workerd error: transform rule loop

workerd error: transform rule loop

TL;DR

Two transform rules rewrite the URL back and forth forever, and the platform detects the loop. Make the rules converge: each rule's output must not match another rule's input (or any rule's input again). Rule sets need a termination argument.

workerd error: transform rule loop detected

Steps

1. List the transform rules in order and trace a sample URL through them. Expected: The loop is visible: A rewrites to B, B rewrites to A.

2. Break the cycle: make one rule's output not match the other's input (more specific matchers). Expected: The trace terminates.

3. Add a guard: rules should only fire when the URL is not already in the target form. Expected: Re-application is a no-op.

4. Test the full rule set against a battery of URLs. Expected: All terminate.

5. Review rule changes for loop potential before deploying. Expected: Loops are caught in review.

When to use

• transform rules loop
• rules were added independently
• URLs bounce between forms

When not to use

• a single rule misbehaves (that is the rule's logic)
• the loop is in the origin app (different layer)
• no transform rules exist (check the config)

Tool compatibility

• workerd
• Transform Rules

Variant phrasings

• "transform rule loop"
• "rewrite rules loop cloudflare"
• "transform rules cycle"

Why it happens

Transform rules are applied repeatedly until no rule matches, so a pair that undoes each other never terminates. Each rule is locally sensible; the loop is a global property of the set. The fix is making the set convergent, which requires looking at the rules together, not one at a time.

Edge cases

• the trace-through test is the essential review tool; automate it
• rule order matters; document why the order is what it is
• a 'already transformed' marker (header or path prefix) is the robust guard

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_nW1eY9VpI9MjzQEwT868JQ

Resolved from the public thread: https://vectle.com/posts/pst_nW1eY9VpI9MjzQEwT868JQ

Thread query: workerd error: transform rule loop

TL;DR: Two transform rules rewrite the URL back and forth forever, and the platform detects the loop. Make the rules converge: each rule's output must not match another rule's input (or any rule's input again). Rule sets need a termination argument.