/**
 * Forward a request through the pooled transport and return the upstream
 * {@link Response}. Throws {@link FALLBACK} for cases it intentionally declines
 * (large/streaming uploads, `Expect`, upgrades) so the caller can use `fetch()`.
 */
export declare function proxyViaPool(reqOpts: PoolRequest): Promise<Response>;
/** Sentinel thrown when the pooled path declines a request; caller uses fetch(). */
export declare const FALLBACK: unique symbol;
/** Thrown when the upstream stalls past the configured timeout; caller maps to 504. */
export declare const TIMEOUT: unique symbol;
/**
 * Thrown when every connection to an upstream is busy and the wait for a free
 * slot exceeded {@link queueWaitMs}, or the waiter queue is already at its cap.
 * The caller maps it to a 503. This is the backstop that keeps a saturated or
 * stalled upstream from making the *listener* appear wedged: instead of parking
 * a request forever with no response (the production incident), rpx fails it
 * fast and loud so the listener keeps answering every other request.
 */
export declare const POOL_BUSY: unique symbol;
export declare interface PoolRequest {
  hostPort: string
  method: string
  path: string
  reqHeaders: Headers
  forwardedHost: string
  originOverride?: string
  body: ReadableStream<Uint8Array> | null
  maxPerHost?: number
}
/**
 * One pooled upstream socket. A connection serves a single request at a time
 * (HTTP/1.1, no pipelining); it is checked out of the pool for the duration of a
 * request and returned once the response body is fully read.
 */
declare class Conn {
  socket: import('bun').Socket<undefined> | null;
  buf: Uint8Array;
  len: unknown;
  fresh: boolean;
  timedOut: boolean;
  idleSince: number;
  bodyQueue: Uint8Array[] | null;
  bodyRemaining: number;
  queuedBytes: number;
  streamingBody: boolean;
  lastActivityAt: number;
  drainWaiter: (() => void) | null;
  writeAll(bytes: Uint8Array): Promise<void>;
  wakeDrain(): void;
  push(chunk: Uint8Array): void;
  resumeIfDrained(): void;
  clearStreaming(): void;
  markClosed(): void;
  markTimedOut(): void;
  waitForData(seen: number): Promise<void>;
  waitForBody(): Promise<void>;
  compact(): void;
  destroy(): void;
}
/**
 * A bounded keepalive connection pool for a single upstream `host:port`.
 *
 * It caps the *total* number of open connections at `maxTotal` and **queues**
 * requests that arrive while every connection is busy, handing each released
 * connection straight to the next waiter. Connections are only ever closed on
 * error or after sitting idle past the timeout — never on the hot release path.
 *
 * Bounding the total (rather than just the idle set) is what makes it
 * collapse-safe: a fixed set of connections is reused indefinitely, so there is
 * no per-request churn to pile sockets into TIME_WAIT and exhaust ephemeral
 * ports under a flood. The price is that at concurrency above `maxTotal`,
 * throughput is bounded by the pool size instead of growing unbounded — exactly
 * the trade nginx makes, and the reason it stays up under load.
 */
declare class UpstreamPool {
  constructor(host: string, port: number, maxTotal: number, key?: string);
  dial(): Promise<Conn>;
  acquireIdleSync(): Conn | null;
  acquireOrDial(): Promise<Conn>;
  release(conn: Conn): void;
  destroy(conn: Conn): void;
}