Error Logging with errno¶

Classification: Pattern

Context: Error handling and logging throughout the codebase, specifically when reporting system errors (where errno is set).

Why it matters: Using LogError(errno, ...) ensures that system error messages are formatted correctly and consistently. It avoids the pitfalls of manual string formatting with strerror or rs_strerror_r, such as buffer management issues or thread-safety concerns (though rs_strerror_r handles the latter). It also simplifies the code by removing the need for temporary error string buffers.

Steps:

Capture errno immediately: Ensure errno is captured or used immediately after the failing system call, before any other function call that might reset it.
Use LogError with errno: Pass the captured errno (or errno directly if safe) as the first argument to LogError.
Do not format manually: Do not use strerror, gai_strerror (unless specifically for getaddrinfo return codes), or rs_strerror_r to manually format the error string into the message. Let LogError handle it.

Example:

/* Bad: Manual formatting */
if (connect(...) < 0) {
    char errStr[1024];
    rs_strerror_r(errno, errStr, sizeof(errStr));
    LogError(0, RS_RET_SUSPENDED, "Connect failed: %s", errStr);
}

/* Good: Using LogError with errno */
if (connect(...) < 0) {
    LogError(errno, RS_RET_SUSPENDED, "Connect failed");
}

Antipattern: Passing 0 as the first argument to LogError when a system error has occurred is a common antipattern. This forces the developer to manually handle the error string, leading to more verbose and potentially error-prone code.

Support: rsyslog Assistant | GitHub Discussions | GitHub Issues: rsyslog source project

Contributing: Source & docs: rsyslog source project