Struct UsageReader 

pub struct UsageReader { /* private fields */ }

Watches one streamed response for its usage.

Feed it the stream as it passes — raw HTTP chunks with push, or websocket text messages with push_message — and take the reading with finish. It borrows what it is given and never alters the stream. Every reading is cumulative: snapshot and finish replace earlier readings rather than adding to them.

Implementations

impl UsageReader

pub fn new( operation: Operation, dialect: Dialect, transport: UsageTransport, ) -> Option<Self>

A reader for a stream of operation in dialect arriving over transport, or None when that stream reports no usage to watch for: an operation without a streamed form, or a transport its dialect does not stream over. An HTTP stream without a declared framing is read the way the dialect streams by default: a JSON array for Gemini, SSE for the rest.

pub fn keep_usage_event(&mut self)

Also keep the latest event that carried usage, for usage_event. A vendor may report fields of its own beside the standard usage object, such as a price it charged; those are not this module’s to read, and whoever reads them needs the event they arrived in. Off by default, because the kept event is a copy: a Responses response.completed repeats the whole answer.

pub fn count_output_characters(&mut self)

Count generated characters for local fallback metering, without retaining the generated text. Call before feeding any chunks. Off by default.

pub fn output_characters(&self) -> u64

Generated characters observed so far; excludes framing and metadata.

pub fn usage_event(&self) -> Option<Value>

The latest event that carried usage, when keep_usage_event asked for it: the Claude message_delta (or the message_start before any delta), the Chat chunk with a usage object, the Responses terminal event, the Gemini chunk with usageMetadata. None when no event carried usage.

pub fn push(&mut self, chunk: &[u8])

Observe raw HTTP bytes. Chunks need not align with events.

pub fn push_message(&mut self, text: &str)

Observe one websocket text message, which is one complete event.

pub fn output_started(&self) -> bool

Whether a nonempty text, reasoning or tool argument delta has arrived. Response headers, keepalives and usage-only events do not count.

pub fn snapshot(&self) -> Option<NormalizedUsage>

The reading so far. It is Partial until the event that settles it has been seen.

pub fn finish(self, end: UsageStreamEnd) -> Option<NormalizedUsage>

The final reading. A stream that was cut is never complete, whatever it reported before it stopped.