Function parse_line 

pub fn parse_line(line: &str, format: &InputFormat) -> Option<EventInputDecoded>

Parse a raw log line using the specified format.

Returns None if:

• the line is empty or whitespace-only,
• InputFormat::Json and the line is not valid JSON, or
• InputFormat::Cef and the line is not valid CEF.

For InputFormat::Auto, invalid JSON falls through to syslog or plain text (never returns None for non-empty lines).