cli/command/registry: refactor reading from stdin

Extract the code as a utility function, and add some GoDoc to
describe the behavior.

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

Author: thaJeztah

cli/command/registry/login.go

@@ -1,6 +1,7 @@
 package registry
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -88,6 +89,38 @@ func verifyLoginFlags(flags *pflag.FlagSet, opts loginOptions) error {
 	return nil
 }
 
+// readSecretFromStdin reads the secret from r and returns it as a string.
+// It trims terminal line-endings (LF, CRLF, or CR), which may be added when
+// inputting interactively or piping input. The value is otherwise treated as
+// opaque, preserving any other whitespace, including newlines, per [NIST SP 800-63B §5.1.1.2].
+// Note that trimming whitespace may still happen elsewhere (see [NIST SP 800-63B (revision 4) §3.1.1.2]);
+//
+// > Verifiers **MAY** make limited allowances for mistyping (e.g., removing
+// > leading and trailing whitespace characters before verification, allowing
+// > the verification of passwords with differing cases for the leading character)
+//
+// [NIST SP 800-63B §5.1.1.2]: https://pages.nist.gov/800-63-3/sp800-63b.html#memsecretver
+// [NIST SP 800-63B (revision 4) §3.1.1.2]: https://pages.nist.gov/800-63-4/sp800-63b.html#passwordver
+func readSecretFromStdin(r io.Reader) (string, error) {
+	b, err := io.ReadAll(r)
+	if err != nil {
+		return "", err
+	}
+	if len(b) == 0 {
+		return "", nil
+	}
+
+	for _, eol := range [][]byte{[]byte("\r\n"), []byte("\n"), []byte("\r")} {
+		var ok bool
+		b, ok = bytes.CutSuffix(b, eol)
+		if ok {
+			break
+		}
+	}
+
+	return string(b), nil
+}
+
 func verifyLoginOptions(dockerCLI command.Streams, opts *loginOptions) error {
 	if opts.password != "" {
 		_, _ = fmt.Fprintln(dockerCLI.Err(), "WARNING! Using --password via the CLI is insecure. Use --password-stdin.")
@@ -97,14 +130,14 @@ func verifyLoginOptions(dockerCLI command.Streams, opts *loginOptions) error {
 		if opts.user == "" {
 			return errors.New("username is empty")
 		}
-
-		contents, err := io.ReadAll(dockerCLI.In())
+		p, err := readSecretFromStdin(dockerCLI.In())
 		if err != nil {
 			return err
 		}
-
-		opts.password = strings.TrimSuffix(string(contents), "\n")
-		opts.password = strings.TrimSuffix(opts.password, "\r")
+		if strings.TrimSpace(p) == "" {
+			return errors.New("password is empty")
+		}
+		opts.password = p
 	}
 	return nil
 }

cli/command/registry/login_test.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"path/filepath"
 	"testing"
+	"testing/iotest"
 	"time"
 
 	"github.com/creack/pty"
@@ -289,6 +290,38 @@ func TestRunLogin(t *testing.T) {
 				},
 			},
 		},
+		{
+			doc:              "password stdin empty",
+			priorCredentials: map[string]configtypes.AuthConfig{},
+			input: loginOptions{
+				serverAddress: "reg1",
+				user:          "my-username",
+				passwordStdin: true,
+			},
+			expectedErr: `password is empty`,
+			expectedCredentials: map[string]configtypes.AuthConfig{
+				"reg1": {
+					Username:      "my-username",
+					ServerAddress: "reg1",
+				},
+			},
+		},
+		{
+			doc:              "password stdin read error",
+			priorCredentials: map[string]configtypes.AuthConfig{},
+			input: loginOptions{
+				serverAddress: "reg1",
+				user:          "my-username",
+				passwordStdin: true,
+			},
+			expectedErr: `TEST_READ_ERR`,
+			expectedCredentials: map[string]configtypes.AuthConfig{
+				"reg1": {
+					Username:      "my-username",
+					ServerAddress: "reg1",
+				},
+			},
+		},
 		{
 			doc:              "password stdin with line-endings",
 			priorCredentials: map[string]configtypes.AuthConfig{},
@@ -315,7 +348,11 @@ func TestRunLogin(t *testing.T) {
 			cli := test.NewFakeCli(&fakeClient{})
 			cli.SetConfigFile(cfg)
 			if tc.input.passwordStdin {
-				cli.SetIn(streams.NewIn(io.NopCloser(bytes.NewBufferString(tc.stdIn))))
+				if tc.expectedErr == "TEST_READ_ERR" {
+					cli.SetIn(streams.NewIn(io.NopCloser(iotest.ErrReader(errors.New(tc.expectedErr)))))
+				} else {
+					cli.SetIn(streams.NewIn(io.NopCloser(bytes.NewBufferString(tc.stdIn))))
+				}
 			}
 
 			for _, priorCred := range tc.priorCredentials {