util: Add a small helper to exec commands simply

util/exec.go

@@ -0,0 +1,121 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package util
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+
+	"github.com/purpleidea/mgmt/util/errwrap"
+)
+
+// SimpleCmdOpts is a list of extra things to pass into the SimpleCmd function.
+type SimpleCmdOpts struct {
+	// Debug represents if we're running in debug mode or not.
+	Debug bool
+
+	// Logf is a logger which should be used.
+	Logf func(format string, v ...interface{})
+
+	// LogOutput is the path to where we can append the stdout and stderr.
+	LogOutput string
+}
+
+// SimpleCmd is a simple wrapper for us to run commands how we usually want to.
+func SimpleCmd(ctx context.Context, name string, args []string, opts *SimpleCmdOpts) error {
+	logf := func(format string, v ...interface{}) {
+		if opts == nil {
+			return
+		}
+		opts.Logf(format, v...)
+	}
+
+	cmd := exec.CommandContext(ctx, name, args...)
+
+	// ignore signals sent to parent process (we're in our own group)
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Setpgid: true,
+		Pgid:    0,
+	}
+
+	// Capture stdout and stderr together. Same as CombinedOutput() method.
+	var b bytes.Buffer
+	cmd.Stdout = &b
+	cmd.Stderr = &b
+
+	logf("running: %s", strings.Join(cmd.Args, " "))
+	if err := cmd.Start(); err != nil {
+		return errwrap.Wrapf(err, "error starting cmd")
+	}
+
+	err := cmd.Wait() // we can unblock this with the timeout
+	out := b.String()
+
+	if opts.LogOutput != "" {
+		if err := os.WriteFile(opts.LogOutput, b.Bytes(), 0600); err != nil {
+			logf("unable to store log: %v", err)
+		} else {
+			logf("wrote log to: %s", opts.LogOutput)
+		}
+	}
+
+	if err == nil {
+		logf("command ran successfully!")
+		return nil // success!
+	}
+
+	exitErr, ok := err.(*exec.ExitError) // embeds an os.ProcessState
+	if !ok {
+		// command failed in some bad way
+		return errwrap.Wrapf(err, "cmd failed in some bad way")
+	}
+	pStateSys := exitErr.Sys() // (*os.ProcessState) Sys
+	wStatus, ok := pStateSys.(syscall.WaitStatus)
+	if !ok {
+		return errwrap.Wrapf(err, "could not get exit status of cmd")
+	}
+	exitStatus := wStatus.ExitStatus()
+	if exitStatus == 0 {
+		// i'm not sure if this could happen
+		return errwrap.Wrapf(err, "unexpected cmd exit status of zero")
+	}
+
+	logf("cmd: %s", strings.Join(cmd.Args, " "))
+	if out == "" {
+		logf("cmd exit status %d", exitStatus)
+	} else {
+		logf("cmd error:\n%s", out) // newline because it's long
+	}
+	return errwrap.Wrapf(err, "cmd error") // exit status will be in the error
+}