Package tee implements utilities for I/O multiplexing.
Write is an asynchronous write multiplexer. Write maintains a small internal buffer but may discard writes for writers that cannot keep up; thus it is meant for log output or similar.
Tee forwards future writes from this writer to wr; forwarding stops after the return cancelation function is invoked. A small buffer is maintained for each writer, but writes are dropped if the writer wr cannot keep up with the write volume. The writer is not forwarded any more writes if returns an error.