import {
type AssistantMessage,
type AssistantMessageEvent,
type Context,
EventStream,
type Model,
parseStreamingJson,
type SimpleStreamOptions,
type StopReason,
type ToolCall,
} from "@earendil-works/pi-ai";
class ProxyMessageEventStream extends EventStream<AssistantMessageEvent, AssistantMessage> {
constructor() {
super(
(event) => event.type === "done" || event.type === "error",
(event) => {
if (event.type === "done") return event.message;
if (event.type === "error") return event.error;
throw new Error("Unexpected event type");
},
);
}
}
export type ProxyAssistantMessageEvent =
| { type: "start" }
| { type: "text_start"; contentIndex: number }
| { type: "text_delta"; contentIndex: number; delta: string }
| { type: "text_end"; contentIndex: number; contentSignature?: string }
| { type: "thinking_start"; contentIndex: number }
| { type: "thinking_delta"; contentIndex: number; delta: string }
| { type: "thinking_end"; contentIndex: number; contentSignature?: string }
| { type: "toolcall_start"; contentIndex: number; id: string; toolName: string }
| { type: "toolcall_delta"; contentIndex: number; delta: string }
| { type: "toolcall_end"; contentIndex: number }
| {
type: "done";
reason: Extract<StopReason, "stop" | "length" | "toolUse">;
usage: AssistantMessage["usage"];
}
| {
type: "error";
reason: Extract<StopReason, "aborted" | "error">;
errorMessage?: string;
usage: AssistantMessage["usage"];
};
type ProxySerializableStreamOptions = Pick<
SimpleStreamOptions,
| "temperature"
| "maxTokens"
| "reasoning"
| "cacheRetention"
| "sessionId"
| "headers"
| "metadata"
| "transport"
| "thinkingBudgets"
>;
export interface ProxyStreamOptions extends ProxySerializableStreamOptions {
signal?: AbortSignal;
authToken: string;
proxyUrl: string;
}
/**
* Stream function that proxies through a server instead of calling LLM providers directly.
* The server strips the partial field from delta events to reduce bandwidth.
* We reconstruct the partial message client-side.
*
* Use this as the `streamFn` option when creating an Agent that needs to go through a proxy.
*
* @example
* ```typescript
* const agent = new Agent({
* streamFn: (model, context, options) =>
* streamProxy(model, context, {
* ...options,
* authToken: await getAuthToken(),
* proxyUrl: "https://genai.example.com",
* }),
* });
* ```
*/
function buildProxyRequestOptions(options: ProxyStreamOptions): ProxySerializableStreamOptions {
return {
temperature: options.temperature,
maxTokens: options.maxTokens,
reasoning: options.reasoning,
cacheRetention: options.cacheRetention,
sessionId: options.sessionId,
headers: options.headers,
metadata: options.metadata,
transport: options.transport,
thinkingBudgets: options.thinkingBudgets,
};
}
export function streamProxy(model: Model<any>, context: Context, options: ProxyStreamOptions): ProxyMessageEventStream {
const stream = new ProxyMessageEventStream();
(async () => {
const partial: AssistantMessage = {
role: "assistant",
stopReason: "stop",
content: [],
api: model.api,
provider: model.provider,
model: model.id,
usage: {
input: 0,
output: 0,
cacheRead: 0,
cacheWrite: 0,
totalTokens: 0,
cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
},
timestamp: Date.now(),
};
let reader: ReadableStreamDefaultReader<Uint8Array> | undefined;
const abortHandler = () => {
if (reader) {
reader.cancel("Request aborted by user").catch(() => {});
}
};
if (options.signal) {
options.signal.addEventListener("abort", abortHandler);
}
try {
const response = await fetch(`${options.proxyUrl}/api/stream`, {
method: "POST",
headers: {
Authorization: `Bearer ${options.authToken}`,
"Content-Type": "application/json",
},
body: JSON.stringify({
model,
context,
options: buildProxyRequestOptions(options),
}),
signal: options.signal,
});
if (!response.ok) {
let errorMessage = `Proxy error: ${response.status} ${response.statusText}`;
try {
const errorData = (await response.json()) as { error?: string };
if (errorData.error) {
errorMessage = `Proxy error: ${errorData.error}`;
}
} catch {
// Keep the status-text fallback when the error body is not JSON.
