Extract common shell logic into shellSession

Deduplicates code between ShellOp and ReadonlyShellOp by extracting
shared logic (context validation, kubeconfig extraction, temp file
management, shell spawning) into a shellSession struct.

Callers configure behavior via:
- printEntry/printExit callbacks for banner messages
- extraEnv for additional environment variables
- transformKubeconfig hook for kubeconfig transformation (e.g. proxy)

Also extracts fzfPickContext for shared interactive mode.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/kubectx/readonly_shell.go

@@ -1,21 +1,15 @@
 package main
 
 import (
-	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"os"
-	"os/exec"
-	"strings"
 	"time"
 
 	"github.com/fatih/color"
 
-	"github.com/ahmetb/kubectx/internal/cmdutil"
 	"github.com/ahmetb/kubectx/internal/env"
-	"github.com/ahmetb/kubectx/internal/kubeconfig"
 	"github.com/ahmetb/kubectx/internal/printer"
 	"github.com/ahmetb/kubectx/internal/proxy"
 )
@@ -31,154 +25,69 @@ type ReadonlyShellOp struct {
 }
 
 func (op InteractiveReadonlyShellOp) Run(_, stderr io.Writer) error {
-	if err := checkIsolatedMode(); err != nil {
+	choice, err := fzfPickContext(op.SelfCmd, stderr)
+	if err != nil || choice == "" {
 		return err
 	}
-
-	kc := new(kubeconfig.Kubeconfig).WithLoader(kubeconfig.DefaultLoader)
-	defer kc.Close()
-	if err := kc.Parse(); err != nil {
-		if cmdutil.IsNotFoundErr(err) {
-			printer.Warning(stderr, "kubeconfig file not found")
-			return nil
-		}
-		return fmt.Errorf("kubeconfig error: %w", err)
-	}
-
-	ctxNames, err := kc.ContextNames()
-	if err != nil {
-		return fmt.Errorf("failed to get context names: %w", err)
-	}
-	if len(ctxNames) == 0 {
-		return errors.New("no contexts found in the kubeconfig file")
-	}
-
-	cmd := exec.Command("fzf", "--ansi", "--no-preview")
-	var out bytes.Buffer
-	cmd.Stdin = os.Stdin
-	cmd.Stderr = stderr
-	cmd.Stdout = &out
-
-	cmd.Env = append(os.Environ(),
-		fmt.Sprintf("FZF_DEFAULT_COMMAND=%s", op.SelfCmd),
-		fmt.Sprintf("%s=1", env.EnvForceColor))
-	if err := cmd.Run(); err != nil {
-		var exitErr *exec.ExitError
-		if !errors.As(err, &exitErr) {
-			return err
-		}
-	}
-	choice := strings.TrimSpace(out.String())
-	if choice == "" {
-		return errors.New("you did not choose any of the options")
-	}
 	return ReadonlyShellOp{Target: choice}.Run(nil, stderr)
 }
 
