chore: tidy up pkgs (#636)

for readability and towards potentially making helmfile usable as a go library

pkg/helmexec/runner.go

@@ -0,0 +1,99 @@
+package helmexec
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"go.uber.org/zap"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+)
+
+const (
+	tmpPrefix = "helmfile-"
+	tmpSuffix = "-exec"
+)
+
+// Runner interface for shell commands
+type Runner interface {
+	Execute(cmd string, args []string, env map[string]string) ([]byte, error)
+}
+
+// ShellRunner implemention for shell commands
+type ShellRunner struct {
+	Dir string
+
+	logger *zap.SugaredLogger
+}
+
+// Execute a shell command
+func (shell ShellRunner) Execute(cmd string, args []string, env map[string]string) ([]byte, error) {
+	preparedCmd := exec.Command(cmd, args...)
+	preparedCmd.Dir = shell.Dir
+	preparedCmd.Env = mergeEnv(os.Environ(), env)
+	return combinedOutput(preparedCmd, shell.logger)
+}
+
+func combinedOutput(c *exec.Cmd, logger *zap.SugaredLogger) ([]byte, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	if c.Stderr != nil {
+		return nil, errors.New("exec: Stderr already set")
+	}
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	err := c.Run()
+
+	o := stdout.Bytes()
+	e := stderr.Bytes()
+
+	if err != nil {
+		// TrimSpace is necessary, because otherwise helmfile prints the redundant new-lines after each error like:
+		//
+		//   err: release "envoy2" in "helmfile.yaml" failed: exit status 1: Error: could not find a ready tiller pod
+		//   <redundant new line!>
+		//   err: release "envoy" in "helmfile.yaml" failed: exit status 1: Error: could not find a ready tiller pod
+		switch ee := err.(type) {
+		case *exec.ExitError:
+			// Propagate any non-zero exit status from the external command, rather than throwing it away,
+			// so that helmfile could return its own exit code accordingly
+			waitStatus := ee.Sys().(syscall.WaitStatus)
+			exitStatus := waitStatus.ExitStatus()
+			err = newExitError(c.Path, exitStatus, string(e))
+		default:
+			panic(fmt.Sprintf("unexpected error: %v", err))
+		}
+	}
+
+	return o, err
+}
+
+func mergeEnv(orig []string, new map[string]string) []string {
+	wanted := env2map(orig)
+	for k, v := range new {
+		wanted[k] = v
+	}
+	return map2env(wanted)
+}
+
+func map2env(wanted map[string]string) []string {
+	result := []string{}
+	for k, v := range wanted {
+		result = append(result, k+"="+v)
+	}
+	return result
+}
+
+func env2map(env []string) map[string]string {
+	wanted := map[string]string{}
+	for _, cur := range env {
+		pair := strings.SplitN(cur, "=", 2)
+		wanted[pair[0]] = pair[1]
+	}
+	return wanted
+}