}
throw new Error(errorMessage);
}
reader = response.body!.getReader();
const decoder = new TextDecoder();
let buffer = "";
while (true) {
const { done, value } = await reader.read();
if (done) break;
if (options.signal?.aborted) {
throw new Error("Request aborted by user");
}
buffer += decoder.decode(value, { stream: true });
const lines = buffer.split("\n");
buffer = lines.pop() || "";
for (const line of lines) {
if (line.startsWith("data: ")) {
const data = line.slice(6).trim();
if (data) {
const proxyEvent = JSON.parse(data) as ProxyAssistantMessageEvent;
const event = processProxyEvent(proxyEvent, partial);
if (event) {
stream.push(event);
}
}
}
}
}
if (options.signal?.aborted) {
throw new Error("Request aborted by user");
}
stream.end();
} catch (error) {
const errorMessage = error instanceof Error ? error.message : String(error);
const reason = options.signal?.aborted ? "aborted" : "error";
partial.stopReason = reason;
partial.errorMessage = errorMessage;
stream.push({
type: "error",
reason,
error: partial,
});
stream.end();
} finally {
if (options.signal) {
options.signal.removeEventListener("abort", abortHandler);
}
}
})();
return stream;
}
function processProxyEvent(
proxyEvent: ProxyAssistantMessageEvent,
partial: AssistantMessage,
): AssistantMessageEvent | undefined {
switch (proxyEvent.type) {
case "start":
return { type: "start", partial };
case "text_start":
partial.content[proxyEvent.contentIndex] = { type: "text", text: "" };
return { type: "text_start", contentIndex: proxyEvent.contentIndex, partial };
case "text_delta": {
const content = partial.content[proxyEvent.contentIndex];
if (content?.type === "text") {
content.text += proxyEvent.delta;
return {
type: "text_delta",
contentIndex: proxyEvent.contentIndex,
delta: proxyEvent.delta,
partial,
};
}
throw new Error("Received text_delta for non-text content");
}
case "text_end": {
const content = partial.content[proxyEvent.contentIndex];
if (content?.type === "text") {
content.textSignature = proxyEvent.contentSignature;
return {
type: "text_end",
contentIndex: proxyEvent.contentIndex,
content: content.text,
partial,
};
}
throw new Error("Received text_end for non-text content");
}
case "thinking_start":
partial.content[proxyEvent.contentIndex] = { type: "thinking", thinking: "" };
return { type: "thinking_start", contentIndex: proxyEvent.contentIndex, partial };
case "thinking_delta": {
const content = partial.content[proxyEvent.contentIndex];
if (content?.type === "thinking") {
content.thinking += proxyEvent.delta;
return {
type: "thinking_delta",
contentIndex: proxyEvent.contentIndex,
delta: proxyEvent.delta,
partial,
};
}
throw new Error("Received thinking_delta for non-thinking content");
}
case "thinking_end": {
const content = partial.content[proxyEvent.contentIndex];
if (content?.type === "thinking") {
content.thinkingSignature = proxyEvent.contentSignature;
return {
type: "thinking_end",
contentIndex: proxyEvent.contentIndex,
content: content.thinking,
partial,
};
}
throw new Error("Received thinking_end for non-thinking content");
}
case "toolcall_start":
partial.content[proxyEvent.contentIndex] = {
type: "toolCall",
id: proxyEvent.id,
name: proxyEvent.toolName,
arguments: {},
partialJson: "",
} satisfies ToolCall & { partialJson: string } as ToolCall;
return { type: "toolcall_start", contentIndex: proxyEvent.contentIndex, partial };
case "toolcall_delta": {
const content = partial.content[proxyEvent.contentIndex];
if (content?.type === "toolCall") {
(content as any).partialJson += proxyEvent.delta;
content.arguments = parseStreamingJson((content as any).partialJson) || {};
partial.content[proxyEvent.contentIndex] = { ...content }; // Trigger reactivity
return {
type: "toolcall_delta",
contentIndex: proxyEvent.contentIndex,
delta: proxyEvent.delta,
partial,
};
}
throw new Error("Received toolcall_delta for non-toolCall content");
}
case "toolcall_end": {
const content = partial.content[proxyEvent.contentIndex];
if (content?.type === "toolCall") {
delete (content as any).partialJson;
return {
type: "toolcall_end",
contentIndex: proxyEvent.contentIndex,
toolCall: content,
partial,
};
}
return undefined;
}
case "done":
partial.stopReason = proxyEvent.reason;
partial.usage = proxyEvent.usage;
return { type: "done", reason: proxyEvent.reason, message: partial };
case "error":
partial.stopReason = proxyEvent.reason;
partial.errorMessage = proxyEvent.errorMessage;
partial.usage = proxyEvent.usage;
return { type: "error", reason: proxyEvent.reason, error: partial };
default: {
const _exhaustiveCheck: never = proxyEvent;
console.warn(`Unhandled proxy event type: ${(proxyEvent as any).type}`);
return undefined;
}
}
}