enable podman-remote on windows

build a podman-remote binary for windows that allows users to use the
remote client on windows and interact with podman on linux system.

Signed-off-by: baude <bbaude@redhat.com>

vendor/github.com/containers/buildah/imagebuildah/chroot_symlink_linux.go

@@ -0,0 +1,266 @@
+package imagebuildah
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/containers/storage/pkg/reexec"
+	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
+)
+
+const (
+	symlinkChrootedCommand = "chrootsymlinks-resolve"
+	symlinkModifiedTime    = "modtimesymlinks-resolve"
+	maxSymlinksResolved    = 40
+)
+
+func init() {
+	reexec.Register(symlinkChrootedCommand, resolveChrootedSymlinks)
+	reexec.Register(symlinkModifiedTime, resolveSymlinkTimeModified)
+}
+
+// resolveSymlink uses a child subprocess to resolve any symlinks in filename
+// in the context of rootdir.
+func resolveSymlink(rootdir, filename string) (string, error) {
+	// The child process expects a chroot and one path that
+	// will be consulted relative to the chroot directory and evaluated
+	// for any symbolic links present.
+	cmd := reexec.Command(symlinkChrootedCommand, rootdir, filename)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		return "", errors.Wrapf(err, string(output))
+	}
+
+	// Hand back the resolved symlink, will be filename if a symlink is not found
+	return string(output), nil
+}
+
+// main() for resolveSymlink()'s subprocess.
+func resolveChrootedSymlinks() {
+	status := 0
+	flag.Parse()
+	if len(flag.Args()) < 2 {
+		fmt.Fprintf(os.Stderr, "%s needs two arguments\n", symlinkChrootedCommand)
+		os.Exit(1)
+	}
+	// Our first parameter is the directory to chroot into.
+	if err := unix.Chdir(flag.Arg(0)); err != nil {
+		fmt.Fprintf(os.Stderr, "chdir(): %v\n", err)
+		os.Exit(1)
+	}
+	if err := unix.Chroot(flag.Arg(0)); err != nil {
+		fmt.Fprintf(os.Stderr, "chroot(): %v\n", err)
+		os.Exit(1)
+	}
+
+	// Our second parameter is the path name to evaluate for symbolic links
+	symLink, err := getSymbolicLink(flag.Arg(1))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error getting symbolic links: %v\n", err)
+		os.Exit(1)
+	}
+	if _, err := os.Stdout.WriteString(symLink); err != nil {
+		fmt.Fprintf(os.Stderr, "error writing string to stdout: %v\n", err)
+		os.Exit(1)
+	}
+	os.Exit(status)
+}
+
+// main() for grandparent subprocess.  Its main job is to shuttle stdio back
+// and forth, managing a pseudo-terminal if we want one, for our child, the
+// parent subprocess.
+func resolveSymlinkTimeModified() {
+	status := 0
+	flag.Parse()
+	if len(flag.Args()) < 1 {
+		os.Exit(1)
+	}
+	// Our first parameter is the directory to chroot into.
+	if err := unix.Chdir(flag.Arg(0)); err != nil {
+		fmt.Fprintf(os.Stderr, "chdir(): %v\n", err)
+		os.Exit(1)
+	}
+	if err := unix.Chroot(flag.Arg(0)); err != nil {
+		fmt.Fprintf(os.Stderr, "chroot(): %v\n", err)
+		os.Exit(1)
+	}
+
+	// Our second parameter is the path name to evaluate for symbolic links.
+	// Our third parameter is the time the cached intermediate image was created.
+	// We check whether the modified time of the filepath we provide is after the time the cached image was created.
+	timeIsGreater, err := modTimeIsGreater(flag.Arg(0), flag.Arg(1), flag.Arg(2))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error checking if modified time of resolved symbolic link is greater: %v\n", err)
+		os.Exit(1)
+	}
+	if _, err := os.Stdout.WriteString(fmt.Sprintf("%v", timeIsGreater)); err != nil {
+		fmt.Fprintf(os.Stderr, "error writing string to stdout: %v\n", err)
+		os.Exit(1)
+	}
+	os.Exit(status)
+}
+
+// resolveModifiedTime (in the grandparent process) checks filename for any symlinks,
+// resolves it and compares the modified time of the file with historyTime, which is
+// the creation time of the cached image. It returns true if filename was modified after
+// historyTime, otherwise returns false.
+func resolveModifiedTime(rootdir, filename, historyTime string) (bool, error) {
+	// The child process expects a chroot and one path that
+	// will be consulted relative to the chroot directory and evaluated
+	// for any symbolic links present.
+	cmd := reexec.Command(symlinkModifiedTime, rootdir, filename, historyTime)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		return false, errors.Wrapf(err, string(output))
+	}
+	// Hand back true/false depending on in the file was modified after the caches image was created.
+	return string(output) == "true", nil
+}
+
+// modTimeIsGreater goes through the files added/copied in using the Dockerfile and
+// checks the time stamp (follows symlinks) with the time stamp of when the cached
+// image was created. IT compares the two and returns true if the file was modified
+// after the cached image was created, otherwise it returns false.
+func modTimeIsGreater(rootdir, path string, historyTime string) (bool, error) {
+	var timeIsGreater bool
+
+	// Convert historyTime from string to time.Time for comparison
+	histTime, err := time.Parse(time.RFC3339Nano, historyTime)
