cli/connhelper: remove dependency on pkg/process

This package will not be included in the api or client modules, and
we're currently only using a single function of it, and only the
unix implementation, so let's fork it for now (although the package
may be moved to moby/sys).

This removes the last dependency on github.com/docker/docker.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/connhelper/commandconn/commandconn_unix_test.go

@@ -4,12 +4,17 @@ package commandconn
 
 import (
 	"context"
+	"errors"
 	"io"
 	"io/fs"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"syscall"
 	"testing"
 	"time"
 
-	"github.com/docker/docker/pkg/process"
 	"gotest.tools/v3/assert"
 	is "gotest.tools/v3/assert/cmp"
 )
@@ -51,16 +56,16 @@ func TestCloseRunningCommand(t *testing.T) {
 		c, err := New(ctx, "sh", "-c", "while true; do sleep 1; done")
 		assert.NilError(t, err)
 		cmdConn := c.(*commandConn)
-		assert.Check(t, process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, processAlive(cmdConn.cmd.Process.Pid))
 
 		n, err := c.Write([]byte("hello"))
 		assert.Check(t, is.Equal(len("hello"), n))
 		assert.NilError(t, err)
-		assert.Check(t, process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, processAlive(cmdConn.cmd.Process.Pid))
 
 		err = cmdConn.Close()
 		assert.NilError(t, err)
-		assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, !processAlive(cmdConn.cmd.Process.Pid))
 		done <- struct{}{}
 	}()
 
@@ -79,7 +84,7 @@ func TestCloseTwice(t *testing.T) {
 		c, err := New(ctx, "sh", "-c", "echo hello; sleep 1; exit 0")
 		assert.NilError(t, err)
 		cmdConn := c.(*commandConn)
-		assert.Check(t, process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, processAlive(cmdConn.cmd.Process.Pid))
 
 		b := make([]byte, 32)
 		n, err := c.Read(b)
@@ -88,11 +93,11 @@ func TestCloseTwice(t *testing.T) {
 
 		err = cmdConn.Close()
 		assert.NilError(t, err)
-		assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, !processAlive(cmdConn.cmd.Process.Pid))
 
 		err = cmdConn.Close()
 		assert.NilError(t, err)
-		assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, !processAlive(cmdConn.cmd.Process.Pid))
 		done <- struct{}{}
 	}()
 
@@ -111,7 +116,7 @@ func TestEOFTimeout(t *testing.T) {
 		c, err := New(ctx, "sh", "-c", "sleep 20")
 		assert.NilError(t, err)
 		cmdConn := c.(*commandConn)
-		assert.Check(t, process.Alive(cmdConn.cmd.Process.Pid))
+		assert.Check(t, processAlive(cmdConn.cmd.Process.Pid))
 
 		cmdConn.stdout = mockStdoutEOF{}
 
@@ -148,7 +153,7 @@ func TestCloseWhileWriting(t *testing.T) {
 	c, err := New(ctx, "sh", "-c", "while true; do sleep 1; done")
 	assert.NilError(t, err)
 	cmdConn := c.(*commandConn)
-	assert.Check(t, process.Alive(cmdConn.cmd.Process.Pid))
+	assert.Check(t, processAlive(cmdConn.cmd.Process.Pid))
 
 	writeErrC := make(chan error)
 	go func() {
@@ -164,7 +169,7 @@ func TestCloseWhileWriting(t *testing.T) {
 
 	err = c.Close()
 	assert.NilError(t, err)
-	assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
+	assert.Check(t, !processAlive(cmdConn.cmd.Process.Pid))
 
 	writeErr := <-writeErrC
 	assert.ErrorContains(t, writeErr, "file already closed")
@@ -176,7 +181,7 @@ func TestCloseWhileReading(t *testing.T) {
 	c, err := New(ctx, "sh", "-c", "while true; do sleep 1; done")
 	assert.NilError(t, err)
 	cmdConn := c.(*commandConn)
-	assert.Check(t, process.Alive(cmdConn.cmd.Process.Pid))
+	assert.Check(t, processAlive(cmdConn.cmd.Process.Pid))
 
 	readErrC := make(chan error)
 	go func() {
@@ -193,8 +198,37 @@ func TestCloseWhileReading(t *testing.T) {
 
 	err = cmdConn.Close()
 	assert.NilError(t, err)
-	assert.Check(t, !process.Alive(cmdConn.cmd.Process.Pid))
+	assert.Check(t, !processAlive(cmdConn.cmd.Process.Pid))
 
 	readErr := <-readErrC
 	assert.Check(t, is.ErrorIs(readErr, fs.ErrClosed))
 }
+
+// processAlive returns true if a process with a given pid is running. It only considers
+// positive PIDs; 0 (all processes in the current process group), -1 (all processes
+// with a PID larger than 1), and negative (-n, all processes in process group
+// "n") values for pid are never considered to be alive.
+//
+// It was forked from https://github.com/moby/moby/blob/v28.3.3/pkg/process/process_unix.go#L17-L42
+func processAlive(pid int) bool {
+	if pid < 1 {
+		return false
+	}
+	switch runtime.GOOS {
+	case "darwin":
+		// OS X does not have a proc filesystem. Use kill -0 pid to judge if the
+		// process exists. From KILL(2): https://www.freebsd.org/cgi/man.cgi?query=kill&sektion=2&manpath=OpenDarwin+7.2.1
+		//
+		// Sig may be one of the signals specified in sigaction(2) or it may
+		// be 0, in which case error checking is performed but no signal is
+		// actually sent. This can be used to check the validity of pid.
+		err := syscall.Kill(pid, 0)
+
+		// Either the PID was found (no error), or we get an EPERM, which means
+		// the PID exists, but we don't have permissions to signal it.
+		return err == nil || errors.Is(err, syscall.EPERM)
+	default:
+		_, err := os.Stat(filepath.Join("/proc", strconv.Itoa(pid)))
+		return err == nil
+	}
+}