osrelease: handle completely empty keys

We hadn't run into this before. This seems like the sensible action to
take when there's no value.

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

Author: hdonnay

osrelease/scanner.go

@@ -178,13 +178,13 @@ func Parse(ctx context.Context, r io.Reader) (map[string]string, error) {
 		case b[0] == '#':
 			continue
 		}
-		eq := bytes.IndexRune(b, '=')
-		if eq == -1 {
+		if !bytes.ContainsRune(b, '=') {
 			return nil, fmt.Errorf("osrelease: malformed line %q", s.Text())
 		}
 		// Also handling spaces here matches what systemd seems to do.
-		key := strings.TrimSpace(string(b[:eq]))
-		value := strings.TrimSpace(string(b[eq+1:]))
+		key, value, _ := strings.Cut(string(b), "=")
+		key = strings.TrimSpace(key)
+		value = strings.TrimSpace(value)
 
 		// The value side is defined to follow shell-like quoting rules, which I
 		// take to mean:
@@ -201,11 +201,12 @@ func Parse(ctx context.Context, r io.Reader) (map[string]string, error) {
 		//
 		// With these in mind, the arms of the switch below implement the first
 		// case and a limited version of the second.
-		switch value[0] {
-		case '\'':
+		switch {
+		case len(value) == 0:
+		case value[0] == '\'':
 			value = strings.TrimFunc(value, func(r rune) bool { return r == '\'' })
 			value = strings.ReplaceAll(value, `'\''`, `'`)
-		case '"':
+		case value[0] == '"':
 			// This only implements the metacharacters that are called out in
 			// the os-release documentation.
 			value = strings.TrimFunc(value, func(r rune) bool { return r == '"' })

osrelease/testdata/EmptyKey.txtar

@@ -0,0 +1,35 @@
+-- os-release --
+NAME=Fedora
+VERSION="30 (Container Image)"
+ID=fedora
+VERSION_ID=30
+VERSION_CODENAME=
+PLATFORM_ID="platform:f30"
+PRETTY_NAME="Fedora 30 (Container Image)"
+LOGO=fedora-logo-icon
+CPE_NAME="cpe:/o:fedoraproject:fedora:30"
+VARIANT="Container Image"
+VARIANT_ID=container
+-- Parsed --
+{
+  "CPE_NAME": "cpe:/o:fedoraproject:fedora:30",
+  "ID": "fedora",
+  "LOGO": "fedora-logo-icon",
+  "NAME": "Fedora",
+  "PLATFORM_ID": "platform:f30",
+  "PRETTY_NAME": "Fedora 30 (Container Image)",
+  "VARIANT_ID": "container",
+  "VARIANT": "Container Image",
+  "VERSION": "30 (Container Image)",
+  "VERSION_CODENAME": "",
+  "VERSION_ID": "30"
+}
+-- Distribution --
+{
+  "cpe": "cpe:/o:fedoraproject:fedora:30",
+  "did": "fedora",
+  "name": "Fedora",
+  "pretty_name": "Fedora 30 (Container Image)",
+  "version": "30 (Container Image)",
+  "version_id": "30"
+}