 func (op ReadonlyShellOp) Run(_, stderr io.Writer) error {
-	if err := checkIsolatedMode(); err != nil {
-		return err
-	}
-
-	kubectlPath, err := resolveKubectl()
-	if err != nil {
-		return err
-	}
-
-	// Verify context exists and get current context for exit message.
-	kc := new(kubeconfig.Kubeconfig).WithLoader(kubeconfig.DefaultLoader)
-	defer kc.Close()
-	if err := kc.Parse(); err != nil {
-		return fmt.Errorf("kubeconfig error: %w", err)
-	}
-	exists, err := kc.ContextExists(op.Target)
-	if err != nil {
-		return fmt.Errorf("failed to check context: %w", err)
-	}
-	if !exists {
-		return fmt.Errorf("no context exists with the name: %q", op.Target)
-	}
-	previousCtx, err := kc.GetCurrentContext()
-	if err != nil {
-		return fmt.Errorf("failed to get current context: %w", err)
-	}
-
-	// Extract minimal kubeconfig for the target context.
-	data, err := extractMinimalKubeconfig(kubectlPath, op.Target)
-	if err != nil {
-		return fmt.Errorf("failed to extract kubeconfig for context: %w", err)
-	}
-
-	// Write original minified kubeconfig to temp file (used by proxy for TLS/auth).
-	origFile, err := os.CreateTemp("", "kubectx-readonly-orig-*.yaml")
-	if err != nil {
-		return fmt.Errorf("failed to create temp kubeconfig file: %w", err)
-	}
-	origPath := origFile.Name()
-	defer os.Remove(origPath)
-
-	if _, err := origFile.Write(data); err != nil {
-		origFile.Close()
-		return fmt.Errorf("failed to write temp kubeconfig: %w", err)
-	}
-	origFile.Close()
-
-	// Start the readonly proxy.
-	p, err := proxy.Start(proxy.Config{
-		KubeconfigPath: origPath,
-		ContextName:    op.Target,
-	})
-	if err != nil {
-		return fmt.Errorf("failed to start readonly proxy: %w", err)
-	}
-	defer p.Shutdown(context.Background())
-
-	// Rewrite kubeconfig to point to the proxy.
-	rewritten, err := proxy.RewriteKubeconfig(data, p.Addr())
-	if err != nil {
-		return fmt.Errorf("failed to rewrite kubeconfig: %w", err)
-	}
-
-	// Write rewritten kubeconfig to a second temp file for the shell.
-	shellFile, err := os.CreateTemp("", "kubectx-readonly-shell-*.yaml")
-	if err != nil {
-		return fmt.Errorf("failed to create temp kubeconfig file: %w", err)
-	}
-	shellPath := shellFile.Name()
-	defer os.Remove(shellPath)
-
-	if _, err := shellFile.Write(rewritten); err != nil {
-		shellFile.Close()
-		return fmt.Errorf("failed to write rewritten kubeconfig: %w", err)
-	}
-	shellFile.Close()
-
-	// Give the proxy a moment to be ready.
-	time.Sleep(10 * time.Millisecond)
-
-	// Print entry message.
 	badgeColor := color.New(color.BgYellow, color.FgBlack, color.Bold)
 	printer.EnableOrDisableColor(badgeColor)
-	fmt.Fprintf(stderr, "%s kubectl context is %s in READ-ONLY mode — type 'exit' to leave.\n",
-		badgeColor.Sprint("[READONLY SHELL]"), printer.WarningColor.Sprint(op.Target))
 
-	// Detect and start shell.
-	shellBin := detectShell()
-	cmd := exec.Command(shellBin)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	cmd.Env = append(os.Environ(),
-		"KUBECONFIG="+shellPath,
-		env.EnvIsolatedShell+"=1",
-		env.EnvReadonlyShell+"=1",
-	)
+	s := &shellSession{
+		target:   op.Target,
+		extraEnv: []string{env.EnvReadonlyShell + "=1"},
+		printEntry: func(w io.Writer, ctxName string) {
+			fmt.Fprintf(w, "%s kubectl context is %s in READ-ONLY mode — type 'exit' to leave.\n",
+				badgeColor.Sprint("[READONLY SHELL]"), printer.WarningColor.Sprint(ctxName))
+		},
+		printExit: func(w io.Writer, prevCtx string) {
+			fmt.Fprintf(w, "%s kubectl context is now %s.\n",
+				badgeColor.Sprint("[READONLY SHELL EXITED]"), printer.WarningColor.Sprint(prevCtx))
+		},
+		transformKubeconfig: func(data []byte) ([]byte, func(), error) {
+			// Write original kubeconfig to temp file for the proxy to load TLS/auth.
+			origFile, err := os.CreateTemp("", "kubectx-readonly-orig-*.yaml")
+			if err != nil {
+				return nil, nil, fmt.Errorf("failed to create temp kubeconfig file: %w", err)
+			}
+			origPath := origFile.Name()
 
-	_ = cmd.Run()
+			if _, err := origFile.Write(data); err != nil {
+				origFile.Close()
+				os.Remove(origPath)
+				return nil, nil, fmt.Errorf("failed to write temp kubeconfig: %w", err)
+			}
+			origFile.Close()
 
