[Bug]: /api/v1/alarm_log always empty - boolean vs rc logic inversion in PREPARE_STATEMENT caller #23364

Bug description

The /api/v1/alarm_log endpoint always returns an empty response (HTTP 200, 0 bytes) on any recent Netdata version. The log shows:

Failed to prepare statement SQL_SELECT_HEALTH_LOG

This happens with:

• netdata/netdata:stable v2.10.4 (SQLite embedded 3.50.4)
• netdata/netdata:latest v2.10.0-980-nightly (SQLite embedded 3.53.3)
• On a fresh regenerated netdata-meta.db created by each binary
• ARM64 (Oracle Cloud Ampere A1)

Root cause analysis

The bug is a boolean vs rc logic inversion between the PREPARE_STATEMENT macro and its caller sql_health_alarm_log2json:

1. PREPARE_STATEMENT (sqlite_functions.h) returns a boolean: _rc == SQLITE_OK → 1 on success, 0 on failure:

#define PREPARE_STATEMENT(db, sql, stmt_ptr) \
    ({ \
        int _rc = simple_prepare_statement((db), (sql), stmt_ptr); \
        if (_rc != SQLITE_OK) { \
            internal_error(true, "Failed to prepare statement \"%s\", rc=%d in %s", (sql), _rc, __FUNCTION__); \
            nd_log(NDLS_DAEMON, NDLP_ERR, "Failed to prepare statement, rc=%d in %s", _rc, __FUNCTION__); \
        } \
        _rc == SQLITE_OK; \
    })

2. sql_health_alarm_log2json (sqlite_health.c) treats the result as an SQLite rc and compares != SQLITE_OK (where SQLITE_OK == 0):

rc = PREPARE_STATEMENT(db_meta, buffer_tostring(command), &stmt_query);
...
if (unlikely(rc != SQLITE_OK)) {
    error_report("Failed to prepare statement SQL_SELECT_HEALTH_LOG");
    return;
}

3. When the prepare succeeds, the macro returns 1, and 1 != 0 evaluates true → the code reports an error and returns an empty response. When the prepare actually fails, the macro returns 0, and the check passes → it continues with a NULL statement.

Expected behavior

/api/v1/alarm_log should return the stored alert history (the SQLite table health_log/health_log_detail is correctly populated — thousands of rows).

Steps to reproduce

1. Run any recent Netdata (stable 2.10.4 or nightly)
2. Wait for some alerts to be stored
3. curl http://localhost:19999/api/v1/alarm_log
4. Response is {} / empty, log shows Failed to prepare statement SQL_SELECT_HEALTH_LOG

Additional evidence

• The exact SQL query works when executed directly against the same netdata-meta.db with system SQLite (3.46.1): returns rows correctly
• PRAGMA integrity_check = ok, user_version = 18, table schemas match what the binary expects
• The macro's own rc error message never appears (only the caller's unconditional error), confirming the prepare actually succeeds and the inversion is the culprit
• Issue [Feat]: Let alert history be queryable / log alerts to file #15399 confirms /api/v1/alarm_log is the intended endpoint for alert history

Environment

• OS: Ubuntu ARM64 (Oracle Cloud Ampere A1)
• Netdata: v2.10.4 (stable) and v2.10.0-980-nightly
• Docker: netdata/netdata containers, dbengine mode