* Returns -1 if no further cleanups are required.
   */
  fun closeConnections(now: Long): Long {
    // Compute the concurrent call capacity for each address. We won't close a connection if doing
    // so would violate a policy, unless it's OLD.
    val addressStates = this.addressStates
    for (state in addressStates.values) {
      state.concurrentCallCapacity = 0
    }
    for (connection in connections) {

Similarly, the reader thread must never block on writing because this can deadlock the connection. Consider a client and server that both violate this rule. If you get unlucky, they could fill up their TCP buffers (so that writes block) and then use their reader threads to write a frame. Nobody is reading on either end, and the buffers are never drained.

#### Do-stuff-later pool

  }
}
```

### Rewriting Responses

Symmetrically, interceptors can rewrite response headers and transform the response body. This is generally more dangerous than rewriting request headers because it may violate the webserver's expectations!