stream_struct library

Turn a language model's token stream into a stream of the structured object as it fills in.

parsePartialJson decodes a truncated JSON buffer into the value it holds so far. streamPartialJson and streamPartialJsonFrom turn a delta stream into a stream of growing values, and streamPartial maps those into a typed object. openAiDelta, anthropicDelta, and geminiDelta pull the text fragment out of each provider's streamed chunk.

sseJson decodes the Server-Sent Events body those providers actually send, so an HTTP response can go straight through without hand-written line handling; sseData gives the raw payloads if you want to decode them yourself.

Constants

sseDoneSentinel → const String

Decoding for Server-Sent Events, the wire format every streaming LLM API uses.

Functions

anthropicDelta(Map<String, dynamic> chunk) → String?

Anthropic Messages stream for tool-based structured output: the JSON of a forced tool call, which arrives as delta.partial_json on the tool block's content_block_delta events.

anthropicTextDelta(Map<String, dynamic> chunk) → String?

Anthropic Messages stream for plain-text output: the model's text block, which arrives as delta.text on content_block_delta events.

geminiDelta(Map<String, dynamic> chunk) → String?

Gemini generateContent stream: the answer text from candidates[0].content.parts.

openAiDelta(Map<String, dynamic> chunk) → String?

OpenAI chat completions stream: choices[0].delta.content.

parsePartialJson(String buffer) → Object?

Decodes a possibly-truncated JSON buffer into the value it represents so far.

sseData(Stream<List<int>> bytes) → Stream<String>

Decodes an SSE response body into the data payload of each event.

sseDataFromLines(Stream<String> lines) → Stream<String>

Like sseData, but for a stream that is already split into lines.

sseJson(Stream<List<int>> bytes) → Stream<Map<String, dynamic>>

Decodes an SSE response body into one JSON object per event, which is what streamPartialJson's callers actually want.

sseJsonFromData(Stream<String> payloads) → Stream<Map<String, dynamic>>

Like sseJson, but starting from payloads you already decoded with sseData or sseDataFromLines.

streamPartial<T>(Stream<String> deltas, T build(Map<String, dynamic> partial)) → Stream<T>

Maps each partial JSON object through build to yield a typed value as the object fills in.

streamPartialFrom<T>(Stream<Map<String, dynamic>> chunks, DeltaExtractor extractor, T build(Map<String, dynamic> partial)) → Stream<T>

streamPartial over a provider's decoded chunks: pulls each text fragment out with extractor, then maps the growing object through build.

streamPartialJson(Stream<String> deltas) → Stream<Object?>

Accumulates a stream of text deltas and, after each one, emits the JSON value parsed so far.

streamPartialJsonFrom(Stream<Map<String, dynamic>> chunks, DeltaExtractor extractor) → Stream<Object?>

Like streamPartialJson but takes provider chunks and a DeltaExtractor, so you can pipe a decoded SSE stream straight in:

Typedefs

DeltaExtractor = String? Function(Map<String, dynamic> chunk)

Pulls the incremental text out of one streamed chunk from a provider.