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borrowed_exec.go
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borrowed_exec.go
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// This file contains code copied almost verbatim from Go 1.12.7
// os/exec/exec.go. Modified lines are marked "// MODIFIED".
//
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//nolint
package dexec
import (
"bytes"
"strconv"
"github.com/pkg/errors"
)
// interfaceEqual protects against panics from doing equality tests on
// two interfaces with non-comparable underlying types.
func interfaceEqual(a, b interface{}) bool {
defer func() {
recover()
}()
return a == b
}
// Run starts the specified command and waits for it to complete.
//
// The returned error is nil if the command runs, has no problems
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the command starts but does not complete successfully, the error is of
// type *ExitError. Other error types may be returned for other situations.
//
// If the calling goroutine has locked the operating system thread
// with runtime.LockOSThread and modified any inheritable OS-level
// thread state (for example, Linux or Plan 9 name spaces), the new
// process will inherit the caller's thread state.
func (c *Cmd) Run() error {
if err := c.Start(); err != nil {
return err
}
return c.Wait()
}
// Output runs the command and returns its standard output.
// Any returned error will usually be of type *ExitError.
// If c.Stderr was nil, Output populates ExitError.Stderr.
func (c *Cmd) Output() ([]byte, error) {
if c.Stdout != nil {
return nil, errors.New("exec: Stdout already set")
}
var stdout bytes.Buffer
c.Stdout = &stdout
captureErr := c.Stderr == nil
if captureErr {
c.Stderr = &prefixSuffixSaver{N: 32 << 10}
}
err := c.Run()
if err != nil && captureErr {
if ee, ok := err.(*ExitError); ok {
ee.Stderr = c.Stderr.(*loggingWriter).writer.(*prefixSuffixSaver).Bytes() // MODIFIED
}
}
return stdout.Bytes(), err
}
// CombinedOutput runs the command and returns its combined standard
// output and standard error.
func (c *Cmd) CombinedOutput() ([]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 b bytes.Buffer
c.Stdout = &b
c.Stderr = &b
err := c.Run()
return b.Bytes(), err
}
// 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
}