mirror of
https://github.com/autc04/Retro68.git
synced 2024-11-04 13:06:01 +00:00
723 lines
20 KiB
Go
723 lines
20 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package exec runs external commands. It wraps os.StartProcess to make it
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// easier to remap stdin and stdout, connect I/O with pipes, and do other
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// adjustments.
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//
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// Unlike the "system" library call from C and other languages, the
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// os/exec package intentionally does not invoke the system shell and
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// does not expand any glob patterns or handle other expansions,
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// pipelines, or redirections typically done by shells. The package
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// behaves more like C's "exec" family of functions. To expand glob
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// patterns, either call the shell directly, taking care to escape any
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// dangerous input, or use the path/filepath package's Glob function.
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// To expand environment variables, use package os's ExpandEnv.
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//
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// Note that the examples in this package assume a Unix system.
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// They may not run on Windows, and they do not run in the Go Playground
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// used by golang.org and godoc.org.
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package exec
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import (
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"bytes"
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"context"
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"errors"
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"io"
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"os"
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"path/filepath"
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"runtime"
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"strconv"
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"strings"
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"sync"
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"syscall"
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)
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// Error records the name of a binary that failed to be executed
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// and the reason it failed.
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type Error struct {
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Name string
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Err error
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}
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func (e *Error) Error() string {
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return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error()
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}
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// Cmd represents an external command being prepared or run.
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//
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// A Cmd cannot be reused after calling its Run, Output or CombinedOutput
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// methods.
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type Cmd struct {
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// Path is the path of the command to run.
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//
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// This is the only field that must be set to a non-zero
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// value. If Path is relative, it is evaluated relative
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// to Dir.
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Path string
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// Args holds command line arguments, including the command as Args[0].
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// If the Args field is empty or nil, Run uses {Path}.
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//
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// In typical use, both Path and Args are set by calling Command.
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Args []string
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// Env specifies the environment of the process.
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// Each entry is of the form "key=value".
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// If Env is nil, the new process uses the current process's
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// environment.
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// If Env contains duplicate environment keys, only the last
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// value in the slice for each duplicate key is used.
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Env []string
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// Dir specifies the working directory of the command.
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// If Dir is the empty string, Run runs the command in the
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// calling process's current directory.
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Dir string
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// Stdin specifies the process's standard input.
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//
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// If Stdin is nil, the process reads from the null device (os.DevNull).
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//
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// If Stdin is an *os.File, the process's standard input is connected
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// directly to that file.
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//
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// Otherwise, during the execution of the command a separate
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// goroutine reads from Stdin and delivers that data to the command
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// over a pipe. In this case, Wait does not complete until the goroutine
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// stops copying, either because it has reached the end of Stdin
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// (EOF or a read error) or because writing to the pipe returned an error.
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Stdin io.Reader
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// Stdout and Stderr specify the process's standard output and error.
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//
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// If either is nil, Run connects the corresponding file descriptor
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// to the null device (os.DevNull).
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//
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// If either is an *os.File, the corresponding output from the process
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// is connected directly to that file.
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//
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// Otherwise, during the execution of the command a separate goroutine
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// reads from the process over a pipe and delivers that data to the
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// corresponding Writer. In this case, Wait does not complete until the
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// goroutine reaches EOF or encounters an error.
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//
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// If Stdout and Stderr are the same writer, and have a type that can
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// be compared with ==, at most one goroutine at a time will call Write.
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Stdout io.Writer
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Stderr io.Writer
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// ExtraFiles specifies additional open files to be inherited by the
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// new process. It does not include standard input, standard output, or
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// standard error. If non-nil, entry i becomes file descriptor 3+i.
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ExtraFiles []*os.File
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// SysProcAttr holds optional, operating system-specific attributes.
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// Run passes it to os.StartProcess as the os.ProcAttr's Sys field.
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SysProcAttr *syscall.SysProcAttr
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// Process is the underlying process, once started.
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Process *os.Process
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// ProcessState contains information about an exited process,
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// available after a call to Wait or Run.
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ProcessState *os.ProcessState
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ctx context.Context // nil means none
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lookPathErr error // LookPath error, if any.
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finished bool // when Wait was called
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childFiles []*os.File
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closeAfterStart []io.Closer
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closeAfterWait []io.Closer
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goroutine []func() error
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errch chan error // one send per goroutine
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waitDone chan struct{}
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}
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// Command returns the Cmd struct to execute the named program with
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// the given arguments.
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//
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// It sets only the Path and Args in the returned structure.
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//
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// If name contains no path separators, Command uses LookPath to
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// resolve name to a complete path if possible. Otherwise it uses name
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// directly as Path.
