Struct MessageParser 

pub struct MessageParser { /* private fields */ }

A stateful parser that reconstructs fully attributed LogsData records from a stream of FXT log packets.

Background & Architecture

In the Fuchsia Trace Format (FXT) structured logging protocol, log attribution metadata is separated from the actual log payload to optimize transmission overhead. Instead of repeating the full moniker and component URL on every log record, the system transmits two distinct types of records:

1. Manifest/Control Records: Sent with the LOG_CONTROL_BIT set. These records map a numeric base tag ID to component identity metadata (ExtendedMoniker and URL).
2. Legacy Log Records: Contain the message content, severity, timestamp, and arguments, along with a tag ID indicating which component produced the log.

Stateful Parsing

MessageParser maintains an internal tag_map to track the active association between numeric tag IDs and their component identity (ExtendedMetadata).

• When parsing a manifest record (is_control == true), MessageParser updates its state mapping for the derived base tag. If the record also reports rolled out (dropped) logs, a LogsData payload representing those dropped logs is returned. Otherwise, it registers the attribution mapping and returns Ok((None, remaining)).
• When parsing a legacy log record (is_control == false), MessageParser resolves the record’s tag to retrieve the component’s identity from the internal mapping, constructing a fully attributed LogsData containing the correct component moniker and URL.

Implementations

impl MessageParser

pub fn parse_next<'a, F: MessageFormatter>( &mut self, bytes: &'a [u8], formatter: F, ) -> Result<(Option<F::Result>, &'a [u8]), MessageError>

Parses the next log record from the given bytes.

This function can handle both standard log records and “Archivist” manifest records. Archivist records update an internal map used to attribute subsequent log records.

Arguments

• bytes: A byte slice containing one or more log records.

Returns

A Result containing:

• Ok((Option<LogsData>, &[u8])): A tuple where the first element is Some(LogsData) if a log message was parsed, or None if it was an Archivist manifest record. The second element is the remaining slice of bytes after parsing the record.
• Err(MessageError): An error if parsing failed.

Trait Implementations

impl Default for MessageParser

fn default() -> MessageParser

Returns the “default value” for a type.