Error Handling Patterns

Development

Express middleware and async error handling for video rendering operations. Use this when implementing try-catch blocks in server routes, defining custom error classes, handling S3 upload failures, or managing Remotion rendering errors. Emphasizes cleanup and structured error responses.

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Error Handling Patterns

This Skill provides Claude Code with specific guidance on how it should handle global error handling.

When to use this skill:

Implementing error handling in Express route handlers
Creating custom error classes (RenderError, ValidationError)
Handling Remotion bundling or rendering failures
Managing S3 upload errors with retry logic
Implementing resource cleanup in finally blocks
Defining JSON error response formats

Instructions

Express Error Middleware: Use centralized error handling middleware in Express for consistent error responses
API Error Format: Return JSON errors with structure: { error: string, details?: any }
Fail Fast and Explicitly: Validate input early; fail with clear error messages rather than allowing invalid state
TypeScript Error Types: Define custom error classes for domain-specific errors (RenderError, ValidationError)
Remotion Error Handling: Wrap Remotion bundling/rendering in try-catch; report specific failure stages
S3 Upload Retry: Implement retry logic for S3 uploads with exponential backoff
Clean Up Resources: Always clean up temporary files and video outputs in finally blocks
SSE Error Streaming: Send error events via SSE when streaming render progress

Examples:

// Good: Specific error, cleanup, structured response
import { S3Client } from '@aws-sdk/client-s3';

class RenderError extends Error {
  constructor(stage: string, cause: Error) {
    super(`Render failed at ${stage}: ${cause.message}`);
    this.name = 'RenderError';
  }
}

app.post('/render', async (req, res) => {
  let tempFile: string | null = null;
  try {
    const { month, year } = req.body;
    if (!month || !year) {
      return res.status(400).json({ error: 'Missing required fields' });
    }

    tempFile = await renderVideo({ month, year });
    const s3Url = await uploadToS3(tempFile);
    res.json({ url: s3Url });
  } catch (error) {
    if (error instanceof RenderError) {
      return res.status(500).json({ error: error.message });
    }
    res.status(500).json({ error: 'Render failed', details: error.message });
  } finally {
    if (tempFile) fs.unlinkSync(tempFile);
  }
});

// Bad: Generic errors, no cleanup, vague messages
app.post('/render', async (req, res) => {
  try {
    const result = await renderVideo(req.body);
    res.json(result);
  } catch (e) {
    res.status(500).json({ error: 'Error' });
  }
});