snapdtool, many: support additional key/value flags in info file

Also set a new key, SNAPD_APPARMOR_REEXEC, to 0 for now, since this key will be
used shortly with the new apparmor vendoring inside the snapd snap.

Signed-off-by: Ian Johnson <ian.johnson@canonical.com>

cmd/snap-preseed/preseed_linux.go

@@ -159,15 +159,15 @@ type targetSnapdInfo struct {
 func chooseTargetSnapdVersion() (*targetSnapdInfo, error) {
 	// read snapd version from the mounted core/snapd snap
 	infoPath := filepath.Join(snapdMountPath, dirs.CoreLibExecDir, "info")
-	verFromSnap, err := snapdtool.SnapdVersionFromInfoFile(infoPath)
+	verFromSnap, _, err := snapdtool.SnapdVersionFromInfoFile(infoPath)
 	if err != nil {
 		return nil, err
 	}
 
 	// read snapd version from the main fs under chroot (snapd from the deb);
 	// assumes running under chroot already.
 	infoPath = filepath.Join(dirs.GlobalRootDir, dirs.CoreLibExecDir, "info")
-	verFromDeb, err := snapdtool.SnapdVersionFromInfoFile(infoPath)
+	verFromDeb, _, err := snapdtool.SnapdVersionFromInfoFile(infoPath)
 	if err != nil {
 		return nil, err
 	}

mkversion.sh

@@ -130,4 +130,5 @@ EOF
 
 cat <<EOF > "$PKG_BUILDDIR/data/info"
 VERSION=$v
+SNAPD_APPARMOR_REEXEC=0
 EOF

snapdtool/info_file.go

@@ -20,34 +20,53 @@
 package snapdtool
 
 import (
-	"bytes"
+	"bufio"
 	"fmt"
-	"io/ioutil"
+	"os"
+	"strings"
 )
 
 // SnapdVersionFromInfoFile returns snapd version read for the
 // given info" file, pointed by infoPath.
-// The format of the "info" file is a single line with "VERSION=..."
-// in it. The file is produced by mkversion.sh and normally installed
-// along snapd binary in /usr/lib/snapd.
-func SnapdVersionFromInfoFile(infoPath string) (string, error) {
-	content, err := ioutil.ReadFile(infoPath)
+// The format of the "info" file are lines with "KEY=VALUE" with the typical key
+// being just VERSION. The file is produced by mkversion.sh and normally
+// installed along snapd binary in /usr/lib/snapd.
+// Other typical keys in this file include SNAPD_APPARMOR_REEXEC, which
+// indicates whether or not the snapd-apparmor binary installed via the
+// traditional linux package of snapd supports re-exec into the version in the
+// snapd or core snaps.
+func SnapdVersionFromInfoFile(infoPath string) (version string, flags map[string]string, err error) {
+	f, err := os.Open(infoPath)
 	if err != nil {
-		return "", fmt.Errorf("cannot open snapd info file %q: %s", infoPath, err)
+		return "", nil, fmt.Errorf("cannot open snapd info file %q: %s", infoPath, err)
 	}
+	defer f.Close()
 
-	if !bytes.HasPrefix(content, []byte("VERSION=")) {
-		idx := bytes.Index(content, []byte("\nVERSION="))
-		if idx < 0 {
-			return "", fmt.Errorf("cannot find snapd version information in %q", content)
+	flags = map[string]string{}
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "VERSION=") {
+			version = strings.TrimPrefix(line, "VERSION=")
+		} else {
+			keyVal := strings.SplitN(line, "=", 2)
+			if len(keyVal) != 2 {
+				// potentially malformed line, just skip it
+				continue
+			}
+
+			flags[keyVal[0]] = keyVal[1]
 		}
-		content = content[idx+1:]
 	}
-	content = content[8:]
-	idx := bytes.IndexByte(content, '\n')
-	if idx > -1 {
-		content = content[:idx]
+
+	if err := scanner.Err(); err != nil {
+		return "", nil, fmt.Errorf("error reading snapd info file %q: %v", infoPath, err)
+	}
+
+	if version == "" {
+		return "", nil, fmt.Errorf("cannot find snapd version information in file %q", infoPath)
 	}
 
-	return string(content), nil
+	return version, flags, nil
 }

snapdtool/info_file_test.go

@@ -20,6 +20,7 @@
 package snapdtool_test
 
 import (
+	"fmt"
 	"io/ioutil"
 	"path/filepath"
 
@@ -33,7 +34,7 @@ type infoFileSuite struct{}
 var _ = Suite(&infoFileSuite{})
 
 func (s *infoFileSuite) TestNoVersionFile(c *C) {
-	_, err := snapdtool.SnapdVersionFromInfoFile("/non-existing-file")
+	_, _, err := snapdtool.SnapdVersionFromInfoFile("/non-existing-file")
 	c.Assert(err, ErrorMatches, `cannot open snapd info file "/non-existing-file":.*`)
 }
 
@@ -42,16 +43,28 @@ func (s *infoFileSuite) TestNoVersionData(c *C) {
 	infoFile := filepath.Join(top, "info")
 	c.Assert(ioutil.WriteFile(infoFile, []byte("foo"), 0644), IsNil)
 
-	_, err := snapdtool.SnapdVersionFromInfoFile(infoFile)
-	c.Assert(err, ErrorMatches, `cannot find snapd version information in "foo"`)
+	_, _, err := snapdtool.SnapdVersionFromInfoFile(infoFile)
+	c.Assert(err, ErrorMatches, fmt.Sprintf(`cannot find snapd version information in file %q`, infoFile))
 }
 
 func (s *infoFileSuite) TestVersionHappy(c *C) {
 	top := c.MkDir()
 	infoFile := filepath.Join(top, "info")
 	c.Assert(ioutil.WriteFile(infoFile, []byte("VERSION=1.2.3"), 0644), IsNil)
 
-	ver, err := snapdtool.SnapdVersionFromInfoFile(infoFile)
+	ver, flags, err := snapdtool.SnapdVersionFromInfoFile(infoFile)
 	c.Assert(err, IsNil)
 	c.Check(ver, Equals, "1.2.3")
+	c.Assert(flags, HasLen, 0)
+}
+
+func (s *infoFileSuite) TestInfoVersionFlags(c *C) {
+	top := c.MkDir()
+	infoFile := filepath.Join(top, "info")
+	c.Assert(ioutil.WriteFile(infoFile, []byte("VERSION=1.2.3\nFOO=BAR"), 0644), IsNil)
+
+	ver, flags, err := snapdtool.SnapdVersionFromInfoFile(infoFile)
+	c.Assert(err, IsNil)
+	c.Check(ver, Equals, "1.2.3")
+	c.Assert(flags, DeepEquals, map[string]string{"FOO": "BAR"})
 }

snapdtool/tool_linux.go

@@ -77,7 +77,7 @@ func distroSupportsReExec() bool {
 // version of core that do not yet have it.
 func coreSupportsReExec(coreOrSnapdPath string) bool {
 	infoPath := filepath.Join(coreOrSnapdPath, filepath.Join(dirs.CoreLibExecDir, "info"))
-	ver, err := SnapdVersionFromInfoFile(infoPath)
+	ver, _, err := SnapdVersionFromInfoFile(infoPath)
 	if err != nil {
 		logger.Noticef("%v", err)
 		return false