# Transfer

> Tag 4: the client names one file of the container, another container by its id, and a destination path; the server reads the file out of this container and writes it into the other on its own connections to their proxies, and answers exactly once, transferred or an error; the client must be running or connected to both containers.

Canonical: https://protocol.diverge.network/2.3.0/endpoints/containers-tools-run/client/transfer/
Specification revision: 2.3.0

The client opens this channel to copy one file out of the container
into another container the server is running. The channel carries the
file, the other container, and the destination; the bytes travel
between the two containers on the server's own connections to their
proxies, and none of them reach the client.

- **The request.** The tag byte `4` followed by the path, the id of
  the other container, and the destination path as JSON.
  [Request](/2.3.0/endpoints/containers-tools-run/client/transfer/request/) states its form.
- **The transferrer.** The client is running both the container of
  the scope and the container the request names. The container of
  the scope is met by the scope itself. For the container named, the
  server determines whether the identity of the connection is the
  identity that runs it at the time of the request. A request naming
  a container the client is not running, and a request naming an id
  under which the server is running no container, are each answered
  with exactly one channel response, the error `{"kind":"denied"}`,
  and the channel response finish; the two are not distinguished.
- **The copy.** The server opens a read scope on the proxy of the
  container of the scope, naming the path, and a write scope on the
  proxy of the container named, naming the destination, and streams
  what the one sends into the other. The server does not read the
  bytes and does not send them to the client.
- **The response.** Exactly one channel response, transferred or an
  error, and the channel response finish.
  [Response](/2.3.0/endpoints/containers-tools-run/client/transfer/response/) states the
  sequence.
- **A read that stops.** A read that ends in an error, or without a
  finish, is a write that did not happen: the server answers with an
  error, and the destination is as it was.