git-lfs/subprocess/subprocess.go

// Package subprocess provides helper functions for forking new processes
// NOTE: Subject to change, do not rely on this package from outside git-lfs source
package subprocess

import (
	"bufio"
	"fmt"
	"os"
	"os/exec"
	"regexp"
	"strings"
	"sync"

	"github.com/rubyist/tracerx"
)

// BufferedExec starts up a command and creates a stdin pipe and a buffered
// stdout & stderr pipes, wrapped in a BufferedCmd. The stdout buffer will be
// of stdoutBufSize bytes.
func BufferedExec(name string, args ...string) (*BufferedCmd, error) {
	cmd := ExecCommand(name, args...)
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, err
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return nil, err
	}

	stdin, err := cmd.StdinPipe()
	if err != nil {
		return nil, err
	}

	if err := cmd.Start(); err != nil {
		return nil, err
	}

	return &BufferedCmd{
		cmd,
		stdin,
		bufio.NewReaderSize(stdout, stdoutBufSize),
		bufio.NewReaderSize(stderr, stdoutBufSize),
	}, nil
}

// SimpleExec is a small wrapper around os/exec.Command.
func SimpleExec(name string, args ...string) (string, error) {
	return Output(ExecCommand(name, args...))
}

func Output(cmd *Cmd) (string, error) {
	out, err := cmd.Output()

	if exitError, ok := err.(*exec.ExitError); ok {
		errorOutput := strings.TrimSpace(string(exitError.Stderr))
		if errorOutput == "" {
			// some commands might write nothing to stderr but something to stdout in error-conditions, in which case, we'll use that
			// in the error string
			errorOutput = strings.TrimSpace(string(out))
		}

		ran := cmd.Path
		if len(cmd.Args) > 1 {
			ran = fmt.Sprintf("%s %s", cmd.Path, quotedArgs(cmd.Args[1:]))
		}
		formattedErr := fmt.Errorf("error running %s: '%s' '%s'", ran, errorOutput, strings.TrimSpace(exitError.Error()))

		// return "" as output in error case, for callers that don't care about errors but rely on "" returned, in-case stdout != ""
		return "", formattedErr
	}

	return strings.Trim(string(out), " \n"), err
}

var shellWordRe = regexp.MustCompile(`\A[A-Za-z0-9_@/.-]+\z`)

// ShellQuoteSingle returns a string which is quoted suitably for sh.
func ShellQuoteSingle(str string) string {
	// Quote anything that looks slightly complicated.
	if shellWordRe.FindStringIndex(str) == nil {
		return "'" + strings.Replace(str, "'", "'\\''", -1) + "'"
	}
	return str
}

// ShellQuote returns a copied string slice where each element is quoted
// suitably for sh.
func ShellQuote(strs []string) []string {
	dup := make([]string, 0, len(strs))

	for _, str := range strs {
		dup = append(dup, ShellQuoteSingle(str))
	}
	return dup
}

// FormatForShell takes a command name and an argument string and returns a
// command and arguments that pass this command to the shell.  Note that neither
// the command nor the arguments are quoted.  Consider FormatForShellQuoted
// instead.
func FormatForShell(name string, args string) (string, []string) {
	return "sh", []string{"-c", name + " " + args}
}

// FormatForShellQuotedArgs takes a command name and an argument string and
// returns a command and arguments that pass this command to the shell.  The
// arguments are escaped, but the name of the command is not.
func FormatForShellQuotedArgs(name string, args []string) (string, []string) {
	return FormatForShell(name, strings.Join(ShellQuote(args), " "))
}

func Trace(name string, args ...string) {
	tracerx.Printf("exec: %s %s", name, quotedArgs(args))
}

func quotedArgs(args []string) string {
	if len(args) == 0 {
		return ""
	}

	quoted := make([]string, len(args))
	for i, arg := range args {
		quoted[i] = fmt.Sprintf("'%s'", arg)
	}
	return strings.Join(quoted, " ")
}

// An env for an exec.Command without GIT_TRACE and GIT_INTERNAL_SUPER_PREFIX
var env []string
var envMu sync.Mutex
var traceEnv = "GIT_TRACE="

// Don't pass GIT_INTERNAL_SUPER_PREFIX back to Git. Git passes this environment
// variable to child processes when submodule.recurse is set to true. However,
// passing that environment variable back to Git will cause it to append the
// --super-prefix command-line option to every Git call. This is problematic
// because many Git commands (including git config and git rev-parse) don't
// support --super-prefix and would immediately exit with an error as a result.
var superPrefixEnv = "GIT_INTERNAL_SUPER_PREFIX="

func fetchEnvironment() []string {
	envMu.Lock()
	defer envMu.Unlock()

	return fetchEnvironmentInternal()
}

// fetchEnvironmentInternal should only be called from fetchEnvironment or
// ResetEnvironment, who will hold the required lock.
func fetchEnvironmentInternal() []string {
	if env != nil {
		return env
	}

	realEnv := os.Environ()
	env = make([]string, 0, len(realEnv))

	for _, kv := range realEnv {
		if strings.HasPrefix(kv, traceEnv) || strings.HasPrefix(kv, superPrefixEnv) {
			continue
		}
		env = append(env, kv)
	}
	return env
}

// ResetEnvironment resets the cached environment that's used in subprocess
// calls.
func ResetEnvironment() {
	envMu.Lock()
	defer envMu.Unlock()

	env = nil
	// Reinitialize the environment settings.
	fetchEnvironmentInternal()
}