fetch(resource, init) → globalThis.fetch(resource, init) on the external URL fallback path.
• test/fixture/server/routes/fetch.ts: Added a regression test case using a URL object to verify external fetch does not recurse.

How to reproduce

Call fetch(new URL('https://example.com')) or fetch('https://example.com') from any Nitro route handler — it crashes with a stack overflow.

Linked Issues

N/A (discovered during code review)

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[coderabbitai]

📝 Walkthrough

Walkthrough

The fetch function in the runtime now delegates to the global fetch implementation instead of recursively calling itself, preventing re-entry loops. A new test case verifies fetch functionality with URL objects.

Changes

Cohort / File(s)	Summary
Runtime fetch implementation src/runtime/internal/app.ts	Modified the recursive fetch call to use globalThis.fetch instead of the module's fetch function, preventing re-entry into the module's fetch handler.
Test fixtures test/fixture/server/routes/fetch.ts	Added a new test case "nitro/runtime.fetch.url" that invokes runtimeFetch with a URL object instead of a string path to verify proper handling.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• serverFetch causes infinite loop (Maximum call stack size exceeded) when route doesn't exist #3916: The primary change directly addresses the infinite recursion issue by replacing the recursive module fetch call with the global fetch implementation, preventing re-entry loops in the fetch handler.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title 'fix(runtime): avoid infinite recursion in fetch for external URLs' follows conventional commits with a 'fix' type, scope 'runtime', and clearly describes the main change.
Description check	✅ Passed	The PR description is comprehensive and directly addresses the changeset, explaining the root cause, the fix applied, and test coverage added.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[pi0]

thnx!

[coderabbitai]

🧹 Nitpick comments (1)

test/fixture/server/routes/fetch.ts (1)

13-15: Add an absolute-string URL regression case to match the reported repro.

Nice coverage for URL objects; consider adding a "http://localhost/..." string case too, since that was also part of the stack-overflow repro path.

Suggested diff

     "nitro/runtime.fetch.url": await runtimeFetch(new URL("http://localhost/api/hello")).then(
       (res) => res.json()
     ),
+    "nitro/runtime.fetch.absoluteString": await runtimeFetch("http://localhost/api/hello").then(
+      (res) => res.json()
+    ),

As per coding guidelines: test/**/*.{ts,js}: Keep tests deterministic and environment-independent.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@test/fixture/server/routes/fetch.ts` around lines 13 - 15, Add a
deterministic regression test using an absolute-string URL alongside the
existing URL object case: update the test to call runtimeFetch with the string
"http://localhost/api/hello" (e.g., add another map entry similar to
"nitro/runtime.fetch.url" but for the string case) and await its .then(res =>
res.json()) so the suite covers both new URL(...) and plain
"http://localhost/..." call paths; locate the call to runtimeFetch in the test
(the existing "nitro/runtime.fetch.url" entry) and add the analogous
string-based entry there.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@test/fixture/server/routes/fetch.ts`:
- Around line 13-15: Add a deterministic regression test using an
absolute-string URL alongside the existing URL object case: update the test to
call runtimeFetch with the string "http://localhost/api/hello" (e.g., add
another map entry similar to "nitro/runtime.fetch.url" but for the string case)
and await its .then(res => res.json()) so the suite covers both new URL(...) and
plain "http://localhost/..." call paths; locate the call to runtimeFetch in the
test (the existing "nitro/runtime.fetch.url" entry) and add the analogous
string-based entry there.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a877b280-87bb-4694-b1d5-2fc95e419451

📥 Commits

Reviewing files that changed from the base of the PR and between 75cc89d and 5efefb6.

📒 Files selected for processing (2)

• src/runtime/internal/app.ts
• test/fixture/server/routes/fetch.ts

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