feat: add stdin support into the Run methods

Luks encryption is passing encryption keys using stdin.

Signed-off-by: Artem Chernyshev <artem.0xD2@gmail.com>

pkg/cmd/cmd.go

@@ -8,15 +8,28 @@ package cmd
 import (
 	"context"
 	"fmt"
+	"io"
 	"os/exec"
 
 	"github.com/armon/circbuf"
 
 	"github.com/talos-systems/go-cmd/pkg/cmd/proc/reaper"
 )
 
+type stdinCtxKey string
+
 // MaxStderrLen is maximum length of stderr output captured for error message.
-const MaxStderrLen = 4096
+const (
+	MaxStderrLen = 4096
+
+	stdin stdinCtxKey = "stdin"
+)
+
+// WithStdin creates a new context from the existing context
+// and sets stdin value.
+func WithStdin(ctx context.Context, stdinData io.Reader) context.Context {
+	return context.WithValue(ctx, stdin, stdinData)
+}
 
 // Run executes a command.
 func Run(name string, args ...string) (string, error) {
@@ -37,6 +50,16 @@ func RunContext(ctx context.Context, name string, args ...string) (string, error
 		return stdout.String(), err
 	}
 
+	stdin := ctx.Value(stdin)
+	if stdin != nil {
+		var ok bool
+
+		cmd.Stdin, ok = stdin.(io.Reader)
+		if !ok {
+			return "", fmt.Errorf("failed to read stdin object from the context")
+		}
+	}
+
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
 

pkg/cmd/cmd_test.go

@@ -5,7 +5,9 @@
 package cmd_test
 
 import (
+	"context"
 	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/suite"
@@ -109,6 +111,10 @@ func (suite *CmdSuite) TestRun() {
 			suite.Assert().NoError(err)
 		}
 	}
+
+	stdout, err := cmd.RunContext(cmd.WithStdin(context.Background(), strings.NewReader("hello")), "xargs", "echo")
+	suite.Assert().NoError(err)
+	suite.Assert().Equal(stdout, "hello\n")
 }
 
 func TestCmdSuite(t *testing.T) {