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//
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// The returned Cmd's Args field is constructed from the command name
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// followed by the elements of arg, so arg should not include the
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// command name itself. For example, Command("echo", "hello").
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// Args[0] is always name, not the possibly resolved Path.
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func Command(name string, arg ...string) *Cmd {
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cmd := &Cmd{
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Path: name,
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Args: append([]string{name}, arg...),
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}
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if filepath.Base(name) == name {
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if lp, err := LookPath(name); err != nil {
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cmd.lookPathErr = err
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} else {
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cmd.Path = lp
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}
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}
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return cmd
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}
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// CommandContext is like Command but includes a context.
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//
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// The provided context is used to kill the process (by calling
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// os.Process.Kill) if the context becomes done before the command
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// completes on its own.
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func CommandContext(ctx context.Context, name string, arg ...string) *Cmd {
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if ctx == nil {
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panic("nil Context")
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}
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cmd := Command(name, arg...)
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cmd.ctx = ctx
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return cmd
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}
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// interfaceEqual protects against panics from doing equality tests on
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// two interfaces with non-comparable underlying types.
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func interfaceEqual(a, b interface{}) bool {
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defer func() {
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recover()
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}()
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return a == b
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}
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func (c *Cmd) envv() []string {
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if c.Env != nil {
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return c.Env
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}
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return os.Environ()
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}
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func (c *Cmd) argv() []string {
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if len(c.Args) > 0 {
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return c.Args
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}
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return []string{c.Path}
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}
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// skipStdinCopyError optionally specifies a function which reports
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// whether the provided stdin copy error should be ignored.
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// It is non-nil everywhere but Plan 9, which lacks EPIPE. See exec_posix.go.
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var skipStdinCopyError func(error) bool
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func (c *Cmd) stdin() (f *os.File, err error) {
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if c.Stdin == nil {
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f, err = os.Open(os.DevNull)
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if err != nil {
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return
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}
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c.closeAfterStart = append(c.closeAfterStart, f)
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return
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}
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if f, ok := c.Stdin.(*os.File); ok {
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return f, nil
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}
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pr, pw, err := os.Pipe()
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if err != nil {
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return
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}
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c.closeAfterStart = append(c.closeAfterStart, pr)
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c.closeAfterWait = append(c.closeAfterWait, pw)
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c.goroutine = append(c.goroutine, func() error {
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_, err := io.Copy(pw, c.Stdin)
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if skip := skipStdinCopyError; skip != nil && skip(err) {
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err = nil
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}
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if err1 := pw.Close(); err == nil {
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err = err1
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}
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return err
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})
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return pr, nil
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}
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func (c *Cmd) stdout() (f *os.File, err error) {
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return c.writerDescriptor(c.Stdout)
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}
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func (c *Cmd) stderr() (f *os.File, err error) {
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if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) {
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return c.childFiles[1], nil
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}
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return c.writerDescriptor(c.Stderr)
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}
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func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err error) {
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if w == nil {
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f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0)
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if err != nil {
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return
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}
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c.closeAfterStart = append(c.closeAfterStart, f)
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return
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}
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if f, ok := w.(*os.File); ok {
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return f, nil
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}
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pr, pw, err := os.Pipe()
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if err != nil {
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return
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}
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c.closeAfterStart = append(c.closeAfterStart, pw)
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c.closeAfterWait = append(c.closeAfterWait, pr)
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c.goroutine = append(c.goroutine, func() error {
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_, err := io.Copy(w, pr)
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pr.Close() // in case io.Copy stopped due to write error
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return err
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})
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return pw, nil
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}
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func (c *Cmd) closeDescriptors(closers []io.Closer) {
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for _, fd := range closers {
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fd.Close()
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}
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}
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// Run starts the specified command and waits for it to complete.
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//
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// The returned error is nil if the command runs, has no problems
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// copying stdin, stdout, and stderr, and exits with a zero exit
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// status.
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//
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// If the command starts but does not complete successfully, the error is of
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// type *ExitError. Other error types may be returned for other situations.
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//
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// If the calling goroutine has locked the operating system thread
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// with runtime.LockOSThread and modified any inheritable OS-level
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// thread state (for example, Linux or Plan 9 name spaces), the new
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// process will inherit the caller's thread state.
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func (c *Cmd) Run() error {
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if err := c.Start(); err != nil {
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return err
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}
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return c.Wait()
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}
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// lookExtensions finds windows executable by its dir and path.
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// It uses LookPath to try appropriate extensions.
