Function startBunRelay

src/upstreamproxy/relay.ts:176–241

(
  wsUrl: string,
  authHeader: string,
  wsAuthHeader: string,
)

}

function startBunRelay(
  wsUrl: string,
  authHeader: string,
  wsAuthHeader: string,
): UpstreamProxyRelay {
  // Bun TCP sockets don't auto-buffer partial writes: sock.write() returns
  // the byte count actually handed to the kernel, and the remainder is
  // silently dropped. When the kernel buffer fills, we queue the tail and
  // let the drain handler flush it. Per-socket because the adapter closure
  // outlives individual handler calls.
  type BunState = ConnState & { writeBuf: Uint8Array[] }

  // eslint-disable-next-line custom-rules/require-bun-typeof-guard -- caller dispatches on typeof Bun
  const server = Bun.listen<BunState>({
    hostname: '127.0.0.1',
    port: 0,
    socket: {
      open(sock) {
        sock.data = { ...newConnState(), writeBuf: [] }
      },
      data(sock, data) {
        const st = sock.data
        const adapter: ClientSocket = {
          write: payload => {
            const bytes =
              typeof payload === 'string'
                ? Buffer.from(payload, 'utf8')
                : payload
            if (st.writeBuf.length > 0) {
              st.writeBuf.push(bytes)
              return
            }
            const n = sock.write(bytes)
            if (n < bytes.length) st.writeBuf.push(bytes.subarray(n))
          },
          end: () => sock.end(),
        }
        handleData(adapter, st, data, wsUrl, authHeader, wsAuthHeader)
      },
      drain(sock) {
        const st = sock.data
        while (st.writeBuf.length > 0) {
          const chunk = st.writeBuf[0]!
          const n = sock.write(chunk)
          if (n < chunk.length) {
            st.writeBuf[0] = chunk.subarray(n)
            return
          }
          st.writeBuf.shift()
        }
      },
      close(sock) {
        cleanupConn(sock.data)
      },
      error(sock, err) {
        logForDebugging(`[upstreamproxy] client socket error: ${err.message}`)
        cleanupConn(sock.data)
      },