Duplicate Code Detected: sendPending batch swap/checkpoint loop in Routerlicious lambdas

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🔍 Duplicate Code Detected: sendPending batch swap/checkpoint loop in Routerlicious lambdas

Analysis of commit 19a716b

Assignee: @copilot

Summary

Multiple Routerlicious lambdas implement near-identical sendPending() logic: early return when work-in-progress or nothing pending, swap current/pending buffers, process all batches via Promise.all(...), checkpoint the batch offset, then recursively call sendPending(); errors trigger context.error(..., { restart: true }).

This is a classic copy/paste maintenance hotspot: small behavioral fixes (checkpoint conditions, retry/backoff, shutdown semantics, metric timing) must be duplicated across lambdas.

Duplication Details

Pattern: Pending-batch drain loop with buffer swap + Promise.all + checkpoint + recurse

• Severity: Medium

• Occurrences: 3 similar implementations

• Locations:

  • server/routerlicious/packages/lambdas/src/moira/lambda.ts (lines 73–102)
  • server/routerlicious/packages/lambdas/src/copier/lambda.ts (lines 71–100)
  • server/routerlicious/packages/lambdas/src/scriptorium/lambda.ts (lines 217–330) — extended with telemetry, batching caps, and circuit-breaker pausing, but retains the same core structure

• Code Sample (common structure, simplified):

  private sendPending(): void {
    // If there is work currently being sent or we have no pending work return early
    if (this.current.size > 0 || this.pending.size === 0) {
      return;
    }
  
    // Swap current and pending
    const temp = this.current;
    this.current = this.pending;
    this.pending = temp;
    const batchOffset = this.pendingOffset;
  
    const allProcessed: Promise(void)[] = [];
    for (const [, messages] of this.current) {
      allProcessed.push(this.processX(messages));
    }
  
    Promise.all(allProcessed)
      .then(() => {
        this.current.clear();
        this.context.checkpoint(batchOffset as IQueuedMessage);
        this.sendPending();
      })
      .catch((error) => {
        this.context.error(error, { restart: true });
      });
  }

Impact Analysis

• Maintainability: Changes to batching strategy, checkpoint timing, shutdown behavior, and error/retry policy likely need to be applied consistently across lambdas, but are currently spread across multiple implementations.
• Bug Risk: Divergence risk is high—future fixes may be applied to one lambda but missed in others, leading to inconsistent restart/checkpoint semantics.
• Code Bloat: The pattern is relatively verbose and repeated; extracting the shared skeleton would reduce repeated control-flow boilerplate.

Refactoring Recommendations

1. Extract a shared “pending batch drain” helper

   • Extract common control-flow into a utility, e.g. server/routerlicious/packages/lambdas/src/utils/pendingBatchDrain.ts.
   • Make it generic over:
     • data structure (Map(K, V) batches vs other queues)
     • processing function (sync/async)
     • checkpoint behavior (when/how to checkpoint)
     • error handling (restart vs pause)
   • Estimated effort: Medium (2–6 hours), depending on desired generality.
   • Benefits: centralized correctness + easier consistent instrumentation.

2. Unify checkpoint + recursion semantics

   • Consider a single implementation that can optionally:
     • checkpoint only on success
     • checkpoint when pending becomes empty
     • schedule the next drain (immediate recursion vs setImmediate/task scheduling)
   • Estimated effort: Medium.

Implementation Checklist

• Review duplication findings
• Prioritize refactoring tasks
• Create refactoring plan
• Implement changes
• Update tests
• Verify no functionality broken

Analysis Metadata

• Analyzed Files: 15 top-churn TS files + Routerlicious lambdas cross-check
• Detection Method: Serena semantic code analysis (symbol-level extraction + cross-file comparison)
• Commit: 19a716b
• Analysis Date: 2026-04-04T21:46:46.663Z

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