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// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
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func lookExtensions(path, dir string) (string, error) {
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if filepath.Base(path) == path {
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path = filepath.Join(".", path)
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}
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if dir == "" {
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return LookPath(path)
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}
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if filepath.VolumeName(path) != "" {
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return LookPath(path)
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}
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if len(path) > 1 && os.IsPathSeparator(path[0]) {
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return LookPath(path)
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}
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dirandpath := filepath.Join(dir, path)
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// We assume that LookPath will only add file extension.
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lp, err := LookPath(dirandpath)
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if err != nil {
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return "", err
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}
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ext := strings.TrimPrefix(lp, dirandpath)
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return path + ext, nil
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}
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// Start starts the specified command but does not wait for it to complete.
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//
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// The Wait method will return the exit code and release associated resources
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// once the command exits.
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func (c *Cmd) Start() error {
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if c.lookPathErr != nil {
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c.closeDescriptors(c.closeAfterStart)
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c.closeDescriptors(c.closeAfterWait)
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return c.lookPathErr
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}
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if runtime.GOOS == "windows" {
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lp, err := lookExtensions(c.Path, c.Dir)
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if err != nil {
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c.closeDescriptors(c.closeAfterStart)
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c.closeDescriptors(c.closeAfterWait)
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return err
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}
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c.Path = lp
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}
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if c.Process != nil {
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return errors.New("exec: already started")
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}
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if c.ctx != nil {
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select {
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case <-c.ctx.Done():
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c.closeDescriptors(c.closeAfterStart)
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c.closeDescriptors(c.closeAfterWait)
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return c.ctx.Err()
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default:
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}
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}
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type F func(*Cmd) (*os.File, error)
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for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} {
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fd, err := setupFd(c)
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if err != nil {
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c.closeDescriptors(c.closeAfterStart)
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c.closeDescriptors(c.closeAfterWait)
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return err
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}
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c.childFiles = append(c.childFiles, fd)
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}
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c.childFiles = append(c.childFiles, c.ExtraFiles...)
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var err error
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c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{
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Dir: c.Dir,
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Files: c.childFiles,
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Env: dedupEnv(c.envv()),
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Sys: c.SysProcAttr,
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})
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if err != nil {
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c.closeDescriptors(c.closeAfterStart)
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c.closeDescriptors(c.closeAfterWait)
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return err
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}
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c.closeDescriptors(c.closeAfterStart)
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c.errch = make(chan error, len(c.goroutine))
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for _, fn := range c.goroutine {
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go func(fn func() error) {
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c.errch <- fn()
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}(fn)
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}
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if c.ctx != nil {
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c.waitDone = make(chan struct{})
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go func() {
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select {
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case <-c.ctx.Done():
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c.Process.Kill()
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case <-c.waitDone:
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}
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}()
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}
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return nil
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}
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// An ExitError reports an unsuccessful exit by a command.
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type ExitError struct {
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*os.ProcessState
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// Stderr holds a subset of the standard error output from the
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// Cmd.Output method if standard error was not otherwise being
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// collected.
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//
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// If the error output is long, Stderr may contain only a prefix
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// and suffix of the output, with the middle replaced with
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// text about the number of omitted bytes.
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//
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// Stderr is provided for debugging, for inclusion in error messages.
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// Users with other needs should redirect Cmd.Stderr as needed.
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Stderr []byte
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}
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func (e *ExitError) Error() string {
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return e.ProcessState.String()
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}
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// Wait waits for the command to exit and waits for any copying to
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// stdin or copying from stdout or stderr to complete.
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//
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// The command must have been started by Start.
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//
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// The returned error is nil if the command runs, has no problems
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// copying stdin, stdout, and stderr, and exits with a zero exit
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// status.
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//
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// If the command fails to run or doesn't complete successfully, the
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// error is of type *ExitError. Other error types may be
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// returned for I/O problems.
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//
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// If any of c.Stdin, c.Stdout or c.Stderr are not an *os.File, Wait also waits
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// for the respective I/O loop copying to or from the process to complete.
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//
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// Wait releases any resources associated with the Cmd.
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func (c *Cmd) Wait() error {
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if c.Process == nil {
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return errors.New("exec: not started")
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}
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if c.finished {
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return errors.New("exec: Wait was already called")
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}
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c.finished = true
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state, err := c.Process.Wait()
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if c.waitDone != nil {
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close(c.waitDone)
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}
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c.ProcessState = state
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var copyError error
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for range c.goroutine {
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if err := <-c.errch; err != nil && copyError == nil {
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copyError = err
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}
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}
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c.closeDescriptors(c.closeAfterWait)
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if err != nil {
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return err
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} else if !state.Success() {
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return &ExitError{ProcessState: state}
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}
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return copyError
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}
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// Output runs the command and returns its standard output.
