Struct SseEncoder 

pub struct SseEncoder {
    pub id: String,
    pub model: String,
    pub created: u64,
}

Stateful encoder that produces OpenAI-shape SSE frames for one response.

The id, model, and created fields are stable across all frames the encoder produces, matching the OpenAI streaming contract.

Fields

id: String

Stable response id, e.g. "chatcmpl-…".

model: String

Model name as advertised to the client (NOT the upstream alias).

created: u64

Unix epoch seconds when the response was created.

Implementations

impl SseEncoder

pub fn new( id: impl Into<String>, model: impl Into<String>, created: u64, ) -> Self

Construct a new encoder with the stable response metadata.

pub fn encode(&self, event: &LlmStreamEvent) -> Option<String>

Encode a single LlmStreamEvent into one or more SSE frames.

Returns None when the event is not meant to appear on the wire (e.g. LlmStreamEvent::NormalizationError, which the proxy logs but never forwards to clients).

For LlmStreamEvent::Done, the returned String is only the terminating chunk (with finish_reason set) — it deliberately does not include the trailing data: [DONE]\n\n sentinel (DONE_SENTINEL). Done is not guaranteed to be the last event on the wire: a trailing LlmStreamEvent::Usage can legitimately arrive afterward (see that variant’s doc), and nothing may follow [DONE] once it’s sent. Callers must append DONE_SENTINEL themselves, exactly once, only after the entire event stream is truly exhausted.

fn usage_frame( &self, prompt_tokens: u32, completion_tokens: u32, total_tokens: u32, cached_tokens: Option<u32>, ) -> String

Encode a LlmStreamEvent::Usage event.

Per the OpenAI stream_options.include_usage convention, the usage-totals chunk carries an empty choices array (not omitted — see crate::LlmStreamEvent::Usage doc) and a top-level usage object.

fn upstream_error_frame(message: &str, error_type: &str, code: &str) -> String

Encode a LlmStreamEvent::UpstreamError event.

Deliberately bare — no id/object/created/model envelope and, crucially, no choices key at all (unlike every other frame this encoder produces). Clients such as the GitHub Copilot LLM Gateway extension detect this exact shape ('error' in obj && !('choices' in obj)) to recognise an inline mid-stream failure; wrapping it in the usual envelope or adding an empty choices: [] would hide it as an ordinary chunk instead.

Does not append DONE_SENTINEL — see Self::encode doc; the caller appends it exactly once after the stream is truly exhausted.

fn frame(&self, choice: &Value) -> String

Wrap a choice value in the standard chunk envelope and SSE framing.

Trait Implementations

impl Clone for SseEncoder

fn clone(&self) -> SseEncoder

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SseEncoder

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.