-	// Print exit message.
-	fmt.Fprintf(stderr, "%s kubectl context is now %s.\n",
-		badgeColor.Sprint("[READONLY SHELL EXITED]"), printer.WarningColor.Sprint(previousCtx))
+			// Start the readonly proxy.
+			p, err := proxy.Start(proxy.Config{
+				KubeconfigPath: origPath,
+				ContextName:    op.Target,
+			})
+			if err != nil {
+				os.Remove(origPath)
+				return nil, nil, fmt.Errorf("failed to start readonly proxy: %w", err)
+			}
 
-	return nil
+			// Rewrite kubeconfig to point to the proxy.
+			rewritten, err := proxy.RewriteKubeconfig(data, p.Addr())
+			if err != nil {
+				p.Shutdown(context.Background())
+				os.Remove(origPath)
+				return nil, nil, fmt.Errorf("failed to rewrite kubeconfig: %w", err)
+			}
+
+			time.Sleep(10 * time.Millisecond)
+
+			cleanup := func() {
+				p.Shutdown(context.Background())
+				os.Remove(origPath)
+			}
+			return rewritten, cleanup, nil
+		},
+	}
+	return s.run(stderr)
 }

cmd/kubectx/shell.go

@@ -1,20 +1,14 @@
 package main
 
 import (
-	"bytes"
-	"errors"
 	"fmt"
 	"io"
 	"os"
 	"os/exec"
 	"runtime"
-	"strings"
 
 	"github.com/fatih/color"
 
-	"github.com/ahmetb/kubectx/internal/cmdutil"
-	"github.com/ahmetb/kubectx/internal/env"
-	"github.com/ahmetb/kubectx/internal/kubeconfig"
 	"github.com/ahmetb/kubectx/internal/printer"
 )
 
@@ -29,122 +23,29 @@ type ShellOp struct {
 }
 
 func (op InteractiveShellOp) Run(_, stderr io.Writer) error {
-	if err := checkIsolatedMode(); err != nil {
+	choice, err := fzfPickContext(op.SelfCmd, stderr)
+	if err != nil || choice == "" {
 		return err
 	}
-
-	kc := new(kubeconfig.Kubeconfig).WithLoader(kubeconfig.DefaultLoader)
-	defer kc.Close()
-	if err := kc.Parse(); err != nil {
-		if cmdutil.IsNotFoundErr(err) {
-			printer.Warning(stderr, "kubeconfig file not found")
-			return nil
-		}
-		return fmt.Errorf("kubeconfig error: %w", err)
-	}
-
-	ctxNames, err := kc.ContextNames()
-	if err != nil {
-		return fmt.Errorf("failed to get context names: %w", err)
-	}
-	if len(ctxNames) == 0 {
-		return errors.New("no contexts found in the kubeconfig file")
-	}
-
-	cmd := exec.Command("fzf", "--ansi", "--no-preview")
-	var out bytes.Buffer
-	cmd.Stdin = os.Stdin
-	cmd.Stderr = stderr
-	cmd.Stdout = &out
-
-	cmd.Env = append(os.Environ(),
-		fmt.Sprintf("FZF_DEFAULT_COMMAND=%s", op.SelfCmd),
-		fmt.Sprintf("%s=1", env.EnvForceColor))
-	if err := cmd.Run(); err != nil {
-		var exitErr *exec.ExitError
-		if !errors.As(err, &exitErr) {
-			return err
-		}
-	}
-	choice := strings.TrimSpace(out.String())
-	if choice == "" {
-		return errors.New("you did not choose any of the options")
-	}
 	return ShellOp{Target: choice}.Run(nil, stderr)
 }
 
