Function Config Warning Once

Context

Use this pattern when a Function depends on optional configuration to build links or other operator-visible output, but can still proceed in a degraded mode.

Patterns

• Read and normalize the configuration value once at function entry, not inside each item-processing loop.
• Treat null, empty, and whitespace-only values as missing configuration.
• Emit a single warning for the run so operators can spot misconfiguration without noisy repeated log entries.
• Return a stable fallback value (for example, an empty base URL that yields a relative path) and pass it into downstream methods.

Examples

• src\JosephGuadagno.Broadcasting.Functions\LinkedIn\NotifyExpiringTokens.cs
  • GetWebBaseUrl() trims the configured URL, warns once when missing, and returns string.Empty
  • RunAsync() resolves the value once and passes it into both notification windows
• PR #910 applies the pattern without changing the existing relative-link fallback behavior
• src\JosephGuadagno.Broadcasting.Functions.Tests\LinkedIn\NotifyExpiringTokensTests.cs
  • RunAsync_WhenWebBaseUrlIsMissingOrEmpty_LogsWarningAndUsesRelativeLink(...) proves the warning is emitted for null/empty/whitespace settings while preserving the relative-link fallback

Anti-Patterns

• Looking up the same config setting inside every per-user send path
• Logging one warning per token or email when the root cause is a single missing app setting
• Silently falling back to relative links with no operator-visible warning