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Read status updates from Mastodon streaming API
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type StreamEvent = | |
| { event: "update"; status: Status } | |
| { event: "status.update"; status: Status } | |
| { event: "delete"; id: string; status?: never }; | |
/** | |
* Use like this: | |
* const { events } = await stream(`https://${instance}/api/v1/streaming/public`); | |
* for await (const { id, status } of events) { | |
* if (status) … do something … | |
* else if (id) … deleted … | |
* } | |
*/ | |
async function stream(url: string): Promise<{ | |
events: AsyncGenerator<StreamEvent, void, unknown>; | |
close: () => void; | |
}> { | |
const response = await fetch(url); | |
if (!response.ok) throw new Error(`Stream failed: ${response.statusText}`); | |
const reader = response.body!.getReader(); | |
const utf8decoder = new TextDecoder(); | |
function close() { | |
reader.cancel(); | |
clearTimeout(timeout); | |
} | |
// Server sends heartbeat every 15 seconds | |
let timeout = setTimeout(close, 20_000); | |
async function* iterator(): AsyncGenerator<StreamEvent, void, unknown> { | |
try { | |
let buffer = ""; | |
while (true) { | |
const { done, value } = await reader.read(); | |
if (done) throw new Error("Stream closed"); | |
const chunk = utf8decoder.decode(value); | |
buffer += chunk; | |
let message; | |
while ((message = buffer.match(/^(.|\n)*\n{2}/m)?.[0])) { | |
yield* yieldEvent(message); | |
clearTimeout(timeout); | |
timeout = setTimeout(close, 20_000); | |
buffer = buffer.slice(message.length); | |
} | |
} | |
} finally { | |
clearTimeout(timeout); | |
} | |
} | |
return { events: iterator(), close }; | |
} | |
const serializer = new SerializerNativeImpl(); | |
function* yieldEvent(message: string): Generator<StreamEvent, void, unknown> { | |
// Message may or may not contain event, eg :thump is just a heartbeat | |
// message. | |
const event = message.match(/^event: (.*)$/m)?.[1]; | |
const data = message.match(/^data: (.*)$/m)?.[1]; | |
if ((event === "update" || event === "status.update") && data) { | |
const status = serializer.deserialize<Status>("application/json", data); | |
yield { event, status }; | |
} else if (event === "delete" && data) yield { event, id: JSON.parse(data) }; | |
} |
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