 func (op ShellOp) Run(_, stderr io.Writer) error {
-	if err := checkIsolatedMode(); err != nil {
-		return err
-	}
-
-	kubectlPath, err := resolveKubectl()
-	if err != nil {
-		return err
-	}
-
-	// Verify context exists and get current context for exit message
-	kc := new(kubeconfig.Kubeconfig).WithLoader(kubeconfig.DefaultLoader)
-	defer kc.Close()
-	if err := kc.Parse(); err != nil {
-		return fmt.Errorf("kubeconfig error: %w", err)
-	}
-	exists, err := kc.ContextExists(op.Target)
-	if err != nil {
-		return fmt.Errorf("failed to check context: %w", err)
-	}
-	if !exists {
-		return fmt.Errorf("no context exists with the name: \"%s\"", op.Target)
-	}
-	previousCtx, err := kc.GetCurrentContext()
-	if err != nil {
-		return fmt.Errorf("failed to get current context: %w", err)
-	}
-
-	// Extract minimal kubeconfig using kubectl
-	data, err := extractMinimalKubeconfig(kubectlPath, op.Target)
-	if err != nil {
-		return fmt.Errorf("failed to extract kubeconfig for context: %w", err)
-	}
-
-	// Write to temp file
-	tmpFile, err := os.CreateTemp("", "kubectx-shell-*.yaml")
-	if err != nil {
-		return fmt.Errorf("failed to create temp kubeconfig file: %w", err)
-	}
-	tmpPath := tmpFile.Name()
-	defer os.Remove(tmpPath)
-
-	if _, err := tmpFile.Write(data); err != nil {
-		tmpFile.Close()
-		return fmt.Errorf("failed to write temp kubeconfig: %w", err)
-	}
-	tmpFile.Close()
-
-	// Print entry message
 	badgeColor := color.New(color.BgRed, color.FgWhite, color.Bold)
 	printer.EnableOrDisableColor(badgeColor)
-	fmt.Fprintf(stderr, "%s kubectl context is %s in this shell — type 'exit' to leave.\n",
-		badgeColor.Sprint("[ISOLATED SHELL]"), printer.WarningColor.Sprint(op.Target))
 
-	// Detect and start shell
-	shellBin := detectShell()
-	cmd := exec.Command(shellBin)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	cmd.Env = append(os.Environ(),
-		"KUBECONFIG="+tmpPath,
-		env.EnvIsolatedShell+"=1",
-	)
-
-	_ = cmd.Run()
-
-	// Print exit message
-	fmt.Fprintf(stderr, "%s kubectl context is now %s.\n",
-		badgeColor.Sprint("[ISOLATED SHELL EXITED]"), printer.WarningColor.Sprint(previousCtx))
-
-	return nil
+	s := &shellSession{
+		target: op.Target,
+		printEntry: func(w io.Writer, ctxName string) {
+			fmt.Fprintf(w, "%s kubectl context is %s in this shell — type 'exit' to leave.\n",
+				badgeColor.Sprint("[ISOLATED SHELL]"), printer.WarningColor.Sprint(ctxName))
+		},
+		printExit: func(w io.Writer, prevCtx string) {
+			fmt.Fprintf(w, "%s kubectl context is now %s.\n",
+				badgeColor.Sprint("[ISOLATED SHELL EXITED]"), printer.WarningColor.Sprint(prevCtx))
+		},
+	}
+	return s.run(stderr)
 }
 
