@Override
    public void fetchSnapshot(final SnapshotRequest request, final OutputStream outputStream) throws IOException {
        // We will have already checked that we have a processing user but check again just in case.
        if (!securityContext.isProcessingUser()) {
            throw new PermissionException(securityContext.getUserRef(), "Only processing users can use this resource");
        }
        shardManager.fetchSnapshot(request, outputStream);
    }
Actually create a snapshot and stream it to the supplied output stream.

@param request      The request to create a snapshot.
@param outputStream The output stream to write the snapshot to.
stroom-state/stroom-planb-impl/src/main/java/stroom/planb/impl/data/FileTransferServiceImpl.java