Add passphrase function with file input

Updates the prompt receiver to take in the in and out files from arguments.
The default function uses stdin and stdout.
Fixed a typo in comment from "directiory" to "directory".

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

pkg/passphrase/passphrase.go

@@ -6,11 +6,13 @@ import (
 	"bufio"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"strings"
 
-	"github.com/docker/docker/pkg/term"
 	"path/filepath"
+
+	"github.com/docker/docker/pkg/term"
 )
 
 // Retriever is a callback function that should retrieve a passphrase
@@ -28,13 +30,20 @@ const (
 the most sensitive key in your signing system. Please choose a long, complex passphrase and be careful
 to keep the password and the key file itself secure and backed up. It is highly recommended that you use
 a password manager to generate the passphrase and keep it safe. There will be no way to recover this key.
-You can find the key in your config directiory.`
+You can find the key in your config directory.`
 )
 
-// PromptRetriever returns a new Retriever which will provide a terminal prompt
+// PromptRetriever returns a new Retriever which will provide a prompt on stdin
-// to retrieve a passphrase. The passphrase will be cached such that subsequent
+// and stdout to retrieve a passphrase. The passphrase will be cached such that
-// prompts will produce the same passphrase.
+// subsequent prompts will produce the same passphrase.
 func PromptRetriever() Retriever {
+	return PromptRetrieverWithInOut(os.Stdin, os.Stdout)
+}
+
+// PromptRetrieverWithInOut returns a new Retriever which will provide a
+// prompt using the given in and out readers. The passphrase will be cached
+// such that subsequent prompts will produce the same passphrase.
+func PromptRetrieverWithInOut(in io.Reader, out io.Writer) Retriever {
 	userEnteredTargetsSnapshotsPass := false
 	targetsSnapshotsPass := ""
 	userEnteredRootsPass := false
@@ -42,14 +51,14 @@ func PromptRetriever() Retriever {
 
 	return func(keyName string, alias string, createNew bool, numAttempts int) (string, bool, error) {
 		if alias == tufRootAlias && createNew && numAttempts == 0 {
-			fmt.Println(tufRootKeyGenerationWarning)
+			fmt.Fprintln(out, tufRootKeyGenerationWarning)
 		}
 		if numAttempts > 0 {
 			if createNew {
-				fmt.Println("Passphrases do not match. Please retry.")
+				fmt.Fprintln(out, "Passphrases do not match. Please retry.")
 
 			} else {
-				fmt.Println("Passphrase incorrect. Please retry.")
+				fmt.Fprintln(out, "Passphrase incorrect. Please retry.")
 			}
 		}
 
@@ -74,7 +83,7 @@ func PromptRetriever() Retriever {
 		term.DisableEcho(0, state)
 		defer term.RestoreTerminal(0, state)
 
-		stdin := bufio.NewReader(os.Stdin)
+		stdin := bufio.NewReader(in)
 
 		indexOfLastSeparator := strings.LastIndex(keyName, string(filepath.Separator))
 
@@ -83,13 +92,13 @@ func PromptRetriever() Retriever {
 		}
 
 		if createNew {
-			fmt.Printf("Enter passphrase for new %s key with id %s: ", alias, keyName)
+			fmt.Fprintf(out, "Enter passphrase for new %s key with id %s: ", alias, keyName)
 		} else {
-			fmt.Printf("Enter key passphrase for %s key with id %s: ", alias, keyName)
+			fmt.Fprintf(out, "Enter key passphrase for %s key with id %s: ", alias, keyName)
 		}
 
 		passphrase, err := stdin.ReadBytes('\n')
-		fmt.Println()
+		fmt.Fprintln(out)
 		if err != nil {
 			return "", false, err
 		}
@@ -109,13 +118,13 @@ func PromptRetriever() Retriever {
 		}
 
 		if len(retPass) < 8 {
-			fmt.Println("Please use a password manager to generate and store a good random passphrase.")
+			fmt.Fprintln(out, "Please use a password manager to generate and store a good random passphrase.")
 			return "", false, errors.New("Passphrase too short")
 		}
 
-		fmt.Printf("Repeat passphrase for new %s key with id %s: ", alias, keyName)
+		fmt.Fprintf(out, "Repeat passphrase for new %s key with id %s: ", alias, keyName)
 		confirmation, err := stdin.ReadBytes('\n')
-		fmt.Println()
+		fmt.Fprintln(out)
 		if err != nil {
 			return "", false, err
 		}