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// Any returned error will usually be of type *ExitError.
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// If c.Stderr was nil, Output populates ExitError.Stderr.
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func (c *Cmd) Output() ([]byte, error) {
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if c.Stdout != nil {
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return nil, errors.New("exec: Stdout already set")
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}
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var stdout bytes.Buffer
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c.Stdout = &stdout
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captureErr := c.Stderr == nil
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if captureErr {
|
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c.Stderr = &prefixSuffixSaver{N: 32 << 10}
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}
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err := c.Run()
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if err != nil && captureErr {
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if ee, ok := err.(*ExitError); ok {
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ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes()
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}
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}
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return stdout.Bytes(), err
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}
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|
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// CombinedOutput runs the command and returns its combined standard
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// output and standard error.
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func (c *Cmd) CombinedOutput() ([]byte, error) {
|
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if c.Stdout != nil {
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return nil, errors.New("exec: Stdout already set")
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}
|
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if c.Stderr != nil {
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return nil, errors.New("exec: Stderr already set")
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}
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var b bytes.Buffer
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c.Stdout = &b
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c.Stderr = &b
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err := c.Run()
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return b.Bytes(), err
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}
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|
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// StdinPipe returns a pipe that will be connected to the command's
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// standard input when the command starts.
|
|
// The pipe will be closed automatically after Wait sees the command exit.
|
|
// A caller need only call Close to force the pipe to close sooner.
|
|
// For example, if the command being run will not exit until standard input
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// is closed, the caller must close the pipe.
|
|
func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
|
|
if c.Stdin != nil {
|
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return nil, errors.New("exec: Stdin already set")
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}
|
|
if c.Process != nil {
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|
return nil, errors.New("exec: StdinPipe after process started")
|
|
}
|
|
pr, pw, err := os.Pipe()
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
c.Stdin = pr
|
|
c.closeAfterStart = append(c.closeAfterStart, pr)
|
|
wc := &closeOnce{File: pw}
|
|
c.closeAfterWait = append(c.closeAfterWait, wc)
|
|
return wc, nil
|
|
}
|
|
|
|
type closeOnce struct {
|
|
*os.File
|
|
|
|
once sync.Once
|
|
err error
|
|
}
|
|
|
|
func (c *closeOnce) Close() error {
|
|
c.once.Do(c.close)
|
|
return c.err
|
|
}
|
|
|
|
func (c *closeOnce) close() {
|
|
c.err = c.File.Close()
|
|
}
|
|
|
|
// StdoutPipe returns a pipe that will be connected to the command's
|
|
// standard output when the command starts.
|
|
//
|
|
// Wait will close the pipe after seeing the command exit, so most callers
|
|
// need not close the pipe themselves; however, an implication is that
|
|
// it is incorrect to call Wait before all reads from the pipe have completed.
|
|
// For the same reason, it is incorrect to call Run when using StdoutPipe.
|
|
// See the example for idiomatic usage.
|
|
func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
|
|
if c.Stdout != nil {
|
|
return nil, errors.New("exec: Stdout already set")
|
|
}
|
|
if c.Process != nil {
|
|
return nil, errors.New("exec: StdoutPipe after process started")
|
|
}
|
|
pr, pw, err := os.Pipe()
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
c.Stdout = pw
|
|
c.closeAfterStart = append(c.closeAfterStart, pw)
|
|
c.closeAfterWait = append(c.closeAfterWait, pr)
|
|
return pr, nil
|
|
}
|
|
|
|
// StderrPipe returns a pipe that will be connected to the command's
|
|
// standard error when the command starts.
|
|
//
|
|
// Wait will close the pipe after seeing the command exit, so most callers
|
|
// need not close the pipe themselves; however, an implication is that
|
|
// it is incorrect to call Wait before all reads from the pipe have completed.
|
|
// For the same reason, it is incorrect to use Run when using StderrPipe.
|
|
// See the StdoutPipe example for idiomatic usage.
|
|
func (c *Cmd) StderrPipe() (io.ReadCloser, error) {
|
|
if c.Stderr != nil {
|
|
return nil, errors.New("exec: Stderr already set")
|
|
}
|
|
if c.Process != nil {
|
|
return nil, errors.New("exec: StderrPipe after process started")
|
|
}
|
|
pr, pw, err := os.Pipe()
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
c.Stderr = pw
|
|
c.closeAfterStart = append(c.closeAfterStart, pw)
|
|
c.closeAfterWait = append(c.closeAfterWait, pr)
|
|
return pr, nil
|
|
}
|
|
|
|
// prefixSuffixSaver is an io.Writer which retains the first N bytes
|
|
// and the last N bytes written to it. The Bytes() methods reconstructs
|
|
// it with a pretty error message.
