Defensive Coding and Assertions¶

Classification: Pattern

Context: Handling “impossible” states or logic paths that should theoretically never be reached.

Why it matters: Rsyslog prioritizes production stability. We use Static Analysis (SA) and CI to detect bugs. assert() tells analyzers/AI that a state is invalid. Defensive checks protect production from crashes if the “impossible” happens.

Steps:

Mandatory Assertion: Always use assert() to define the invariant. This informs SA tools and AI assistants that this state is invalid.
Optional Defensive Fallback: Follow the assert with an if check to handle the failure gracefully. This is recommended but optional if the fallback handler would be excessively complex or introduce more risk than it solves.
No UB: Never use __builtin_unreachable().
Order: Place the assert() before the defensive check.

Example:

/* 1. Inform SA/AI */
assert(pPtr != NULL);

/* 2. Defensive check (optional if complex) */
if (pPtr == NULL) {
    LogMsg(0, NO_ERRCODE, LOG_ERR, "logic error: pPtr is NULL");
    return;
}

/* 3. Logic */
do_something(pPtr);

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