Validate data loaded from SQLite to prevent crashes on corrupted databases - #22679

sequenceDiagram
    participant Agent as Agent (Startup/Runtime)
    participant SQLite as SQLite Database
    participant Valid as Validation Helpers
    participant CLI as CLI Commands
    participant Cloud as Netdata Cloud

    Agent->>SQLite: Read host_info table
    SQLite-->>Agent: (key, value) row
    alt Invalid row (NULL key/value)
        Agent->>Agent: NEW: Skip row (ignore corrupted data)
    else Valid row
        Agent->>Agent: Process system info
    end

    Agent->>SQLite: Read chart type from context
    SQLite-->>Agent: chart_type string (possibly NULL)
    alt Missing chart type
        Agent->>Agent: NEW: Default to RRDSET_TYPE_LINE
    else Valid type
        Agent->>Agent: Use provided chart type
    end

    Agent->>SQLite: Load context entries (rrdcontext_load_context_callback)
    SQLite-->>Agent: VERSIONED_CONTEXT_DATA with hub.version
    alt Version not set (0)
        Agent->>Agent: NEW: Skip entry (avoid dangling pointers)
    else Version set
        Agent->>Agent: Process context normally
    end

    Agent->>SQLite: Read schema migration table names/indexes
    SQLite-->>Agent: table_name (possibly NULL)
    alt NULL table name
        Agent->>Agent: NEW: Skip corrupted entry
    else Valid name
        Agent->>Agent: Apply schema upgrade
    end

    Agent->>SQLite: Read alert log entries for Cloud push
    SQLite-->>Agent: chart, name columns (possibly NULL)
    alt Missing chart or name
        Agent->>Agent: NEW: strdupz("") for empty values
        Agent->>Cloud: Send alert with empty fields
    else Valid chart/name
        Agent->>Cloud: Send alert normally
    end

    CLI->>SQLite: remove-stale-node: Read host entries
    SQLite-->>CLI: host_id UUID blob
    alt Invalid or truncated UUID
        CLI->>CLI: NEW: Skip entry (continue loop)
    else Valid UUID
        CLI->>Agent: Process host removal
    end

    CLI->>SQLite: sqlite-alert-cleanup: Read host entries
    SQLite-->>CLI: host_id, hostname columns
    alt Invalid host_id (uuid_copy fails)
        CLI->>CLI: NEW: Log "skipping host", continue
        CLI->>CLI: Loop to next row
    else Valid host_id
        CLI->>CLI: Process alert cleanup for host
    end

    Note over Agent,SQLite: All reads now use safe validation helpers<br/>(sqlite3_column_uuid_copy, sqlite3_text_strdupz_empty,<br/>null checks) before dereferencing

sequenceDiagram
    participant Agent as Netdata Agent
    participant SQLite as SQLite Database
    participant FS as File System
    participant Cloud as Netdata Cloud

    Note over Agent,Cloud: READ FLOW: Corrupted SQLite rows handled safely

    Agent->>SQLite: SELECT system_key, system_value FROM host_info
    SQLite-->>Agent: Row with NULL key/value (corrupted)
    alt Valid row (key AND value NOT NULL)
        Agent->>Agent: rrdhost_system_info_set_by_name(key, value)
    else NEW: NULL key or value
        Agent->>Agent: Skip bad row → no crash
    end

    Agent->>SQLite: SELECT type FROM context_entry
    SQLite-->>Agent: NULL type (corrupted)
    alt Valid type
        Agent->>Agent: rrdset_type_id(type)
    else NEW: NULL type
        Agent->>Agent: Return RRDSET_TYPE_LINE (default)
    end

    Agent->>SQLite: SELECT version, id, ... FROM context_data
    SQLite-->>Agent: Row with version = 0 (unset)
    alt version > 0
        Agent->>Agent: rrdcontext_load_context_callback() — copy strings
    else NEW: version == 0
        Agent->>Agent: Skip row → no dangling pointer
    end

    Agent->>SQLite: SELECT chart, name, ... FROM alert_log
    SQLite-->>Agent: Row with NULL chart or name
    alt Valid chart/name
        Agent->>Agent: strdupz(chart), strdupz(name)
    else CHANGED: NULL chart or name
        Agent->>Agent: sqlite3_text_strdupz_empty() → empty string
        Agent->>Cloud: Send alert with empty chart/name
    end

    Note over Agent,SQLite: READ FLOW: CLI commands safe against corrupted host_id

    Agent->>SQLite: SELECT host_id, hostname FROM host
    SQLite-->>Agent: Row with invalid/truncated host_id
    alt Valid UUID
        Agent->>Agent: uuid_unparse_lower() → process host
    else NEW: Invalid UUID
        Agent->>Agent: Skip host → log warning, no crash
    end

    Note over Agent,SQLite: MIGRATION FLOW: Schema upgrades skip corrupted metadata

    SQLite->>FS: Read sqlite_schema for table/index names
    alt Valid name (non-NULL text)
        Agent->>SQLite: ALTER TABLE/ANALYZE/DROP INDEX
    else NEW: NULL name (corrupted catalog)
        Agent->>Agent: Skip bad table/index → migration continues
    end