Enabling event-streaming operations
Server-sent events (SSE) is a core web feature that provides servers with a low overhead solution to push real-time events to the client when they become available. It can be used to stream chat completions from a large language model, real-time stock prices and sensor readings to clients. SSE is similar to web sockets in that it uses a persisent connection but differs in that it is unidirectional - only the server is sending events - and simpler to implement in many existing backend HTTP frameworks.
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Speakeasy makes it easy to build this feature into your SDKs without any vendored extensions or heuristics. It can be leveraged purely by modeling SSE streams as text/event-stream
responses with pure OpenAPI!
Here's a short example of using an SDK to chat with an LLM and read its response as a stream.
import { SDK } from '@speakeasy/sdk';const sdk = new SDK()const response = await sdk.chat.create({ prompt: "What are the top 3 French cheeses by consumption?"})for await (const event of response.chatStream) { process.stdout.write(event.data);}
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This feature is currently supported in TypeScript, Python and Go. Let us know if you'd like to see support for other languages.
Modelling SSE in OpenAPI
To get started, you'll need to model an API endpoint that serves an event stream in your OpenAPI document. The main requirement to consider is that each server-sent event can contain up to 4 types of fields: id
, event
, data
, retry
. Below is an example of an operation that streams events containing only a data
field that holds string content:
paths: /chat: post: summary: Create a chat completion from a prompt operationId: create tags: [chat] requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/ChatRequest' responses: '200': description: Chat completion created content: text/event-stream: schema: $ref: '#/components/schemas/ChatStream'components: schemas: ChatRequest: type: object required: [prompt] properties: prompt: type: string ChatStream: description: A server-sent event containing chat completion content type: object required: [data] properties: data: type: string
We aren't limited to string data however. If you specify that data
is an object then SDKs will assume the field will contain JSON content. When raw data is received from the server, it will be deserialized into an object for application code to consume.
components: schemas: ChatStream: description: A server-sent event containing chat completion content type: object required: [data] properties: data: type: object properties: content: type: string model: type: string enum: ["foo-gpt-tiny", "foo-gpt-small"] created: type: integer
As an example for Typescript, the generated SDK will now allow users to access this object:
for await (const event of response.chatStream) { const { content, model, created } = event.data; process.stdout.write(content);}
Other streaming APIs send multiple types of events which have an id
and event
fields. These can be described as a union (oneOf
) with the event
field acting as a discriminator:
components: schemas: ChatStream: oneOf: - $ref: '#/components/schemas/HeartbeatEvent' - $ref: '#/components/schemas/ChatEvent' discriminator: propertyName: event mapping: ping: '#/components/schemas/HeartbeatEvent' completion: '#/components/schemas/ChatEvent' HeartbeatEvent: description: A server-sent event indicating that the server is still processing the request type: object required: [event] properties: event: type: string const: "ping" ChatEvent: description: A server-sent event containing chat completion content type: object required: [id, event, data] properties: id: type: string event: type: string const: completion data: type: object required: [content] properties: content: type: string
Note that across all these examples the schema for the events only ever specifies one or more of the 4 recognized fields. Adding other fields will trigger a validation error when generating an SDK with the speakeasy
CLI or GitHub action.