revid: fix manual input reader and writer

The reader and writer pipes should be created on call to Start
and not in NewManualInput. This is so that if Close is called,
which will close the reader and the writer, a call to start will
create them again.

Approved-by: Alan Noble
Approved-by: David Sutton

device/device.go

@@ -31,6 +31,7 @@ package device
 import (
 	"fmt"
 	"io"
+	"errors"
 
 	"bitbucket.org/ausocean/av/revid/config"
 )
@@ -89,12 +90,14 @@ type ManualInput struct {
 
 // NewManualInput provides a new ManualInput.
 func NewManualInput() *ManualInput {
-	r, w := io.Pipe()
-	return &ManualInput{reader: r, writer: w}
+	return &ManualInput{}
 }
 
 // Read reads from the manual input and puts the bytes into p.
 func (m *ManualInput) Read(p []byte) (int, error) {
+	if !m.isRunning {
+		return 0, errors.New("manual input has not been started, can't read")
+	}
 	return m.reader.Read(p)
 }
 
@@ -109,6 +112,7 @@ func (m *ManualInput) Set(c config.Config) error { return nil }
 // to satisfy the Device interface.
 func (m *ManualInput) Start() error {
 	m.isRunning = true
+	m.reader, m.writer = io.Pipe()
 	return nil
 }
 
@@ -131,5 +135,8 @@ func (m *ManualInput) IsRunning() bool { return m.isRunning }
 
 // Write writes p to the ManualInput's writer side of its pipe.
 func (m *ManualInput) Write(p []byte) (int, error) {
+	if !m.isRunning {
+		return 0, errors.New("manual input has not been started, can't write")
+	}
 	return m.writer.Write(p)
 }