|
|
type prefixSuffixSaver struct {
|
|
N int // max size of prefix or suffix
|
|
prefix []byte
|
|
suffix []byte // ring buffer once len(suffix) == N
|
|
suffixOff int // offset to write into suffix
|
|
skipped int64
|
|
|
|
// TODO(bradfitz): we could keep one large []byte and use part of it for
|
|
// the prefix, reserve space for the '... Omitting N bytes ...' message,
|
|
// then the ring buffer suffix, and just rearrange the ring buffer
|
|
// suffix when Bytes() is called, but it doesn't seem worth it for
|
|
// now just for error messages. It's only ~64KB anyway.
|
|
}
|
|
|
|
func (w *prefixSuffixSaver) Write(p []byte) (n int, err error) {
|
|
lenp := len(p)
|
|
p = w.fill(&w.prefix, p)
|
|
|
|
// Only keep the last w.N bytes of suffix data.
|
|
if overage := len(p) - w.N; overage > 0 {
|
|
p = p[overage:]
|
|
w.skipped += int64(overage)
|
|
}
|
|
p = w.fill(&w.suffix, p)
|
|
|
|
// w.suffix is full now if p is non-empty. Overwrite it in a circle.
|
|
for len(p) > 0 { // 0, 1, or 2 iterations.
|
|
n := copy(w.suffix[w.suffixOff:], p)
|
|
p = p[n:]
|
|
w.skipped += int64(n)
|
|
w.suffixOff += n
|
|
if w.suffixOff == w.N {
|
|
w.suffixOff = 0
|
|
}
|
|
}
|
|
return lenp, nil
|
|
}
|
|
|
|
// fill appends up to len(p) bytes of p to *dst, such that *dst does not
|
|
// grow larger than w.N. It returns the un-appended suffix of p.
|
|
func (w *prefixSuffixSaver) fill(dst *[]byte, p []byte) (pRemain []byte) {
|
|
if remain := w.N - len(*dst); remain > 0 {
|
|
add := minInt(len(p), remain)
|
|
*dst = append(*dst, p[:add]...)
|
|
p = p[add:]
|
|
}
|
|
return p
|
|
}
|
|
|
|
func (w *prefixSuffixSaver) Bytes() []byte {
|
|
if w.suffix == nil {
|
|
return w.prefix
|
|
}
|
|
if w.skipped == 0 {
|
|
return append(w.prefix, w.suffix...)
|
|
}
|
|
var buf bytes.Buffer
|
|
buf.Grow(len(w.prefix) + len(w.suffix) + 50)
|
|
buf.Write(w.prefix)
|
|
buf.WriteString("\n... omitting ")
|
|
buf.WriteString(strconv.FormatInt(w.skipped, 10))
|
|
buf.WriteString(" bytes ...\n")
|
|
buf.Write(w.suffix[w.suffixOff:])
|
|
buf.Write(w.suffix[:w.suffixOff])
|
|
return buf.Bytes()
|
|
}
|
|
|
|
func minInt(a, b int) int {
|
|
if a < b {
|
|
return a
|
|
}
|
|
return b
|
|
}
|
|
|
|
// dedupEnv returns a copy of env with any duplicates removed, in favor of
|
|
// later values.
|
|
// Items not of the normal environment "key=value" form are preserved unchanged.
|
|
func dedupEnv(env []string) []string {
|
|
return dedupEnvCase(runtime.GOOS == "windows", env)
|
|
}
|
|
|
|
// dedupEnvCase is dedupEnv with a case option for testing.
|
|
// If caseInsensitive is true, the case of keys is ignored.
|
|
func dedupEnvCase(caseInsensitive bool, env []string) []string {
|
|
out := make([]string, 0, len(env))
|
|
saw := map[string]int{} // key => index into out
|
|
for _, kv := range env {
|
|
eq := strings.Index(kv, "=")
|
|
if eq < 0 {
|
|
out = append(out, kv)
|
|
continue
|
|
}
|
|
k := kv[:eq]
|
|
if caseInsensitive {
|
|
k = strings.ToLower(k)
|
|
}
|
|
if dupIdx, isDup := saw[k]; isDup {
|
|
out[dupIdx] = kv
|
|
continue
|
|
}
|
|
saw[k] = len(out)
|
|
out = append(out, kv)
|
|
}
|
|
return out
|
|
}
|