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import type {
ChatDeltaMessage,
ChatErrorMessage,
WsClientMessage,
WsServerMessage,
} from "@dispatch/transport-contract";
import type {
CatalogMessage,
SurfaceErrorMessage,
SurfaceMessage,
SurfaceUpdateMessage,
} from "@dispatch/ui-contract";
const VALID_SERVER_TYPES = new Set([
"catalog",
"surface",
"update",
"error",
"chat.delta",
"chat.error",
]);
/** Serialize a client message to a JSON string for the wire. */
export function serialize(msg: WsClientMessage): string {
return JSON.stringify(msg);
}
function isRecord(v: unknown): v is Record<string, unknown> {
return v !== null && typeof v === "object" && !Array.isArray(v);
}
/**
* Parse a raw server message string into a typed WsServerMessage.
* Returns null for malformed JSON or shapes that don't match the protocol.
*/
export function parseServerMessage(data: string): WsServerMessage | null {
let parsed: unknown;
try {
parsed = JSON.parse(data);
} catch {
return null;
}
if (!isRecord(parsed)) {
return null;
}
const t = parsed.type;
if (typeof t !== "string" || !VALID_SERVER_TYPES.has(t)) {
return null;
}
switch (t) {
case "catalog": {
if (!Array.isArray(parsed.catalog)) return null;
return { type: "catalog", catalog: parsed.catalog as CatalogMessage["catalog"] };
}
case "surface": {
const spec = parsed.spec;
if (!isRecord(spec)) return null;
if (typeof spec.id !== "string") return null;
if (typeof spec.region !== "string") return null;
if (typeof spec.title !== "string") return null;
if (!Array.isArray(spec.fields)) return null;
return { type: "surface", spec: spec as unknown as SurfaceMessage["spec"] };
}
case "update": {
const update = parsed.update;
if (!isRecord(update)) return null;
if (typeof update.surfaceId !== "string") return null;
const spec = update.spec;
if (!isRecord(spec)) return null;
if (typeof spec.id !== "string") return null;
if (typeof spec.region !== "string") return null;
if (typeof spec.title !== "string") return null;
if (!Array.isArray(spec.fields)) return null;
return { type: "update", update: update as unknown as SurfaceUpdateMessage["update"] };
}
case "error": {
if (typeof parsed.message !== "string") return null;
const surfaceId = parsed.surfaceId;
if (surfaceId !== undefined && typeof surfaceId !== "string") return null;
const msg: SurfaceErrorMessage =
surfaceId !== undefined
? { type: "error", surfaceId, message: parsed.message }
: { type: "error", message: parsed.message };
return msg;
}
case "chat.delta": {
const event = parsed.event;
if (!isRecord(event)) return null;
if (typeof event.type !== "string") return null;
return { type: "chat.delta", event: event as unknown as ChatDeltaMessage["event"] };
}
case "chat.error": {
if (typeof parsed.message !== "string") return null;
const conversationId = parsed.conversationId;
if (conversationId !== undefined && typeof conversationId !== "string") return null;
const msg: ChatErrorMessage =
conversationId !== undefined
? { type: "chat.error", conversationId, message: parsed.message }
: { type: "chat.error", message: parsed.message };
return msg;
}
default:
return null;
}
}
/**
* Bounded exponential backoff with jitter.
* Base: 500ms, doubles each attempt, caps at 30s, adds ±20% jitter.
*/
export function nextBackoffMs(attempt: number): number {
const base = 500;
const max = 30_000;
const exponential = base * 2 ** Math.max(0, attempt);
const capped = Math.min(exponential, max);
const jitter = 0.8 + Math.random() * 0.4;
return Math.round(capped * jitter);
}
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