Module: AiStream

Defined in:

lib/ai_stream.rb,
lib/ai_stream/stream.rb,
lib/ai_stream/writer.rb,
lib/ai_stream/version.rb

Overview

AiStream is a pure-Ruby implementation of the Vercel AI SDK “Data Stream Protocol” (UI Message Stream Protocol) — the Server-Sent-Events wire format that drives the AI SDK’s ‘useChat` / `useCompletion` / `useObject` frontend hooks.

The protocol is language-agnostic by design (Vercel documents non-JS backends such as Python/FastAPI speaking it), but Ruby had no implementation. This gem lets a Rails/Rack backend stream text, reasoning, tool calls, sources, files, and custom data parts to a Vercel-AI-SDK frontend with the exact frames it expects.

AiStream is provider-agnostic: it sits downstream of whatever produced the tokens (ruby_llm, ruby-openai, a raw HTTP stream, or canned text), so it composes with the existing Ruby AI stack rather than competing with it.

See AiStream::Writer for the encoder and AiStream::Stream for the lazy, Rack-compatible response body.

Defined Under Namespace

Classes: ClosedError, Error, Stream, Writer

Constant Summary

HEADERS =

The HTTP response header the Vercel AI SDK requires to treat a response as a UI message stream. Merge this into your Rack/Rails headers.

{
  "x-vercel-ai-ui-message-stream" => "v1"
}.freeze

PROTOCOL_VERSION =

Protocol version implemented by this gem (the ‘v1` of the header above).

"v1"

DONE_SENTINEL =

The SSE terminator the frontend watches for to know the stream is complete.

"[DONE]"

VERSION =

"0.1.0"