New upstream version 1.0.0+git20191223.292995b

1 files changed, 113 insertions, 5 deletions

diff --git a/commands.go b/commands.go
index 0ea2b9a..52704c5 100644
--- a/commands.go
+++ b/commands.go
@@ -2,8 +2,10 @@ package debos
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"log"
 	"os"
 	"os/exec"
@@ -115,9 +117,101 @@ func (cmd *Command) AddBindMount(source, target string) {
 	cmd.bindMounts = append(cmd.bindMounts, mount)
 }
 
+func (cmd *Command) saveResolvConf() (*[sha256.Size]byte, error) {
+	hostconf := "/etc/resolv.conf"
+	chrootedconf := path.Join(cmd.Chroot, hostconf)
+	savedconf := chrootedconf + ".debos"
+	var sum [sha256.Size]byte
+
+	if cmd.ChrootMethod == CHROOT_METHOD_NONE {
+		return nil, nil
+	}
+
+	// There may not be an existing resolv.conf
+	if _, err := os.Lstat(chrootedconf); !os.IsNotExist(err) {
+		if err = os.Rename(chrootedconf, savedconf); err != nil {
+			return nil, err
+		}
+	}
+
+	/* Expect a relatively small file here */
+	data, err := ioutil.ReadFile(hostconf)
+	if err != nil {
+		return nil, err
+	}
+	out := []byte("# Automatically generated by Debos\n")
+	out = append(out, data...)
+
+	sum = sha256.Sum256(out)
+
+	err = ioutil.WriteFile(chrootedconf, out, 0644)
+	if err != nil {
+		return nil, err
+	}
+
+	return &sum, nil
+}
+
+func (cmd *Command) restoreResolvConf(sum *[sha256.Size]byte) error {
+	hostconf := "/etc/resolv.conf"
+	chrootedconf := path.Join(cmd.Chroot, hostconf)
+	savedconf := chrootedconf + ".debos"
+
+	if cmd.ChrootMethod == CHROOT_METHOD_NONE || sum == nil {
+		return nil
+	}
+
+	// Remove the original copy anyway
+	defer os.Remove(savedconf)
+
+	fi, err := os.Lstat(chrootedconf)
+
+	// resolv.conf was removed during the command call
+	// Nothing to do with it -- file has been changed anyway
+	if os.IsNotExist(err) {
+		return nil
+	}
+
+	mode := fi.Mode()
+	switch {
+	case mode.IsRegular():
+		// Try to calculate checksum
+		data, err := ioutil.ReadFile(chrootedconf)
+		if err != nil {
+			return err
+		}
+		currentsum := sha256.Sum256(data)
+
+		// Leave the changed resolv.conf untouched
+		if bytes.Compare(currentsum[:], (*sum)[:]) == 0 {
+			// Remove the generated version
+			if err := os.Remove(chrootedconf); err != nil {
+				return err
+			}
+
+			if _, err := os.Lstat(savedconf); !os.IsNotExist(err) {
+				// Restore the original version
+				if err = os.Rename(savedconf, chrootedconf); err != nil {
+					return err
+				}
+			}
+		}
+	case mode&os.ModeSymlink != 0:
+		// If the 'resolv.conf' is a symlink
+		// Nothing to do with it -- file has been changed anyway
+	default:
+		// File is not regular or symlink
+		// Let's get out here with verbose message
+		log.Printf("Warning: /etc/resolv.conf inside the chroot is not a regular file")
+	}
+
+	return nil
+}
+
 func (cmd Command) Run(label string, cmdline ...string) error {
 	q := newQemuHelper(cmd)
 	q.Setup()
+	defer q.Cleanup()
 
 	var options []string
 	switch cmd.ChrootMethod {
@@ -128,7 +222,8 @@ func (cmd Command) Run(label string, cmdline ...string) error {
 		options = append(options, cmd.Chroot)
 		options = append(options, cmdline...)
 	case CHROOT_METHOD_NSPAWN:
-		options = append(options, "systemd-nspawn", "-q", "-D", cmd.Chroot)
+		// We use own resolv.conf handling
+		options = append(options, "systemd-nspawn", "-q", "--resolv-conf=off", "-D", cmd.Chroot)
 		for _, e := range cmd.extraEnv {
 			options = append(options, "--setenv", e)
 
@@ -147,6 +242,8 @@ func (cmd Command) Run(label string, cmdline ...string) error {
 	exe.Stdout = w
 	exe.Stderr = w
 
+	defer w.flush()
+
 	if len(cmd.extraEnv) > 0 && cmd.ChrootMethod != CHROOT_METHOD_NSPAWN {
 		exe.Env = append(os.Environ(), cmd.extraEnv...)
 	}
@@ -158,11 +255,22 @@ func (cmd Command) Run(label string, cmdline ...string) error {
 		defer services.Allow()
 	}
 
-	err := exe.Run()
-	w.flush()
-	q.Cleanup()
+	// Save the original resolv.conf and copy version from host
+	resolvsum, err := cmd.saveResolvConf()
+	if err != nil {
+		return err
+	}
+
+	if err = exe.Run(); err != nil {
+		return err
+	}
+
+	// Restore the original resolv.conf if not changed
+	if err = cmd.restoreResolvConf(resolvsum); err != nil {
+		return err
+	}
 
-	return err
+	return nil
 }
 
 type qemuHelper struct {