 func resolveKubectl() (string, error) {

cmd/kubectx/shell_session.go

@@ -0,0 +1,161 @@
+package main
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/ahmetb/kubectx/internal/cmdutil"
+	"github.com/ahmetb/kubectx/internal/env"
+	"github.com/ahmetb/kubectx/internal/kubeconfig"
+	"github.com/ahmetb/kubectx/internal/printer"
+)
+
+// shellSession holds the configuration for spawning an isolated sub-shell.
+type shellSession struct {
+	target   string
+	extraEnv []string // additional env vars beyond KUBECONFIG + KUBECTX_ISOLATED_SHELL
+
+	printEntry func(stderr io.Writer, ctxName string)
+	printExit  func(stderr io.Writer, prevCtx string)
+
+	// transformKubeconfig optionally transforms the minified kubeconfig bytes
+	// before writing them to the shell's temp file. The returned cleanup func
+	// is called after the shell exits (e.g. to shut down a proxy).
+	// If nil, the kubeconfig is used as-is.
+	transformKubeconfig func(data []byte) (newData []byte, cleanup func(), err error)
+}
+
+func (s *shellSession) run(stderr io.Writer) error {
+	if err := checkIsolatedMode(); err != nil {
+		return err
+	}
+
+	kubectlPath, err := resolveKubectl()
+	if err != nil {
+		return err
+	}
+
+	// Verify context exists and get current context for exit message.
+	kc := new(kubeconfig.Kubeconfig).WithLoader(kubeconfig.DefaultLoader)
+	defer kc.Close()
+	if err := kc.Parse(); err != nil {
+		return fmt.Errorf("kubeconfig error: %w", err)
+	}
+	exists, err := kc.ContextExists(s.target)
+	if err != nil {
+		return fmt.Errorf("failed to check context: %w", err)
+	}
+	if !exists {
+		return fmt.Errorf("no context exists with the name: %q", s.target)
+	}
+	previousCtx, err := kc.GetCurrentContext()
+	if err != nil {
+		return fmt.Errorf("failed to get current context: %w", err)
+	}
+
+	// Extract minimal kubeconfig for the target context.
+	data, err := extractMinimalKubeconfig(kubectlPath, s.target)
+	if err != nil {
+		return fmt.Errorf("failed to extract kubeconfig for context: %w", err)
+	}
+
+	// Optionally transform the kubeconfig (e.g. rewrite for readonly proxy).
+	var cleanup func()
+	if s.transformKubeconfig != nil {
+		data, cleanup, err = s.transformKubeconfig(data)
+		if err != nil {
+			return err
+		}
+		if cleanup != nil {
+			defer cleanup()
+		}
+	}
+
+	// Write kubeconfig to temp file.
+	tmpFile, err := os.CreateTemp("", "kubectx-shell-*.yaml")
+	if err != nil {
+		return fmt.Errorf("failed to create temp kubeconfig file: %w", err)
+	}
+	tmpPath := tmpFile.Name()
+	defer os.Remove(tmpPath)
+
+	if _, err := tmpFile.Write(data); err != nil {
+		tmpFile.Close()
+		return fmt.Errorf("failed to write temp kubeconfig: %w", err)
+	}
+	tmpFile.Close()
+
+	// Print entry message.
+	s.printEntry(stderr, s.target)
+
+	// Detect and start shell.
+	shellBin := detectShell()
+	cmd := exec.Command(shellBin)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Env = append(os.Environ(),
+		append([]string{
+			"KUBECONFIG=" + tmpPath,
+			env.EnvIsolatedShell + "=1",
+		}, s.extraEnv...)...,
+	)
+
+	_ = cmd.Run()
+
+	// Print exit message.
+	s.printExit(stderr, previousCtx)
+
+	return nil
+}
+
+// fzfPickContext launches fzf for interactive context selection.
+func fzfPickContext(selfCmd string, stderr io.Writer) (string, error) {
+	if err := checkIsolatedMode(); err != nil {
+		return "", err
+	}
+
+	kc := new(kubeconfig.Kubeconfig).WithLoader(kubeconfig.DefaultLoader)
+	defer kc.Close()
+	if err := kc.Parse(); err != nil {
+		if cmdutil.IsNotFoundErr(err) {
+			printer.Warning(stderr, "kubeconfig file not found")
+			return "", nil
+		}
+		return "", fmt.Errorf("kubeconfig error: %w", err)
+	}
+
+	ctxNames, err := kc.ContextNames()
+	if err != nil {
+		return "", fmt.Errorf("failed to get context names: %w", err)
+	}
+	if len(ctxNames) == 0 {
+		return "", errors.New("no contexts found in the kubeconfig file")
+	}
+
+	cmd := exec.Command("fzf", "--ansi", "--no-preview")
+	var out bytes.Buffer
+	cmd.Stdin = os.Stdin
+	cmd.Stderr = stderr
+	cmd.Stdout = &out
+
+	cmd.Env = append(os.Environ(),
+		fmt.Sprintf("FZF_DEFAULT_COMMAND=%s", selfCmd),
+		fmt.Sprintf("%s=1", env.EnvForceColor))
+	if err := cmd.Run(); err != nil {
+		var exitErr *exec.ExitError
+		if !errors.As(err, &exitErr) {
+			return "", err
+		}
+	}
+	choice := strings.TrimSpace(out.String())
+	if choice == "" {
+		return "", errors.New("you did not choose any of the options")
+	}
+	return choice, nil
+}