Currency Service Zero Amount Conversion Bug

[osw282]

Issue Diagnosis

After analyzing the logs from the currencyservice pod and examining the source code in src/currencyservice/server.js, I've identified a potential issue with the currency conversion logic.

Problem Description

The currency service contains logic that checks for zero-amount conversions and attempts to "switch back" to the original currency when this occurs. However, this approach has several problems:

1. Silent Failure: The logs show only successful conversion messages, but the code contains error handling for zero-amount conversions that may be triggering silently
2. Circular Logic: When a conversion results in zero, the service switches back to the original currency, which defeats the purpose of currency conversion
3. Lack of Error Visibility: The error condition is logged but may not be properly surfacing to calling services

Code Analysis

In the convert function (lines ~168-195), there's logic that:

• Checks if conversion result is zero: if (result.units === 0 && result.nanos === 0)
• Logs an error and sends a Slack notification
• Reverts to the original currency instead of failing the request

Recommended Fix

1. Remove the automatic fallback logic: Instead of silently switching back to the original currency, the service should return an error when conversion results in zero
2. Improve error handling: Return a proper gRPC error with details about why the conversion failed
3. Add proper validation: Validate input currencies and amounts before attempting conversion

Proposed Code Changes:

// Replace the current zero-check logic with proper error handling
if (result.units === 0 && result.nanos === 0) {
  const errorMsg = `Currency conversion from ${request.from.currency_code} to ${request.to_code} resulted in zero amount`;
  logger.error(errorMsg);
  notifySlack();
  
  // Return proper gRPC error instead of silently switching back
  const error = new Error(errorMsg);
  error.code = grpc.status.INVALID_ARGUMENT;
  callback(error);
  return;
}

Impact

This fix will:

• Provide clear error messages when conversions fail
• Prevent silent failures that could lead to incorrect pricing
• Improve debugging and monitoring capabilities
• Maintain data integrity by not silently changing currencies

Testing Recommendations

• Test with very small amounts that might round to zero
• Test with unsupported currency codes
• Verify error propagation to calling services
• Test the Slack notification functionality