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package pipe
import (
"context"
"io"
)
// Stage is an element of a `Pipeline`.
type Stage interface {
// Name returns the name of the stage.
Name() string
// Start starts the stage in the background, in the environment
// described by `env`, and using `stdin` as input. (`stdin` should
// be set to `nil` if the stage is to receive no input, which
// might be the case for the first stage in a pipeline.) It
// returns an `io.ReadCloser` from which the stage's output can be
// read (or `nil` if it generates no output, which should only be
// the case for the last stage in a pipeline). It is the stages'
// responsibility to close `stdin` (if it is not nil) when it has
// read all of the input that it needs, and to close the write end
// of its output reader when it is done, as that is generally how
// the subsequent stage knows that it has received all of its
// input and can finish its work, too.
//
// If `Start()` returns without an error, `Wait()` must also be
// called, to allow all resources to be freed.
Start(ctx context.Context, env Env, stdin io.ReadCloser) (io.ReadCloser, error)
// Wait waits for the stage to be done, either because it has
// finished or because it has been killed due to the expiration of
// the context passed to `Start()`.
Wait() error
}
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