+	if err != nil {
+		return false, errors.Wrapf(err, "error converting string to time.Time %q", historyTime)
+	}
+
+	// Since we are chroot in rootdir, we want a relative path, i.e (path - rootdir)
+	relPath, err := filepath.Rel(rootdir, path)
+	if err != nil {
+		return false, errors.Wrapf(err, "error making path %q relative to %q", path, rootdir)
+	}
+
+	// Walk the file tree and check the time stamps.
+	err = filepath.Walk(relPath, func(path string, info os.FileInfo, err error) error {
+		// If using cached images, it is possible for files that are being copied to come from
+		// previous build stages. But if using cached images, then the copied file won't exist
+		// since a container won't have been created for the previous build stage and info will be nil.
+		// In that case just return nil and continue on with using the cached image for the whole build process.
+		if info == nil {
+			return nil
+		}
+		modTime := info.ModTime()
+		if info.Mode()&os.ModeSymlink == os.ModeSymlink {
+			// Evaluate any symlink that occurs to get updated modified information
+			resolvedPath, err := filepath.EvalSymlinks(path)
+			if err != nil && os.IsNotExist(err) {
+				return errors.Wrapf(errDanglingSymlink, "%q", path)
+			}
+			if err != nil {
+				return errors.Wrapf(err, "error evaluating symlink %q", path)
+			}
+			fileInfo, err := os.Stat(resolvedPath)
+			if err != nil {
+				return errors.Wrapf(err, "error getting file info %q", resolvedPath)
+			}
+			modTime = fileInfo.ModTime()
+		}
+		if modTime.After(histTime) {
+			timeIsGreater = true
+			return nil
+		}
+		return nil
+	})
+
+	if err != nil {
+		// if error is due to dangling symlink, ignore error and return nil
+		if errors.Cause(err) == errDanglingSymlink {
+			return false, nil
+		}
+		return false, errors.Wrapf(err, "error walking file tree %q", path)
+	}
+	return timeIsGreater, err
+}
+
+// getSymbolic link goes through each part of the path and continues resolving symlinks as they appear.
+// Returns what the whole target path for what "path" resolves to.
+func getSymbolicLink(path string) (string, error) {
+	var (
+		symPath          string
+		symLinksResolved int
+	)
+	// Splitting path as we need to resolve each part of the path at a time
+	splitPath := strings.Split(path, "/")
+	if splitPath[0] == "" {
+		splitPath = splitPath[1:]
+		symPath = "/"
+	}
+	for _, p := range splitPath {
+		// If we have resolved 40 symlinks, that means something is terribly wrong
+		// will return an error and exit
+		if symLinksResolved >= maxSymlinksResolved {
+			return "", errors.Errorf("have resolved %q symlinks, something is terribly wrong!", maxSymlinksResolved)
+		}
+		symPath = filepath.Join(symPath, p)
+		isSymlink, resolvedPath, err := hasSymlink(symPath)
+		if err != nil {
+			return "", errors.Wrapf(err, "error checking symlink for %q", symPath)
+		}
+		// if isSymlink is true, check if resolvedPath is potentially another symlink
+		// keep doing this till resolvedPath is not a symlink and isSymlink is false
+		for isSymlink == true {
+			// Need to keep track of number of symlinks resolved
+			// Will also return an error if the symlink points to itself as that will exceed maxSymlinksResolved
+			if symLinksResolved >= maxSymlinksResolved {
+				return "", errors.Errorf("have resolved %q symlinks, something is terribly wrong!", maxSymlinksResolved)
+			}
+			isSymlink, resolvedPath, err = hasSymlink(resolvedPath)
+			if err != nil {
+				return "", errors.Wrapf(err, "error checking symlink for %q", resolvedPath)
+			}
+			symLinksResolved++
+		}
+		// Assign resolvedPath to symPath. The next part of the loop will append the next part of the original path
+		// and continue resolving
+		symPath = resolvedPath
+		symLinksResolved++
+	}
+	return symPath, nil
+}
+
+// hasSymlink returns true and the target if path is symlink
+// otherwise it returns false and path
+func hasSymlink(path string) (bool, string, error) {
+	info, err := os.Lstat(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			if err = os.MkdirAll(path, 0755); err != nil {
+				return false, "", errors.Wrapf(err, "error ensuring volume path %q exists", path)
+			}
+			info, err = os.Lstat(path)
+			if err != nil {
+				return false, "", errors.Wrapf(err, "error running lstat on %q", path)
+			}
+		} else {
+			return false, path, errors.Wrapf(err, "error get stat of path %q", path)
+		}
+	}
+
+	// Return false and path as path if not a symlink
+	if info.Mode()&os.ModeSymlink != os.ModeSymlink {
+		return false, path, nil
+	}
+
+	// Read the symlink to get what it points to
+	targetDir, err := os.Readlink(path)
+	if err != nil {
+		return false, "", errors.Wrapf(err, "error reading link %q", path)
+	}
+	// if the symlink points to a relative path, prepend the path till now to the resolved path
+	if !filepath.IsAbs(targetDir) {
+		targetDir = filepath.Join(filepath.Dir(path), targetDir)
+	}
+	// run filepath.Clean to remove the ".." from relative paths
+	return true, filepath.Clean(targetDir), nil
+}