pkg/jsonmessage: export "Stream" interface

This interface is used as part of an exported function's signature,
so exporting the interface as well for callers to know what the argument
must have implemented.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/jsonmessage/jsonmessage.go

@@ -271,13 +271,19 @@ func DisplayJSONMessagesStream(in io.Reader, out io.Writer, terminalFd uintptr,
 	return nil
 }
 
-type stream interface {
+// Stream is an io.Writer for output with utilities to get the output's file
+// descriptor and to detect wether it's a terminal.
+//
+// it is subset of the streams.Out type in
+// https://pkg.go.dev/github.com/docker/cli@v20.10.17+incompatible/cli/streams#Out
+type Stream interface {
 	io.Writer
 	FD() uintptr
 	IsTerminal() bool
 }
 
-// DisplayJSONMessagesToStream prints json messages to the output stream
-func DisplayJSONMessagesToStream(in io.Reader, stream stream, auxCallback func(JSONMessage)) error {
+// DisplayJSONMessagesToStream prints json messages to the output Stream. It is
+// used by the Docker CLI to print JSONMessage streams.
+func DisplayJSONMessagesToStream(in io.Reader, stream Stream, auxCallback func(JSONMessage)) error {
 	return DisplayJSONMessagesStream(in, stream, stream.FD(), stream.IsTerminal(), auxCallback)
 }