Error Handling

1. Overview

Error handling is implemented using native Unlang constraints to ensure:

  • Invalid requests are safely ignored

  • Malformed sessions are dropped early

  • System stability is maintained without crashes

  • Processing remains lightweight and predictable

All error handling is designed to be silent to avoid unnecessary system overhead.

2. Handling Strategies

2.1. Missing Variables

  • Uses safe fallback expansion:

    %{%{Huawei-Service-Info}:-0}

  • Prevents null or undefined attribute failures

  • Ensures default values are applied dynamically

  • Avoids breaking policy execution

Always define fallback values for optional attributes.

2.2. Regex Boundaries

  • Input strings are validated using strict regex patterns

  • Malformed or unexpected values are automatically rejected

  • Prevents incorrect parsing and downstream failures

  • Ensures only valid formats are processed

Invalid regex matches result in immediate request drop.

2.3. Double Deductions Prevention

  • Checks applied before quota or usage updates

  • Prevents duplicate accounting or billing calculations

  • Ensures idempotent processing of accounting packets

  • Maintains consistency across Start / Alive / Stop flows

3. Error Handling Flow

on request:

    if missing required attribute:
        apply default or skip safely

    else if regex validation fails:
        drop request

    else if duplicate accounting detected:
        ignore update

    else:
        process normally

4. Key Benefits

  • Robust handling of malformed inputs

  • Prevents system crashes and inconsistencies

  • Ensures predictable and stable execution

  • Supports high-volume environments efficiently